Stable precatalyzed epoxy resin compositions

Claim 1

In a precatalyzed epoxy resin composition containing a mixture of (A) a relatively low equivalent weight epoxy resin having an average of more than one glycidyl ether group per molecule and (B) a phosphonium compound as a catalyst for the reaction between said epoxy resin and a phenolic-hydroxyl containing compound which is subsequently blended with said precatalyzed epoxy resin composition; the improvement which provides a stable precatalyzed epoxy resin composition as evidenced by, (1) after subjecting said precatalyzed epoxy resin composition to a temperature of about 200° F. (93.3° C.) for about 48 hours; (a) not more than 50% of the phosphonium groups originally present in said mixture are deactivated; (b) the viscosity has not increased by more than 30% of the original value; and (2) after subjecting said precatalyzed resin composition to a temperature of 200° F. (93.3° C.) for about 63 hours, the product resulting from its reaction with a phenolic hydroxyl-containing compound having an average of more than one phenolic hydroxyl group per molecule has a % epoxide value not greater than the value obtained by dividing the theoretical % epoxide value by 0.9; by employing as the catalyst, a phosphonium salt of phosphoric acid, phosphorous acid, polyphosphoric acid or mixture thereof, which salts are represented by the formula ##STR10## wherein each R is independently a hydrocarbyl group having from 1 to about 20 carbon atoms or the group R 1 Y wherein R 1 is a aliphatic hydrocarbon group having from 1 to about 20 carbon atoms and Y is Cl, Br, I, NO 2 or OH and Z is a phosphate group having the formula ##STR11## a phosphite group having the formula ##STR12## a polyphosphate group or mixture thereof.