Ewa Bogalska-Martin
email: ewa.martin@iepg.fr

Implementing a "non-discrimination" policy in a country

Keywords: non-discrimination policy, racial discrimination, foreigners, xenophobia, homophobia

Implementing a "non-discrimination" policy in a country "without foreigners" : the case of Poland

Ewa Bogalska-Martin

To cite this version:

Ewa Bogalska-Martin. Implementing a "non-discrimination" policy in a country "without foreigners" : the case of Poland.

Introduction

Non-discrimination policies are often thought of as a set of actions that cut across all policy mechanisms and are aimed, in particular, at populations identified as targets of discrimination. Drawing on studies on 'policies against discrimination', we will analyse non-discrimination as a political project whose more or less voluntary implementation is reflected in the development of prevention and monitoring actions to ensure that both political and legal constitutional principles of equal treatment are followed by deeds.

Our reflection is in line with the findings established during the Durban Conference in 2001 and since developed by several policy players and by national and international associations. The final declaration adopted at Durban states that, "Despite efforts undertaken by the international community, Governments and local authorities, the scourge of racism, racial discrimination, xenophobia and related intolerance persists." Indeed, beyond the proliferation of legal measures prohibiting discrimination and declarations of intention, the implementation of the policy project for a nondiscriminating society has come up against structural obstacles, including in the countries attached to the ideals of tolerance and equal treatment.

To speed up the practical application of these ideals across Europe, the EU has taken up the issue. European directives, respectively, 2000/43, appertaining to equality without distinction as to race or ethnic origin, 2000/78, appertaining to equality of treatment in employment and work and 2002/73, appertaining to equality between men and women, state that Governments of EU countries should provide national institutions to fight against discrimination (where it exists, or whenever it becomes necessary to set these institutions up), with at least the following competences: independent assistance to victims of discrimination, independent studies, independent reports and recommendations on issues related to discrimination. European policy recommendations suggest that specialised national institutions should be entrusted with the following functions: educate the public and public training institutions on discrimination issues; monitor the content and impact of existing and envisaged laws and national policies in the light of relevant international standards; advise all public authorities on discrimination; receive complaints concerning alleged cases of discrimination and address them either through peaceful settlement or legally binding decisions.

All these recommendations seek to encourage the implementation of policies that can ensure an ideal and civil non-discriminating society. From the early 2000s, all EU countries committed to this area, but each one drew on its own references and its own traditions, meaning that the countries did not advance at the same rhythm. Drawing on the practices and issues encountered in a new Member State of the EU, i.e., Poland, this article will analyse what lies at the core of policies against racial discrimination.

Analysing racial discrimination in Poland requires one to consider the historical, sociological and political contexts of the country. Indeed, this is necessary to highlight the difficulties, advances and stalemates encountered in the creation of nondiscrimination policies driven by associations and public stakeholders in this country. In view of the post-1989 social and political changes in Poland, we will analyse the change in the scope of action and the social climate. Moreover, we will examine the greater responsibility of all those involved in a country that has been an EU member since 2004.

The historical framework of the reflection on "foreigners" in Poland

Poland, a country where religious wars have never occurred, is often thought of as one of the European countries most affected by anti-Semitism, which marked the social relationships between multi-ethnic groups in the Polish community in the 19th and 20th century. Historically, the relationship to national, ethnic or religious minorities have always been and are still -perhaps even more so -at the heart of all questions revolving around social cohesion and national identity. They are at the centre of the debate on the context of "otherness" perceived in Poland as an existential problem of a historical nature, no doubt accentuated by the process of European integration and by all the facts relating to the consequences of "globalisation".

Since the beginning of the 19th century, when successive generations of Poles fought against Russian or Prussian oppression and for political independence, the relationship to the "other", identified as "foreign" to the national cause, was always central in the debate on national duties, sacrifices made, and the sharing of a common destiny. Since then, the "other" (Jewish, communist, collaborator2 ) has often been the object of a far from glorious political policy [START_REF] Jean-Yves | Pologne 2006-2007[END_REF]. It is worth mentioning, however, that an attachment to democratic values and the rejection, notably of anti-Semitism, has always been defended as a symbol of Poland's tolerance by a some part of the political elite (K. Zaluski 1971;[START_REF] Adam | Ksenofobia i dyskryminacja na tle etnicznym w Polscezarys sytuacji[END_REF], bringing together modern and progressive Polish society. The attitude to minorities (particularly Jewish) was considered as necessary to affirm the spirit of tolerance and show the political maturity of the Polish society after the re-recreation of the independent Polish state in 1918 as well as after the change of regime in 1989. It must be borne in mind that anti-Semitism, in both its "traditional" form of the rejection of strangers and in the changes it has undergone, provided the negative or positive reference to reflect on racial discrimination and, beyond that, on all forms of discrimination in Poland.

According to the 2010 Demographic Yearbook, only 1,133 people who declared themselves "Jewish" lived in Poland in 2002, the year the last census was conducted. In addition, approximately 3,000 people of Israeli citizenship officially lived in Poland. At the same time, Jewish restaurants have met with great success in all major cities and many tourists have shown an interest in visiting Jewish districts (particularly the Kazimierz district in Kraków). What remains of Polish anti-Semitism? Is it, as we argue, a container without content? Studies conducted after 1990 by the Public Opinion Research Center (CBOS) confirmed that a latent anti-semitism still persisted. In 1993, 50% of respondents were openly hostile to "Jews" (only 15% expressed sympathy). In 2002 the same studies highlighted that 46% of respondents remained hostile, and only 23% expressed sympathy for Jews. A 2013 CBOS survey showed that 63% of respondents believed in a "Jewish conspiracy". The hostility of close to 50% of Polish people against Jews is consistent with the findings of another study conducted in 2017 [START_REF] Dominika | Powrot zabobonu : Antysemityzm w polsce na podstawie Polskiego Sondazu Uprzedzen 3, Centrum Badan nad Uprzedzeniami[END_REF]. Other studies suggest that the stereotype of "Jews" has always been associated with the negative figure of "those who govern Poland"3 . This stereotype has been somewhat supported by the process of the "ethnicising" of social relationships introduced notably by European standards which call for the recognition of ethnic and national minorities, as we mentioned earlier.

As Jacek Kubiak stated in the "Polityka" 4 newspaper of February 2008, "Polish anti-Semitism is expressed in the graffiti on the walls, in the negative connotation in everyday language given to the word "Jew", in the publications of Leszek Bubel, in the xenophobic and anti-Semitic programmes of Maryja Radio or even in the fascistic Nasz Dziennik daily newspaper. It is a toothless anti-Semitism, whose image is as violent as it is obsolete. But it is anti-Semitism lying in wait, able to rise from its ashes. At the same time, the attitudes of Polish people with regard to Israel are generally friendly. Without knowing it, communists have played a vital role in shaping this outcome. The attitude of the communist authorities of the socialist Poland seeking to create hostility towards the imperialism of the Jewish State has aroused radically contrary attitudes among the Polish people. The Poland of today is on a path that will finally allow it to erase the ghosts of the past. Everything will depend not on the generation that remembers the German occupation, the pogrom at Kielce5 , or the year 1968, but on the younger generation who, in most cases, have never met Polish Jews (Kubiak, 2008).

Since the beginning of the political changes in 1989, this issue has been a recurring subject. Today, both the historians working on the plunder of Jewish property at the Institute of National Remembrance and a few politicians argue that there is a need to call into question the relationship that the Polish society has had and continues to have with the "emblematic figure of the Jew"'. We believe that this figure can be defined as one that threatens the established order, perceived as both inferior and superior to the Polish people (Bogalska-Martin, 2005, p.41).

Poland's anti-semitic past recently caught up with it following revelations made by Jan Tomasz Gross, a Polish-born professor of history at Princeton University. Gross These books, notably the former, opened up a "Pandora's box" and held up a mirror into which the Polish people did not want to look. It was at the centre of the debate throughout the 2000s. The debate continued later with the publication of Gross's third book, which was somewhat more terrifying than the previous two. Its title Zlote zniwa ("Harvest of gold"), published in March 2011, brought to light the excavations carried out in the former concentration and extermination camps by surrounding populations in their quest for gold and other precious objects. As he had done in his previous books, Gross suggested that this was a real industry, a source of enrichment and, above all, the expression of a structural and deep anti-semitism.

The revelations made in Gross's first book concerning the massacre at Jedwabne in 1941 led the President of the Republic, Aleksander Kwasniewski, to convey the regrets of the Polish people to the Jewish people on 10 th July 2001 in the presence of the Ambassador of Israel. This act, however, did not put an end to the debate. One might even say that a few progressive Poles consider that the debate is yet to begin.

"A Silent consensus" around the introduction of European standards in the fight against discrimination

After the fall of the socialist regime in 1989, surrounded by an aura of the liberator of the people, strengthened by its "Solidarnosc" movement -the greatest expression of "civil society" -Poland aspired to regain its place in Europe. For the Polish people, the EU was and continued to be the bearer of a long dreamed about ideal: peace, democracy and especially prosperity, which was quickly assimilated to the logic of consumption.

Soon after began legislative work to introduce a multi-party system, civil liberties, democracy, and the rule of law and a market economy in Poland, anticipated because it promised genuine westernisation. Gradually, absorbed by the will to catch up on the "civilisation" delay, the Poles went to work to earn money, and thus, social issues slowly disappeared from their view. The impact of the disappearance of the critical and active civil society behind the Solidarnosc movement was especially felt with regard to the fight for human rights and for the equality of treatment. This absence was observed by many Polish analysts [START_REF] Rafal | Ankieta. Czego brakuje w polskiej sferze[END_REF].

In 1989, the split, expressed by T. Mazowiecki as a "big hyphen" which was to separate a Poland reborn from its ashes from the socialist regime without giving way to reprisals and vengeance, showed Poland that there was a pressing need for a new model of governance. In the vacuum left by the totalitarian state (both repressive and protective) and the dismantling of its institutions that began in 1989, the Polish people began to seek references for the organisation of political life and the governance of the third Republic. These stemmed from two sources: from the 20-year period of independence (second Republic) between the two wars and/or the political organisation model of democratic societies promoted by the European Union. However, these two models differ largely; they were and still have conflicting values and standards.

