Poor Solvents Improve Yield of Grafting-Through Radical Polymerization of OEO(19)MA

摘要

Radical polymerization of poly(ethylene glycol) methyl ether methacrylate (OEO(19)MA, M-n similar to 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 degrees C converged at approximately the same equilibrium monomer concentration ([M](eq)) of similar to 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 1xPBS buffered water were taken to approximately 98% thermal initiator decomposition to determine [M](eq) at reaction completion within a broad temperature range. The enthalpy (Delta H-p) and entropy (Delta S-p degrees) of polymerization were solvent-dependent. Polymerizations in 1xPBS were the most thermodynamically favorable, followed by those in DMF, toluene, and anisole. -Delta H-p and -Delta 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.