3,144,452 United States Patent Office Patented Aug. 11, 1964 2 2-chloro-1: 4-phenylenediisocyanate, 3,144,452 4-methoxy-1:3-phenylene diisocyanate, POLYMERSATION OF ORGANIC SOCYANATES - m-phenylenediisocyanate, James Harry Wild and Francis Edward Gervase Tate, p-phenylenediisocyanate, Manchester, England, assignors to Imperia Chemical 4:4'-diisocyanatodiphenylmethane, raditEstries Limited, London, England, a corporation of 3-methyl-4:4'-diisocyanatodiphenyl-methane, Great Britaia 4:4'-diisocyanatodiphenyl ether, No Drawing. Fied Jan. 19, 1962, Ser. No. 67,436 2:4:4'-trisocyanatodiphenylether, 9 Claims. (C. 260-248) 2:4:4'-triisocyanatodiphenylmethane, This invention relates to the polymerisation of aryl iso 10 2:4:6-triisocyanatotoluene cyanates and the present application is a continuation-in and in general all the isocyanates where polymerisation part of Serial No. 46,049. has already been achieved with the use of other catalysts. It has already been proposed to polymerise isocyanates, The course taken by the polymerisation is largely de with the production of the dimeric, uretedione form by termined by the choice of polymerisation conditions. In contacting the isocyanates with pyridine or with a mono 5 general the dimeric, uretedione form is produced under or di-methyl pyridine, it is also known to polymerise iso mild reaction conditions, and can only be obtained when cyanates to the trimeric form in which the iso-cyanurate no substituent is present, ortho to the isocyanate group to ring structure is present, as represented below, be polymerised. Lower temperatures, reduced amounts of catalyst, and the selection of an inert solvent in which -ce 20 to conduct the reaction such that the dimeric form of the R-N N-R isocyanate is only sparingly soluble therein, favour the O to formation of the dimeric form. The isocyanurate form N / of polymer on the other hand is predominant at high re N action temperatures and its formation is favoured by in R 25 creased amounts of catalyst and the selection of an inert wherein R is an aromatic substituent which may or may reaction medium which has appreciable solvent power for not carry an NCO group. It has now been found that the dimeric form of polymer. Although as already stated certain substituted pyridines are effective catalysts for polymerisation conditions greatly influence the course these polymerisations. of the reaction, it is not unusual for the dimeric uretedione Thus according to the present invention there is pro 30 form to be present in the reaction mixture together with vided a process for polymerising aryl isocyanates con the trimeric isocyanurate form at the end of the reaction taining at least one isocyanate group preferably having time. no substituent ortho thereto, which comprises contacting The polymerisation process may be performed at a such isocyanates with a 3- and/or 4- substituted pyridine temperature between -40° C. and 140° C. Where the of such basicity that, when substituted in benzoic acid in 35 dimeric form of polymer is desired the temperature will the meta or para position respectively, said 3- and/or 4 usually be between 0° C. and 100° C. but is preferably substituent increases the pKa value of the Substituted ben about normal atmospheric temperature. Where the tri zoic acid, measured in water at 25 C. to greater than meric form is desired the temperature will usually be 4.35. between 0° C. and 140° C. but is preferably above normal Any 3- and/or 4-substituted pyridine of the specified 40 atmospheric temperature. basicity may be used as catalyst, provided the substituent The reaction may be carried out in the presence or ab does not react with the isocyanate group. Especially sence of solvents which are inert with respect to isocy valuable substituted pyridines are 4-alkoxy pyridines anates for example chlorobenzene, aromatic and aliphatic wherein the alkoxy group is for example methoxy, ethoxy hydrocarbons, and others. The reaction which results in or propoxy, 4-aralkoxy pyridines wherein the aralkoxy 45 the formation of the uretedione form is reversible so that group is for example benzyloxy, 3- and 4-dialkylamino where a solvent is used, the reaction is influenced as men pyridines wherein the alkyl group is for example methyl tioned above by the solubility of this form of polymer in or ethyl, 3- and 4-alkarylamino pyridines such as the 3 the solvent. and 4-methylphenylaminopyridines, and pyridines con 50 By the process of this invention organic