Reference to the second Republic The second reference corresponds to all the gains made in terms of tolerance and equality of treatment. We refer to these norms which today appear in the Charter of the Rights of European Citizens and are driven by EU directives as norms of nondiscrimination. These values have been upheld by part of the Polish political elite as well as by a section of Polish society which aspires to "genuine European democracy" and supports the project of European integration.

From the beginning of the transition, political life in Poland was marked by continuous tension between these two references. Paradoxically, while the political parties associated with the Solidarnosc movement progressively began to refer to the Endecja model, especially after J. Olszewski's7 coup, left-wing parties (which had resulted from the mutation of the Communist Party) to which the president Aleksander Kwasniewski (1995Kwasniewski ( -2005) ) belonged, adopted a distinctly pro-European orientation. This tension reached its peak during the Government led by J. Kaczynski between 2006 and 2007 and became the breaking point between two Polish political parties (pro-European and nationalist) after the accession to power of his PiS party in 2006 and 2015. The fight against discrimination was at the heart of this tension, not as a subject that divided but rather as an absent and hidden subject. For very different reasons, both right-wing and left-wing governments were unfavourable to the adoption of the framework law prohibiting discrimination in Poland as required by European directives.

who became Prime Minister in December 1991, shared the "true -false list of collaborators of the Communist police" with Polish MPs in April 1992. Among the people named on this list was L. Walesa. This initiative was interpreted as a "coup attempt from within" and precipitated the fall of his government in June 1992. Political parties created by Jan Olszewski in the aftermath of these events (Movement for the Republic -1992, Movement for the Reconstruction of Poland -1995) were associated with nationalist parties such as the League of Polish Families, which participated in the Government of Jaroslaw Kaczynski, 2006Kaczynski, -2007. . In 2004, citing the need to control public finances, the Government of Leszek Miller (left-wing) refused to create a post of Commissioner responsible for the fight against discrimination. In 2005, the Polish parliament (mostly right-wing) rejected the bill on gender equality and on the prohibition of all forms of discrimination (gender, religion, origin, age, sexual orientation), and thus failed to guarantee their implementation as required by EU directives. The project envisioned the creation of an office responsible for gender equality and for the fight against discrimination; its director was to be appointed by the Prime Minister. Engaged in negotiations with the EU in relation to directive 2002/73, which postulates that active efforts should be made towards gender equality, Poland fell increasingly behind in this area, as in other areas relating to the respect of equality of treatment. Since then, the situation has worsened in many respects (right to legal abortion, protection in the event of rape, assistance to female victims of domestic violence, and so on).

Indeed, between 2005 and 2008, no Commissioner was responsible for equality.

Although the institution had been created in 2001, it was done away with in 2005 and replaced by the Office for the Protection of the Family, whose reference was the traditional family ideology. This political decision was taken by men belonging to conservative and xenophobic political parties who had been members of two governments, i.e., K. Marcinkiewicz's and Jaroslaw Kaczynski's governments of 2005-2007 (some of the members of the latter government were from radical right-wing parties). Moreover, the scope of this position (the actions it could take were very limited) was often challenged by conservative feminist organisations: the Forum of Polish Women and the League of Polish Families. In April 2008, the Prime Minister Donald Tusk finally re-established the function of Commissioner responsible for equality of treatment. For the social actors who had been active against discrimination, this was seen as a mere "formal gesture". Indeed, deemed inadequate and lacking specific targets, the actions of the Minister were strongly opposed by Polish associations fighting discrimination against women and homosexuals. Upon returning to power in 2015, PiS reversed this decision not only by doing away with this function but also by leading a real policy of repression against feminist associations8 and the Centre for Monitoring Racist and Xenophobic Behaviour.

From the very beginning of the transition and the negotiations with the EU, the relationship with ethnic minorities was a central aspect on which European authorities expected Polish authorities to take action (notably with regard to the treatment of the Roma population). However, the political climate in Poland did not view this as a central issue. Studies on the attitudes of politicians in Poland after 1994 show that these politicians attached little importance to this subject and did not consider that democratic maturity depended on the regulation of the issue of national and ethnic minorities (Wesolowski, 2001). Besides, the debates in Parliament on the introduction of special guarantees allowing minority identities to express themselves in the public space revealed neither disagreements nor conflicts. The recordings of discussions we were able to listen to showed that much of the debate was focused on the use of minority languages in the administration of the State and on the specific provisions regarding the parliamentary inclusion of minorities. At the same time, the Defender of Civil Rights (whose function was created in 1988) received very few complaints from members of national or ethnic minorities concerning the breaching of their rights (33 in 2002, including 8 from individuals)9 . It is thus likely that this particular problem reflected a mismatch between EU policy objectives and Polish reality, with the latter on a wholly different level.

Throughout the period of transition, the majority of Polish people did not understand why discrimination was a major problem. The dominant view was that the denial of rights simply boiled down to the oppression of political opponents. Inherited from the past, the interpretation of the concept of human rights remained rather essentialist (political rights), and even today many Poles believe that they are neither discriminating nor discriminated against. Polish sociologists (Mikulska, 2008) speak of a lack of awareness of the problem, notably when it comes to racial discrimination, even though studies have shown that feelings of hostility towards the few foreigners that are visible -such as Vietnamese or Arabs -are on the increase, especially since 2015 following the official positions taken by J.Kaczynski, leader of the PiS, who referred to immigrants as "carriers of infectious diseases."

While constitutional and legal guarantees are now in place, their mobilisation remains highly dependent on the sensitivity of judges, which explains why the struggle for an independent judiciary is important. Indeed, since the law of July 12, 2017, the Minister of Justice, who names all court presidents and dismisses those who are not loyal to the ruling party, controls this judiciary.

However, at the start of negotiations with the EU in 1994, Poland formally adopted all the minimum standards set to affirm its membership to the European space. The legal framework exists, i.e., it is stated in the texts, but it not respected by public authorities, notably the Ministry of Interior, which has remained very "tolerant" or even "blind" to increasing racist and xenophobic acts in Poland.

In the Polish Constitution adopted on 2 nd April 1997, article 32 rules on all forms of discrimination, but there are many other items that redefine and mention discrimination, such as articles 30, 31, 35, among others. Ever since its adoption in 1974, the Labour Code has undergone numerous modifications in an attempt to take into account the new social and economic context; the last modification was carried out on 18 th January 2009.

The Polish Penal Code, adopted in 1998 in articles 119, 256, and 257, rules on the prosecution of xenophobic and racist acts, even in speech. The 1996The , 1999[START_REF]Popyt na prace cudzoziemcow. Polska i sasiedzi[END_REF] Today, Poland is at the heart of the debate in the European Parliament around the disrespect of "European values" and the Commission is expected to initiate the procedure provided for in article 7 of the treaty, which could deprive the country of some of its rights within the EU.

The undermining of non-discrimination

All legal mechanisms mentioned earlier and which were expected to lead to the construction of a social space without discrimination were adopted in Poland but they did not spark major public or parliamentary debate. Yet Poland had taken seven years to adopt the framework law on equality of treatment, and there was no real pressure to speed up the debate (except for a few feminist associations and associations engaged in the defence of the rights of homosexual people). An analysis of the reports of the discussions that took place during the parliamentary committees reveals a semantic and political vacuum; in other words, the discussions lacked a specific objective. The parliamentarians present had in mind the requirements of the EU and nothing else.

These meetings seemed to revolve around an implicit idea: Poland must adopt the framework law to satisfy the requirements of the EU but it must be careful to avoid opening the debate on the situation in Poland. The framework law adopted the principle of "the adjustment of the burden of proof" laid down in EU guidelines, but its application stopped where the private sphere begun -a space for the expression of individual freedom. However, in 2007, the interpretation of the notion of "private sphere" led the Polish Supreme Court to decide that the "private sphere" can be applied to a private company. The court thus judged that complaints of discrimination related to wage differences between Polish and German employees (the latter were better paid than the former who had been laid off) did not fall within the scope of the law on nondiscrimination.

Adopting the framework law in December 2010, Polish society once again skirted around the subject. The actual problem of the equality of treatment in Poland calls for the questioning of the attitudes related to homosexuals and the treatment they receive in both the public and social sphere and in the media. Let us focus on this fact.

Beyond the political rupture after 1989, it is clear that the implementation of a proactive public policy to combat discrimination has today gotten lost in the intricacies of Polish political life, and the sources of this discrimination are rather deeply rooted. This issue cuts across -without reaching equilibrium -the foundations of the catholic tradition and the moral standards promoted by the very powerful and highly politicised Polish church, which has adopted an increasingly hostile attitude to all forms of 'foreignness', and by the democratic standards driven by a section of Polish society and its elites, standards promoted by EU directives. Although Polish legislation today contains all the guarantees of equality of treatment, the attitudes of a large proportion of the society and even some of its elites, notably those belonging to the radical right, have remained at odds with the standards and the values underlying the principles of a non-discriminating society (Smolar, 2006). In 1995, during the discussions on the text of the new constitution (adopted in 1997), pressure from the church meant that discrimination for reasons of sexual orientation was not prohibited in the text. No Polish court interpreted the failure to comply with the principle of equal treatment by evoking the notion of sexual orientation. It may be argued that today, in the absence of foreigners, the frame of reference for xenophobia is homosexual people. They have now become "the new Polish foreigners". Analysing the situation in France, Eric Fassin evoked the superposition of sexual and racial registers (Fassin D, Fassin E., 2006, p.) (249); the same can be said about Poland. The rhetoric used to politicise homosexuality today is the same that was used against semitism in the past.

