Chain-length dependence of the propagation rate coefficient for methyl acrylate polymerization at 25 °C investigated by the PLP-SEC method

When applying the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) method to determine the propagation rate coefficient (k(p)) for bulk methyl acrylate at 25 degrees C, the characteristic ratio L-1/L-2 of chain lengths controlled by pulsing is found experimentally to be markedly higher than the expected value of 0.5. In addition, the k(p) values determined are dependent on the pulse repetition rate. These results are interpreted with a power-law representation of the chain length (L) dependence of the value of k(p) for long radicals according to kL(p) = k0(p)L(-beta), where k0(p) represents the maximum "virtual" propagation rate coefficient for monomeric radicals. New equations are derived to estimate the values of beta and k0(p) from experimental molar mass distributions (MMDs), with the validity of the procedure checked in silico by simulations. A comparison of the calculated and experimental MMDs is used to correct chain lengths obtained by the PLP-SEC method, with beta and k0(p) estimated to be 0.12 +/- 0.01 and 28 000 +/- 2000 L mol(-1) s(-1), respectively, for chain lengths within 350 <= L <= 1200.