FR2897613A1 - Preparation of polyisocyanates containing uretdione groups, comprises cyclodimerization of polyisocyanates in the presence of a super acid catalyst - Google Patents

Abstract

Cyclodimerization of polyisocyanates is carried out in the presence of a super acid catalyst at specified temperature range. The catalyst is then inactivated or eliminated and unreacted monomers are removed. A process for the preparation of polyisocyanates by cyclodimerization of the isocyanate functions of isocyanate monomers comprises: (1) providing a reaction medium containing the isocyanate monomers, optionally in the present of a solvent; (2) adding to the medium a super acid (cyclo)dimerization catalyst, maintaining the reaction medium at a temperature of 0-300 [deg]C (preferably 20-200 [deg]C) until the desired degree of transformation (1-95%, preferably 5-50% of the initial isocyanate groups) is attained; (3) inactivating or eliminating the catalyst; and (4) eliminating the unreacted monomers. An independent claim is included for an isocyanate composition containing polyisocyanate uretdiones, prepared by the above process.

Description

The subject of the invention is a process for preparing polyisocyanates

  oligomers comprising at least one uretdione group by dimerization of starting monomeric isocyanates using new catalysts.

  The invention more particularly relates to a process for the selective catalytic cyclodimerization of isocyanate monomers. Polyisocyanates containing uretdione groups, known as "dimers" are synthesized by cycloaddition (2 + 2) of two aliphatic or aromatic isocyanate molecules. While aromatic isocyanates can cyclodimerize in the absence of a catalyst at room temperature, the other isocyanates require the use of basic catalysts, such as trialkylphosphines, N, N, N ', N'-tetraalkyl guanidines. 1,2-dialkylimidazoles, etc. In general, these catalysts are not very selective and, besides the dimerization reaction, also promote the formation of trimeric polyisocyanates of predominantly isocyanurate structure by cyclotrimerization of the starting monomeric isocyanates, resulting in the formation of polyisocyanate compositions having a proportion greater than or equal to less important isocyanurate group compounds besides polyisocyanates containing uretidione groups. To remedy the problem of the selectivity of the dimerization catalysts, it has been proposed to use compounds belonging to the generic classes of N, N-di-alkylaminopyridines, 4- (N-arylalkyl-Nalkyl) amino-pyridines and the tris (N, N-dialkyl) phosphotriamides. Concrete examples of the first group are 4-N, N-dimethylaminopyridine (designated "DMAP"), 4-pyrrolidinylpyridine, while a concrete example of the second group is 4- (N-benzyl-N-methyl) aminopyridine (designated "BMAP") and a concrete example of the third group hexamethyl phosphotriamide (HMPT). These catalysts may also be useful for acylation or urethane formation reactions.

  For more information, please refer to E.F.V. Scriven, Chem. Soc. Rev., 129 (1983) and G. Hofle et al., Augew. Chem. Int. Ed. Engl., 17, 569 (978). The work of the inventors who led to the present invention has made it possible to demonstrate that certain sulphonic acid derivatives possessing a strongly electron-withdrawing group, constituted excellent dimerization catalysts, making it possible to obtain dimeric polyisocyanates with a uretdione pattern with selectivity and high efficiency. By "high selectivity" within the meaning of the invention it is meant that the isocyanate functions of the starting monomers react mainly and almost exclusively with each other to form compounds having uretdion groups other than compounds having isocyanurate groups. The compounds may have a single uretdione group, in which case they will be referred to as "true dimers" or uretdione groups in which case they will be referred to as "oligo-" or "polydimers". The latter compounds may especially be bis- or tris-uretdiones or heavy compounds having more than three uretdiones cycles. However, it is not excluded and it may even be advantageous that the compounds of the invention also catalyze the reaction of isocyanate functional groups with other functions which are reactive with the isocyanate function, in particular the alcohol functional groups.