isocyanates may be conveniently polymerised without the use of taining a substituent of the type poisonous or malodorous or otherwise objectionable cata -N-Cla lysts, which the activity of the catalysts is such that there is little difficulty in controlling the exothermic polymerisa in the 3- or 4-positions, wherein X represents an aliphatic 55 tion. The polymerisation may be instantly stopped, if chain with or without a hetero-link; thus for example the desired, by the addition of acyl halides or of Friedel substituent may be a morpholino, pyrrolidino or piperi Crafts catalyst such as boron trifluoride or its complexes dino-group. in substantially equimolecular amount with respect to the Any aryl mono or polyisocyanate preferably contain catalyst. Furthermore, the amount of catalyst necessary ing no substituent ortho to an isocyanate group at which 60 is small compared with the amount of pyridine or methyl polymerisation is to occur can be polymerised according pyridines necessary to polymerise the isocyanate at a simi to the process of this invention; the presence of such an lar rate. The amount of catalyst may be varied to con ortho substituent tends to inhibit polymerisation, espe trol the rate of polymerisation but will in general be be cially polymerisation to the dimeric form. Thus for ex tween .005% and 15% of the weight of isocyanate used ample there may be used 65 where dimerisation is desired, and between 0.05% and phenyl isocyanate, 15% where trimerisation is desired. p-chlorophenylisocyanate, The polymerisation isocyanates, which have the advan p-nitrophenylisocyanate, tage of low toxicity due to the absence of volatile mono m- and p-cyanophenylisocyanate, mers, may be used in place of or in addition to isocyanates 2-naphthylisocyanate, 70 for the wide variety of purposes, the dimeric forms, and 2:4-toluenediisocyanate, those trimeric forms which contain free isocyanate 4-chloro-1:3-phenylenediisocyanate, groups may be used for example as adhesives, curing a. 3,144,452 es 4. agents for resins, and for the manufacture of polyurethane solid or cellular articles. dine itself is illustrated in the following tables, where all The invention is illustrated but not limited by the fol reactions were carried out by mixing the components at lowing examples in which parts and percentages are by room temperature (20-24° C.). weight. EXAMPLE 8 EXAMPLE 1. Polymerisation of Phenyl Isocyanate To 57 parts of phenyl isocyanate was added 1 part of Parts by weight Duration Percent 4-ethoxypyridine. After 22 hours standing at room tem of Con- of di perature of 23 C. the mixture had set to a hard solid Catalyst tact in Inerisa and analysis indicated that the compound had been con Isocya- Catalyst Chloro- Hours tion verted completely to N:N-diphenyl uretedione. rate benzene Pyridine.------2.5 0. 22 EXAMPLE 2 4-Ethoxypyridine- 5.7 0 22 100 4-Dimethylamino To 57 parts of phenylisocyanate was added a solution of pyridine------690 33 58 1 part of 4-dimethylaminopyridine dissolved in 33 parts 4-N-Morpholino of chlorobenzene. After 1 hour standing at room tem 3-Dimethylaminopyridine------179 i 248 22 71 perature of 23 C. the solution had set to a solid mass pyridine------18 1. 0 22 98 and analysis indicated that 58% of the isocyanate had been converted to uretedione. 20 EXAMPLE 9 EXAMPLE 3 Polymerisation of 2:4-Toluene Diisocyanate To 26 parts of 2:4-toluene diisocyanate was added 1. part of 4-ethoxypyridine. The liquid solidified within a Parts by weight few minutes and after 2 and a half hours standing at room Catalyst Durationcontact ofPercent dinneri temperature analysis of the product indicated that the Isocya- Catalyst Chloro- in hours sation isocyanate had been completely converted to N:N'-bis nates benzene (4-methyl-3-isocyanatophenyl)uretedione. Pyridine.------26 O 2.5 9 4-Ethoxypyridine- 26 1. 