| 摘要 |
Synthetic sponges are made by subjecting to foaming and to acetalization in the presence of a strong acid, an aqueous solution of a polyvinyl acetal of which the molecule has been modified by the introduction of acid groups or ester groups or by polyalkylene glycol residues. Foaming may be effected by heating air or other inert gas into the solution which may contain a wetting agent. The modified polyvinyl acetals may be prepared (a) by the acetalization of polymers obtained by the saponification or reesterification of copolymers of vinyl esters (especially vinyl acetate) with maleic acid or anhydride, crotonic acid, itaconic acid, fumaric acid, acrylic acid, methacrylic acid, diethyl maleate, methyl itaconate, vinyl sulphonic acid, vinyl phosphonic acid or diesters of unsaturated phosphonic acids; (b) by the acetalization of polymers obtained by the hydrolysis of graft polymers of vinyl acetate on to polyalkylene oxides or hydroxyalkylated amines or amides or of polymers obtained by the hydroxyalkylation of polyvinyl alcohol; or (c) by using in the acetalization process an aldehyde containing an acidic group, e.g. glyoxlic acid, butyraldehyde sulphonic acid or benzaldehyde sulphonic acid. The acid catalyst used in the acetalization and foaming process may be sulphuric, hydrochloric, phosphoric, nitric, trichloracetic or organic sulphonic acids. Examples describe the manufacture of sponges from aqueous acidic solutions containing (1) a copolymer of vinyl acetate and vinyl phosphonic acid, and formaldehyde; (2) a copolymer of vinyl acetate and methyl-itaconate, and formaldehyde; (3) a copolymer of vinyl acetate and crotonic acid, polyvinyl alcohol and formaldehyde; (4) a copolymer of vinyl acetate and maleic acid, and formaldehyde; (5) a graft copolymer of vinyl acetate, polypropylene glycol and diethyl maleate, and formaldehyde, (6) a graft copolymer of vinyl acetate and polypropylene glycol, and formaldehyde; (7) a graft copolymer of vinyl acetate and polyethylene glycol, polyvinyl alcohol and formaldehyde; (8) a mixture of the copolymers of examples 1 and 6 and formaldehyde; (9) the copolymer of Example 2, formaldehyde and the sodium salt of benzaldehyde sulphonic acid; (10) a polyvinyl butyrol sulphonate containing free -OH groups, the copolymer of Example 5 or polyvinyl alcohol and formaldehyde. In some of the examples, the sulphonate of cetyl alcohol is used as a wetting agent. |
