FR2808528A1 - Cyclotrimerization of isocyanate functions using substituted onium ions as catalyst, in which the substituents are aliphatic compounds - Google Patents

Abstract

Branched isocyanates are cyclotrimerized using quaternary ammonium or phosphonium catalysts, where the onium substituents are aliphatic and the counter ion has a pKA \- 12. A process for cyclotrimerization of branched isocyanate functions using quaternary ammonium or phosphonium catalysts (C) containing 30-12C atoms and where the counter ion is selected from anions corresponding to weak acids with pKA \- 8 and preferably \-12. The substituents in the catalyst are aliphatic compounds with no beta unsaturation and the onium ion comprises at least 2 radicals of more than 6 and preferably more than 12C atoms. An Independent claim is included for compositions comprising 20-80 wt.% cyclic isocyanurates produced from cycloaliphatic monomers; 10<-6> to 10<-2> of catalyst (C); 20-80 wt.% cycloaliphatic monomers and coloration such that the Hazen value is more than 0.5.

Description

The present invention relates to a process for preparing polyisocyanates-polyisocyanurates by catalytic cyclotrimerization of monomeric polyisocyanates. It relates more particularly to cyclotrimerization of isocyanate functions carried by sp 'hybridization carbons of a particular nature. These carbons are carbons, either in the neopentyl position, that is to say that said carbon is linked to a tertiary radical such as tert-butyl, or that said carbon is a secondary or tertiary carbon, preferably entering an aliphatic ring.

Cyclotrimerization of isocyanates has been known for several decades. These trimerizations generally implement mechanisms of a basic nature. These bases can be ionic in nature such as hydroxides or strong base and weak acid salts. These bases can also be nonionic bases but having a very accessible and very basic doublet.

The first trimerizations carried out were on aromatic isocyanates, that is to say isocyanates carried by a carbon which is a member of an aromatic nucleus. These trimerizations do not present any particular difficulty and it is easy to find catalysts capable of easily carrying out trimerizations of aromatic isocyanates.

The problems inherent in aromatic isocyanates lead to the development of aliphatic isocyanates which exhibit distinct and often very improved chemical and physical properties compared to aromatic isocyanates.

Most aliphatic isocyanates are too volatile to be used as they are. So we have to weigh down their molecules by producing either oligomers (biurets, trimers, ...), or oligo-condensates with polyols.

The trimerization of linear chain aliphatic isocyanates is now well controlled and catalysts are available which are capable of carrying out trimerizations under good conditions, that is to say with good yields and developing little color.

On the other hand, for reasons which are not completely elucidated, the trimerization of branched aliphatic isocyanates and, in particular, of cycloaliphatic isocyanates or in neopentyl position, remains difficult on the one hand, because of the difficulty of finding catalysts giving satisfactory yields and productivity and, on the other hand, because these derivatives have a strong propensity to develop undesirable colorations within them.

The coloring problems, as was mentioned previously, have already been treated for linear aliphatic isocyanates such as HDI (hexamethylenediisocyanate) but the techniques used are difficult to transpose to isocyanates of branched nature such as isocyanates neopentylic or cycloaliphatic positions. tertiary sector, and this, in particular, because the reactivity of these branched isocyanates is very significantly less than that of linear isocyanates, so that the catalysts used for linear aliphatic isocyanates often give low, or even very low, yields in the case of linear isocyanates. branched isocyanates.

Thus, it has been proposed 'to use a fluoride anion as a basic anion to carry out cyclotrimerizations of linear aliphatics without coloring, but this technique is difficult to use for cycloaliphatics because the yields are very significantly lower in their case.

This is why one of the aims of the present invention is to provide a process which makes it possible to obtain trimers of branched isocyanates while avoiding the development of an undesirable coloration.

Another object of the present invention is to provide a process which allows good yields and good productivity.

Another object of the present invention is to provide a process which allows trimerization of cycloaliphatic isocyanates and in particular of IPDI (often designated by the name of isophoronediisocyanate).

Another object of the present invention is to provide a process which allows the trimerization of cycloaliphatic isocyanates by improving the reactivity of the catalytic system used for this purpose.

