a polyvinyl alcohol graft terpolymer comprises 70 - 30 % by weight of polyvinyl alcohol and 30 - 70 % by weight of acrylate / maleic anhydride copolymer having 95 - 30 mole % of acrylate and 50 - 70 mole % of maleic anhydride , which is prepared by a condensation - coupling reaction through esterification being performed between the hydroxy groups of the polyvinyl alcohol and the anhydride groups of the acrylate / maleic anhydride copolymer . the polyvinyl alcohol graft terpolymer may be further subjected to a heat treatment to have better water resistance and mechanical properties due to the interchain ester linkage between the hydroxyl groups and the anhydride groups therein . alternatively , the polyvinyl alcohol graft terpolymer may be reacted with an amine to produce a maleamic acid intermediate , and then dehydated to form a maleimide derivative .