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 °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 k L p = k 0 p L − β , where k 0 p represents the maximum "virtual" propagation rate coefficient for monomeric radicals. New equations are derived to estimate the values of β and k 0 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 β and k 0 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. The marked chain-length dependence of the propagation rate coefficient of long-chain radicals has been determined for methyl acrylate bulk polymerization at 25 °C through the analysis of data obtained by the PLP-SEC method applying novel approaches.