Critically evaluated rate coefficients for free-radical polymerization, 3: Propagation rate coefficients for alkyl methacrylates

Pulsed-laser polymerization (PLP) in conjunction with the analysis of the molecular weight distribution (MWD) via size-exclusion chromatography (SEC) remains recommended by the IUPAC Working Party on Modeling of polymerisation kinetics and processes as the method of choice for the determination of propagation rate coefficients, k_p, in free-radical polymerization. k_p data from PLP-SEC studies in several laboratories for ethyl methacrylate (EMA), butyl methacrylate (BMA) and dodecyl methacrylate (DMA) bulk free-radical polymerizations at low conversion and ambient pressure are collected. The data fulfill consistency criteria and the agreement among the data is remarkable. These values are therefore recommended as constituting benchmark data sets for each monomer. The results are best fit by the following Arrhenius relations: EMA : k_p = 10^6.61 L · mol^-1 · s^-1 exp(-23.4 kJ·mol^-1/R · T) BMA : k_p = 10^6.58 L · mol^-1 ·. s^-1 exp(-22.9 kJ·mol^-1/R · T) DMA : k_p = 10^6.40 L · mol^-1 · s^-1 exp(-21.0 kJ·mol^-1/R · T) For the methacrylates under investigation k_p increases with the size of the ester group. For example, in going from MMA to DMA, k_p at 50°C is enhanced by a factor of 1.5.