Propagation and Termination Kinetics of Poly(Ethylene Glycol) Methyl Ether Methacrylate in Aqueous Solution

Abstract

The propagation rate coefficient, kp, of poly(ethylene glycol) methyl ether methacrylate (Mn ≈500 g mol−1) has been measured via pulsed-laser polymerization (PLP)–size-exclusion-chromatography in aqueous solution between 5 wt% monomer and bulk polymerization at temperatures from 22 to 77 °C. kp increases significantly toward higher water content, as is observed for other water-soluble monomers. This entropy-motivated effect enhances the pre-exponential. The activation energy, EA(kp), is more or less identical to the characteristic value of methacrylates. The chain-length-dependent rate coefficient, kti,i, for termination of two radicals of chain length i has been investigated at low degrees of monomer conversion via the single-pulse–PLP–electron paramagnetic resonance technique. kti,i turned out to be adequately represented by the composite model designed by the Russell group. The power-law exponents for the chain-length dependence of small and long radicals are close to the numbers reported for other monomers. The rate coefficient for termination of two radicals of chain length unity scales with the fluidity of the reaction mixture. Viscosity measurements prior to polymerization thus enable estimates of termination rate.