These aims, and others which will appear subsequently, are achieved by means of a process for preparing polyisocyanates by cyclotrimerization of isocyanate functions carried by isocyanates having a branched hydrocarbon backbone, characterized in that it comprises the following steps: starting monomeric isocyanates; b) removal of reactive gases from said isocyanate monomers; c) optionally, providing a starting reaction medium comprising said starting monomeric isocyanates; d) addition of a cyclotrimerization catalyst consisting of a quaternary ammonium or phosphonium compound, chosen from those whose carbon sum is at most equal to 30 and at least equal to 12; the counterion of which is chosen from the anions corresponding to weak acids, the pKA of which is less than 8, preferably 10, more preferably 12; the substituents of which are aliphatic and do not have beta unsaturation; said ammonium or phosphonium comprising more than 2 radicals of more than 12 atoms, advantageously of more than 10 atoms, preferably of more than 6 carbon atoms; reaction until the desired degree of transformation is obtained; and optionally removing unreacted monomers; the order of steps b) and c) being irrelevant.

Thus, the elimination of the reactive gases can take place on the starting isocyanates themselves or after introduction of the latter into an optional reaction medium comprising an appropriate solvent.

<B> It </B> goes without saying that when the reaction is carried out without solvent, directly in the mass of isocyanates, step c) can be omitted. Degassing of isocyanate monomers has elsewhere already been described with a view to the cyclotrimerization of HDI.

Thus, EP 330 966 describes a process for the trimerization of HDI using a quaternary ammonium hydroxide in which the starting HDI is freed from carbon dioxide to a residual content of less than 20 ppm by weight, this in order to reduce the amount of catalyst to a value less than 0.03% by weight in order to reduce the coloring of the final reaction medium.

524 501 describes a process for preparing polyisocyanates comprising isocyanurate and allophanate groups from HDI using as catalyst a trimethylbenzylammonium hydroxide or a quaternary ammonium hydroxide in which the substituents are C 1 -C 21 alkyl groups optionally substituted with hydroxyl groups. It is specified in this document that the starting HDI mixture comprises less than 10 ppm of CO 2.

The catalysts illustrated in this document, however, all have three methyl substituents, the fourth being either a benzyl group or a hydroxyalkyl group.

No. 5,232,988 describes a process for preparing masked polyisocyanates comprising the reaction of trimerization of cyclic diisocyanates such as PPDI in the presence of quaternary ammonium carboxylates, phenolates or hydroxides in which the starting diisocyanate is treated by bubbling an inert gas.

No. 5,914,383 describes the preparation of a polyisocyanate composition comprising trimers of iminooxadiazine dione type and optionally isocyanurate groups in the presence of a polyfluoride as catalyst.

This document describes in particular the preparation of a composition of the aforementioned type from HDI and IPDI in which, before the catalytic reaction proper, the dissolved in the starting mixture of isocyanates are removed.

DE 197 54 748 and EP 927 731 describe processes for preparing polyisocyanates from IPDI using starting monomers having low chlorine contents, obtained in particular by the process called "urea".

Conversely, EP 379 914 and US Pat. No. 5,013,838 recommend the addition of carbon dioxide during the trimerization of aliphatic and / or cycloaliphatic organic diisocyanates, using a catalyst consisting of an ammonium or phosphonium fluoride.

The work of the inventors who were the authors of the present invention has now made it possible to discover that the polymerization of isocyanates of the type described above can be carried out with a high yield, and a substantially reduced coloration by the combination of a catalyst of the type described above. - Below and a step for removing the reactive gases dissolved in the reaction medium comprising the starting monomers on which the subsequent polymerization reaction is carried out.

The term “reactive gases” is understood to mean gases capable of interfering with the catalytic polymerization reaction, in particular trimerization, as opposed to inert materials.

It acts in particular of CO 2, but also of reactive gases of the air, that is to say gases other than nitrogen and rare gases, in particular oxygen, as well as chlorine or optionally chlorinated volatile compounds. , originating in particular from the phosgenation stage.

The inventors have furthermore determined that if the sensitivity of the reaction is influenced by the content of CO 2 dissolved in the reaction medium, other gases present, in particular air, have a substantial influence on the course of the reaction. Thus, the elimination of reactive gases greatly promotes the trimerization reaction, even when the CO 2 content of the starting monomers is as low as of the order of 1 to 2 ppm.

The inventors have moreover found that the content of chlorinated compounds, defined as the content of total chlorine, has only a minimal influence on the sensitivity of the reaction.

The elimination of the reactive gases can be carried out by any means known to those skilled in the art, in particular by placing under vacuum, diffusion of an inert gas or even the use of molecular sieves or chemical traps, or a combination of one or several of these methods.

