| 摘要 |
Polyvinyl alcohol prepared by partially saponifying under substantially anhydrous conditions to 75 to 95% conversion a vinyl acetate polymer in the presence of a polyhydric alcohol compatible with polyvinyl alcohol, may be melt extruded under substantially anhydrous conditions to form water-soluble films. The vinyl acetate polymer may be polyvinyl acetate or a copolymer of vinyl acetate with minor proportions of acrylic, maleic or itaconic acids or esters or vinyl ethers. Specified polyhydric alcohols are glycerol, 1,3-butanediol, ethylene glycol and polyethylene glycols. In examples, films are melt extruded from polyvinyl alcohols prepared by polymerizing vinyl acetate in the presence of methanol, azodiisobutyronitrile and (1) ethylene glycol or (3) diethylene glycol, saponifying in the presence of methanol and sodium hydroxide, and drying; and prepared by saponifying polyvinyl acetate in the presence of methanol, sodium hydroxide and (2) 1,3-butanediol and (4) polyethylene oxide. |
