Synthesis of high molecular weight poly(vinyl alcohol) by low temperature polymerization of vinyl acetate in tertiary butyl alcohol and the following saponification

Vinyl acetate (VAc) was polymerized at 30, 40, and 50 °C using 2,2′ -azobis (2,4-dimethylvaleronitrile) (ADMVN) and tertiary butyl alcohol (TBA) as the initiator and the solvent, respectively. High molecular weight (HMW) atactic poly(vinyl alcohol) (PVA) was prepared by saponifying the poly(vinyl acetate) (PVAc) synthesized. The effect of polymerization conditions were investigated in terms of conversion, degree of branching for acetyl group of PVAc, and molecular weight of both PVAc and PVA. The polymerization rate of VAc in TBA was proportional to the 0.49th power of ADMVN concentration in good accordance with the theoretical value of 0.5. HMW-PVA with high yield could be obtained successfully, probably due to lower polymerization temperature and decreased chain transfer reaction rate which was achieved by adopting ADMVN and TBA. PVAc having average degree of polymerization (P_n) of 10000-13000 was obtained at the conversion of 35-70%. Saponification of so prepared PVAc yielded PVA having P_n of 2400-6100. The syndiotactic diad content increased with decreasing polymerization temperature and increasing VAc concentration due to a steric hindrance effect of TBA during polymerization.