When the starting isocyanate monomers have been stored for a prolonged period, generally for more than two months, leading to an argument for dissolved reactive gases, it is generally preferable to remove the dissolved reactants by subjecting the reaction medium to a vacuum followed by the introduction of an inert gas.

The vacuum is generally less than 1.104 Pa (100 mbar). When the starting monomers have been stored for a shorter period of time, the introduction by diffusion into the liquid reaction medium of an inert gas is generally sufficient. The inert gas is advantageously nitrogen or a rare gas, for example argon. Diffusion is carried out at a temperature of the order of 0 to 70 C. Higher temperatures can be used.

diffusion can be achieved by bubbling. However, the more efficient the degassing the smaller the size of the gas bubbles generated. In effect, the diffusion tools will be adapted in such a way that the reactive gases are removed quickly without causing clogging of the diffusion devices used.

The evacuation and / or the diffusion are carried out for a sufficient time to lower the rate of reactive gases in the starting reaction medium. In particular, it is considered that there is good degassing when the dissolved CO 2 is less than 20 ppm, preferably less than 2 ppm. The measurement of the CO 2 content as well as the content of gases other than CO 2 are advantageously determined by conventional analytical techniques, in particular by gas chromatography, using profiles obtained with injections of variable volumes of pure CO 2 and / or as standards. other pure gases.

Optimal degassing conditions also depend on the treatment conditions of the isocyanates after their synthesis, in general phosgenation, and on the storage conditions.

In particular the degassing operation can be carried out after the phosgenation of the amines, once the mixture has been purified and has stabilized. And this under the conditions below. If stored in good conditions (dark, temperature below 30 ° C in airtight containers and especially moisture), isocyanate monomer can be used in the trimerization process even after a period of prolonged storage (two to four months or more).

However, to be sure of obtaining a weak coloration, it is preferable to treat the isocyanates stored for an extended period as described below.

Advantageous conditions for removing the quantities of dissolved reactive gases are, in the case of quantities of starting monomers of the order of 500 g, stored for a period greater than two months, a vacuum of 5 mbar for a sufficient period of time, generally of one hour at room temperature, followed by diffusion of an inert gas, for example nitrogen by bubbling or the like in the liquid or the mass for about minutes.

For starting monomers which have been stored for a shorter period of time, a simple diffusion of nitrogen generally by bubbling for a period of 30 minutes at room temperature sufficient, for the same quantity of starting monomers.

Advantageously, no substituent of the "onium" compounds (ammonium or phosphonium) carries a hydroxyl function (such as phenol or alcohol).

In addition, according to one of the preferred embodiments of the present invention, no substituent has less than 2 atoms, advantageously less than 3 carbon atoms.

According to another preferred embodiment, the set of substituents comprises at least 1 and at most 2 radicals of more than 12 atoms, advantageously of more than 10 atoms, preferably of more than 6 carbon atoms.

The substituents are advantageously chosen from alkyls, including aralkyls and cycloalkyls. It is preferable that they do not carry branching in alpha and even in beta. It is also desirable that they are not functionalized. However, ether functions are acceptable and in particular of the type of those which result from the opening of epoxides with an alcohol or an alcoholate.

According to the present invention, not only the usual protic acids but also water and alcohols and any compound capable of undergoing the tearing of a proton are considered to be acids.

The preferred acids are essentially water and alcohols, which implies that the quaternary ammonium counterions are introduced in the form of hydroxide or alkoxide.

However, no departure will be made from the present invention which manufactures compounds of this type in situ. In fact, during the study which led to the present invention, it was demonstrated that the structure of ammonium or phosphonium played an important role in the development of the coloration subsequent to the polymerization reaction.

It appeared in particular that the presence of methyl and of compounds of a benzylic nature played a detrimental role on the coloration of the composition after trimerization.

The best results were obtained when the radicals substituting ammonium or phosphonium, which were identical or different, were chosen from propyl, butyl and pentyl, these radicals preferably all being linear. the gas to be eliminated is strongly acidic, that is to say having a pH value less than 3 (Handbook, 67th Ed., p D-146 of Chemistry and Physics), it is preferable to carry out the degassing before the introduction of the catalyst, to avoid irreversible poisoning of the catalyst. Conversely, when the gas to be eliminated is not strongly acidic, in particular in the case of CO 2, the degassing can be carried out before or after introduction of the catalyst and also during the step of trimerization of the starting isocyanates.

