| 摘要 |
Acetals are derived from linear organic polymers containing hydroxyl groups and aromatic aldehydes containing at least one alkali metal sulphonate group. The acetals also may contain residues of aromatic aldehydes not containing sulphonate groups. The acetals may be derived from polyvinyl alcohol which may contain some acetyl or propionyl groups, partially hydrolysed copolymers of vinyl chloride and vinyl esters, and copolymers of vinyl esters with acrylic acid, methacrylic acid, fumaric acid, maleic acid anhydride and esters of these acids, styrene, vinyl alkyl ethers, ethylene or propylene. They may be obtained by reacting polymers of vinyl esters in alcoholic solution with an aldehyde sulphonic acid whereby acetalization occurs with cleavage of the ester groups. In an example, polyvinyl alcohol, benzaldehyde and sodium benzaldehyde-2 : 4-disulphonate are heated in methanol with sulphuric acid catalyst and the reaction mixture neutralized with caustic soda diluted with methanol and precipitated by adding acetone to yield a polymer soluble in a mixture of water or acetone and methanol. By a similar method, a partially hydrolysed copolymer of vinyl chloride and vinyl acetate is reacted with sodium benzaldehyde-2 : 4-disulphonate. The acetal may contain dyes or be mixed with photographic gelatino-silver halide emulsions, or be used in protective layers by mixing, for example, with gelatin, saponin and 1 : 3 : 5-triacryloyl perhydrotriazine-1 : 3 : 5. |
