POLYURETHANE TYPE POLYMERS AND ADHESIVE SYSTEMS THEREFROM

1364866 Polyurethanes MINNESOTA MINING & MFG CO 16 Aug 1971 [17 Aug 1970] 38390/71 Heading C3R Solid polyurethanes, polyurethane-ureas or polyureas containing at least 20% by weight pendant chains connected to branching sites in the backbone of the polymer, the backbone containing between 5 and 15% by weight of aromatic nuclei based on the total weight of the polymer may be prepared by capping a polyurethane, polyurea or polyurethane-urea prepolymer having a functionality of at least 2À5 with at least 0À5 equivalent of a monofunctional capping agent, the prepolymer having at least 20% by weight of pendant chains, each of the pendant chains having a weight of 600 to 4000 atomic mass units, and f-m (f-2) free NCO groups wherein m is 0À5 to 1-35 and f is the functionality of the prepolymer prior to capping and reacting the capped prepolymer with a chain extender. The capped prepolymer may be obtained (1) by partially capping an isocyanate-terminated prepolymer with a monofunctional active hydrogen reactant, e.g. a monool or a N,N-dialkyl alkanolamine or with epsilon caprolactam, (2) by adding a monoisocyanate to a prepolymer-forming reaction mixture in which the polyol used is at least trifunctional or (3) by modifying one or more OH groups of an at least trifunctional polyol, e.g. by esterification or etherification before reacting the polyol with a polyisocyanate to form the prepolymer. The capped prepolymer may contain hydrophilic groups in the backbone, e.g. protonatable tertiary nitrogens by chain extension with an alkyldiethanolamine. Extremely stable latices may be provided by chain extension of the capped prepolymer in water or an aqueous solution containing a diamine chain extender. Films produced from solutions of the polymers, preferably aqueous solutions, are pressure-sensitive without the use of external tackifiers. In a typical example a mixture of poly(oxypropylene)triol and poly(oxypropylene/ oxyethylene)tetrol is reacted with toluene diisocyanate to form a prepolymer which is partially end-capped with diethylethanolamine and then formed into a latex by chain extension in water containing acetic acid. Other end capping agents are butanol and poly(oxyethylene)- glycol mono-oleate. The latex is cast into a film which is tacky to the touch.