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

摘要

The role of grafting in the particle nucleation mechanism during the emulsion polymerization of vinyl acetate (VAc) using partially hydrolyzed poly(vinyl alcohol) (PVA) as emulsifier and potassium persulfate as initiator was investigated. The polymerizations were carried out in batch using a low solids (10%) recipe. 1H-NMR, 13C-NMR and HPLC techniques were used to characterize the PVA with respect to its acetyl sequence distribution (degree of blockiness). Temperature dependent 1H-NMR and DSV coupled with DLS was used to elucidate the aqueous phase conformation of the pVAs. 13C-NMR and 13C-APT NMR was used to characterize the grafted PVA (PVA-g-PVAc) to determine the predominant grafting site. An automated reaction calorimeter (Mettler RC1) was used to directly monitor the kinetics of the emulsion polymerization using PVAs with different degrees of blockiness and molecular weight. The amount of grafted PVA and grafted PVAc during the emulsion polymerization of VAc were quantified for two PVAs with different degrees of blockiness. The surface morphology of the PVAc latex films made with PVAs having different degrees of blockiness and molecular weights were monitored using Atomic Force Microscopy.; It was found that the PVA adopts different conformations in the aqueous solution, depending on the molecular weight and degree of PVA blockiness (Poval 217EE > 217E > 217) and the initial solution conformation of the PVA molecule regulates the grafting in the aqueous phase and control the particle nucleation mechanism.; The kinetics of the emulsion polymerization of VAc using PVA followed Smith-Ewart case 1 kinetics (n 0.5) and there was no constant rate period during Interval IL A non-linear relationship was observed between R_p and N_p and the final R_p was found to be independent of the degree of blockiness but dependent of the molecular weight of the PVA. Continuous nucleation was accompanied by extensive limited aggregation during the particle growth stages and chain transfer to PVA leading to grafting.; Using this low solids recipe, grafting appears to be primarily a solution event, occurring predominantly in the aqueous phase and not at the particle-water interface as was previously speculated.