| 摘要 |
Polyvinyl acetal resins containing substantially only acetal and hydroxy groups are prepared by reacting polyvinyl alcohol, derived from a polyvinyl ester having an average macromolecular weight of at least 7000, with a saturated aliphatic aldehyde containing 3 to 5 carbon atoms in solution in the presence of an inorganic acidic catalyst, the reaction being continued until there is produced a resin about 39 to 88 per cent acetalized, and the kind of aldehyde and the degree of acetalization being so correlated that the resin is water-insoluble and substantially insoluble in ester plasticizers at ordinary temperatures, but capable of absorbing large quantities of ester plasticizers to form homogeneous, extensible, resilient compositions of high ultimate strength. The resins are preferably prepared by adding mineral, e.g. hydrochloric, acid to an aqueous solution of polyvinyl alcohol, then adding, simultaneously and with stirring, aldehyde and a water-miscible solvent for the acetal resin, so that no precipitation occurs. The polyvinyl ester preferably has an average macromolecular weight of at least 15,000, preferably in excess of 25,000; the aldehydes are preferably straight-chained, the preferred one being butyraldehyde; more than one aldehyde may be employed. The desirable range of acetalization is 52 to 88 per cent, preferably 62 to 88 per cent, for propionaldehyde, 42 to 82 per cent, preferably 54 to 78 per cent, for butyraldehyde, and 39 to 62 per cent, preferably 41 to 58 per cent, for valeraldehyde. The resins are soluble in water-soluble liquids, e.g. lower alcohols, glycol monoalkyl ethers, (except that valeraldehyde acetals are insoluble in methanol and ethanol) and highly acetalized resins may be soluble in chlorinated hydrocarbons and in ketones. The ester plasticizer used may be triethyleneglycol di-(2-ethyl butyrate). The resins may be used in making safety glass or fabric-coating materials. |
