The effect of some metal cations on the gel content of epoxy ACM and the mechanism of ring opening of epoxy group under the catalysis of polyvalency metal cations were studied.The results show that the gel content of epoxy ACM was increased with the positive charge of metal cations and the catalyzing abilities of metal cations to open epoxy group were in following order Fe3+ >Al3+ >Fe2+ >Mg2+ >ca2+ ≈Na+.These phenomena agreed with both the acidic dissociation constant ( K 1) of hydration cations and the epoxy-opening mechanism catalyzing by metal cations.Based on the relationship of [η]～Mηestablished in polyethylacrylate

through proximate calculation

the critical value of ring-opened number of epoxy group in copolymer at which the gel content of copolymer was less than 1% were obtained.