Effect of the Ester Side-Chain on the Propagation Kinetics of Alkyl MethacrylatesAn Entropic or Enthalpic Effect?

Abstract

The technique of pulsed-laser polymerization (PLP) was used to measure homopropagation rate coefficients for styrene (STY), methyl methacrylate (MMA), ethyl methacrylate (EMA), n-butyl methacrylate (BMA), and benzyl methacrylate (BzMA). Special attention was given to the molecular weight analysis of PLP distributions by size exclusion chromatography (SEC) with online low-angle laser-light scattering (LALLS), differential viscometry (DV), and differential refractive index (DRI) detectors connected in series. The PLP distributions were analyzed using two different approaches: first, by transformations to the universal calibration curve via Mark−Houwink−Sakurada (MHS) constants and, second, by direct analysis of the molecular weight distributions using absolute detection methods. The accuracy and precision of the two approaches is discussed with reference to the measured Arrhenius parameters. The variation in the propagation rate coefficients with ester side chain size is attributed primarily to the preexponential factor. This is consistent with theoretical predictions but in opposition to a recent PLP study of this series. An explanation for this apparent contradiction is suggested.

Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerization

“…The rate constants and Arrhenius parameters for DMA are in fair agreement with those obtained by the PLP method. 24 A similar relation was observed for k p values of nBMA 21,49 and BzMA. 25 Reasonable agreement was found in estimated k p values for styrene between the ESR and PLP methods, as shown in Figure 14(b).…”

Critically evaluated propagation rate coefficients in free-radical polymerizations: Part III. Methacrylates with cyclic ester groups (IUPAC Technical Report)

“…A significant fraction of these free radicals is terminated by radicals originating from the subsequent laser pulse resulting in polymer molecules of a characteristic degree of polymerization L 0 . According to the original suggestion [5] and in full agreement with extended simulation studies [8][9][10][11][12], the point of inflection on the low-molecular-weight side of the peak maximum of the molecular weight distribution (MWD) obtained via SEC provides a robust measure of L 0 . From the known monomer concentration, c M , the time t 0 between two subsequent laser pulses and from L 0 , k p is found according to eq.…”

“…Data for BzMA are provided by Zammit et al [11] and Hutchinson et al [9]. The data sets for OMA (46 experiments) and for CHMA (68 experiments) cover a temperature range from −10 to 110 °C and −0.4 to 110 °C, respectively.…”

“…k p values for BzMA (40 experiments) are reported for a temperature interval from 6.1 to 110 °C: The reactions are initiated with laser pulse repetition rates varied between 1 and 100 Hz, and different initiators, initiator concentrations, and laser pulse energies were used. For details, see the original publications [9][10][11]. For the three monomers, no systematic trend in k p with initiator-derived primary free-radical concentration is seen.…”

“…Only k p data for BzMA provided by the group of Davis [11] are determined on the basis of absolute SEC calibration employing a multidetector SEC.…”