Free-Radical Propagation Kinetics of N-Vinyl Formamide in Aqueous Solution Studied by PLP-SEC

摘要

The propagation rate coefficients, k(p), were determined for free-radical polymerization of N-vinyl formamide (NVF) in aqueous solution by pulsed-laser-initiated polymerization in conjunction with size-exclusion chromatography. The polymerizations were carried out in the temperature range from 5 to 60 degrees C for concentrations between 3 and 100 wt.-% NVF. A six-fold decrease in k(p) was observed between polymerization of NVF in dilute aqueous solution and in bulk monomer. Intermolecular hydrogen bonding and dipolar interactions between solvent molecules and the transition state structure for NVF propagation are proposed to be responsible for these observed solvent effects, which are compared to similar effects found for the aqueous solution polymerizations of nonionized methacrylic acid and N-vinyl pyrrolidone (NVP). Batch aqueous-phase polymerizations of NVF and NVP demonstrate that the difference in initial rates of fractional conversion correlates with the differences in k(p) values for these two monomers. 2D NMR is used to study transfer reactions that occur at higher temperatures and NVF concentrations to the formic group and to the polyNVF backbone.