Synthesis of syndiotacticity-rich high molecular weight poly(vinyl alcohol) by suspension polymerization of vinyl pivalate and saponification

Abstract

Vinyl pivalate (VPi) was suspension-polymerized to synthesize high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with a high conversion above 95% for a precursor of syndiotacticity-rich HMW poly(vinyl alcohol) (PVA). Also, the effects of the polymerization conditions on the conversion, molecular weight, and degree of branching (DB) of PVPi and PVA prepared by the saponification of PVPi were investigated. Bulk polymerization was slightly superior to suspension polymerization in increasing the molecular weight of PVA. On the other hand, the latter was absolutely superior to the former in increasing the conversion of the polymer, indicating that the suspension polymerization rate of VPi was faster than that of the bulk one. These effects could be explained by a kinetic order of a 2,2'-azo-bis(2,4-dimethylvaleronitrile) concentration calculated by the initial rate method. Suspension polymerization of VPi at 55degreesC by controlling various polymerization factors proved to be successful in preparing PVA of HMW [number-average degree of polymerization (Pn): 8200-10,500], high syndiotactic diad content (58%), and very high yield (ultimate conversion of VPi into PVPi: 94-98%). In the case of the bulk polymerization of VPi at the same conditions, the maximum P-n and conversion of 10,700-11,800 and 32-43% were obtained, respectively. The DB was lower and the P-n was higher with PVA prepared from PVPi polymerized at lower initiator concentrations. (C) 2003 Wiley Periodicals, Inc.