The inventors have also shown that formulation of the catalyst also had an influence on the reaction kinetics. In particular, in the case of aqueous formulations, water reacts with the isocyanate to give biuret and CO2. The CO 2 generated would lead to a decrease in the reaction rate. Therefore, it is preferable to maintain a continuous diffusion of inert gas when using aqueous catalyst formulations.

This also makes it possible to use very small amounts of catalyst and avoids the successive introduction of small amounts of catalyst in order to maintain reactivity.

The aqueous or hydroalcoholic formulations are preferred, because of the solubility of the oniums in these media before introduction into the reaction medium, due to the hydrogen dissolved in these solutions. The present invention relates to the trimerization of polyisocyanate compounds in general and, preferably, carrying two isocyanate functions, designated in the present description by monomeric isocyanates. During the reaction, other compounds can however be formed depending on the nature and the formulation of the catalyst and, where appropriate, of the cocatalyst as described in application WO 99I23128, in particular dimers, aminooxadiazinediones, carbamates, allophanates, biurets, etc. Although the present invention may be aimed at trimerization of branched monomers with unbranched monomers, that is to say linear monomers such as HDI, it mainly relates to the trimerization or trimerization between different compounds belonging to the same family branched monomers.

By “branched monomers” as has already been mentioned, is meant either a monomer of which at least one isocyanate function is in the cycloaliphatic, secondary, tertiary or neopentyl position. These monomers are advantageously cycloaliphatic monomers.

Thus, among these products, those which are preferred are cycloaliphatic. These monomers are advantageously such that at least one, advantageously the two isocyanate functions, is distant from the closest cycle by at most one carbon and, preferably, is linked directly to it. In addition, these cycloaliphatic monomers advantageously exhibit at least one, preferably two isocyanate functions chosen from secondary, tertiary or neopentyl isocyanate functions.

The best results are obtained when the conformational freedom of the cycloaliphatic monomer is low. As monomers capable of giving good results, mention may be made, by way of example, of the following monomers - the compounds corresponding to the hydrogenation of the aromatic ring (s) carrying isocyanate functions of aromatic isocyanate monomers and in particular of TDI (toluenediisocyanate) and diisocyanato-biphenyls, the compound known by the acronym H12MD1, the various BICs [Bis (isocyanato-methylcyclohexane)] and optionally substituted cyclohexyldiisocyanates; and above all - norbornanediisocyanate, often referred to as its acronym NBDI; - isophoronediisocyanate, or IPDI, or more precisely 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate. The starting monomers can also be products of oligomerization of isocyanates of lower molecular mass, products of oligomerization carrying isocyanate functions. In this case, it is not necessary to separate the unconverted oligomer from the reaction product formed.

The operating conditions of the process of step e) according to the present invention can be those which are usually used for linear aliphatic trimerizations, in particular the temperature can be chosen between and 100 ° C., preferably between 50 and 90 ° C.

particularly satisfactory operating point is between 60 and it is moreover possible to start heating the reaction medium before the end of step b) of elimination of the dissolved reactive gases, in particular when this consists of a simple bubbling of d 'an inert gas.

During the study which led to the present invention, it was possible to show that other parameters influence the reduction in coloration. The effects of these parameters are favorable alone or in combination with the other parameters in the present application mentioned above.

Thus, it has been demonstrated that a prior distillation of the starting monomers made it possible to reduce the coloration developed during the trimerization reaction.

Usually, trimerization reactions using quaternary oniums are blocked by heating. During the study which led to the present invention, it was shown that this technique for deactivating the catalyst gave very poor results with regard to coloring. Also, it has been shown that it was preferable to use another technique, known for linear aliphatics, namely the addition of an acid of high strength such as sulfonic acids, for example mesylic and tosylic acids. , or phosphonic, or medium, preferably an ester of phosphorus acid.

Mention may be made, as esters of phosphorus acids, of phosphate esters, in particular of diesters, of phosphonates, preferably monoesterified, and of phosphinates.

The poisoning of the catalyst is however preferably carried out by means of acid esters of phosphoric acid, and in particular dialkyl phosphoric esters, in particular such as dibutyl phosphate and di-2-ethylhexyl phosphate.

The way in which the catalyst according to the present invention is introduced also plays a role. Thus, when the catalyst is introduced into an aqueous mixture, the coloring develops less than when the catalyst is introduced into an alcoholic mixture.

Hydroalcoholic solvents, however, give fairly good results. To avoid runaway zones of the reaction, it is desirable to introduce the catalyst in the form of a solution with good dilution by mass. Solutions of 0.5% to 40% by mass of catalysts give good results.