0 2.5 00 EXAMPLE 4 4-Dimethylamino To 947 parts of 2:4-toluene diisocyanate was added a 30 pyridine------964 70 0.25 70 Solution of one part of 4-dimethylaminopyridine in 70 parts of chlorobenzene. After 15 minutes standing at EXAMPLE 10 room temperature analysis indicated that 70% of the 2:4- 1 part of 4-dimethylaminopyridine was added to a mix toluenediisocyanate had been converted to the uretedione. ture of 76 parts of toluene-2:4-diisocyanate and 72 parts EXAMPLE 5 of dry n-butyl ether, at room temperature. The mixture was heated under reflux. After 4 hours, the mixture was 1 part of 4-dimethylaminopyridine and 128 parts of 2:4- allowed to cool, and 1 part of acetyl chloride was added. toluenediisocyanate were dissolved in 376 parts of chloro The infra-red absorption spectrum of the solid product benzene. The system, initially at 20° C., was maintained obtained, showed the compound to contain both isocyan under adiabatic conditions with stirring. The temperature 40 urate and uretedione carbonyl groups in approximately rose slowly and a solid separated. The temperature equal amounts. The isocyanurate structure was identified reached a maximum of 37.5 C. after 30 minutes and after one hour analysis of the slurry indicated that 42% by its absorption in the infra-red at 5.83 and 7.07 microns. of the isocyanate had dimerised. After removing solid EXAMPLE 11 product by filtration a further 85 parts of the diisocyanate 1 part of 4-dimethylaminopyridine was added to a mix were added to the chlorobenzene solution. The tempera ture of 191 parts of toluene-2:4-diisocyanate and 102 parts ture again rose reaching a maximum of 44° C. during 15 of dry ethyl acetate at room temperature. The initially minutes. The solid product was identified as N:N'-bis formed precipitate disappeared when the mixture was (4-methyl-3-isocyanatophenyl) uretedione by comparison heated under reflux giving an orange-red solution. After of its infra-red absorption spectrum with that of an 50 5 hours the mixture was cooled in ice, when after a few authentic sample prepared by pyridine catalysed dimerisa minutes a yellow solid separated from the clear brown tion of 2:4-toluene diisocyanate. solution. The mixture was again heated under reflux for a further 15 hours. A brown solid separated leaving a EXAMPLE 6 supernatant viscous oil. The infra-red absorption spec To 179 parts of phenyl isocyanate was added a solu 5 5 trum of the viscous oil showed strong bands at 5.85 and tion of 1 part of 4-N-morpholinopyridine in 248 parts of 7.05 microns due to the isocyanurate ring and at 4.35 chlorobenzene. microns due to the free isocyanate groups. A weak band After standing 22 hours at room temperature (22-23 at 5.6 microns indicated the presence of a trace of the C.), analysis indicated that 71.2% of the phenylisocyanate uretedione derived from toluene-2:4-diisocyanate. has been converted to the uretedione. 60 4-N-morpholinopyridine (M.Pt. 105-106° C. uncorr.; EXAMPLE 12 picrate M.Pt. 189-190° C. uncorr.), was prepared by the 1 part of 4-dimethylaminopyridine was added to a solu action of boiling morpholine on 4-chloropyridine-N-oxide tion of 100 parts of toluene-2:4-diisocyanate in 185 parts in the presence of hydrated copper sulphate. of dry ethyl acetate. The mixture was maintained at re 65 flux temperature for 12 hours and allowed to cool for 9% EXAMPLE 7 hours, when a solid separated. The mixture was again To 18 parts of phenyl isocyanate was added 1 part of brought to reflux temperature, when the solid dissolved, 3-dimethylaminopyridine. The mixture solidified after 1 and the refluxing was continued for a further 8 hours. On hour, and after a further 21 hours standing at room tem cooling in ice, 1.4 parts of a precipitate formed after 15 perature, analysis indicated that 97.7% of the phenyl iso 70 minutes. No further increase in precipitates was noticed cyanate had been converted to the uretedione. on standing the mixture for a further 3 days at room tem The time taken for the degree of dimerisation to reach a perature. The catalyst was destroyed by adding an equiv given value varies with the isocyanate and with the solu bility of the uretedione formed in the solvent used. The alent amount of boron trifluoride as its ether complex, advantage of the Substituted pyridine catalysts over pyri- 75 bleand matter the reaction by decantation. mixture separated from unwanted insolu 3,144,452 5 6 The isocyanate content of the clear supernatant liquid of boron trifluoride as its ether complex. A small por was determined by the method of Staff (Analyst, 71, tion of the product was dried at 110° C. Its infra-red 557, 1946) which showed that 58.3% of the original iso absorption spectrum showed strong bands typical of the cyanate content had been polymerised. The infra-red isocyanurate ring and free isocyanate groups, a weak absorption spectrum of the solution showed strong bands band, due to the uretedione ring, being scarcely percepti at 5.82 and 7.0 microns due to the isocyanurate ring, and ble. The reaction mixture was shaken with excess dry at 4.35 microns due to the free isocyanate groups. An petroleum ether and filtered to separate 45 parts of a extremely weak hand at 5.6 microns, indicated that only white powder which melted over the range 310-320° C. traces of the dimeric form of toluene-2:4-diisocyanate The isocyanate equivalent of the product was 227. were present, thus proving to those skilled in the art that 10 EXAMPLE 17 any monomeric diisocyanate was present in even smaller A solution of 0.9 part 4-(N-pyrrollidino)pyridine in amount. 