| 摘要 |
Polyvinyl alcohol is prepared by hydrolysing or alcoholysing a polymer of a vinyl ester of a monocarboxylic acid in the presence of an acid catalyst and a dialdehyde, the aldehyde groups of which are separated by at least one carbon atom. Specified polyvinyl esters are polyvinyl formate, acetate, propionate, butyrate and stearate. Specified aldehydes are terephthalic aldehyde, cyclohexane dial-1,4, propane dial, butane dial, pentane dial, hexane dial, phthalic aldehyde, isophthalic aldehyde and diphenyl dial-4,41. Alcoholysis may be effected in the presence of a C1-4 alkanol, e.g. methanol. Specified acid catalysts are perchloric, sulphuric, hydrochloric and sulpho acids. Partial conversions may be effected by using a limited quantity of water or catalyst, regulating the reaction temperature, or neutralizing the catalyst. In examples, polyvinyl acetate is alcoholysed (1) in methanol in the presence of sulphuric acid and cyclohexane dial-1,4 and (2 and 3) in aqueous methanol in the presence of perchloric acid and terephthalic aldehyde. |
