Solvent Effects on Free-Radical Copolymerization Propagation Kinetics of Styrene and Methacrylates

Solvent effects on free-radical copolymer composition and propagation kinetics of styrene (ST) with three methacrylates, 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), and n-butyl methacrylate (BMA), arc investigated using pulsed-laser polymerization combined with size exclusion chromatography and proton NMR. Three representative solvents, n-butanol, toluene, and DMF (N,N-dimethylformamide), are selected based on their polarity and structure. It was found that all three solvents have an effect on ST/HEMA copolymer composition compared to bulk copolymerization, with a systematic variation in monomer reactivity ratios observed with solvent polarity. Only butanol affects ST/BMA copolymer composition, and solvent choice has no effect on composition for the STIGMA system. Butanol increases the composition-averaged copolymerization propagation rate coefficient, k(p,cop), only for the ST/BMA system, while DMF causes a uniform decrease of for all three systems and toluene has no observable effect on k(p,cop). These rate effects are linked to corresponding solvent effects on homopropagation kinetics. It is difficult to reconcile the combined copolymer composition and k(p,cop), data for ST/HEMA systems and for ST/BMA in butanol using the implicit penultimate model of chain-growth, suggesting that H-bonding interactions need to be explicitly considered.