Kilohertz Pulsed-Laser-Polymerization: Simultaneous Determination of Backbiting, Secondary, and Tertiary Radical Propagation Rate Coefficients for tert-Butyl Acrylate

For the first time, a 1000 Hz pulse laser has been applied to determine detailed kinetic rate coefficients from pulsed laser polymerization-size exclusion chromatography experiments. For the monomer tert-butyl acrylate, apparent propagation rate coefficients k_p ^app have been determined in the temperature range of 0-80 °C. k_p ^app in the range of few hundreds to close to 50 000 L·mol^-1·s^-1 are determined for low and high pulse frequencies, respectively. The apparent propagation coefficients show a distinct pulse-frequency dependency, which follows an S-shape curve. From these curves, rate coefficients for secondary radial propagation (k_p ^SPR), backbiting (k_bb), midchain radical propagation (k_p ^tert), and the (residual) effective propagation rate (k_p ^eff) can be deduced via a herein proposed simple Predici fitting procedure. For k_p ^SPR, the activation energy is determined to be (17.9 ± 0.6) kJ·mol^-1 in excellent agreement with literature data. For k_bb, an activation energy of (25.9 ± 2.2) kJ·mol^-1 is deduced. A simple, but robust evaluation method for pulse-frequency-dependent pulsed laser polymerization-size exclusion chromatography data for acrylate monomers is presented and secondary radical propagation, backbiting, and midchain radical propagation rate coefficients for tert-butyl acrylate in the temperature interval of 0-80 °C are provided.