| The kinetic characteristics of free radical polymerization of N-Vinyl Pyrrolidone (NVP) in aqueous phase have been studied. Pulsed laser polymerization (PLP) in conjunction with aqueous-phase size exclusion chromatography (SEC) was used to determine propagation rate coefficients, kp. It was found that kp decreased with increasing monomer concentration, a phenomenon consistent with the results obtained for other water-soluble monomer, such as methacrylic acid (MAA) and acrylic acid (AA). This behaviour is influenced by specific solvent effects operative in aqueous-phase polymerization due to the action of hydrogen bonding and hydrophobic interactions.; Batch polymerizations of NVP were carried out at various monomer (to 37.5 vol. % in water) and initiator levels at 70°C to provide a better understanding of how polymerization conditions affect rate and polymer properties. The time-conversion profiles are used to estimate values of the termination rate coefficient, kt, assuming that the kp value not only varies with initial monomer level in the system, but also changes with conversion. kt is controlled mainly by segmental diffusion at lower NVP weight fractions. Trends in polymer molecular weights are consistent with the changing kinetic rate coefficients. |
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