Anion-exchange resins from vinylbenzyl choride: control of hydrolysis during polymerization

Abstract

Anion-exchange resins can be prepared by amination of vinylbenzyl chloride-divinylbenzene (VBC-DVB) copolymers. A limitation of the VBC route is that significant hydrolysis of benzyl chloride to benzyl alcohol occurs during copolymerization, which can reduce the ion-exchange capacity of the final resin. This article documents a novel technique to control hydrolysis with a staged polymerization process using a package of azo and peroxy initiators. The polymerization is initiated at low temperature to minimize hydrolysis, run to high conversion at moderate temperature and completed at high temperature to burn off residual monomer. The aqueous phase is buffered with bicarbonate salt to prevent low pH conditions. The technique effectively controls hydrolysis to less than 5%, producing a high capacity anion-exchange resin. The technique can be used to synthesize VBC-DVB resins that are equivalent to conventional styrene-DVB resins by incorporating additional crosslinking agent during polymerization to compensate for the lack of methylene bridging during functionalization