The diluents must, on the one hand, ensure the dissolution of the ionic compound that constitutes the catalyst and, on the other hand, ensure the diffusion in the lipophilic medium constituted by the monomers of the reaction mixture. mixtures of water (0 to 50%, advantageously 5 to 40%), butanol (0 to 50%, preferably 5 to 40%) and heavy alcohol (s) (greater than or equal to Ca) or alcohols ethers (2-ethoxy ethylene glycol) (qs 100%) give good results.

Although it is preferable to work using relatively dilute solutions of catalysts, it is possible, according to the present invention, to use very concentrated solutions of catalysts, provided the introduction is carried out at low temperature, advantageously at temperature. room or preferably below room temperature and homogenize before starting the process of heating the reaction mixture.

In general, the trimerization is carried out to the desired degree of conversion. For obvious economic reasons, it is preferred to stop the reaction at conversion rates of the isocyanate functions of at least 10% and preferably between 10 and 50%. Once the polymerization reaction has stopped, the remainder of the monomers is generally removed by evaporation or distillation on a thin film and under high vacuum. The amount of catalyst used is advantageously between 10-5 and 10 times the total mass of the isocyanate monomers introduced, preferably 10-3, expressed in mass amounts of the catalyst without solvent. In the case of oligomers, preferred amounts of catalysts such that the mass ratio of catalyst / mass of isocyanate functions is between 10-5 and 10-2. The following non-limiting examples illustrate the invention. Method for measuring CO 2 CO 2 is measured using a gas chromatography technique. Analysis conditions GC chromatograph: Hewlett-Packard HP5890 n 6658 05 84 stainless steel column: PORAPAK T 80-100 Mesh L: 3m di: 2 mm oven temperature: 50 C isothermal carrier gas: helium column flow rate: 46.7 ml / min at 50 C for P-243.7 Kpa (Fpmeter) (column + reference: 66.7) injection: in U-shaped glass stripping tube detector temperature: 230 C detector: low sensitivity katharometer range 0 volume injected: 0.5 ml of liquid sample injected into the glass stripping tube calibration: external calibration by injections of variable volumes of pure C02. Small volumes (less than 0.1 ml) are obtained by diluting 1 ml of CO 2/227 ml of helium. The hydrolysable chlorine dosage method is carried out according to the AFNOR NF T 52-135 standard. <B><U>EXAMPLE</U></B> <U> 1 </U> Reagents (% <I> expressed in </I> weightlweight) - IPDI = 504 g, the initial C02 content evaluated at 45 mg / kg of IPDI, the IPDI is distilled before use - catalyst tetrabutylammonium hydroxide (TBA OH), catalytic solution 6% TBA OH / 2-ethylhexanol-butanol- (in a mass ratio 83:12: 5) = 1.47 g - blocking solution, 8% APTS (p-toluene sulfonic acid) / ethylene glycol diethyl ether = 1.06 g <I> Procedure </I> reaction is carried out in a 1 L reactor with stirring mechanics, temperature regulation and argon bubbling by plunging rod.

After introduction into the reactor, the IPDI is heated for 1 hour at 68 ° C., with stirring, a partial vacuum of 39 mbar and bubbling with argon. The CO 2 content is then evaluated by the method described above, less than 2 mg / kg of IPDI catalytic solution is introduced over 26 minutes. The reaction medium maintained at a temperature of 68 ° C., with stirring. The progress of the reaction is followed by titration of the residual isocyanate functions. After a total time of 1 h 15 min, the degree of conversion of the IPDI reaches 41%, the blocking solution is introduced and, 15 minutes later, the reaction mass is cooled to room temperature. The coloration of the reaction mass is evaluated at 12 Hazen.

The reaction mass is distilled on a double thin-film evaporator at a temperature of <B> 191 ° C </B> and a vacuum of 0.3 mbar. The final product has a clear appearance and coloration evaluated at 40 Hazen, an NCO content of 12.5% and a viscosity of 342 mPa.s. <U> EXAMPLE 2 </U> <I> Reagents </I> (% <I> expressed in </I> weightlweight) - IPDI = 504 g, the initial C02 content is evaluated to be less than 2 mg / kg d 'IPDI, IPDI is distilled before use - tetrabutylammonium hydroxide catalyst (TBA OH), catalytic solution 6% TBA OH I 2-ethylhexanol-butanol-water (according to a <B> 83: </B> 12: mass ratio: 5) = 1.71 g - blocking solution, 10% APTS I 2-ethylhexanol = 0.76 g <I> Procedure </I> The reaction is carried out in a 1 L reactor with mechanical stirring, regulation of the . .temperature and argon bubbling by plunging rod.

