| 摘要 |
Polyvinyl acetal resins containing not more than 12 per cent of hydroxyl groups (calculated as polyvinyl alcohol) and not more than 10 per cent of ester groups (calculated as polyvinyl ester) are prepared by treating a partially or completely hydrolyzed polyvinyl ester (other than formate), or polyvinyl alcohol, in the presence of an acid acetalysis catalyst with formaldehyde and acetaldehyde (in monomeric or polymeric form), either simultaneously or successively, at a temperature above 30 DEG C., the proportion of aldehydes in the reaction mixture being such that the acetal portion of the resin contains about 15 to 25 per cent by mols. of formaldehyde acetal. When polyvinyl alcohol is used as starting material it may be suspended in a resin solvent, e.g. isopropyl or other alcohol, benzene or heptane, there being then added the aldehyde mixture together with the acetalysis catalyst which may be strong acid, e.g. sulphuric acid. The resin may be separated by precipitation or steam-distillation, which may be followed by reprecipitation and washing. Alternatively, a polyvinyl ester may be used as starting material and the reaction carried out in the presence of a de-esterifying agent. The ester may be dispersed in a medium comprising the de-esterifying agent, which may be an aqueous or anhydrous primary or secondary alcohol, e.g. methyl, ethyl, n- or isopropyl, n-butyl alcohol, or ethylene glycol, with or without additional solvents, e.g. benzene, heptane, nitroethane, ethyl acetate, methyl propionate or dibutyl ether. There are then added the aldehydes together with not more than 5 per cent (reckoned on the reaction mixture) of an acid de-esterification and acetalysis catalyst which may be any strong acid or acid-reacting salt having no substantial oxidizing action, e.g. sulphuric and sulphonic acids or zinc, ferric or aluminium chlorides. Suitable esters include polyvinyl acetate, propionate, and butyrate, and interpolymers of vinyl acetate and propionate and of vinyl acetate and oleate. In either case the resulting resin may be de-hydroxylated by esterification (e.g. in suspension in pyridine by the action of organic acid chlorides or anhydrides) or etherification, or may be de-esterified by an acidic or basic de-esterifying agent. The hydroxyl group content of the resins is determined by suspending a sample in pyridine, warming for an hour with a known excess of acetic anhydride, adding water, and titrating the acetic acid produced. The ester group content is determined by suspending a sample in pyridine, warming with a known excess of caustic soda, and titrating. The resins may be plasticized, e.g. with triphenyl, tricresyl and tributyl phosphates; butyl and amyl phthalates, particularly the n- and isoisomers; di- and tri-glyceryl esters such as acetins, propionins and butyrins; glycerol acetal esters such as the butyraldehyde acetals of mono-acetin, -butyrin, and -valerin; glycerol acetal ethers such as the acetaldehyde acetal of glycerol mono-ethyl or -dodecyl ether; and monochlornaphthalenes: they may be pressed into blocks and skived to lamin suitable for use in the production of safety glass or made into films by coating a solution of the resin in a non-corrosive solvent, e.g. acetone, on to a glass or metal plate or a revolving drum, evaporating, stripping, and curing by heating with warm air. In examples: (1) and (2) 100 parts by weight of polyvinyl acetate, 34 parts of paracetaldehyde, and 5,8 parts of paraformaldehyde were dissolved in ethyl alcohol and ethyl acetate and warmed for 144 or 161 hours at 40 DEG C. in the presence of sulphuric acid, yielding a resin soluble in acetone and having hydroxyl group content 6,4 or 9,6 per cent, acetate content 4,0 or 4,1 per cent, and the acetal portion of the resin containing 19,7 or 18,5 per cent of formaldehyde acetal; (3) 1300 parts of polyvinyl acetate and 48 parts of trioxy - methylene were dissolved in ethyl alcohol and ethyl acetate, heated to 70 DEG C. for 5 hours in the presence of sulphuric acid, then 266,4 parts of paracetaldehyde added and heating continued for 20 hours, yielding a resin soluble in a mixture of alcohol and acetone and having hydroxyl group content 10,1 per cent, acetate group content 3,2 per cent, and the acetal portion of the resin containing 20 per cent of formaldehyde acetal. Specifications 351,082*, 430,136, and 445,565 are referred to. |
