Synthesis of branched poly(methyl methacrylate)s: Effect of the branching comonomer structure

Branched poly(methyl methacrylate)s have been prepared using conventional solution phase free radical polymerization of methyl methacrylate (MATA) in the presence of a branching divinyl comonomer with appropriate levels of dodecanethiol (DDT) chain transfer agent added to inhibit gelation. The branching comonomers employed were five ethylene glycol dimethacrylates with varying lengths of PEG chains, divinylbenzene (DVB), and ethylene glycol diacrylate (EGDA). Soluble branched polymers were obtained in good yield with a MMA/brancher mole ratio up to 100/15. The minimum mole ratio of DDT required to avoid gelation was evaluated. The isolated polymers were characterized by elemental analysis to determine the level of DDT incorporated, by H-1 NMR spectroscopy, to determine the molecular composition and in particular the level of brancher incorporated (both as a branch unit and as a pendant functionality), and by double detection SEC in order to evaluate the level of branching. The differing behaviors of the branchers are discussed with a focus on a comparison of ethylene glycol dimethacrylate (EGDMA), EGDA and DVB. The latter brancher has been shown to produce the most regularly branched material with the smallest molar mass distributions. In general, however, the latter are broad or very broad.