  The subject of the invention is a process for preparing polyisocyanates by cyclodimerization of isocyanate functional groups borne by starting monomeric isocyanates, characterized in that it comprises the steps of: a) providing a reaction medium comprising isocyanates 30 of starting optionally in the presence of a solvent; b) bringing this reaction medium into contact with a cyclodimerization catalyst comprising a compound comprising at least one S (O) mOH function, m being equal to 1 or 2 bonded to an atom or electron-withdrawing group, or a precursor of said compound; c) heating at a temperature in the range of 20 to 150 C until the desired degree of conversion is achieved; and d) optionally removing the unreacted monomers. The atom or attracting group is preferably chosen from functional groups whose Hammett constant ap is at least equal to 0.1. It is furthermore preferable that the inductive component of ap, ai is at least 0.2, advantageously 0.3. In this regard reference is made to March, "Advanced Organic Chemistry", Third Edition, John Wiley and Son, pp. 242-250, and particularly Table 4 of this section. Advantageously, the catalyst comprises a compound of formula (1): Rf-S (O) n OH (1) in which Rf consists of an atom or an electron-withdrawing group and m represents 1 or 2. More particularly, the entity The stripping tracer can be chosen from halogen atoms, preferably light ones, in particular fluorine and chlorine, or from preferably C1-C6 hydrocarbon groups containing at least one halogen atom, preferably chosen from fluorine and chlorine. Preferred electron-withdrawing groups are the perhalogenated C 1 -C 6 hydrocarbon groups, in particular perchlorinated and preferably perfluorinated. In general, it is preferred that the halogen atoms are borne by carbon atoms located as close as possible to the S (O) mOH group; preferably at 13 or 13. However, they may be carried by more distant carbon atoms. In this case, it is advantageous that the carbon atom carrying the halogen atoms is perhalogenated, preferably perfluorinated. The hydrocarbon group may be an alkyl group or an alkylenyl group; alkynyl, aryl, aralkyl or alkaryl having 20 carbon atoms, preferably 4 carbon atoms, at most, optionally substituted with a non-reactive or reactive group with respect to an isocyanate function. A group of compounds of general formula (1) is preferred wherein Rf has the following general formula (2): - (CR1 R2) p-GEA (2) in which - R1 and R2, which are identical or different, are chosen from hydrogen, halogen, especially fluorine, a C1-C6 alkyl group, an NO2, CN, COOH, COOR3 group where R3 is a C1-C6 alkyl group, a C1-C20 perfluoroalkyl group, or C 6 -C 20 perfluoroaryl; p represents an integer from 0 to 2; - the symbol GEA represents H, a halogen atom, especially fluorine, a C 1 -C 6 alkyl group or a C 6 -C 12 aryl group; C6-C12alkyl (C1-C2) -alkyl, optionally substituted by one or more electron-withdrawing groups or atoms, or an electron-withdrawing group, provided that the Hammett constant of the group (CR1R2) p-GEA is at least equal to at 0.1. Advantageously, the symbols R 1 and R 2 which are identical or different represent a fluorine atom or a CnF 2n + 1 group, with n being an integer between 1 and 20, advantageously 1 and 5, and preferably between 1 and 2, and GEA advantageously represents a fluorine atom or a perfluorinated residue of formula CnF2n + 1, with n as defined above. In particular, the following atoms and electron-withdrawing groups may be mentioned for Rf: F, CH2F, CHF2, CF3, CH2-CH2F, CH2-CHF2, CH2-CF3, CHFCH2F2, CHF-CHF2, CHF-CF3, CF2-CH3, CF2. -CH2F, CF2-CHF2, CF2-CF3, CH2-CH2-CH2F, CH2-CH2-CHF2, CH2-CH2-CF3, CH2-CHF-CH3, CH2-CHF-CH2F, CH2-CHF-CHF2, CH2-CHF -CF3, CH2-CF2-CH3, -CH2-CF2-CH2F, CH2-CF2-CHF2, CH2-CF2-CF3, CHF-CH2-CH3, CHF-CH2-CH2F, CHF-CH2-CHF2, CHF-CH2 -CF3, CHF-CHF-CH3, CHF-CHF-CH2F, CHF-CHF-CHF2, CHF-CHF-CF3, CHF-CF2-CH3, CHF-CF2-CH2F, CHF-CF2-CHF2, CHF-CF2-CF3 , CF2-CH2-CH3, CF2-CH2-CH2F, CF2-CH2-CHF2, CF2-CH2-CF3, CF2-CHF-CH3, CF2-CHF-CH2F, CF2-CHF-CHF2, CF2-CHF-CF3, CF2 -CF2-CH3, CF2-CF2-CH2F, CF2-CF2-CHF2, CF2-CF2-CF3, CF3 CF3-CF3 and CF3 CH2 CF3 CH2 F as well as the corresponding groups in which the fluorine atom is replaced by a atom of chlorine. A preferred subgroup of compounds is that in which m is 2. The catalyst of the invention may also comprise a mixture of at least two different compounds described above. A particularly preferred compound is triflic acid CF 3 SO 3 H. When the compound of general formula (1) is introduced into the reaction medium in precursor form, it is a compound capable of releasing a compound of general formula (1) in the reaction medium under the reaction conditions. These are then latent catalysts which regenerate the S (O), OH acid function by a chemical, physical or physicochemical process. Examples of precursor compounds of compounds of the general formula (1) are ester compounds of the general formula (3) or silyles of the general formula (4): ## STR1 ## CH3 Rf-S (O) mOS iC- (C H3) 3 CH3 Rf and m being as defined above, and R4 representing a C1-C20 alkyl group.

