Hydrophilic polyurethanes of improved strength

Claim 1

A substantially noncovalently crosslinked hydrophilic, substantially nonfoaming polyurethane resin having improved tear strength and a urea content of from about 13.6 to 33.7 weight percent, consisting essentially of the reaction product of a mixture of: A. a diol component selected from at least one of (1) a long chain poly(oxyethylene) glycol, having a molecular weight of from about 2500 to about 12000, (2) a medium chain poly(oxyethylene) glycol or polyester glycol, having a molecular weight of from about 250 to about 2500, B. at least one organic chain extender having a molecular weight of less than 250; C. water; and D. an organic diisocyanate; wherein alternative mole ratios of the diol component A and water per mole of chain extender B are as follows: (i) 0.4 to 0.5 of diol component (1), 1.5 to 10.0 of water; (ii) 0.1 to 0.25 of diol component (2), 0.05 to 0.72 of water; (iii) 0.25 to 0.50 of diol component (2), 0.25 to 1.00 of water; (iv) 0.5 to 0.75 of diol component (2), 0.3 to 3.3 of water; or (v) 0.06 to 0.07 of diol component (1), 0.1 to 0.2 of diol component (2) and 0.25 to 1.25 of water; wherein the effective NCO:OH ratio is in the range of 0.85:1 to 1.1:1 and the amount of water in the reaction mixture is in the range of about 1 to about 2.5 wt. %.