A new copolymer has been synthesized by the copolymerization of acrylic acid with crotonaldehyde in water using K2S2O8 as initiator．The copolymer was characterized by DSC

IR and 13C-NMR．The effects of pH on the rate and conversion of copolymerization and copolymer’s composition have been investigated．The results show that

as pH increases

the rate and conversion decrease

especially at pH 5～7

while the content of crotonaldehyde in copolymer increases．It has been proved by IR that there is hydrogen bond between acrylic acid and crotonaldehyde at low pH．The study indicates that hydrogen bond improves the ability of polymerization．However

at high pH

acrylic acid was found as electron acceptor；crotonaldehyde as electron donor．A model of “charge transfer polymerization” was employed to illustrate the copolymerization at high pH．