Critically evaluated rate coefficients for free-radical polymerization, 4 -: Propagation rate coefficients for methacrylates with cyclic ester groups

Propagation rate coefficients, k(p), which have been previously reported by several groups for free-radical bulk polymerizations of cyclohexyl methacrylate (CHMA), glycidyl methacrylate (GMA), benzyl methacrylate (BzMA), and isobomyl methacrylate (iBoMA) are critically evaluated. All data were determined by the combination of pulsed-laser polymerization (PLP) and subsequent polymer analysis by size-exclusion chromatography (SEC). This-so-called PLP-SEC technique has been recommended as the method of choice for the determination of k(p) by the IUPAC Working Party on Modeling of Polymerisation Kinetics and Processes. The present data fulfill consistency criteria and the agreement among the data from different laboratories is remarkable. The values for CHMA, GMA, and BzMA are therefore recommended as constituting benchmark data sets for each monomer. The data for iBoMA are also considered reliable, but since SEC calibration was established only by a single group, the data are not considered as a benchmark data set. All k(p) data for each monomer are best fitted by the following Arrhenius relations: CHMA: k(P) = 10(6.80) L . mol(-1) . s(-1) exp( -23.0 kJ.mol(-1) / (R.T), GMA: k(p) = 10(6.79) L . mol(-1) . s(-1) exp (-22.9 kJ.mol(-1)) / (R.T), BzMA: k(p) = 10(6.83) L . mol(-1) .s(-1) exp(-22.9 kJ.mol(-1)) / (R.T), iBoMA: k(p) =10(6.79)L . mol(-1) . s(-1) exp(-23.1 kJ.mol(-1)) / (R.T). Rather remarkably, for the methacrylates under investigation, the k(p) values are all very similar. Thus, all data can be fitted well by a single Arrhenius relation resulting in a pre-exponential factor of 4.24 x 10(6) L . mol(-1) . s(-1) and an activation energy of 21.9 kJ . mol(-1). All activation parameters refer to bulk polymerizations at ambient pressure and temperatures below 100degreesC. Joint confidence intervals are also provided, enabling values and uncertainties for k(p) to be estimated at any temperature.