It is clear that the legacy of the Endecja party is yet to "pass into the past". Kaczynski 2006-2007, the "historic anti-Semitism" transformed into homophobia, and the hunt for Jews was replaced by the hunt for homosexuals. Homophobic arguments today mobilise the same symbolic and political registers as those used by Endecja in the 1930s around the "Jewish threat". As a member of the far-right/right government coalition, Giertych's intention was to exclude persons suspected of homosexuality from the exercise of certain professions, notably teaching. He withdrew from circulation all textbooks in which the word "homosexuality" was used. More recently, other male and female politicians have continued to assert that it is obvious and natural that there is no place for homosexuals in education.

The position of the "stranger within", as defined by Simmel, formerly occupied by Jews in the Polish imaginary, has been replaced by homosexuals, who fall outside the norm of "sexually correct". The moral standards of homosexuality have been imposed by catholic morality hammered in by Polish priests during Sunday mass and by the conservative Torun-based "Maryja" radio station. This station is strictly followed by the members of the ultra-catholic and nationalist youth movement "Mlodziez Wszechpolska" (Ultra Polish youth) 10 and the members of all the political parties that make up the National Radical Movement (ONR) which paraded during the national day of independence on 11/11/2017 and on 2018 brandishing slogans of "a white Europe", swastikas and incitement to the massacre of Muslims. This suggests the existence of a mechanism that unceasingly produces the excluded and one to which Geneviève Fraisse has described as "the friends of our friends". Broadly speaking, in every era, "those close to us" become the object of discrimination. They are always the same, nonconformists excluded from the dominant symbolic order (Fraisse, 2010, p. 41.). In a country without foreigners and where many people are devout catholics, a country with a long-standing symbolic register for the identification of foreigners, xenophobic thought can easily find its object: homosexual, Arab, or assimilated to one of the other.

It seems clear that to arrive at a non-discriminating Polish society, significant progress must be made in the fight against homophobia and white and catholic nationalism. However, the conditions to accomplish this progress are yet to be met.

While there has been a certain revival of the Polish public opinion and awareness of the problem, it is worth noting, as Monika Baer (Baer, 2010, p. 247) has done, the political and social invisibility of the problem posed by the relationship to others in Polish society, as it was with regard to Jews in the past. Today, the most active associations engaged in the fight against discrimination (permitted since 2001) are confronted with an attitude of incomprehension or even hostility to their cause on a daily basis, even among the core institutions of the Polish State 11 .

Conclusion

Although absent from collective thought, the fight against discrimination was introduced as one of the essential aspects of the adoption of the "acquis 10 This refers to the nationalist catholic youth organisation, whose founder and Chairman was also R. Giertych. During clashes that often took place on the streets of Polish cities during demonstrations for equality and tolerance around the defence of the rights and freedoms of homosexual people (particularly in 2004 in Krakow and Poznan), this organisation adopted very violent provocation methods. 11 During a discussion on Polish television on September 24th 2010, Ms. E. Radziszewska (Commissioner responsible for equality in Tusk) government used openly homophobic language in the presence of a member of an association for the defence of homosexual people. Despite pressure from progressive groups, left-wing parties, and the progressive feminist movement, she was not dismissed by Prime Minister D. Tusk.

communautaire" during negotiations for the integration of Poland into the EU. It is during the period that began in 1994, under the watchful eye of EU institutions (Council of Europe, the European Commission, etc.), that Polish authorities were compelled to adopt legislation and mechanisms to ensure the respect of European standards in the field of the prevention of and the fight against discrimination. Throughout this period, the public attention accorded to what was viewed as discrimination in Poland was closely linked to the intervention of European authorities and the obligations introduced by these authorities.

After the burst of civic and citizen actions at the beginning of the transition period, Polish society today appears to be hardly mobilised around the issues of civil rights and the fight against discrimination. Once again, the fight is political and would require the ousting of PiS from power to establish the rule of law and respect for democratic principles. The market economy, with its spirit of competitiveness and personal enrichment, has weakened social mobilisation and the vigilance necessary to prevent the activation of xenophobic backgrounds in Poland by providing new content despite the absence of foreigners. Given the existing tension between the need for freedom and the aspiration to equality -underscored by Tocqueville as a major challenge democratic societies must address -Polish society, which emerged from 50 years of totalitarianism, still views freedom as being of primary importance. The lack of reflection on the concept of equality and on the social and political conditions necessary to implement it today affect the fate of the non-discriminating society in Poland. Polish society now seems to be suffering from a sense of anomie, preventing it from actively combating the return of past ghosts in a new form.

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"Polityka" is a weekly newspaper whose political line is comparable to the French "Nouvel observateur". Between 1970 and 1980, its journalists actively supported the process of political transformation and in 1988 its editor, Mieczyslaw Rakowski, became the Prime Minister after the organisation of the Round Table which led to the change of political regime.

This refers to a pogrom (massacre) of the Jewish population instigated by the local police and people from the Kielce neighbourhood located in the centre of Poland. It took place in 1945.

This refers to the powerful National Democracy party (Endecja) founded in the early 20th century and led by Roman Dmowski. The author of the book "The Jewish Question"' published in 1930' asserted at the time that the presence of the Jewish community in Poland posed a real danger to the integrity and sovereignty of the nation State.

This lawyer, defender of political opponents in the 1980s (A. Michnik, J. Kuron, among others), and

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Fatima-Zohra Belmokaddem

Julie Dagonneau

Julien Lhomme

Romain Blanc

Azucena Garduno-Alva

Christian Maliverney

Antoine Baceiredo

Eddy Maerten

Etienne Fleury

Françoise Méchin

Françoise Mechin
email: francoise.mechin@insa-lyon.fr

Novel nucleophilic/basic and acidic organocatalysts for reaction between poorly reactive diisocyanate and diols

Keywords: polyurethane, prepolymers, organocatalysis, guanidine, phenylphosphonic acid, water/alcohol selectivity

Novel nucleophilic/basic and acidic organocatalysts for reaction between poorly reactive diisocyanate and diols

Introduction

Polyurethanes (PUs) constitute an important class of polymers with widespread application (foams, adhesives, coatings, elastomers, materials for aeronautics industry…). [START_REF] Hepburn | Polyurethane Elastomers[END_REF][START_REF] Wirpska | Poly(urethane)s: Chemistry, Technology, and Application[END_REF][START_REF] Szycher | Szycher's Handbook of Polyurethanes[END_REF][START_REF] Delebecq | On the versatility of urethane/urea bonds: reversibility, blocked isocyanate, and non-isocyanate polyurethane[END_REF][START_REF] Yilgör | Critical parameters in designing segmented polyurethanes and their effect on morphology and properties: a comprehensive review Polymer[END_REF] To date, the most straightforward route for their preparation, based on the pioneer work of Bayer, is the reaction between diisocyanates and diols, often in presence of a catalyst. [START_REF] Bayer | The diisocyanate polyaddition process (polyurethanes). Description of a new principle for building up high-molecular compounds (1937-1945)[END_REF][START_REF] Bayer | The structure of Vulkollan urethan elastomers[END_REF] Nowadays, two types of metal-based catalysts are mainly used in the polyurethane industry: tin (e.g. dibutyltin dilaurate, DBTDL) [START_REF] Lipatova | On the mechanism of polyurethane formation catalyzed by metal chelates and organotin compounds[END_REF][START_REF] Frisch | Catalysis in isocyanate reactions[END_REF][START_REF] Reegen | Catalysis in isocyanate reactions[END_REF][START_REF] Thiele | Reactions of isocyanates and catalysis in polyurethanes[END_REF][START_REF] Han | Kinetics and mechanisms of catalyzed and non-catalyzed reactions of OH and NCO in acrylic polyol-1,6-hexamethylene diisocyanate (HDI) polyurethanes. VI[END_REF] and mercury (such as [bis(phenyl mercury) dodecenyl succinate or bis(t-butyl mercury) dodecenyl succinate]) [START_REF] Abbate | Organometallic catalysis of the reaction of alcohols with isocyanates[END_REF][START_REF] Robins | Minnesota Mining & Manufacturing Company, assignee[END_REF] compounds. The former present exceptional catalytic activity, and the latter are ideal latent catalysts which allow for more time to handle the formulation. However, the use of tin and mercury derivatives will be restricted in a near future for environmental reasons. [START_REF] Smith | Toxicological Data on Organotin Compounds[END_REF][START_REF]Toxicological Profile for Tin and Tin compounds[END_REF][START_REF]Revised assessment of the risks to health and the environment associated with the use of the four organotin compounds TBT[END_REF][START_REF] Gitlitz | Kirk-Othmer Encyclopedia of Chemical Technology[END_REF] As an alternative, less toxic organometallic catalysts such as bismuth, aluminum, zirconium and zinc derivatives were proposed, [START_REF] Blank | Catalysis of the isocyanate-hydroxyl reaction by non-tin catalysts[END_REF][START_REF] Blank | New developments in catalysis[END_REF][START_REF] Sardon | Synthesis of isophorone diisocyanate (IPDI) based waterborne polyurethanes: comparison between zirconium and tin catalysts in the polymerisation process[END_REF] but none of them appears to be entirely satisfactory in terms of both reaction rates and molar masses. The intensive research in the field of organocatalysis during the last years has led to the design of a number of catalysts offering new green alternatives to traditional organometallic catalysts; [START_REF] Dalko | Enantioselective organocatalysis[END_REF][START_REF] Dalko | In the golden age of organocatalysis[END_REF][START_REF] Enders | Nucleophilic carbenes in asymmetric organocatalysis[END_REF][START_REF] List | Introduction: organocatalysis[END_REF][START_REF] Kamber | Organocatalytic ring-opening polymerization[END_REF] very recently an interesting review gathered the main results newly obtained on this subject. [START_REF] Sardon | Synthesis of polyurethanes using organocatalysis: a perspective[END_REF] The most efficient small organic molecules, able to catalyze the synthesis of PUs, are mostly organic bases and/or nucleophiles (see Scheme 1). Tertiary amines such as 1,4diazabicyclo[2,2,2]octane (DABCO), N-alkyl morpholines and amidines (e.g. 1,8diazabicyclo [START_REF] Yilgör | Critical parameters in designing segmented polyurethanes and their effect on morphology and properties: a comprehensive review Polymer[END_REF][START_REF] Delebecq | On the versatility of urethane/urea bonds: reversibility, blocked isocyanate, and non-isocyanate polyurethane[END_REF],0]undec-7-ene, DBU) have been shown to accelerate the reaction between diols and diisocyanates, however their overall efficiencies remain low compared to tincatalysts. [START_REF] Silva | Recent developments in polyurethane catalysis: catalytic mechanisms review[END_REF] Landais and Cramail have disclosed very interesting results showing the enhanced catalytic activity of bicyclic pentaalkylated guanidines (MTBD), [START_REF] Alsarraf | Cyclic guanidines as efficient organocatalysts for the synthesis of polyurethanes[END_REF][START_REF] Alsarraf | Latent catalysts based on guanidine templates for polyurethane synthesis[END_REF] leading to PU molar masses similar to those obtained with tin catalysts. Recently, Destarac and al.