  Mention may also be made of energetically activatable amine or onium salts such as phosphonium, sulphonium and iodonium salts.

  For example, the compounds described by Huang et al., Polymer 41 (2000); p. 5001-5009.

  The dimerization can be carried out in the absence of a solvent or in a non-reactive solvent with the isocyanate function. The following solvents may be mentioned in particular: toluene, chlorobenzene, n-butyl acetate, tert-butyl-methyl ether, etc.

  The reaction is preferably carried out without a solvent.

  It is preferred to carry out the reaction at a temperature at which the isocyanate is in a partially liquid or molten state. (3) (4) The present invention relates to the dimerization of isocyanate compounds in general and, preferably, carrying at least two isocyanate functional groups. It may be isocyanate monomers with hydrocarbon backbone, aliphatic, cycloaliphatic or aromatic. In particular, hexamethylene diisocyanate (HDI) is a linear aliphatic monomer, and 2-methyl pentamethylene-1,5-diisocyanate is a branched aliphatic monomer. Surprisingly, it has been found that the catalysts described above allow the cyclodimerization of isocyanates that are difficult to react with one another to form compounds with a uretdione group in the presence of conventional catalysts. In particular, these are monomers in which at least one isocyanate functional group is in the cycloaliphatic, secondary, tertiary or neopentyl position. Thus, among these products, those that give good results are cycloaliphatic monomers. These monomers are advantageously such that at least one, advantageously the two isocyanate functional groups, is distant from the ring closest to at most one carbon and, preferably, is directly connected to it. In addition, these cycloaliphatic monomers advantageously have at least one, preferably two isocyanate functions borne by a secondary, tertiary or neopentyl carbon atom. The process according to the invention gives good results, even when the conformational freedom of the cycloaliphatic monomer is low. By way of example, mention may be made 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 TDI (toluene diisocyanate) and diisocyanato biphenyls, compound known as H12MDI, various BIC (isocyanato-methylcyclohexane)] and optionally substituted cyclohexyldiisocyanates; and especially norbornanediisocyanate, often referred to as NBDI; isophorone diisocyanate, or IPDI, or more precisely 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate.

