Grafting reactions in the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier.

摘要

uring the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates out from the aqueous phase to form polymer particles.;The kinetics behavior and the evolution of the number of particles with conversion were obtained. VAc emulsion polymerization where the initiator concentration was varied showed that the rate of VAc grafting in the aqueous phase ceased when the locus of polymerization becomes the polymer particles (constant number of particles). The total amount of grafted PVA decreased with the decrease in the initiator concentration, whereas the amount of grafted PVAc was independent of its concentration. The addition of water-soluble chain transfer agent (CTA) increased the rate of polymerization, while the addition of the water-insoluble CTA did not affect it. Using either CTA's the amount of grafted PVAc was higher only at the initial conversions, while the amount of grafted PVA decreased at all conversions. A decrease in the molecular weight of the PVAc homopolymer and the water-soluble PVA was observed when using either CTA's. When a high molecular weight PVA with similar acetate content but higher degree of blockiness was used, the amounts of grafted PVAc and grafted PVA were lower. By increasing the degree of blockiness the rate of polymerization increases and the nucleation period is extended.;In order to monitor the grafting reactions, a separation method of the PVAc latex components was developed, based on the acetonitrile/hot water selective solubilization of the latex (not of the dried latex film). Fourier Transform Infrared (FTIR) spectroscopy and