Patent GB-1533066-A (GB)
Title: Process for the production of polyurethane
IPC: C08G18/38
Filed: 1976-09-22
Abstract: 1533066 Crosslinked polyurethanes BAYER AG 22 Sept 1976 [26 Sept 1975] 39261/76 Heading C3R A process for the production of a polyurethane from an oligomer prepolymer and a crosslinking agent comprises adding, in coarse powder or lump form, an isocyanate group free, storage stable, oligomer prepolymer of Mol. Wt. <20,000, containing 4 to 120 milliequivalents per 100 g. of ionic groups or groups capable of conversion to ionic groups and/or 2 to 20% by weight of oxyethylene groups, to water at a temperature below the softening point of the prepolymer to form a storage stable dispersion; converting to ionic groups part or all of any groups present which are capable of conversion to ionic groups before, during or after the prepolymer is dispersed; applying the dispersion to a substrate and allowing it to dry, the crosslinking agent being added before, during or after the application of the dispersion and immediately or subsequently reacted to form a crosslinked polyurethane. The oligomer prepolymer may be synthesized from (a) a di- and/or triisocyanate and optionally at least one monoisocyanate and (b) compounds containing at least one group capable of reacting with isocyanate groups, either of which may contain the ionic and/or oxyethylene groups, the amounts of each used being sufficient to give the prepolymer the aforementioned properties. Additionally, at least one compound which in addition to containing at least one group capable of reacting with isocyanate groups contains reactive groups which do not react with isocyanate groups but which do react with the crosslinking agent, e.g. urea; N,N-dimethylethanolamine; ethanolamine and glycidol, may be used in the synthesis. The crosslinking agent used depends on the functional groups present in the prepolymer but a preferred crosslinking agent is formaldehyde which reacts with for example -CO-NH-, -NH-NH-, -OH and -NH 2  groups, the molar proportion of prepolymer to crosslinking agent being suitably 5 : 1 to 1 : 4. The proportion by weight of prepolymer to water in the dispersion may be from 65 : 35 to 5 : 95 and the dispersion may be formed at a temperature of from 1 to 150 C. In typical examples (i) a polypropylene oxide ether started on bisphenol A (Mol. Wt. 570), a propoxylated adduct of 2-butene diol and sodium bisulphite (Mol. Wt. 425) and urea are reacted with hexamethylene diisocyanate giving a prepolymer having a M. pt. of 60 C., Mol. Wt. 2225 and an SO 3 - content of 19 milliequivalents/100 g. which is dissolved in water at 20 C. and crosslinked by adding formaldehyde to the dispersion (ii) a prepolymer prepared in a similar manner to (i) but in which urea is replaced by glycidol is crosslinked with diethylene triamine (iii) a butane diol/adipic acid polyester, N-methyldiethanolamine, urea, hexamethylene diisocyanate and a polymer Mol. Wt. 2250 obtained by reacting a polyethylene oxide polyether started on butanol with hexamethylene diisocyanate and N,N-diethanolamine are reacted to form a prepolymer having a M. pt. of 48 C., Mol. Wt. 3070 and 7À7% by weight ethylene oxide units which is crosslinked with formaldehyde. Polyurethanes prepared by this process may be used as leather dressings, textile coatings, glass fibre sizes, adhesives or as binders for synthetic resin dispersions.