A compound represented by formula: and a treated filler having the compound on at least a portion of its surface. R is hydrogen or alkyl. X is alkylene, arylalkylene, or alkylarylene, each optionally interrupted by at least one of an ether, thioether, amine, amide, ester, thioester, carbonate, thiocarbonate, carbamate, thiocarbamate, urea, or thiourea, with alkylene optionally interrupted by arylene. W is hydroxyl, a sulfonic acid group, a phosphonic acid group, carboxylic acid group, —NHR1, epoxy, or —Si(Y)x(Z)3-x. Y is alkyl, aryl, arylalkylenyl, or alkylarylenyl. Z is halide, hydroxyl, alkoxy, aryloxy, acyloxy, polyalkyleneoxy, —O— covalently bonded to the surface of the filler, or —O bonded to another silicon atom, and x is 0 or 1. A composition including the treated filler, a method of making the treated filler, and a method of determining the degree of cure of a curable polymeric resin are also disclosed.