described the catalytic activity of 1,3-bis-(di-tert-butyl)imidazole-2-ylidene (tBuNHC) for the polymerization of aliphatic diisocyanates and diols, using relatively low catalyst loading and mild conditions. [START_REF] Coutelier | N-heterocyclic carbene-catalyzed synthesis of polyurethanes[END_REF] However, all these studies are exclusively devoted to primary alcohols, which are the most reactive towards isocyanates. In contrast, secondary alcohols are much less reactive, although this family of alcohols such as poly(oxypropylene) polyols are widely used in polyurethane industry, and very little literature addresses this issue in terms of innovating catalysts.

[Scheme 1 near here] Surprisingly, only a few studies concern the use of organic acids as catalysts for the synthesis of PUs. Preliminary results have been reported by Nordstrom (organic acids) [START_REF] Nordstrom | Acid catalysis of two component urethane clearcoats for automotive applications[END_REF] and by Yezrielev (with a disulfonic acid) [START_REF] Subrayan | Reactions of phenolic ester alcohol with aliphatic isocyanates-transcarbamoylation of phenolic to aliphatic urethane: a 13 C-NMR study[END_REF] for the activation of the reaction between isocyanates and alcohols. However, in both cases, the results are less favorable compared to those observed with tin-based catalysts. Recently, a catalyst screening study of organic acids (sulfonic acids, carboxylic acids, phosphonic acids) was reported by Hedrick. [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF][START_REF] Sardon | Highly tunable polyurethanes: organocatalyzed polyaddition and subsequent post-polymerization modification of pentafluorophenyl ester side chains[END_REF] Among them, sulfonic acids exhibit very interesting activities at room temperature and were found to compete with DBTDL, both in terms of efficiency and of PUs molar mass. Interestingly, Hedrick has demonstrated that no PU degradation was observed when acidic catalysts were used, contrary to what could be observed after several days when strong bases were used. [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF][START_REF] Sardon | Highly tunable polyurethanes: organocatalyzed polyaddition and subsequent post-polymerization modification of pentafluorophenyl ester side chains[END_REF] Herein we report the evaluation of novel organocatalysts (guanidine and acidic phosphorus derivatives) for the polymerization reaction of isophorone diisocyanate (IPDI) and poly(oxypropylene) macrodiols, monomers which often require harsh reaction conditions and/or large catalyst loading.

Experimental

Materials

Isophorone diisocyanate (IPDI) and ,-dihydroxy poly(oxypropylene) (PPG-2000) were gifts from Allrim-Juxta (Audincourt, France). The hydroxyl number of the macrodiol was estimated as IOH = 56 mg KOH/g using both chemical titration with acetic anhydride (French standard NF T 52-112) and 1 H NMR. Tetramethylguanidine (TMG), t-butyl tetramethylguanidine (t-BuTMG), phosphonic acid, ethyl phosphonic acid, vinyl phosphonic acid, phenyl phosphonic acid and trifluoromethane sulfonic acid (triflic acid), as well as 1methoxy-2-propanol (PGME) and di(propylene glycol) dimethyl ether (DPGDME) were purchased from Aldrich France. 1-butyl-2,3-dicyclohexyl-1-methylguanidine (Cy2MeBuG), 1-cyclohexyl-2,2,3,3-tetrapropylguanidine (CyPr4G) and 1-octyl-2,2,3,3-tetramethylguanidine (OctTMG) were synthesized by Bluestar Silicones (Saint-Fons, France). Allyl phosphonic acid was obtained from Specific Polymers (Castries, France). All the other catalysts, i.e. perfluorophenyl phosphonic acid, mesityl phosphonic acid, mesityl phosphinic acid and 3,5bis(trifluoromethyl)phenyl phosphonic acid ("CF3 phenyl") were synthesized at the LHFA.

Full experimental procedures and characterization data for non-commercial derivatives can be found in the supporting information. The chemical structures of all the guanidine and acidic phosphorus catalysts are given in Schemes 2 & 3.

All solvents and reagents were used as received.

[Scheme 2 near here] [Scheme 3 near here] Kinetic studies PPG-2000 was reacted in bulk with excess IPDI (initial ratio [NCO]/[OH] = 2.00) at various temperatures (20 -80°C) and using different amounts of catalysts (1 mol%, i.e. between 0.15 and 0.50 wt% depending on the chemical structure), leading to bis(isocyanato-terminated) polyurethane prepolymers. A typical experiment can be described as follows: the PPG macrodiol was first systematically dried under vacuum at 100 °C for 3 h; whereas the NCO index of IPDI was also systematically checked by titration (see below). When a catalyst was used, an appropriate amount was mixed with the macrodiol. Since the reaction between IPDI (~66 g, i.e. ~0.594 mol NCO) and PPG-2000 (~300 g, i.e. ~0.299 mol OH) was always very slow at room temperature, and since these compounds were rather fluid they could then be pre-mixed in a beaker under magnetic stirring. This mixture was finally poured in a thermoregulated 1 L jacketed reactor under nitrogen blanket. This reactor was equipped with a mechanical stirrer (300 rpm) and a bottom outlet gate was used for easy sampling.

In the case of water/IPDI reactions, a solvent was added in order to maintain the OHconcentration similar to that of the bulk PPG-2000/IPDI experiments (ca 0.82 mol/kg). The OH equivalent weight is indeed 9 g/mol OH for water, vs 1002 g/mol OH for the macrodiol.

Di(propylene glycol) bis(methyl ether) (DPGDME) was chosen for this purpose as it could provide the medium with a polarity rather similar to that of the polyether chain. The water content of this solvent was 0.14 wt%. In a typical experiment, DPGDME (290 g) was mixed with water (2 g), and then the blend was homogenized 1 night at room temperature. A proper amount of this mixture was then added to a pre-weighed amount of IPDI (~60 g) in a beaker, in order to obtain [OH]/[NCO] = 0.5. The blend was homogenized once more with a mechanical stirrer, and the catalyst was then added. The reaction mixture could then finally be poured into the thermo-regulated reactor.

Isocyanate titration

The kinetics were estimated by monitoring the amount of residual NCO groups. Isocyanate functions were determined following the French standard AFNOR NF T 52-132 by reacting them with an excess of N,N-di(n-butyl) amine and back-titrating the excess amine with 1N HCl in anhydrous acetone, using bromocresol green as indicator. A blank titration was also carried out without isocyanate, using precisely the same amount of N,N-di(n-butyl) amine.

Size exclusion chromatography (SEC)

Molar mass distributions were assessed by Size Exclusion Chromatography, SEC, using tetrahydrofurane (THF), at 35 °C as eluent. The THF flow rate was 1.0 mL/min. Analyses were run on a Viscotek chromatograph equipped with 3 Styragel HR 4E columns; detectors consisted of a differential refractometer VE3580 and a Dual T60A detector (combining a right angle light scattering detector and a viscosimeter).

H and 13 C Nuclear Magnetic Resonance

The chemical structures of the prepolymers were determined by 1 H or 13 C NMR spectroscopy performed on a Bruker DRX 400 spectrometer operating at 400 ( 1 H) or 100 ( 13 C) MHz.

Samples were prepared in DMSO-d6 or CDCl3.

Results and discussion

New guanidine derivatives catalysts

Following the promising results obtained by Alsarraf et al [START_REF] Alsarraf | Cyclic guanidines as efficient organocatalysts for the synthesis of polyurethanes[END_REF][START_REF] Alsarraf | Latent catalysts based on guanidine templates for polyurethane synthesis[END_REF] and by Maliverney [START_REF] Maliverney | Bluestar Silicones France, assignee. Novel catalysts for reaction between an isocyanate and an alcohol[END_REF], the kinetics of the reaction between IPDI and PPG-2000 was first monitored in the presence of 1 mol% of catalyst (with respect to the NCO groups, i.e. between 0.19 and 0.50 wt%) chosen among five different guanidine derivatives with different basicity (see Table 1 in supporting information). At 60 °C, the NCO conversion curves obtained (xNCO vs time) are represented in Figure 1.

[Figure 1 near here] First, although the amount of added catalyst is non-negligible, it appears that none of the tested species displays a real efficient catalytic activity for the considered reactive system.

Typically it would take only about 40 min to reach complete conversion (xNCO = 0.5) at 45 °C using 0.017 mol% of dibutyl tin dilaurate; [START_REF] Lhomme | Nouveaux catalyseurs et systèmes catalytiques appliqués à la synthèse du polyuréthane via la réaction isocyanatealcool [New catalysts and catalytic systems applied to polyurethane synthesis via the isocyanate-alcohol reaction[END_REF] whereas here only 3 guanidines (TMG, tBuTMG and OctTMG) allow to reach complete NCO conversion within 1 day or so (Figure 1a). Moreover, the conversion obtained with tBuTMG clearly exceeds 0.5 (the theoretical maximal conversion if only urethanes were formed), denoting that this catalyst probably induces secondary reactions such as the formation of uretidione dimers, isocyanurate trimers, or allophanate branching points.

