| 摘要 |
Condensation products of polyvinyl alcohol with one or more carbonyl compounds selected from aldehydes and ketones are prepared in an aqueous phase in the presence of an acid catalyst by adding a proportion of said carbonyl compound(s) to the aqueous solution of polyvinyl alcohol at a temperature above 10 DEG C., said proportion being insufficient to cause the resulting condensation product to precipitate, the remainder of said carbonyl compound(s) being added at -6 DEG C. to +20 DEG C. and at a lower temperature than that at which the first stage of the reaction is carried out, in order to complete the condensation reaction and precipitate the resulting condensation product. The carbonyl compound may be propionaldehyde, valeraldehyde, acetaldehyde, caproaldehyde, butyraldehyde, heptaldehyde, citral, formaldehyde, caprylaldehyde, acrolein, crotonaldehyde, bezaldehyde, salicylaldehyde, furfural, pelargonic aldehyde, acetone, cyclohexanone, acetophenone, or p-nitro or p-chlorobenzaldehyde. The polyvinyl alcohol may contain some residual ester groups and the difference of temperature between the two stages is preferably over 5 DEG C. The acid catalyst may be hydrochloric, sulphuric, phosphoric, boric, acetic, oxalic or citric acids or acid salts such as ammonium chloride, aluminium or zinc chloride or sodium bisulphate. The carbonyl compound used in the second stage may be different from that in the first stage and mixtures may be used. The carbonyl compound may be added incrementally in each stage. The product is in the form of granules or a fine powder. |