  As aromatic monomers, mention may be made of: 2,4-toluene diisocyanate (TDI); 2,6-4,4'-diphenylmethane diisocyanate (MDI); -1,5-naphthalene diisocyanate (NDI); io-tolidine diisocyanate (TODI); p-phenylene diisocyanate (PPDI). Diisocyanate monomers bearing non-reactive functions with the isocyanate functional group, in particular ester functional groups, may be used. By way of example, mention may be made of the following compound: OCN NCO, also called LDI (lysine diisocyanate). The starting monomers may also be triisocyanates, such as 4-isocyanato-methyl-octamethylene-1,8-disocyanate, also called TTI or the compound of formula:

  OCN ~ NCO CH3O NCO- (C H2) 2O 30 also called LTI (lysine triisocyanate).

  The starting isocyanates may also be oligomerization products of low molecular weight isocyanates as described above, these oligomerization products carrying isocyanate functional groups or isocyanate-functional prepolymers of various types (polyurethane, polyester, polyacrylate, etc.). In this case, it is not necessary to separate the unconverted oligomer from the reaction product formed after the dimerization reaction. When the starting isocyanate is an oligomerization product having an isocyanurate ring, especially a trimer isocyanate, the final reaction product comprises isocyanurate units. However, the number of isocyanurate units is substantially that present in the starting reaction medium before the dimerization reaction. It is also possible to use mixtures of at least one or two different compounds as defined above, in particular mixtures of isocyanate monomers of low molecular weight. In this case, a mixed or asymmetric dimer or polydimer is obtained, in addition to symmetrical dimers or polydimers (obtained by dimerization of a single monomeric isocyanate of a single type of monomeric isocyanate). The dimerization temperature is between room temperature and 150.degree. C. and advantageously between 40.degree. And 120.degree. C. When the starting monomer is IPDI, the reaction temperature is advantageously between 60.degree. C. and 100.degree. The functions S (O) mOH with respect to the NCO functions of the catalyst generally vary between 6 × 10 -4 and 1.5 × 10 -2, and below the lower limit the reaction kinetics are insufficient. There are problems with the solubility of the catalyst in the reaction medium: When the starting reaction medium contains an alcohol, the catalysts of the invention promote the formation of allophanate compounds, in addition to dimeric compounds.

  When the formation of allophanates is desired, it may be advantageous to add in the reaction medium a Lewis acid type catalyst, such as tin dibutyl dilaurate. The compounds of general formula (1) also make it possible to obtain crosslinked dimeric isocyanates by addition in the starting reaction medium of a hydroxyl compound, optionally oligomeric or polymeric, comprising at least one, preferably two OH functions such as ethylene glycol, hexane diol, trimethylolpropane, pentaerythritol, polyethylene glycol, acrylic polyols, polyol esters. In this case also, one can work in the absence or in the presence of solvent. The destruction of the catalyst is complete when substantially all the acid catalyst is neutralized or absorbed on a support, preferably basic or amphoteric (silica, alumina, zeolite, etc.). In general, the dimerization is conducted to the desired degree of conversion of between 1 and 95% of the isocyanate functions present. For obvious economic reasons, it is preferred to stop the reaction at isocyanate conversion rates of at least 5% and preferably between 10 and 50%. Once the dimerization reaction is stopped, the rest of the monomers are generally removed by evaporation or thin-film distillation under high vacuum. The reaction can be stopped by destroying the catalyst, as obtained by addition of a base, in particular sodium acetate, or sodium hydrogen carbonate, or by removal of the catalyst, for example by absorption of the latter. on a mineral support, for example (silica, alumina, charcoal), distillation of the reaction medium, absorption on an ion exchange resin, basic tertiary amine or quaternary ammonium whose counterion has a lower acidity than the catalyst , especially an -OH-, -COO- or -0000- anion may be mentioned Amberlite type resin.