58.7 parts of anhydrous ethyl acetate was mixed with EXAMPLE 13 223.3 parts of phenyl isocyanate. Crystals commenced 1 part of 4-dimethylaminopyridine was added to 100 to separate immediately and after 15 minutes the mix parts of p-tolyl isocyanate and 200 parts of dry ethyl 5 ture completely solidified. After 24 hours the product acetate, and the mixture boiled under reflux for 24 hours. was washed with dry petroleum ether (B.P. 40-60° C.) 1 part of acetyl chloride was added to the cooled mix dried and weighed to give 221.1 parts of a white solid. ture, which was then shaken with petroleum ether and One crystallisation from dry benzene gave white flakes the solid product separated from the washings by filtra melting at 176-178° C. mixed melting point with authen tion. 46 parts of product which melted at 264 C. were 20 tic N:N'-diphenyl uretedione was 176-178° C. obtained. Recrystallisation from ethanol raised the melt What we claim is: ing point to 268 C., undepressed on admixture with 1. In a process for polymerising an aryl isocyanate in authentic tri-p-tolyl isocyanurate. Infra-red absorption which the isocyanate is contacted with a polymerisation spectrum of the product showed strong bands at 5.85 and catalyst under substantially anhydrous condition; the im 7.05 microns, typical of the isocyanurate ring. 25 provement comprising utilising as a catalyst a member of the group consisting of 3- and 4-substituted pyridines EXAMPLE 1.4 in which the substituents are selected from the group 1 part of 4-dimethylaminopyridine was added to a mix consisting of 4-alkoxy, 4-aralkoxy, 3- and 4-alkylaryl ture of 100 parts of p-nitrophenylisocyanate and 200 parts amino, 3- and 4-dialkylamino, 3- and 4-N-morpholino, of dry ethyl acetate. The mixture was maintained at 30 3- and 4-N-piperidino, and 3- and 4-N-pyrrolidino, said reflux temperature for 24 hours, allowed to cool, and the pyridine being of such basicity that, when substituted in solid product recrystallised from a mixture of ethanol benzoic acid in the 3- and 4- positions respectively, said and acetone. 20 parts of white microcrystals which did 3- and 4- Substituent increases the pKa value of the sub not melt below 350° C. were obtained. The infra-red 35 stituted benzoic acid, measured in water at 25° C. to absorption spectrum of the product and that of an authen greater than 4.35. tic sample of tri-p-nitrophenyl isocyanurate were identical. 2. The process of claim 1 in which the catalyst is 3-di methylaminopyridine. EXAMPLE 1.5 3. The process of claim 1 in which the catalyst is 4-di 1 part of 4-dimethylaminopyridine was added to a mix methylaminopyridine. ture of 45 parts of 2-nitro-4-isocyanatotoluene and 136 40 4. The process of claim 1 in which the catalyst is 4-N- parts of dry ethyl acetate, and the mixture heated to re piperidinopyridine. flux temperature at which point a vigorous reaction oc 5. The process of claim 1 in which the catalyst is 4-N- curred. After heating for 2% hours, the mixture was morpholinopyridine. cooled and filtered and the white residue washed with 6. The process of claim 1 in which the catalyst is 4 ethanol. 17 parts of a white powder which did not melt ethoxypyridine. below 360° C. were obtained. The infra-red absorp 7. The process of claim 1 in which the catalyst is 4 tion spectrum of the product was typical of the isocy benzyloxypyridine. anurate ring and the structure tri-(3-nitro-4-methylphen 8. The process of claim 1 in which the catalyst is 4-N- yl)-iso-cyanurate was confirmed by microanalysis. 50 pyrrolidinopyridine. EXAMPLE 16 9. The process of claim 1 in which the temperature 1 part of 4-dimethylaminopyridine was added to a mix is between 0° C. and 100° C. ture of 50 parts of anisole-2:4-diisocyanate and 100 parts of dry ethyl acetate and the mixture heated under reflux References Cited in the file of this patent for 40 hours. After cooling in ice for 15 minutes the 55 FOREIGN PATENTS catalyst was destroyed by adding an equivalent amount 856,372 Great Britain ------Dec. 14, 1960