| 摘要 |
Polyvinyl alcohol is produced from polyvinyl esters by dissolving the ester in a solvent comprising methanol or ethanol, emulsifying the solution in an immiscible heavy paraffinic hydrocarbon oil of boiling point above 300 DEG C. and then alcoholyzing in the presence of a catalyst. Hydrocarbon oils specified are white oils and viscous lubricating oils and the catalyst, which may be added incrementally, may be an acid or sodium or potassium hydroxide or methoxide. A solvent diluent such as methyl acetate may be included. To assist the emulsification, a surface-active agent, of which examples are given, may be added to the oil and/or solvent. The reaction, which may be carried out in a plurality of stages with intermediate separation of polyvinyl alcohol, may be stopped by neutralization of the catalyst, e.g. with glacial acetic acid. The product is obtained in the form of particles or grains. |