  For the termination of the reaction, it is not necessary to inactivate the catalyst, a simple filtration being sufficient especially when the process is batch.

  The products obtained optionally include functions such as urea, biuret, carbonate, ester, allophanate, ether, etc., in addition to the uretidinedione functions.

  The following nonlimiting examples illustrate the invention.

  EXAMPLE 1: 1% triflic acid Reagents (% expressed by weight / weight): -IPDI = 20 g-catalyst CF3SO3H = 0.2 g-blocking agent = sodium acetate = 0.5 g

  Procedure The reaction is carried out in a 1 liter reactor with mechanical stirring and temperature regulation and bubbling argon by dipping rod. The isocyanate is introduced successively into the reactor and then the catalyst. The catalytic solution is introduced in 10 minutes with stirring so as to maintain the reaction medium at a temperature of 60 ° C. The progress of the reaction is monitored by titration of the residual isocyanate functions. After a total duration of 6 hours, the transformation rate of the IPDI reaches about 20%. The blocking agent is introduced and, 15 minutes later, the reaction mass is cooled to room temperature. The reaction mass is distilled on a double thin-film evaporator at a temperature of 180 ° C and a vacuum of 0.3 mbar to remove the residual isocyanate monomer. The composition of the reaction medium before addition of the blocking agent and removal of the monomeric IPDI is given in the following table: Product 10% by weight IPDI 81.3 Dimmer 12.6 Bis-dimer 3.2 Tris dimer 2.7 dimer ratio true / sum of dimers EXAMPLE 2: triflic acid at 2.5% The operating conditions of example 1 are repeated except that the amount of CF 3 SO 3 H added is 0.5 g and the amount of sodium acetate is 1 g.

  EXAMPLE 3 1% TFOH + 10% molar n-butanol (relative to the IPDI) The operating conditions of Example 1 are repeated except that 0.74 g of n-butyl alcohol are added to the starting reaction medium. butanol.

  EXAMPLE 4 5% TFOH + 10% molar by weight of n-butanol The operating conditions of Example 2 are repeated except that 0.74 g of n-butanol is added to the starting reaction medium.

EXAMPLE 5 Example 1 was repeated using 2.5% by weight of the catalyst and raising the reaction temperature to 100 C.

EXAMPLE 6 Example 5 is repeated replacing the IPDI with HDI. The composition of the final reaction medium of Examples 1 to 6 is given below: Examples 1 2 3 4 5 6 IPDI 81.3% 72.3% 65.0% 50.6% 80.7% HDI 93.6 % Dimer 12.6% 16.9% 15.7% 18.5% 7.3% 1.62% Bis-dimer 3.2% 5.5% 7.1% 4.1% 2.5% Tris 2.7% 5.3% 4.0% Allophanate 8.2% 5.4% Butyl and IPDI Bis-dimer * 10.6% Heavy Tris - - 4.0% 14.9 % 6,9% 1,8% dimer * ratio dimer 68 61 59 true / sum of dimers * with allophanate functions of butyl and IPDI 10

Claims (13)

