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

Abstract

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 L₁/L₂ 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 = k⁰_pL^−β, where k⁰_p represents the maximum “virtual” propagation rate coefficient for monomeric radicals. New equations are derived to estimate the values of β 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 β 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.