A closer look at the relative activities of the different guanidines used is given in Figure 1b. The most hindered guanidines, CyPr4G and Cy2MeBuG, showed a poor ability to catalyze the polymerization reaction, indicating that the catalytic activity should be related to the nucleophilicity instead of the basicity. Indeed, with the less hindered compounds, therefore more nucleophilic, the kinetics of the reaction increased notably. However, the case of TMG is particular since its bears a labile hydrogen atom (in fact, Cy2MeBuG also has one, but it is a secondary conjugated amine and this proton should not be very reactive towards isocyanates or should only lead to an equilibrium). TMG can therefore easily react with the diisocyanate IPDI to yield a stable adduct (note that other guanidines, not bearing labile protons, are also susceptible to yield 2:1 adducts with a heterocyclic triazinedione moiety, but this was not observed for the case of IPDI and tBuTMG because of steric hindrance [START_REF] Polenz | Thermally cleavable imine base/isocyanate adducts and oligomers suitable as initiators for radical homo-and copolymerization[END_REF]).

Apart from consuming a slight amount (1 % at the most) of isocyanate functions, the formation of the IPDI-TMG adduct could also participate in the catalytic activation. This was already observed by Alsarraf for other guanidines, [START_REF] Alsarraf | Latent catalysts based on guanidine templates for polyurethane synthesis[END_REF] but in this case the guanidines had no labile hydrogen and the adducts were rather pseudo isocyanurates involving 2 isocyanate molecules; moreover the actual catalyst was found to be the guanidine that was regenerated in the presence of OH groups above 60 °C. In the present work the bis(urea) adduct was thus synthesized by reacting stoichiometric amounts of IPDI and TMG in bulk at room temperature ([NCO]/[NH] = 1, see Scheme S1 in supporting information). A solid product was rapidly obtained that was then characterized by NMR spectroscopy ( 1 H and 13 C). In contrast to this quasi-instantaneous process, the reaction between aliphatic isocyanates and Cy2MeBuG takes several hours in bulk at room temperature, and the catalytic activity of the IPDI-(Cy2MeBuG)2 adduct was not studied.

In order to be able to properly assess the NMR signals detected in the various prepolymers, a model reaction was first conducted between IPDI (1 eq.) and 1-methoxy-2propanol (PGME, 1 eq.), i.e. with [NCO]/[OH] = 2 (20 °C, catalyst 0.2 mol% phenylmercury neodecanoate). The residual NCO groups were then neutralized using an excess of di(n-butyl) amine (DBA). The reaction is depicted in Scheme 4, and the resulting 1 H NMR spectrum is shown in Figure 2. This allows to associate signals between 6.4 and 7.2 ppm to the NH groups of the urethane functions, whereas urea NH groups appear between 5.4 and 6.0 ppm.

The urea comes mainly from the capping reaction with DBA; however, the starting PGME also contains about 0.015 wt% of water that could react with IPDI leading to additional alkyl urea functions exactly in the same  range; this could account for the slightly higher integration of the urea peak (1.098 instead of 1.00 for the urethane). [START_REF] Shi | Quantitative IR characterization of urea groups in waterborne polyurethanes[END_REF] [Scheme 4 near here] [Figure 2 near here] NMR-spectra of the pure IPDI-TMG adduct and of the IPDI-PPG prepolymer synthesized in the presence of 1 mol% of TMG at 60 °C are represented in Figure 3. The spectrum of the polyaddition product of IPDI and PPG-2000 obtained in the presence of a large amount (~32 mol% / NCO) of TMG was added for comparison.

[Figure 3 near here]

In the prepolymer spectrum, several signals appear in the urea proton range between 5.4 and 6.0 ppm. They might be due to the partial hydrolysis of NCO groups by moisture brought by the PPG-2000 macrodiol or the highly hygroscopic guanidine catalyst. But no trace of the adduct can be detected in the prepolymer spectrum; however, only 1 mol% of TMG was added and even if this compound was formed, it might be in too low quantities to appear clearly in this spectrum. In contrast, the spectrum of the polyurethane synthesized in the presence of non-negligible amounts of TMG clearly displays the urea peaks associated with this adduct between 6.1 and 6.4 ppm, even though large amounts of alcoholic protons were also present and moreover supposed to be activated by TMG. This confirms a competition between the nucleophilic and basic activations that can be attributed to guanidine compounds as already mentioned by Alsarraf. [START_REF] Alsarraf | Cyclic guanidines as efficient organocatalysts for the synthesis of polyurethanes[END_REF] The use of the adduct (pre-dissolved in 1 mL THF before addition to the macrodiol) as catalyst in the IPDI-PPG reaction resulted in a clear enhancement of the kinetics, as shown in Figure 4. Its catalytic efficiency seems rather similar or even a little higher than that of TMG under these conditions (60 °C); the shapes of all the curves are also quite similar and do not particularly suggest a regeneration of the parent guanidine in the case of the adduct, contrary to Alsarraf's latent catalysts. [START_REF] Alsarraf | Latent catalysts based on guanidine templates for polyurethane synthesis[END_REF] (It should be noted that although a second order is very classically observed for catalyzed isocyanate-alcohol reactions, here such a kinetic analysis could not be precisely performed, since in bulk the process is not isothermal as the reaction is exothermic).

[Figure 4 near here]

At 80 °C though, the situation is a little bit different. Figure 5a shows that the order of catalytic efficiency is about the same as that found at 60 °C, although the various kinetic curves are closer to each other than at lower temperature. But under these conditions almost every tested catalyst finally leads to conversions higher than 0.5; i.e. while catalyzing the isocyanate-alcohol reaction, they probably all induce side reactions of the NCO functions at the same time. Moreover the time to reach 0.5 is very long (10 h or more) compared to classical metal catalysts. The kinetics recorded for DBTDL at 80°C was added in Figure 5 for comparison, but even using only 0.0056 mol% (~ 0.006 wt%), i.e. 180 times less than the tested guanidines, the reaction was incomparably faster. Together, these 2 observations suggest that none of the tested guanidine derivatives appears to be a very suitable catalyst for the considered "low reactive" polyurethane system (aliphatic isocyanate / secondary alcohol at temperatures below 100 °C).

[Figure 5 near here] Furthermore in Figure 5b, it appears that the curve associated with the adduct has a rather sigmoidal shape that is not observed with simple guanidines. This might reveal a more complex mechanism in this case. First, a possible thermally induced, at least partial redissociation of the adduct to yield free TMG molecules could occur at 80 °C (possibly activated by the presence of OH groups). Guanidines and amidines have indeed been mentioned as blocking agents for isocyanates, but this remains rather occasional. [START_REF] Polenz | Thermally cleavable imine base/isocyanate adducts and oligomers suitable as initiators for radical homo-and copolymerization[END_REF][START_REF] Wicks | Blocked isocyanates III. A. Mechanisms and chemistry[END_REF][START_REF] Wicks | Blocked isocyanates III. B. Uses and applications of blocked isocyanates[END_REF] Moreover a comparison between Figure 4 and 5 suggests that the adduct has in fact rather similar effects on the kinetics at the beginning of the reaction, although the conditions are different (0.1 mol%, 60 °C vs 1 mol%, 80 °C). But the final conversions are nevertheless very different, since xNCO almost stops increasing after about 3 hours in the first case, whereas it keeps on increasing to reach 0.5 and above in the second case. This could mean that only a very small fraction of this catalytic compound is in fact soluble in the reactive medium at the beginning, about the same in both cases; but as isocyanate functions are consumed and more and more urethane bonds are formed, this solubility might increase; and finally at 80 °C and starting with higher amounts of IPDI-TMG adduct, a higher fraction of the catalyst could become active above xNCO ≈ 0.2.

Guanidine derivatives are thus interesting organocatalysts for the synthesis of polyurethanes through the isocyanate-alcohol addition reaction, with a much lower toxicity than the usual metal catalysts. But they are not exceptionally efficient, especially as far as systems with low reactivity are concerned. Morever, they also catalyze the isocyanate-water reaction, which is an important drawback for their use in the preparation of solid polyurethane materials, especially if they are transparent. In agreement with this, it can be noted that guanidines have been mentioned as good accelerators for moisture-curable systems. [START_REF] Baghdachi | Fast-cure polyurethane sealant composition containing silyl-substituted guanidine accelerators[END_REF] Considering that this would not be sufficiently satisfying from an industrial point of view, and taking into account the recent studies of Sardon et al, [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF][START_REF] Sardon | Highly tunable polyurethanes: organocatalyzed polyaddition and subsequent post-polymerization modification of pentafluorophenyl ester side chains[END_REF] new attempts were made with a family of organic acids derived from phenyl phosphonic acid.

New acidic phosphorus derivatives catalysts

Sardon et al recently obtained interesting results for the catalysis of the reaction between poly(ethylene glycol) and hexamethylene diisocyanate (HDI) using sulfonic acids and especially triflic acid. [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF] From molecular modeling, ternary adducts between acid, isocyanate and alcohol were assumed to be formed. Furthermore the efficiency of such derivatives was shown to be related to the strength of the acid as well as to the nucleophilicity of the conjugate base. Since triflic acid even proved to be an efficient catalyst for the bulk polyaddition reaction of HDI with PPG (Mn = 1000 g.mol -1 ) at 60 °C, it was obviously very interesting to test it under our own experimental conditions. Surprisingly, a comparatively low activity was found for both carboxylic acids (acetic and trifluoroacetic acids) and diphenyl phosphate. [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF] However, strong phosphonic acids such as phenyl phosphonic acid or its derivatives have never been tested, and therefore we have decided to evaluate their catalytic activity, first at 60°C (see Figure S1 in supporting information) then at 80°C. & Figure S2). Here again the case of DBTDL in very low amounts (0.0056 mol%, i.e. ~0.006 wt%) was added for comparison. It appears first in Figure 6a that for all the used catalysts except perfluorophenyl phosphonic acid, the maximal conversion is below or only very slightly above (case of phenyl phosphonic acid) xNCO = 0.5, denoting only few secondary reactions for NCO groups. The case of perfluorophenyl phosphonic acid is strikingly different with a maximal NCO conversion close to 0.8; in this case the final prepolymer was also highly viscous, unlike all the others. Numerous side reactions can thus be suspected (see below).

