Poor Solvents Improve Yield of Grafting-Through Radical Polymerization of OEO₁₉MA

Radical polymerization of poly(ethylene glycol) methyl ether methacrylate (OEO 19 MA, M n ∼ 950) at an initial monomer concentration of 150 mM was investigated as a function of solvent composition. Conventional and controlled radical polymerizations in anisole at 60 °C converged at approximately the same equilibrium monomer concentration ([M] eq ) of ∼38 mM, suggesting that livingness or diminished termination did not affect the thermodynamic parameters of polymerization. Conventional radical polymerizations (RPs) in anisole, dimethylformamide (DMF), toluene, and 1×PBS buffered water were taken to approximately 98% thermal initiator decomposition to determine [M] eq at reaction completion within a broad temperature range. The enthalpy (Δ H p ) and entropy (Δ S p ° ) of polymerization were solvent-dependent. Polymerizations in 1×PBS were the most thermodynamically favorable, followed by those in DMF, toluene, and anisole. −Δ H p and −Δ S p increased with the square of the difference in the Hansen solubility parameters of poly(ethylene glycol) and the solvent. It is proposed that poor solvents favor polymer–polymer interactions over polymer–solvent interactions, which improves the thermodynamic polymerizability.