The objective is to provide a complete set of rate coefficients of all elementary reactions that are relevant for modeling of acrylate polymerization processes, hence monomers of high industrial and academic importance.
Polyacrylates are an important class of polymers in the academic and industrial field with broad applications ranging from adhesives to drug delivery materials. Yet, their design is often hampered by the significant occurrence of side reactions such as inter- and intramolecular transfer to polymer reactions. These transfer reactions (and their follow up reactions, such as monomer addition) render polymerizations hard to predict and pose a significant hurdle in precision polymer design, be it on industrial scale or for high-added value materials. The aforementioned reactions influence free radical as well as controlled polymerizations (reversible deactivation radical polymerization). Since polymer properties are tightly correlated with the polymerization conditions, extensive modeling at largely varying conditions is required. The knowledge of reliable rate coefficients for all elementary reactions is an indispensible requirement for reaching this goal.
The IUPAC Subcommittee on Modeling of Polymerization Kinetics and Processes has in the previous years gathered a significant amount of kinetic data, especially from the IUPAC-recommended pulsed-laser (initiated) polymerization (PLP) in conjunction with size-exclusion chromatography (SEC) as the method of choice. Whereas availability of accurate propagation rate coefficients was the biggest problem in the understanding and modelling of acrylate polymerizations, focus has shifted towards transfer to polymer reactions, as already discussed in the two IUPAC benchmark publications on acrylate propagation kinetics (see Asua et al. Macromol. Chem. Phys. 2004, 205(16), 2151-2160; doi.org/10.1002/macp.200400355 and Barner-Kowollik et al. Polym. Chem. 2014, 5, 204-212; doi.org/10.1039/C3PY00774J). In fact, without a deeper understanding of the transfer reactions (and the associated fate of the tertiary midchain radicals stemming from therefrom), no meaningful modelling of the overall polymerizations is possible.
This project aims at defining criteria for the measurement of transfer to polymer rate coefficients (specifically values for intramolecular transfer, also referred to as “backbiting”), and to provide benchmark values for two monomer, butyl acrylate and methyl acrylate. In previous years, several methods have been proposed in literature that yield seemingly high quality data on transfer kinetics. These techniques will be critically reviewed with regards to their reliability and broad applicability and published on the example of butyl acrylate as a first publication. A second publication will then gather data for methyl acrylate (and other acrylates should more kinetic data have come available until then). Next to evaluation of transfer to polymer rate coefficients, also the rate coefficient for addition of monomer to tertiary radicals will be addressed, as meaningful modelling of polymerizations is only achievable when both parameters are known.
May 2021 update – Although the project group has not had a formal meeting over the past year, acrylate backbiting remains an active research topic for group members. A PhD student in the Junkers group is working on acquiring new data, and the Hutchinson group has published (Macromol. Theory Simul., https://doi.org/10.1002/mats.202000093 (first published 27 Jan 2021)) a simulation study of high-temperature acrylate polymerization demonstrating that, while considerable uncertainty still remains in reported beta-scission rate coefficients, there is reasonable agreement among literature estimates for backbiting rate coefficients and addition rates to the midchain radical.
Page last updated 27 May 2021