[Figure 6 near here]

In Figure 6b, the initial catalytic activities of all the used compounds can be compared. Most of them are much more efficient catalysts than all the tested guanidines (Figure 5b). Among the phenyl phosphonic acid derivatives, a global tendency with some exceptions can be observed: roughly, within this family the efficiency of the catalyst seems to be directly related to its acidity with the most acidic compounds leading to the highest catalytic activity. This was also observed by Sardon et al. The attractive effect of the phenyl moiety is even enhanced by the presence of fluorine atoms or CF3 groups, and this seems favorable for the catalytic activity of the considered molecule. However mesityl phosphonic acid (pKa = 2.11), supposed to be more acidic than ethyl phosphonic acid (pKa = 2.64), was found less active. It might be because this molecule is sterically hindered and cannot interact easily with isocyanate and alcohol groups to form adducts like in the case of sulfonic acids catalysts. [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF] Although phosphonic acid is also highly acidic, a very low catalytic activity was found for the presently studied system. The high polarity of this molecule that does not display any organic substituents probably lead to a poor solubility in the IPDI/PPG-2000 mixture compared to all the other derivatives, justifying the particularly low efficiency of this catalyst.

Finally triflic acid, although highly acidic and presumably showing sufficient solubility in the reacting medium, also displayed a rather disappointing medium catalytic activity. In Sardon's work, [START_REF] Sardon | Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates[END_REF] the bulk polyaddition IPDI + PPG-1000 was found completed after about 6 h at 60 °C in the presence of 2.5 mol% triflic acid (with respect to the NCO groups). In our case the maximal conversion xNCO = 0.5 seems to be reached after about the same time at 80 °C, but using only 1 mol% of triflic acid. Both results are thus rather consistent, and the fact that triflic acid does not appear as the best catalyst for the IPDI-PPG reaction is finally rather due to the remarkably high efficiency of phenyl phosphonic acid derivatives.

In dichloromethane solution, Sardon observed well-defined kinetic orders (second order with respect to the alcohol + isocyanate, first order with respect to the acid catalyst). In contrast no clear order with respect to the concentration of the reactive functions was found in our case (bulk reaction, with possibly non-isothermal conditions at the beginning because the reaction is exothermic). Moreover as shown in Figure 7, the kinetics are indeed logically enhanced by the increased concentration of phenyl phosphonic acid at 80 °C, but the constants that could be grossly deduced from the first 3 data assuming second order for the reactants do not increase linearly with acid concentration. If the order with respect to phenyl phosphonic acid was 1, the reaction catalyzed with 0.15 mol% catalyst would be much slower.

[Figure 7 near here]

Figure 8 depicts the effect of temperature on the kinetics of the model IPDI/PPG-2000 reactions catalyzed with 1 mol% (with respect to NCO groups) phenyl phosphonic acid or 3,5-bis(trifluoromethyl)phenyl phosphonic acid ("CF3 phenyl"). Both catalysts present very similar activities, whatever the temperature; the conversion obtained with phenyl phosphonic acid is only generally very slightly higher. The strong electron-withdrawing effect of the trifluoromethyl groups strongly influences the pKa of the acid (see Table 2 in supporting information) but not really the catalytic activity; however it might also be counterbalanced by a negative effect on the solubility of the catalyst in the medium. Quite logically, increases in temperature speed up reactions, however the lack of a well-defined kinetic constant did not allow the strict application of Arrhenius' law to our data.

[Figure 8 near here]

For some applications, it can be necessary to perform the IPDI-PPG-2000 polyaddition at room temperature, and toxic metal-catalysts, such as tin or mercury derivatives are typically used for such purpose. [START_REF] Florio | New tin and mercury free organometallic catalysts for CASE urethane applications[END_REF] Replacing these metal catalysts by organic catalysts is now a burning issue. However Figure 8 shows that although phenyl phosphonic acid seems rather efficient, at room temperature the use of only 1 mol% with respect to NCO groups does not allow to reach full conversion in a reasonable time. Higher amounts, up to 10 mol%, were thus tested. It appears that under such conditions the use of 5 mol% is not really satisfying; only 10 mol% phenyl phosphonic acid allows an immediate and sharp increase in the NCO conversion. Nevertheless, in this case, the maximal xNCO = 0.5 was not reached after 1 day. However, keeping in mind that the gel conversion for the polyaddition of a [A3 + B2] system is about 0.7, [START_REF] Pascault | Thermosetting Polymers[END_REF] gelation of such a reactive system (PPG triol + IPDI) at room temperature could still be obtained within a reasonable time using 10 mol% of phenyl phosphonic acid as catalyst.

In many applications, transparent polyurethane materials are needed, and the reaction between isocyanate functions and water that tends to create CO2 bubbles is strictly prohibited.

Ideally, a catalyst that could enhance the reaction of NCO groups with alcohol while hampering that with water would be desired in this case. Such a catalyst is said to have a good water/alcohol selectivity. In Figure 9, a simple comparison was drawn between the final polyurethane prepolymers obtained in bulk at 80 °C, using 1 mol% of 4 efficient catalysts taken among those presented above (tBuTMG, TMG, phenyl phosphonic acid and 3,5bis(trifluoromethyl)phenyl phosphonic acid). Their 1 H NMR spectra clearly show that a large amount of urea protons is present in the case of the guanidine catalysts. The largest amount is logically obtained with TMG, but even for tBuTMG that does not bear any labile proton, urea groups are clearly detected in non-negligible amounts; whereas these protons are almost absent in the case of the phenyl phosphonic derivatives. However all these prepolymers were obtained under the same experimental conditions, starting from the same, similarly dried reagents; it can therefore be assumed that the water/alcohol selectivity of the phosphorus derivatives is much better than that of the guanidines, i.e. that they do not catalyze as much the reaction of NCO groups with adventitious moisture. Since this was particularly interesting from an industrial point of view, further investigation was carried out regarding the kinetics of the reaction between water and IPDI in the presence of these promising new catalysts.

[Figure 9 near here]

Reaction between IPDI and water

For an appropriate comparison with the PPG macrodiol, the kinetics of the reaction between water and IPDI was studied in solution in DPGDME (see experimental part), using from 1 to 10 mol% (0.26 to 2.55 wt%) of phenyl phosphonic acid as catalyst. The conversion of NCO groups was once again monitored vs time and the data compared with those recorded for PPG-2000 as plotted in Figure 10.

[Figure 10 near here]

Unfortunately, for the 3 tested concentrations the reaction with water is notably fastened by the catalyst, and its kinetics are even more enhanced than that of the urethane formation, especially for low concentrations. Two other efficient organic catalysts, namely perfluorophenyl phosphonic acid and 3,5-bis(trifluoromethyl)phenyl phosphonic acid were tested for comparison but the water/alcohol selectivity in both cases was not better, and in fact it was even worse in the latter case (see Figure S6 in the supporting information). Therefore the use of these phosphorus derivatives for the preparation of solid transparent PU materials, although interesting from an environmental point of view, will probably not avoid the formation of bubbles that can sometimes be bothersome.

The hydrolysis products of IPDI obtained with perfluorophenyl phosphonic acid, 3,5bis(trifluoromethyl)phenyl phosphonic acid and phenyl phosphonic acid were then analyzed by SEC in THF (Figure 11). In the latter case, several concentrations were tested. Oligomers with increasing mass should be formed from the hydrolysis of 1 NCO group to an amine function and the subsequent addition of this amine on another isocyanate. The first steps of this reaction are shown in Scheme 5, and indeed these molecules and analogous higher oligomers can presumably be associated with the distinctive peaks (elution volumes: 20.32, 20.81, 21.51 and 22.56 mL, respectively) detected in the chromatograms. One could even imagine the formation of the uretdione dimer of IPDI (M = 444, See Scheme S2 in supporting information). As the catalyst concentration increases, oligomers with increasing molar masses are formed, whereas decreasing amounts of unreacted IPDI are present, consistently with an increasingly fast hydrolysis of the IPDI molecules. In the same way, when used at 1 mol%, phenyl and 3,5-bis(trifluoromethyl)phenyl phosphonic acid ("CF3 phenyl") lead to very similar chromatograms with the same relative amount of residual IPDI, whereas oligomers with slightly lower molar masses and higher amounts of residual IPDI are detected for 1 mol% of perfluorophenyl phosphonic acid. From this point of view, this catalyst might therefore be the most interesting, since it does not seem to promote IPDI hydrolysis as much as the others. However the side reactions observed during the prepolymer synthesis at 80 °C should be kept in mind, and additional analyses were performed on some of them.

[Figure 11 near here] [Scheme 5 near here]

Analysis of the side reactions during prepolymer synthesis

As abnormally high NCO conversions were sometimes obtained for the prepolymer synthesis and especially in the presence of perfluorophenyl phosphonic acid, size exclusion chromatography as well as FTIR and 13 C NMR spectroscopies were performed on the reaction product recovered at 80 °C using 1 mol% of C6F5P(O)(OH)2. In FTIR, the carbonyl elongation peak was considered but all the prepolymers displayed very similar peaks with a maximum at 1716-1717 cm -1 . However, comparison of prepolymer prepared with the fluorinated catalyst (final xNCO = 0.78) with another one displaying a low final NCO conversion (mesityl phosphinic acid, final xNCO = 0.25) reveals the presence of a shoulder around 1690-1700 cm -1 in the first case (see Figure S4 in supporting info). This could be associated to urea or isocyanurate groups in this prepolymer.

