Patent GB-752589-A (GB)
Title: Hidden polyisocyanates
IPC: C08G18/80
Filed: 1954-03-31
Abstract: Masked polyisocyanates for admixture and reaction with polyesters in the production of lacquers, are the reaction products of an hydroxy-ethyl carbamic acid aryl ester with a polyisocyanate or polycarboxylic acid or a functional derivative of the latter (see Group IV (b)).  These masked polyisocyanates when heated above 150 DEG  C. split off a monofunctional compound, for example phenol, when a phenyl ester is used, and behave as isocyanates.  In examples: (1) 2:4- or 2:6-toluylene diisocyanate or a mixture thereof is reacted with a hydroxyl-ethyl carbamic acid phenyl ester, the reaction product dissolved in ethylene glycol monomethyl ether acetate and mixed with a polyester containing free hydroxy groups obtained from a dicarboxylic acid and a polyhydric alcohol, to give a varnish solution which on heating to temperatures above 150 DEG  C. gives a lacquer coating; (2) and (3) phthalyl or succinyl chloride is reacted with hydroxy-ethyl carbamic acid phenyl ester, the compound prepared from phthalyl chloride being a soft resin which splits off phenol at elevated temperatures; (4) and (5) hydroxyethyl carbamic acid phenyl ester is reacted with 2:4:6-triisocyanatotoluene, and 1:6-hexane-diisocyanate; (6) the polyisocyanate obtained by reaction of 1:1:1-trimethylol propane with 2:4- or 2:6-toluylene diisocyanate or a mixture thereof, is reacted with hydroxy-ethyl carbamicacid cresyl ester.ALSO:Hidden polyisocyanates, i.e. compounds having terminal groups, each of which on heating splits off a mono-functional compound and leaves a terminal isocyanate group, are prepared by a process which comprises reacting a hydroxyethyl-carbamic acid aryl ester with a polyisocyanate, polycarboxylic acid or functional derivative of the latter, at a temperature below 150 DEG  C.  They are prepared by mixing equivalent amounts of reactants, preferably in an inert solvent.  Reaction between a diisocyanate and hydroxyethyl-carbamic acid phenyl ester is as follows: <FORM:0752589/IV(a)/1> R being a divalent hydrocarbon radical.  A similar product which contains ester groups is obtained when a dicarboxylic acid or a derivative thereof is reacted.  All the compounds have terminal urethane groups, which on heating to a temperature above 150 DEG  C. split off the hydroxy-aryl compound from which the hydroxyethyl-carbamic acid aryl ester was derived leaving terminal isocyanate groups.  For example: <FORM:0752589/IV(a)/2> The hydroxyethyl carbamic acid aryl ester may be obtained by reacting an aryl chlorocarbonate and ethanolamine. Specified polyisocyanates are tetramethylene 1 : 4-diisocyanate, hexamethylene 1 : 6-diisocyanate, p-phenylene diisocyanate, 4 : 41 - dicyclohexylmethane diisocyanate, 1 - methylbenzene - 2 : 4 : 6-triisocyanate, polyisocyanates, obtained by reaction of diisocyanates with polyhydric alcohols and 2 : 4- or 2 : 6-toluylene diisocyanate or a mixture thereof.  Specified carboxylic acids or anhydrides thereof are oxalic, succinic, adipic, methyl adipic, sebacic, thiodiglycollic, phthalic, terephthalic and citric acids and maleic anhydride.  Functional derivatives of the polycarboxylic acids such as esters or halides may also be used.  The hidden polyisocyanate may be admixed with polyesters containing free hydroxy groups, the mixture on heating giving a lacquer coating (see Groups IV (a) and III).  In Examples (1-5) hydroxyethyl carbamic acid phenyl ester is reacted with 2 : 4- or 2 : 6-toluylene diisocyanate or a mixture thereof, phthalyl chloride, succinyl chloride, 2 : 4 : 6 - triisocyanato - toluene, or 1 : 6-hexamethylene diisocyanate; (6) 1 : 1 : 1-trimethylol-propane is reacted with 2 : 4- or 2 : 6-toluylene diisocyanate or a mixture thereof, to form a polyisocyanate which is reacted with hydroxyethyl carbamic acid cresyl ester.ALSO:Lacquer coatings are obtained from mixtures of hidden polyisocyanates, i.e. compounds having terminal groups which on heating split off a mono-functional compound and leave terminal isocyanate groups (see Group IV(b)) and polyesters containing free hydroxy groups, by stoving at temperatures above 150 DEG C.