GB929371A - Improvements relating to polyurethane elastomers - Google Patents

Abstract

A method of preparing a prepolymer comprises reacting a polyether, polyester or polyesteramide having primary, secondary or tertiary hydroxyl groups in molecular chain terminal positions by agitating therewith, without the application of heat, an aromatic polyisocyanate in an amount which is sufficient, or substantially sufficient, to make an isocyanate group available for reaction with each of the hydroxyl groups, allowing the reaction to follow its course until the heat evolved is dissipated, heating the reaction mixture progressively to a temperature of the order of from 70 DEG to 120 DEG C. and adding gradually a second amount of aromatic polyisocyanate so that the final prepolymer contains free isocyanate groups and cooling the resulting prepolymer. The second addition is preferably controlled so that the viscosity of the mixture stays constant. A foamed polyurethane elastomer is obtained by mixing the prepolymer at room temperature with water and one or more catalysts and preferably with a foam stabilizing agent. N-ethyl- and methyl-morpholines, triethylamine and trimethylamine are suitable catalysts. In Example (1) polypropylene glycol is reacted with toluene 2:4- and 2:6-diisocyanates in amount calculated to react the OH groups without application of heat, the temperature rising to 40 DEG C. When the exothermic reaction has finished the mixture is heated progressively to 100 DEG C. until the viscosity is 12,000 centipoises and more of the toluene diisocyanate is then added in such a way that the viscosity remains constant. The prepolymer is rapidly cooled to 35 DEG to 40 DEG C. and a small addition of diisocyanate is made. Foaming is carried out by adding an aqueous solution of N-methylmorpholine and triethylamine. In Example (2) a similar process using a mixture of polypropylene glycol and a polypropylene glycol triol as starting material is described.ALSO:A method of preparing a prepolymer comprises reacting a polyether, polyester or polyesteramide having primary, secondary or tertiary hydroxyl groups in molecular chain terminal positions by agitating therewith, without the application of heat, an aromatic polyisocyanate in an amount which is sufficient or substantially sufficient to make an isocyanate group available for reaction with each of the hydroxyl groups, allowing the reaction to follow its course until the heat evolved is dissipated, heating the reaction mixture progressively to a temperature of the order of from 70 DEG C. to 120 DEG C. and adding gradually a second amount of aromatic polyisocyanate so that the final prepolymer contains free isocyanate groups and cooling the resulting prepolymer. The second addition is preferably controlled so that the viscosity of the mixture stays constant. A foamed polyurethane elastomer is obtained by mixing the prepolymer at room temperature with water and one or more catalysts and preferably with a foam stabilizing agent. N-Ethyl- and methyl-morpholines triethylamine and trimethylamine are suitable catalysts. In Example (1) polypropylene glycol is reacted with toluene 2 : 4- and 2 : 6-diisocyanates in amount calculated to react the OH groups without application of heat, the temperature rising to 40%C. When the exothermic reaction has finished the mixture is heated progressively to 100 DEG C. until the viscosity is 12000 centipoises and more of the toluene diisocyanate is then added in such a way that the viscosity remains constant. The prepolymer is rapidly cooled to 35 DEG C. to 40 DEG C. and a small addition of diisocyanate is made. Foaming is carried out by adding an aqueous solution of N-methyl-morpholine and triethylamine. In Example (2) a similar process using a mixture of polypropylene glycol and a polypropylene glycol triol as starting material is described.