Dependence of termination kinetics in methyl acrylate-dodecyl acrylate free-radical copolymerization on comonomer composition, pressure, temperature and conversion

摘要

The termination of the free-radical bulk copolymerization of dodecyl acrylate (DA) and methyl acrylate (MA) has been investigated at various monomer mole fractions between 15 and 50degreesC and up to 2000 bar. The ratio of termination to propogation rate coefficients, (k(t)/k(p))(copo), is measured via the single pulse-pulsed laser polymerization (SP-PLP) technique. Chain-length averaged kt,copo are deduced from (k(t)/k(p))(copo) in conjunction with k(p,copo)data that are estimated via a simplified version of the implicit penultimate unit effect (IPUE) model. At low and moderate degrees of monomer cenversion extended ranges of almost constant kt are observed where termination is controlled by segmental diffusion with important contributions of steric effects. These plateau k(t) values are significantly - by almose two orders of magnitude - different for MA and DA. The increase with MA content of k(t,copo) is adequately described buy a penultimate unit model which uses the geometric mean approximation for estimating rate coefficients of cross-termination betwen radicals of different free-radical terminus. The model applies within the entire pressure and temperature range of the present study. At high degrees of monomer conversion, at and above 50, homo-k(t) and k(t,copo) are almost insensitive toward the composition of the monomer mixture. The termination rate under these conditions is essentially controlled by reaction diffusion. References: 43