Termination kinetics of methyl methacrylate free-radical polymerization studied by time-resolved pulsed laser experiments

The SP-PLP technique has been applied to measure k(t)/k(p), the ratio of termination to propagation rate coefficients, for the free-radical bulk polymerization of methyl methacrylate at 1000 bar and several temperatures ranging from 40 to 100 degrees C. k(t)/k(p), is obtained from time resolved (mu s) near-infrared measurement of monomer conversion induced by a single laser pulse of about 20 ns width. A total of 80 such single pulse (SP) signals were co-added to yield a concentration vs time trace of sufficient signal-to-noise quality to deduce k(t)/k(p), with an accuracy of better than +/-40%. With k(p) being known from the well-established PLP-SEC procedure, k(t)/k(p) data directly yield individual (chain-length averaged) termination rate coefficients, referring to a fairly narrow range of monomer conversion. The SP-PLP technique, which seemed to be restricted to investigations into high k(p) monomers such as ethene (at high temperatures) and the acrylates, within the present work on MMA is demonstrated to be suitable for kinetic studies on slowly propagating monomers, too.