What is described herein is a terpolymer of maleic acid (MAA)/maleic anhydride (MAN)/alkylvinylether (AVE), made by partial cyclization, e.g. 1-99%, of a maleic acid/alkylvinylether copolymer, preferably comprising, in mole %, 1-49% MAA/1-49% MAN/50% AVE, and derivatized terpolymers thereof.