| 摘要 |
Hydrophilic film-forming polymers containing 0.4 to 2.5 mol per cent of units of formula (a) <FORM:0809340/IV (a)/1> or (b) <FORM:0809340/IV (a)/2> where X is -COCH2CN and R is H or CH3, the remainder of the units in the polymers being -CH2CH(OH)-, may be prepared by (a) partially esterifying polyvinyl alcohol with cyanoacetic acid or with chloracetic acid and reacting the product with potassium cyanide, or (b) copolymerizing N-allylcyanoacetamide or N-methallylcyanoacetamide with a vinyl ester, e.g. vinyl acetate, propionate or butyrate, and alcoholysing the ester groups in the presence of an acid catalyst. Copolymerization may be effected in bulk or in solution, e.g. in methanol, in the presence of catalyst, e.g. potassium persulphate and benzoyl peroxide, and excess vinyl ester removed from the product by distillation. Photographic emulsions (see Group XX), may be prepared by mixing a dispersion of silver halide in aqueous solutions of the polymers, or by precipitating silver halides in such solutions, and may be coated on paper or cellulose ester films, and hardened by treating with alkali or an aldehyde or derivative thereof, e.g. formaldehyde, trioxymethylene, sodium formaldehyde bisulphite, b -methyl glutaraldehyde or its bisulphite complex. When coated on an alkaline support or on paper containing an aldehyde the emulsions harden on drying. Specification 649,545, [Group IV (b)], is referred to.ALSO:N-allyl cyanoacetamide and N-methallyl cyanoacetamide are prepared by condensing ethyl cyanoacetate with allylamine and methallylamine respectively. |
