Preparation of High Molecular Weight Poly(vinyl Alcohol) With High Yield Using Low-Temperature Solutoin Polymerization of Vinyl Acetate

摘要

Vinyl acetate (VAc) was solution-polymerized in tertiary butyl alcohol (TEA) and in dimethyl sulfoxide (DMSO) having low chain transfer constant at 30, 40, and 50°C, using a low temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures ofpoly(vinyl acetate) (PVAc) and corresponding poly(vinyl alcohol) (PVA) obtained by saponification with sodium hydroxide. The polymerization rates of V Ac in TBA and in DMSO were proportional to the 0.49 and 0. 72 powers of ADMVN concentration, respectively. For the same polymerization conditions, TBA was absolutely superior to DMSO in increasing the molecular weight of PV A. In contrast, TEA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate ofV Ac in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concen- tration calculated using initial rate method and by an activation energy difference of polymerization obtained from the Arrhenius plot. Low-temperature solution polymer- ization of V Ac in TBA or DMSO by adopting ADMVN proved successful in obtaining PV A of high molecular weight (number-average degree of polymerization (P n): 4100- 6100) and of high yield (ultimate conversion ofVAc into PVAc: 55-80%) with dimin- ishing heat generated during polymerization. In the case of bulk polymerization ofV Ac at the same conditions, maximum p n and conversion of 5200-6200 and 20-30% was obtained, respectively. The p n and lightness were higher, and the degree of branching was lower with PVA prepared from PV Ac polymerized at lower temperatures in TBA.