Preparation of poly(vinyl alcohol) having various molecular weights by the low temperature solution polymerization of vinyl acetate in methanol

Vinyl acetate (VAc) was solution-polymerized at 30, 40, and 50°C using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) as initiator and methanol as solvent, and effects of polymerization temperature, monomer to solvent ratio, and initiator concentration were investigated in terms of conversion of VAc into poly(vinyl acetate) (PVAc), degree of branching (DB) for acetyl group of PVAc, molecular weights of PVAc and resulting PVA obtained by saponifying it with sodium hydroxide. Low polymerization temperature by adopting ADMVN proved to be successful in obtaining PVA of high molecular weight. PVAc having number-average degree of polymerization (P_n) of 4000-15000 was obtained at conversion of 5-85%. Saponifying so prepared PVAc yielded PVA having P_n of 1000-5500, and syndiotactic diad (S-diad) content of 51-54%. DB for acetyl group was increased with increasing polymerization temperature, methanol concentration, conversion, and ADMVN concentration. The S-diad content of PVA was higher with PVA prepared from PVAc polymerized at lower temperature and at higher methanol concentration.