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 kp (app) have been determined in the temperature range of 0-80 °C. kp (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 (kp (SPR) ), backbiting (kbb ), midchain radical propagation (kp (tert) ), and the (residual) effective propagation rate (kp (eff) ) can be deduced via a herein proposed simple Predici fitting procedure. For kp (SPR) , the activation energy is determined to be (17.9 ± 0.6) kJ·mol(-1) in excellent agreement with literature data. For kbb , an activation energy of (25.9 ± 2.2) kJ·mol(-1) is deduced.

Solvent Effects on kp in Organic Media?: Statement to the Response.

A recent response on a publication from our team investigating solvent effects on propagation rate coefficients is commented. Among other issues, we point to the fact that the response interprets only a subset of the data provided in our original contribution.

Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching.

The branching stemming from midchain radical formation in n-butyl acrylate polymerization is investigated via melt-state (13) C NMR measurements. The dependence of the degree of branching (DB) on the monomer conversion of the system is examined for photoinduced polymerizations, revealing a steady increase in branching with conversion. For polymerization at moderate light intensities, an increase in branching from 0.03% to 0.37% is observed for polymerizations at 60 °C, which is fivefold below the level of branching observed in thermally initiated polymerizations under otherwise identical reaction conditions. The reason for this overall reduction in branching remains momentarily unclear; yet, a strong dependence of branching on light intensity is observed. While polymerization under a 1 W LED lamp results at almost full monomer conversion in branching degrees of 0.22%, polymerization under a 400 W lamp yields 1.81% of chain branches.

Solvent effects on acrylate kp in organic media?-A systematic PLP-SEC study.

The Arrhenius parameters of the propagation rate coefficient, kp , are determined employing high-frequency pulsed laser polymerization-size exclusion chromatography (PLP-SEC) for the homologous series of five linear alkyl acrylates (i.e., methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), stearyl acrylate (SA), and behenyl acrylate (BeA)) in 1 m solution in butyl acetate (BuAc) as well as in toluene. The comparison of the obtained kp values with the literature known values for bulk demonstrates that no significant solvent influence neither in BuAc nor in toluene on the propagation reaction compared to bulk is detectable. Concomitantly, the kp values in toluene and in BuAc solution display a similar increase with increasing number of C-atoms in the ester side chain as was previously reported for the bulk systems. These findings are in clear contrast to earlier studies, which report a decrease of kp with increasing ester side chain length in toluene. The additional investigation of the longest and shortest ester side chain acrylate (i.e., BeA and MA) over the entire experimentally available concentration range at one temperature (i.e., 50 °C) does not reveal any general concentration dependence and all observed differences in the kp are within the experimental error.