The objective is to provide benchmark values for the propagation rate coefficient in alkyl acrylate systems, with a particular emphasis on methyl acrylate. The particular challenges associated with measuring kp for acrylates will be addressed anew, taking new insights into the transfer to polymer reactions into account that occur extensively in acrylate polymerizations.
Since the 2004 publication of the IUPAC task group (project 2002-023-1-400) on the propagation rate coefficient in n-butyl acrylate free radical polymerizations (Macromol. Chem. Phys. 205, 2151-2160 (2004); https://dx.doi.org/10.1002/macp.200400355), a substantial knowledge increase on the polymerization kinetics of this class of monomers has taken place. Today, a refined understanding of the individual reactions typically occurring in acrylate polymerizations has been reached. New methods and techniques have been developed for the determination of rate coefficients, in particular for the backbiting reaction and for the addition of monomer to midchain radicals (which are generated upon backbiting in transfer to polymer reactions). These methods are based on pulsed-laser polymerization, time-resolved electron spin resonance, and NMR.
In the literature, various sets of data are to be found which are in more-or-less good agreement with each other. Still, variations occur, and since mutual dependencies of the rate parameters exist, not entirely consistent data sets are obtained. It is thus a matter of priority to critically review the existing data and to give benchmark values for propagation rate coefficients.
Recommendations for the determination of kp already exist, but their implementation for acrylates is particularly challenging for two reasons: (i) The very high value of kp in acrylate systems, and (ii) the occurrence of backbiting. Since the first IUPAC paper in this series (Asua JM, Beuermann S, Buback M, Castignolles P, Charleux B, Gilbert RG, Hutchinson RA, Leiza JR, Nikitin AN, Vairon J-P, van Herk AM. Critically evaluated rate coefficients for free-radical polymerization, 5. Propagation rate coefficient for butyl acrylate. Macromol. Chem. Phys. 2004, 205, 2151-2160 [link above]), there has been concomitant improvement in both understanding and instrumentation, meaning that kp for acrylates can now be measured much more accurately and widely. These advances will be reviewed and the data for all alkyl acrylates critically evaluated, with the aim of establishing whether the kp trends already published by IUPAC for methacrylates – viz. constant Ea and A that increases with side-group length (Beuermann S, Buback M, Davis TP, Gilbert RG, Hutchinson RA, Kajiwara A, Klumperman B, Russell GT. Critically evaluated rate coefficients for free-radical polymerization, 3. Propagation rate coefficients for alkyl methacrylates.
The following publication constitutes the main outcome of this project:
Critically evaluated rate coefficients in radical polymerization – 7. Secondary-radical propagation rate coefficients for methyl acrylate in the bulk Christopher Barner-Kowollik, Sabine Beuermann, Michael Buback, Patrice Castignolles, Bernadette Charleux, Michelle L. Coote, Robin A. Hutchinson, Thomas Junkers, Igor Lacik, Gregory T. Russell, Marek Stach, and Alex M. van Herklm Polym. Chem., 2014,5, 204-212 https://dx.doi.org/10.1039/C3PY00774J
Page last updated 13 Nov 2014
> Link to the Subcommittee on Modeling of Polymerization Kinetics and Processes >www.iupac.org/body/428