Preparation of fine powdery copolymer with crosslinkage and monoalkyl maleate unit

In order to prepare fine powdery and crosslinked copolymer as a foaming agent and a modifier for polypropylene, the following processes were investigated: (1) polymerization of monoalkyl maleate–styrene–divinylbenzene; (2) polymerization of monoalkyl maleate–maleic anhydride–styrene–divinylbenzene; (3) polymerization of maleic anhydride–styrene–divinylbenzene and esterification of the copolymer with methanol, and (4) polymerization of maleic anhydride–styrene–divinylbenzene in the presence of methanol. The thermal treatment of copolymer thus obtained and the foaming ability for polypropylene were then investigated.