Chain-Length-Dependent Termination of Sodium Methacrylate Polymerization in Aqueous Solution Studied by SP-PLP-EPR

Abstract

Via the single pulse-pulsed laser polymerization-electron paramagnetic resonance (SP-PLP-EPR) technique, the chain-length-dependent termination of 5 and 10 wt % sodium methacrylate (NaMAA) in aqueous solution was measured from 5 to 60 degrees C. The rate coefficients k(t)(i,i) for termination of two ionized radicals of identical size i were analyzed by the composite model. Three out of the four composite-model parameters behave similarly to nonionized monomers, whereas the fourth parameter, the rate coefficient for termination of two radicals of chain length unity, k(t)(1,1), exhibits a distinctly different behavior. The temperature dependence of k(t)(1,1) is significantly below the one of fluidity (inverse solution viscosity). Moreover, absolute k(t)(1,1) increases with NaMAA concentration, i.e., toward higher viscosity. Both observations indicate that the termination kinetics of ionized radicals largely differs from the Smoluchowski-type behavior.