After introduction into the reactor, the IPDI is maintained for 1 h at 25 ° C., with stirring and bubbling with argon.

catalytic solution is introduced over 20 minutes. The reaction medium heated to a temperature of 50 ° C. with stirring. The progress of the reaction is followed by titration of the residual isocyanate functions. After a total time of 3 h 7 min, the degree of conversion of the IPDI reaches 47%, the blocking solution is introduced and, 1 minute later, the reaction mass is cooled to room temperature. coloration of the reaction mass is evaluated at 8 Hazen.

reaction mass is distilled on a double thin-film evaporator at a temperature of 191 ° C. and a vacuum of 0.3 mbar.

The final product has a clear appearance and coloration evaluated at 13 Hazen, an NCO content of 12.5% and a viscosity of 885 mPa.s. <U> EXAMPLE 3 </U> (comparative) <I> Reagents </I> (% <I> expressed in </I> weightlweight) IPDI = 35 g 2-hydroxyethyltrimethylammonium hydroxide catalyst, in solution in methanol = 0.032 g <I> Procedure </I> The reaction is carried out in a 0.1 L reactor with mechanical stirring, temperature regulation and C02 bubbling by plunging rod under the same conditions as Example 1.

The reaction is carried out at 80 ° C., after a period of 1 h 30 min, the degree of conversion of IPDI reaches 35%. The reaction mass is cooled to room temperature and the coloring is evaluated for 191 Hazen.

Claims (1)

<B><U>REVENDICATIONS</U> </B> 1. Process for the preparation of polyisocyanates by (cyclo) trimerization of isocyanate functions carried by isocyanates having a branched hydrocarbon skeleton, characterized in that it comprises the following steps a) providing starting monomeric isocyanates; b) removal of reactive gases from said isocyanate monomers; c) optionally, providing a starting reaction medium comprising said starting monomeric isocyanates; d) addition of a (cyclo) trimerization catalyst consisting of a quaternary ammonium or phosphonium compound, chosen from those in which the sum of the carbons is at most equal to 30 and at least equal to 12, the counterion of which is chosen from the anions corresponding to weak acids whose pKA is at least equal to 8, preferably 10, more preferably 12, whose substituents are aliphatic and do not have beta unsaturation; said ammonium or phosphonium comprising at most 2 radicals of more than 12 atoms, advantageously more than 10 atoms, preferably more than 6 carbon atoms; e) reaction until the desired degree of transformation is obtained; optionally removing unreacted monomers; the order of steps b) and c) being irrelevant. Process according to Claim 1, characterized in that the elimination of reactive gases from the reaction medium is carried out by diffusion of an inert gas. Process according to Claim 1, characterized in that the reactive gas elimination is carried out by placing the reaction medium under vacuum at a vacuum of less than 1.104 Pa, followed by diffusion of an inert gas. 4. Method according to any one of the preceding claims, characterized in that in step b), the CO2 is removed. 5. Method according to any one of the preceding claims, characterized in that in step b), the air dissolved in the liquid or the mass of the starting monomers is removed. 6. Method according to one of claims 1 to 5, characterized in that no substituent of said opium carries a hydroxyl function. Process according to one of Claims 1 to 6, characterized in that the said counterion is a hydroxide or an alcoholate or anions which induce in the reaction medium. Process according to one of Claims 1 to 7, characterized in that the catalyst content of the reaction mixture is between 10-5 and 0-2 times the total mass of the isocyanate monomers. Process according to one of Claims 1 to 8, characterized in that no substituent of the said opium has less than 2 atoms, advantageously less than 3 carbon atoms. 0. Method according to one of claims 1 to 9, characterized in that the set of substituents of said opium comprises at least one and at most two radicals of more than 12 atoms, advantageously preferably of 6 carbon atoms. 11. Method according to one of claims 1 to 10, characterized in that the reaction is stopped by the addition of an acid medium or chosen from sulfonic acids, advantageously liposoluble; and phosphoric acids, advantageously a mono or a diester of phosphoric acid. 12. Method according to one of claims 1 to 11, characterized in that the isocyanate functions are carried by cycloaliphatic monomeric isocyanates. 13. The method of claim 12, characterized in that the isocyanate functions are carried by isophorone diisocyanate.