Free-Radical microwave-assisted polymerization of Butyl Acrylate

Abstract

[EN] Microwave-assisted polymerization is a branch of polymer chemistry that has attracted a lot of interest and development in the last decade. Several authors have reported that microwave heating presents numerous advantages over conventional heating, including faster polymerization times and molecular weight increase. With the significant growth in the number of books and reviews on the matter, a certain topic of discussion has arisen: whether the benefits are caused by “thermal effects”, due to fast heating by the microwaves, or by “non-thermal effects”, caused by intrinsic irradiation effect that cannot be replicated by conventional heating. While some report that the increase in polymerization rate (Rp) is caused by fast heating of the mixture and formation of hotspots, other investigations have shown a mutual increase in Rp and MW, suggesting the existence of non-thermal effects in the kinetic constants.

There are some data showing that, in the presence of enough irradiation power, terpenoid acrylates present microwave effects that cannot be explained by differences in temperature, whereas the effect is not observed for terpenoid methacrylates. The goal of this project is to investigate if these findings are limited to this specific family of monomers or are also present for conventional, commercially available monomers. Therefore, the microwave-assisted free radical polymerization of butyl acrylate was studied and the results compared to conventional heating. Attention was paid to the evolutions of the monomer conversion and molar mass distributions. Since accurate control of reaction temperature is crucial to be able to confirm a non-thermal effect, attention was paid to the level of control over the temperature of the microwave device used and to our purposes. Three different polymerization systems with distinct characteristics were investigated: polymerization in solution, miniemulsion polymerization and RAFT polymerization.