Polyurethane elastomers having improved physical properties and a process for the production thereof
View Patent ↗A polyol composition having a number average molecular weight of from about 1,000 to about 3,000 Daltons is made up of (1) at least 60% by weight of a low monol polyoxypropylene polyol having a number average molecular weight of from about 2,000 to 12,000 Da and a degree of unsaturation less than or equal to 0.02 meq/g and (2) no more than 40% by weight of a polyol having a number average molecular weight of from about 400 to about 1,000 Da and a polydispersity index greater than 1.1. This polyol composition is reacted with a diisocyanate, a polyisocyanate, an isocyanate-terminated prepolymer or an isocyanate-terminated quasi-prepolymer to produce polyurethane elastomers having good physical and mechanical properties. Any of the known processes for producing polyurethane elastomers, including one-shot processes, may be used to produce elastomers in accordance with the present invention.
1. An NCO-terminated prepolymer or quasi-prepolymer having an NCO content of from about 3 to about 20% which is the reaction product of
a) a diisocyanate or polyisocyanate and
b) a polyol composition having a number average molecular weight of from about 1,000 to about 3,000 Da comprising
(1) at least 60% by weight, based on total weight of the polyol composition, of a polyoxypropylene polyol having a molecular weight of from about 2,000 to about 12,000 Da, a random or block or block/random oxyethylene moiety content no greater than 30% by weight, based on weight of the polyoxypropylene polyol, and a degree of unsaturation less than or equal to 0.02 meq/g and
(2) from 5 to 40% by weight, based on total weight of the polyol composition, of a polyol having a number average molecular weight of from about 400 to about 1,000 Da and a polydispersity index greater than 1.1.
2. The prepolymer of claim 1 in which the diisocyanate or polyisocyanate is 4,4′-diphenylmethane diisocyanate or an isomeric mixture thereof.
3. The prepolymer of claim 1 in which the diisocyanate or polyisocyanate is toluene diisocyanate, isophorone diisocyanate, or 1,4-cyclohexane diisocyanate.
4. The prepolymer of claim 1 in which the diisocyanate or polyisocyanate is a urea-modified isocyanate, urethane-modified isocyanate, carbodiimide-modified isocyanate, allophanate-modified isocyanate, biuret-modified isocyanate or a uretonimine-modified isocyanate.
5. The prepolymer of claim 1 in which polyol (1) has a number average molecular weight of from about 3,000 to about 8,000 Da.
6. The prepolymer of claim 1 in which polyol (1) has a number average molecular weight of from about 3,000 to about 6,000.
7. The prepolymer of claim 1 in which polyol (1) has a degree of unsaturation of less than 0.010 meq/g.
8. The prepolymer of claim 1 in which polyol (1) has a degree of unsaturation of less than 0.007 meq/g.
9. The prepolymer of claim 1 in which the polyol composition further includes up to 20% by weight, based on total weight of polyol composition, of a triol having a number average molecular weight of from about 250 to about 7,000 Da.
10. The prepolymer of claim 1 in which the polyol composition further includes up to 20% by weight, based on total weight of polyol composition, of a triol having a number average molecular weight up to about 7,000 Da selected from propoxylates of glycerin, propoxylates of trimethylolpropane, ethylene oxide/propylene oxide copolymers of glycerin and ethylene oxide/propylene oxide copolymers of trimethylolpropane.
11. The prepolymer of claim 1 in which the diisocyanate or polyisocyanate is 4,4′-diphenylmethane diisocyanate and the polyol composition comprises from 60 to 95% by weight, based on total weight of polyol composition, polyoxypropylene polyol and from 5 to 40% by weight, based on total weight of polyol composition, polytetramethylene ether glycol.
12. The prepolymer of claim 1 in which up to 20% by weight of the polyol composition is a triol having a number average molecular weight of from about 250 to about 7,000 Da.