Katrin B. Kockler

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.

An alternative method to estimate the bulk backbiting rate coefficient in acrylate radical polymerization

Based on a pulsed laser polymerization-size exclusion chromatography (PLP-SEC) analysis, an alternative method to estimate the bulk backbiting rate coefficient kbb in acrylate radical polymerization is presented. For different solvent volume fractions (0–0.75), using the unsaturated analogue of the monomer as a solvent to rule out solvent effects, regression analysis is applied to inflection point data in the low frequency range (<ca. 100 s−1) only, which can be scanned with less expensive PLP equipment. Variation of the solvent volume fraction allows the independent alteration of the average mid-chain radical lifetime and improvement in the sensitivity of the method to estimate kbb confidently. The robustness of the method is verified considering in silico generated data including large artificial errors. The method is applied to experimental data of 2,2-dimethoxy-2-phenylacetophenone (DMPA) initiated PLP of n-butyl acrylate, taking butyl propionate as the solvent. A kbb value of 171 ± 21 s−1 (303 K) is found, in good agreement with literature data. The method presents a generic approach for the estimation of kbb for other acrylate monomers, allows a complete statistical analysis, and can be used as a complementary tool for existing methods. In the long term, the method can even be extended for the simultaneous estimation of the bulk kbb and mid-chain radical propagation rate coefficient kp,m.

Investigating the propagation kinetics of a novel class of nitrogen-containing methacrylates via PLP-SEC

The Mark–Houwink–Kuhn–Sakurada parameters as well as Arrhenius parameters of the propagation rate coefficient for a new group of nitrogen-containing methacrylates were determined via triple detector SEC and pulsed laser polymerization–size exclusion chromatography, respectively. The data obtained for 2-(N-ethylanilino)ethyl methacrylate (NEAEMA, A = 1.77 (−0.75 to +5.74) × 106 L mol−1 s−1; EA = 20.17 (−2.57 to +2.87) kJ mol−1), 2-morpholinoethyl methacrylate (MOMA, A = 1.48 (−0.58 to +4.22) × 106 L mol−1 s−1; EA = 19.59 (−2.12 to +2.72) kJ mol−1), and 2-(1-piperidyl)ethyl methacrylate (PipEMA, A = 1.96 (−0.65 to +2.92) × 106 L mol−1 s−1; EA = 20.27 (−1.47 to +1.97) kJ mol−1) can be described with joint Arrhenius parameters of A = 1.83 (−0.72 to +3.65) × 106 L mol−1 s−1; EA = 20.14 (−2.17 to +2.28) kJ mol−1 and introduce a new family of nitrogen-containing branched methacrylates. The data of this novel family are critically evaluated and compared to the existing data sets for methacrylates with branched and cyclic ester side chains, respectively.

Estimating the photodissociation quantum yield from PLP-SEC peak heights

A fast method for the reliable estimation of the photodissociation quantum yield Φdiss is presented. Pulsed laser polymerization (PLP) experiments are performed at various pulse energies (1.5–6 mJ) and regression analysis is performed to the ratio of the peak heights identified in the size exclusion chromatography (SEC) trace. The high accuracy of the method is demonstrated for PLP initiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA), considering in silico generated data including large theoretical errors (up to 20%). The method has also been successfully applied to experimental data of DMPA based isothermal PLP of n-butyl acrylate at 306 K, with an estimated Φdiss of 0.42 ± 0.04. In the long term, the method will facilitate the evaluation of current and the design of new highly efficient photoinitiators.

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.

Macromol. Rapid Commun. 2/2016

Back Cover: Since the introduction of high-frequency pulsed lasers with pulse repetition rates of up to 500 Hz, the PLP-SEC method has allowed the investigation of a wide variety of rapidly propagating monomers. The investigation of, for example, acrylates in extended temperature ranges led to a broad database of industrially and academically highly relevant precision kinetic data. Further details can be found in the article by K. B. Kockler, A. P. Haehnel, T. Junkers,* and C. Barner-Kowollik* on page 123.