  A process for the preparation of polyisocyanates by cyclodimerization of isocyanate functional groups carried by starting monomeric isocyanates, characterized in that it comprises the steps of: a) providing a reaction medium comprising starting isocyanates, optionally in the presence of a solvent; b) bringing this reaction medium into contact with a cyclodimerization catalyst comprising a compound comprising at least one S (O) mOH function, m being equal to 1 or 2 bonded to an atom or electron-withdrawing group, or a precursor of said compound; c) heating at a temperature in the range of 20 to 150 C until the desired degree of conversion is achieved; and d) optionally removing the unreacted monomers.   The process according to claim 1, wherein the dimerization catalyst comprises a compound of the formula: Rf-S (O) mOH (1) wherein Rf is an atom or an electron withdrawing group and m is 1 or 2.   3. Process according to claim 1 or 2, characterized in that said atom or electron-withdrawing group is chosen from atoms or electron-withdrawing groups whose Hammett constant 6p is at least equal to 1.   4. Process according to claim 2, characterized in that Rf corresponds to the general formula (2): ## STR3 ## in which Rf corresponds to the following general formula (2): - (CR1R2) p GEA (2) in which R 1 and R 2, which are identical or different, are chosen from a hydrogen, halogen, especially fluorine, a C 1 -C 6 alkyl group, a NO 2, CN, COOH, COOR 3 group where R 3 is a C 1 -C 6 alkyl group, a C 1 -C 20 perfluoroalkyl group, C 6 -C 20 perfluoroaryl, s - p represents an integer between 0 and 2, the GEA symbol represents H, a halogen atom, in particular fluorine, a C1-C6 alkyl, C6-C12 aryl, C6-C12 alkyl (C1-C2) -aryl, optionally substituted by one or more electron-withdrawing groups or atoms, or an electron-withdrawing group, subject to that the Hammett constant of the (CR2) p-GEA group is at least 0.1.   5. Process according to claim 2 or claim 4, characterized in that R1 and R2 are selected from a fluorine atom or a CnF2n + 1 group, where n is an integer between 1 and 20 and GEA represents an atom of fluorine or a group CnF2n + 1, with n as defined above.   6. Process according to any one of the preceding claims, characterized in that said electron-withdrawing group is selected from the following groups: F, CH2F, CHF2, CF3, CH2-CH2F, CH2-CHF2, CH2-CF3, CHFCH2F2, CHF -CHF2, CHF-CF3, CF2-CH3, CF2-CH2F, CF2-CHF2, CF2-CF3, CH2-CH2-CH2F, CH2-CH2-CHF2, CH2-CH2-CF3, CH2-CHF-CH3, CH2-CHF -CH2F, CH2-CHF-CHF2, CH2-CHF-CF3, CH2-CF2-CH3, -CH2-CF2-CH2F, CH2-CF2-CHF2, CH2-CF2-CF3, CHF-CH2-CH3, CHF-CH2 -CH2F, CHFCH2-CHF2, CHF-CH2-CF3, CHF-CHF-CH3, CHF-CHF-CH2F, CHF-CHF-CHF2, CHF-CHF-CF3, CHF-CF2-CH3, CHF-CF2-CH2F, CHF -CF2-CHF2, CHF-CF2-CF3, CF2-CH2-CH3, CF2-CH2-CH2F, CF2-CH2-CHF2, CF2-CH2-CF3, CF2-CHF-CH3, CF2-CHF-CH2F, CF2-CHF -CHF2, CF2-CHF-CF3, CF2-CF2-CH3, CF2-CF2-CH2F, CF2-CF2-CHF2, CF2-CF2-CF3, CF3 CF3 CF3 CF3 CH2 CF3 CH2 FF as well as the corresponding groups in which the fluorine atom is replaced by a chlorine atom.   7. Process according to claim 1, characterized in that m is equal to 2   8. Process according to any one of claims 1 to 7, characterized in that the dimerization catalyst is triflic acid.   9. Process according to any one of the preceding claims, for the cyclodimerization of monomers in which at least one isocyanate functional group is in the cycloaliphatic position or carried by a secondary, tertiary or neopentyl atom.   10. Process according to claim 9, characterized in that the starting monomer is IPDI.   11. Method according to any one of the preceding claims, characterized in that the amount of the cyclodimerization catalyst of formula (1) is between 0.1% and 20%, preferably 0.5 and 5% by weight relative to the weight of S (O) n, OH functions present in the reaction medium, relative to the total weight of the reaction medium.   12. Process according to any one of the preceding claims, characterized in that an alcohol is added to the reaction medium, so as to form allophanates in addition to the dimers.   13. Process according to any one of the preceding claims, characterized in that an alcohol comprising at least two OH functions is added to the reaction medium, so as to form crosslinked dimers.