Kinetic and mechanistic studies on the block copolymerization of methyl methacrylate initiated by Ce4+-poly (ethylene glycol) redox system

Abstract

The kinetic and mechanistic features of tetravalent cerium-poly(ethylene glycol) (PEG, molecular weight 6000) redox couple initiated block copolymerization of methyl methacrylate (MMA) have been investigated in aqueous acidic medium in the temperature range 30–50°C. The block copolymerization behavior as a function of [Ce4+], [PEG], [MMA], [H+], [NO3−], as well as temperature, have been studied. The overall rate of polymerization (Rp), the rate of disappearance of Ce4+ (RCe), and the number average molecular weight (Mn) have been determined from gravimetry, cerimetry, and gel permeation chromatography, respectively. Rp has been found to bear a square dependence on [MMA] and independent of both [Ce4+] and [H+]. RCe has been found to be directly proportional to [Ce4+] and [H+], and independent of [MMA]. Both Rp and RCe have been found to be retarded on adding nitrate ions, while increase of temperature accelerated the rates. The Mn of the block copolymer has been found to depend on [Ce4+], [PEG], [MMA], and [H+] as well as on temperature. A plausible reaction scheme has been derived and suitable kinetic expressions have been evaluated based on these observations. It has been concluded that by varying the temperature and concentration of the components of the redox system, it is possible to control the rate of polymerization and the molecular weight of the resulting block copolymer. © 1997 John Wiley & Sons, Inc.