Stable precatalyzed epoxy resin compositions

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.degree. F. (93.3.degree. 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.degree. F. (93.3.degree. 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.sup.1 Y
• wherein R.sup.1 is a aliphatic hydrocarbon group having from 1 to about 20 carbon atoms and Y is Cl, Br, I, NO.sub.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.