The 13 C NMR spectrum of this highly converted prepolymer was recorded rapidly after synthesis (Figure 12). Quite surprisingly this spectrum appears very simple, since only 3 signals, between 121.7 and 122.8 associated with the isocyanate functions were observed (residual IPDI and terminal groups). [START_REF] Götz | Preparation of isophorone diisocyanate terminated star polyethers[END_REF] Three other well defined peaks corresponding to the various urethane groups appear clearly at 155.4, 156.4 and 156.6 ppm. [START_REF] Désilets | 13 C-NMR spectroscopy study of polyurethane obtained from azide hydroxyl-terminated polymer cured with isophorone diisocyanate (IPDI)[END_REF][START_REF] Prabhakar | Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI)-based polyurethane prepolymer by 1D and 2D NMR spectroscopy[END_REF] Therefore only 2 unassigned peaks remain at 134.9 and 116.7 ppm, but they cannot be associated with allophanate or biuret (expected around 155 ppm) nor isocyanurate (expected between 150 and 153 ppm) [START_REF] Lapprand | Reactivity of isocyanates with urethanes: conditions for allophanate formation[END_REF][START_REF] Song | The 13 C-NMR analysis of polyisocyanurate made from isophorone diisocyanate[END_REF] or between 157 and 159 ppm [START_REF] Qi | Synthesis, characterization of a novel light stable crosslinker-isophorone diisocyanate terpolymer composite[END_REF]. They do not correspond to urea carbonyls either (generally found between 158 and 160 ppm), [START_REF] Désilets | 13 C-NMR spectroscopy study of polyurethane obtained from azide hydroxyl-terminated polymer cured with isophorone diisocyanate (IPDI)[END_REF] nor uretdione (156.5, 157.3 and 158.1 ppm), [START_REF] Spyrou | Isophorone diisocyanate in blocking agent free polyurethane powder coating hardeners: analysis, selectivity, quantum chemical calculations[END_REF] and finally they do not belong to the catalyst.

[Figure 12 near here] Finally the SEC chromatograms of these prepolymers (recorded after several weeks at room temperature) were carefully analyzed. High molar masses are detected in the case of perfluorophenyl phosphonic acid. A special attention was also paid to the low-molar mass species detected between IPDI (24.85 mL) and the first great peak associated with the bis(IPDI)-terminated PPG-2000 macromolecule (18.14 mL, see Figures S3 andS5, supporting information). Three small peaks can be detected in this elution volume range, but they are not always present. The 1 st 2 peaks (21.50 and 22.56 mL) seem to be the same as those detected during the reaction of IPDI with water (see above and Figure 11) and could thus correspond to a partial hydrolysis of the diisocyanate molecules.

-The 22.56 mL peak is especially high for mesityl phosphinic acid (Fig. S5) and also clearly visible for triflic and mesityl phosphonic acids -The 21.50 mL peak is clearly detected only for mesityl phosphonic and perfluorophenyl phosphonic acids Finally a 3 rd peak at 22.90 mL is always present, with a rather constant but modest height. In fact, taking a closer look at Figure 11, the species associated with this 22.90 mL peak may also be present in IPDI / water reactions, since the 22.56 mL peaks all display a shoulder on their right side. However the concentrations are not comparable, except for the product obtained with 10 mol% of phenyl phosphonic acid. Starting from the lower molar mass side of the chromatograms, a plausible assignment would therefore associate 22.90 mL with low amounts of the uretdione dimer; its close neighbor 22.56 mL with the urea dimer (see Scheme 5); and finally 21.50 mL with a trimer. This trimer would be rather of the biuret type, since no isocyanurate could be detected in the 13 C NMR spectrum. The uretdione dimer, or even the biuret trimer could possibly be more or less superimposed with the urethanes in the 13 C NMR spectrum; and indeed small peaks that could be associated with this molecule appear on the left basis ( ~155.7 ppm) of the urethane peak at 155.4 ppm (Figure 12). However this interpretation remains hypothetical and other techniques such as preparative chromatography would be needed to confirm it.

To conclude on these side products, it can be assumed that at 80 °C the acidic catalysts notably enhance the isocyanate-alcohol addition kinetics, but at the same time trigger the formation of branched side products such as allophanates or biurets leading to an increase conversion NCO-groups, and to an increasing viscosity of the final product. Moreover as time goes by, the presence of catalytic species in the prepolymers also favors the hydrolysis of some isocyanate functions during storage at room temperature, leading to additional urea-type by products.

Conclusion

In order to discover new organocatalysts that could be interesting and safer alternatives to toxic tin and mercury derivatives that are widely used for polyurethane synthesis, various nucleophilic/basic or acidic organic compounds were screened in the polyaddition of a "lowreactive polyurethane system" (aliphatic dissymmetric diisocyanate / macrodiol bearing secondary hydroxyl groups) at medium and low temperature. It was found that guanidines can be interesting since they display a medium catalytic activity, but only at high enough temperature. The catalytic efficiency of these compounds seems to be related to their nucleophilicity, instead of their basicity. However, these catalysts also favor the reaction of isocyanate groups with water to a too high extent, which is a negative point.

In comparison, strongly acidic compounds such as phenyl phosphonic acid derivatives show an enhanced catalytic activity and a better water/alcohol selectivity. In this series the efficiency of the catalyst is often related to its acidity. Even though some side reactions were observed at high temperature, these derivatives and especially perfluorophenyl phosphonic acid can be seen as really promising new environmentally friendly catalysts, even for challenging polyurethane materials such as transparent elastomers prepared by the casting of low-reactivity precursors at room temperature.

Figure captions

Figure 6

 6 Figure 6 shows all the kinetic curves obtained for the bulk reaction of IPDI with PPG-2000 ([NCO]/[OH] = 2) at 80 °C, in the presence of various acidic catalysts (a more complete study with additional catalysts can be found in the supporting information, see Scheme S3

Figure 1 .Figure 2 . 1 HFigure 3 . 1 HFigure 4 .Figure 5 .Figure 6 .Figure 7 .Figure 8 .Figure 9 . 1 HFigure 10 .Figure 11 .Scheme 5 .Figure 1 .

 121314567891101151 Figure 1. Kinetics of the reaction between IPDI and PPG-2000 ([OH]/[NCO] = 0.5) at 60 °C in bulk, in the presence of 1 mol% guanidine catalyst Figure 2. 1 H NMR spectrum (DMSO-d6) of the reaction product of IPDI (1 eq.) with PGME (1 eq.) capped with di(n-butyl) amine (see assignations in Scheme 4) Figure 3. 1 H NMR spectra (DMSO-d6) of the IPDI-NCO prepolymer ([NCO]/(OH] = 2) synthesized at 60 °C in the presence of 1 mol% TMG, of the IPDI-PPG polymer ([NCO]/[OH] = 1) synthesized at 60 °C in the presence of ~32 mol% TMG, and of the pure IPDI-TMG adduct Figure 4. Kinetics of the reaction between IPDI and PPG-2000 ([OH]/[NCO] = 0.5) at 60 °C in bulk, in the presence of TMG or IPDI-TMG adduct as catalyst Figure 5. Kinetics of the reaction between IPDI and PPG-2000 ([OH]/[NCO] = 0.5) at 80 °C in bulk, in the presence of 1 mol% guanidine derivative as catalyst; the case of DBTDL (0.0056 mol%) was added for comparison Figure 6. Kinetics of the reaction between IPDI and PPG-2000 ([OH]/[NCO] = 0.5) at 80 °C in bulk, in the presence of 1 mol% acidic derivative as catalyst; the case of DBTDL (0.0056 mol%) was added for comparison Figure 7. Kinetics of the reaction between IPDI and PPG-2000 ([OH]/[NCO] = 0.5) at 80 °C in bulk, in the presence of increasing amounts of phenyl phosphonic acid as catalyst; comparison with DBTDL (0.0056 mol%) Figure 8. Effect of the temperature on the kinetics of the reaction between IPDI and PPG-2000 ([OH]/[NCO] = 0.5) catalyzed by 1 mol% phenyl phosphonic acid or 3,5-bis(trifluoromethyl)phenyl phosphonic acid ("CF3 phenyl") Figure 9. 1 H NMR spectra (DMSO-d6) of the prepolymers obtained by the bulk reaction between IPDI and PPG-2000 at 80 °C ([NCO]/[OH] = 2) using 1 mol% catalyst Figure 10. Kinetics of the reaction between IPDI and PPG-2000 or water at 20 °C ([NCO]/[OH] = 2), in the presence of increasing amounts of phenyl phosphonic acid as catalyst Figure 11. Size exclusion chromatography analysis of the products of the reaction between water and IPDI ([NCO]/[OH] = 2) in DPGDME solution at 20 °C, in the presence of various catalysts (after 3-4 weeks at room temperature) Figure 12. 13 C NMR analysis (carbonyl signals, CDCl3, 100 MHz) of the PPG2000-IPDI prepolymer ([NCO]/[OH] = 2) synthesized at 80 °C in the presence of 1 mol% perfluorophenyl phosphonic acid and displaying a final conversion xNCO = 0.78

Figure 2 . 1 HFigure 3 . 1 HFigure 4 .Figure 5 .Figure 6 .Figure 7 .Figure 8 .Figure 10 .Figure 11 .

 2131456781011 Figure 2. 1 H NMR spectrum (DMSO-d6) of the reaction product of IPDI (1 eq.) with PGME (1 eq.) capped with di(n-butyl) amine (see assignations in Scheme 4)

Acknowledgements

This work was funded by the French FUI (Fond Unique Interministériel), under the aegis of Techtera Competitivity Pole, as the Collaborative Project "ECOMAT" (Ecomatériaux souples [Textile et Papier fonctionnalisés]). We gratefully acknowledge all the partners from the ECOMAT Project for fruitful discussions. Special thanks are addressed to Juxta-Allrim (especially Dominique Benazet and Guy Rosier), also for providing several catalysts and reagents. We also thank the NMR Polymer Center of the "Institut de Chimie de Lyon" (FR3023), for assistance and access to the NMR facilities. We thank Dr Nguyen Viet-Hoang for the preparation of one catalyst. This paper is dedicated to the memory of our colleague and friend Laurent Saint-Jalmes (Bluestar Silicones France), who managed the whole ECOMAT project with remarkable efficiency, skill and warmth. * IP IP IP IP IP IP IP IP IP IP IP IP IP IP IP


G R Lemaitre
email: gerard.lemaitre@lam.fr

R Grange

S Quiret

B Milliard

S Pascal

V Lamandé

Multi Object Spectrograph of the Fireball-II Balloon Experiment

Fireball-II is a NASA/CNES balloon-borne telescope and MOS to study faint diffuse emissions of galaxies in the space ultraviolet. The MOS is based on two identical reflective Schmidt systems sharing an plane-aspherized grating obtained by active optics methods.

