Structure of Poly(vinyl alcohol) Microfibrils Produced by Saponification of Copoly(vinyl pivalate/vinyl acetate)

Abstract

High molecular weight specimens of syndiotacticity-rich poly(vinyl alcohol) (PVA) have been prepared by saponification of copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc). VPi and VAc were copolymerized using the low-temperature initiator 2,2‘-azobis(2,4-dimethylvaleronitrile) and saponified in KOH/methanol/water with vigorous stirring, i.e., under shear. The PVAs obtained had number-average degrees of polymerization in the range (5.6−16.5) × 103 and syndiotactic diad (S-diad) contents of 52.8−61.5%. The highest molecular weight and S-diad content were obtained for specimens derived from homopoly(VPi) prepared at low initiator concentration, and these parameters declined progressively with increasing VAc content in the parent copolymers. The structures of these PVAs show a consistent sharp transition between 55 and 56% S-diad content. Specimens with lower S-diad contents have shapeless morphologies, but at 56% S-diad content the polymers were fibrous, with a higher degree of crystallinity and orientation of the crystallites. The order improves steadily with the S-diad content above the transition and correlates with the observed changes in the thermal and mechanical properties. The results suggest that the small increase in S-diad content from 55 to 56% facilitates a major change in the crystallization process, such that the crystallinity improves, and leads at the same time to the development of a fibrous morphology when the saponification is performed under shear.

Low‐temperature photoinitiation solution polymerization behavior of N‐vinylcarbazole in tetrahydrofuran

“…The photoinitiator 2,2Ј-azobis(2,4-dimethylvaleronitrile) (ADMVN) [33][34][35] (Wako Co.) was recrystallized at low temperature twice from absolute methanol. Other extra-pure grade reagents were used without further purification.…”

Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

“…Moreover, PVA hydrogels prepared by aging methods have shown properties superior to those of hydrogels prepared by other methods. [9][10][11][12][13][14][15][16][17] (R,S)-2-(3-Benzoylphenyl)propionic acid (ketoprofen), a potent nonsteroidal anti-inflammatory drug that inhibits prostaglandin synthetase cyclooxygenase, is used as a peroral treatment for rheumatoid arthritis and other related diseases. Its gastrointestinal side effects could be avoided with transdermal forms.…”

Preparation of poly(vinyl acetate) microspheres with narrow particle size distributions by low temperature suspension polymerization of vinyl acetate

“…[22][23][24][25][26][27] Especially, when VAc and VPi was suspension-polymerized at low temperature, the resulting PVAc and PVPi had ultrahigh molecular weight and was obtained at high yield, over 90%. 28,29 In this study, VAc was suspension-polymerized at low temperature, using ADMVN, to obtain PVAc microspheres with a narrow PSD, which is expected to be a profitable precursor of PVA microspheres applicable to embolization.…”