Identification of β scission products from free radical polymerizations of butyl acrylate at high temperature

Abstract

Acrylate polymerizations are associated with intra- and intermolecular H transfer to polymer and the formation of tertiary midchain radicals. At high temperatures β scission reactions of the midchain radicals may occur. To obtain more insights into the reaction mechanism in free radical butyl acrylate polymerizations at high temperature batch and semi-batch reactions were carried out in two solvents. The polymerizations were thermally initiated either by the monomer itself or a peroxide initiator. Molar mass distributions determined by size-exclusion chromatography (SEC) indicate the presence of low molar mass species in all products. To facilitate further analyses each sample was fractionated via preparative SEC. The separated low molar mass species were characterized via electro spray ionization – mass spectrometry and various nuclear magnetic resonance spectroscopy methods. Macromonomer species of chain lengths two to twelve were identified. The data are indicative of significant radical migration along the backbone prior to β scission.