Introduction

Fireball-II (Faint Intergalactic Redshifted Emission Balloon) is a NASA/CNES balloon-borne experiment to study the faint diffuse intergalactic medium from the line emissions in the ultraviolet (200nm) above 37km flight altitude. For the 2009 flight, Fireball-I relied on a fiber bundle Integral Field Unit (IFU) spectrograph fed by a 1 meter diameter parabola. This latter design used a reflective convex grating in Offner Littrow mounting [START_REF] Grange | Three-dimensional spectroscopy[END_REF].

As the science goals are concentrating on the circumgalactic medium, Fireball-II will use a Multi Object Spectrograph (MOS) for the 2015 flight that takes full advantage of the new high QE, low noise 13.5µm pixels UV CCD. This will increase the number of targets per flight while keeping the fast f-number (f /2.5) to maintain a high signal to noise ratio. The R ~ 2200 and 1.5arcsec FWHM MOS has a much larger field of view (600 arcmin 2 ) than the IFU (16 arcmin 2 ) for Fireball-I and thus we designed a two-mirror parabola field corrector to reimage the sky onto a spherical slit mask optimized to produce a flat field at the spectrograph focal plane.

After the field corrector system and beyond the mask the new spectrograph is based on two identical Schmidt systems acting as collimator and camera both sharing a 2400g/mm reflective Schmidt grating. The aspherization of the grating is achieved by double replication technique of a metal deformable matrix whose quasi-constant thickness active clear aperture zone is built-in to a rigid elliptical contour. We will present the optical design of the system and the elasticity design of the deformable matrix for obtaining the aspheric grating replica.

Optical Design for Fireball-II

The light from the sky is first reflected on a 1x1.3m steerable holed plane mirror allowing field acquisition and tip-tilt slewing control during exposure. A 1m concave parabolic mirror upside down provides an f /2.5 focal surface -which require coma correction -through the hole of the steerable mirror. The optical design of the multi-object spectrograph (MOS) is based on a two-mirror field corrector f /2.5-f /2.5 for coma correction which provides the field of 600 arcmin 2 . Then the output focal surface allows use of a multi-holed reflective mask for the direct input of object spots to the spectrograph and a channel from reflection on the mask for acquisition control and guiding. The f /2.5-f /2.5 spectrograph is made of two identical folded reflective Schmidt systems sharing a reflective aspherical grating (Fig. 1).The optical system provides a spectral resolution of 0.1nm at 200nm. Compared to Fireball-I, the new design should provide several gains in throughput : a factor 6 on QE efficiency of the detector and a factor 2 on the grating efficiency. Compared to the pixel size, the better image quality of the new design should also improve the limiting magnitude. Taking into account the increase number of optical surfaces and the gain in image quality, one expects a gain of 2.7 or 3 in limiting magnitude.

Aspherization of Reflective Gratings by Active Optics Methods

Among possible methods to achieve aberration corrections directly with a diffraction grating, our optical lab (LOOM) investigated active optics methods which are based on a double replication technique via a deformable matrix, also called active submaster. These methods were applied to obtain as well to elastically generate balanced a primary spherical aberration mode Sphe3 in combination with a curvature mode Cv1 -for planeaspheric gratings -as to generate a primary astigmatism mode Astm3 -for toroid gratings [START_REF] Lemaitre | Astronomical Optics and Elasticity Theory -Active Optics Methods[END_REF].

Balanced primary spherical aberration z = A 20 r 2

+ A 40 r 4 A combination of Cv1 and Sphe3 modes with A 20 A 40 < 0 allows reducing the stress level in the deformable substrate. Such profiles are of particular interest for any reflective systems as, for instance, high-throughput Schmidt cameras of spectrograph types equipped with aspheric reflective gratings. Balancing Cv1 and Sphe3 modes also substantially improve the optical performance by minimizing field residual aberrations. For reflective gratings used in normal diffraction, i.e. 𝛽=0, an important law, established by Lemaitre [START_REF] Lemaitre | Astronomical Optics and Elasticity Theory -Active Optics Methods[END_REF][START_REF] Lemaitre | Sur la résolution des télescopes de Schmidt de type catoptrique[END_REF], states that:

A pupil reflective surface with balanced radial variation of its local curvatures minimizes the field aberrations of any reflective Schmidt system.

For a diffraction angle 𝛽≠0, this law also applies to the principal directions of the elliptic pupil. For 𝛽=0, one shows that its best surface is of rotational symmetric and then the equation of the aspheric surface must be

z = z 0 (3𝜌 2 -𝜌 4 ), (1)
where z 0 is a constant and 𝜌 ∈ [0,1] the dimensionless aperture radius r/r max . Hence, from (1), the optics nullpower zone -no deviation of a ray -is located at 𝜌 = √(3/2) = 1.225… i.e. outside the clear optical aperture of diameter 2r max . Many deformable submasters with built-in boundary at the edge, quasi-constant thickness distribution (q-CTD) and bent by a uniform loading q were developed at LOOM to generate aspherized gratings through the double replication technique. For fast f-ratios the slight decrease of the thickness from center towards edge provides the 5 th -order correction Sphe5 (Figs. 2 and3).

Primary astigmatism mode

z = A 22 r 2 cos2θ
The primary astigmatism mode, Astm3, can be generated either from constant thickness distribution (CTD) and variable thickness distribution (VTD) mirror class [START_REF] Lemaitre | Astronomical Optics and Elasticity Theory -Active Optics Methods[END_REF]. The flexure to be achieved is a saddle-like surface i.e., with opposite curvatures in main orthogonal directions. Within VTD class, the basic solution is a cycloid-like thickness on which a net shearing force of the form cos2θ is applied along the mirror contour. Practicable configurations were developed at LOOM by use of either four outer bending bridges for CTDs or opposite forcepairs on simply-supported outer ring for VTDs [START_REF] Lemaitre | Astronomical Optics and Elasticity Theory -Active Optics Methods[END_REF]. Stainless steel submasters from the VTD class were designed with the cycloid-like thickness distribution t / t 0 = (1ρ 2 ) 1/3 and four 90 o bridges [START_REF] Lemaitre | Astronomical Optics and Elasticity Theory -Active Optics Methods[END_REF]. A second stage used two opposite couple of forces for the stressing and final replication on rigid Zerodur substrates. This was developed for the single surface spectrographs UVCS and CDS of the SOHO Mission ESA/NASA orbiting at Lagrange point L 1 (Fig. 4)

Aspherization of a Freeform Reflective Grating for Fireball-II

An active optics development to obtain the freeform surface of a reflective Schmidt first mirror was carried out by Lemaitre [START_REF] Lemaitre | Reflective Schmidt anastigmat telescope and pseudo-flat made by elasticity[END_REF] for an f /1.5 prototype telescope, 20cm aperture, using a tulip form thickness distribution with a set of punctual axial forces. Taking into account the law stated in above section 3.1, the best optical performance is achieved when the sizes of elliptic clear aperture and elliptic null-power zone (outside) are set in the ratio �3/2. This law is equivalent in setting the algebraic balance of local curvatures -∂ 2 z/∂x 2 and ∂ 2 z/∂y 2 -in the principal directions. It was retained for the design of the giant-segmented telescope LAMOST. From (1), the equation of the stressed matrix surface, of opposite sign to that of the grating surface, becomes in 3 rd -order [START_REF] Lemaitre | Astronomical Optics and Elasticity Theory -Active Optics Methods[END_REF]

z = -z 0 [3(h 2 x 2 +y 2 ) -(h 2 x 2 +y 2 ) 2 ], (2)
where h 2 is close to unity and a function of the incidence and diffraction angles at the grating (Fig. 5) Fig. 5. Freeform grating surface defined by homothetic ellipses. Fig. 6. Deformable matrix for Fireball-II grating replica.

Similarly to Figure 2, the elasticity design of the active matrix is basically a constant thickness plate clamped into an elliptical contour at the null power zone level and bent by a uniform gas pressure q (Fig. 6). If t is the thickness of the plate and D∝ t 3 its rigidity, the bilaplacian Poisson's equation, ∇ 4 z(x,y) -q/D = 0, provides solutions t (q). One selected stainless steel AISI420, t=6.7mm, q=6.5Atm and an ellipse built-in size 132x140mm.

Conclusion

Active optics methods provide fascinating imaging quality in astronomy either in high angular resolution or limiting magnitude detection. These methods are key features to generate extremely smooth freeform surfaces.

Fig. 1

 1 Fig. 1 Optical design of Fireball-II with two-mirror coma corrector and twin reflective Schmidt with shared aspherized grating.

Fig. 2 .

 2 Fig. 2. Left: Deformable submasters of quasi-constant thickness distribution (q-CTD) for on-axis or off-axis grating aspherizations by double replicas. Right: View of an intermediate replica on active submaster (LOOM).

Fig. 3 .

 3 Fig. 3. He-Ne fringes with respect to flat of on-and off-axis (freeform) reflective grating replicas aspherized from 2 nd replication on Zerodur substrate for the MARLY, CARELEC and ISARD faint object spectrographs (LOOM).

Fig. 4 .

 4 Fig. 4. Left: Cycloid-like deformable submaster generating Astm3 mode from four forces. Thickness distributions t / t0 = (1ρ 2 ) 1/3 . Right: He-Ne fringes of a first replica grating on active submaster for obtaining by replication one of the toroid Astm3-corrected grating replicas of spectrographs UVCS and CDS of SOHO Mission (LOOM, ETH-Zurich, Bach Research Corp-Boulder).