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The acylation of polyvinyl alcohols is carried out by a process in which these alcohols are esterified with an activated carboxylic acid derivative in the presence of, as the catalyst, an aminopyridine derivative of the general formula (I) ##STR## where R 1 and R 2 are each alkyl, or R 1 and R 2 tog

The acylation of polyvinyl alcohols is carried out by a process in which these alcohols are esterified with an activated carboxylic acid derivative in the presence of, as the catalyst, an aminopyridine derivative of the general formula (I) ##STR## where R 1 and R 2 are each alkyl, or R 1 and R 2 together form an alkylene radical. The acylation is particularly advantageously carried out in the heterogeneous phase. The acylated polyvinyl alcohols prepared in this manner are used in photopolymerizable and/or photocrosslinkable mixtures.

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1. A process for the acylation of a polyvinyl alcohol comprising esterifying the polyvinyl alcohol with a carboxylic acid derivative suitable for acylation reactions, in the heterogeneous phase in an aprotic dispersant, in the presence of a pyridine derivative catalyst of the formula I ##STR## where

1. A process for the acylation of a polyvinyl alcohol comprising esterifying the polyvinyl alcohol with a carboxylic acid derivative suitable for acylation reactions, in the heterogeneous phase in an aprotic dispersant, in the presence of a pyridine derivative catalyst of the formula I ##STR## where R 1 and R 2 are each alkyl, or R 1 and R 2 together form an alkylene radical. 2. A process as claimed in claim 1, wherein the activated carboxylic acid derivative is an anhydride of a monocarboxylic or dicarboxylic acid. 3. A process as claimed in claim 1, wherein the activated carboxylic acid derivative is an activated derivative of an olefinically unsaturated carboxylic acid of 3 to 10 carbon atoms. 4. A process as claimed in claim 2 wherein the activated carboxylic acid derivative is an anhydride of an α,β-olefinically unsaturated carboxylic acid of 3 or 4 carbon atoms. 5. A process as claimed in claim 1, wherein the polyvinyl alcohol is a hydrolyzed polyvinyl acetate in which more than 75 mole % of the acetate groups are hydrolyzed. 6. A process as claimed in claim 1, wherein the polyvinyl alcohol also contains copolymerized ethylene oxide units. 7. A process as claimed in claim 1, wherein the catalyst is p-dimethylaminopyridine. 8. A process as claimed in claim 1, wherein the catalyst is p-pyrrolidinopyridine. 9. A process as claimed in claim 1, wherein the esterification is further conducted in contact with one or more additional tertiary amines. 10. A process as claimed in claim 1, wherein the esterification is conducted at from 10° to 100° C. 11. A photopolymerizable or photocrosslinkable mixture which contains an acylated polyvinyl alcohol prepared by the process of claim 3, a photopolymerizable ethylenically unsaturated monomer or oligomer and a photoinitiator. 12. The process of claim 1, wherein the amount of catalyst of the formula I is from 0.1 to 15% by weight based on the polyvinyl alcohol. 13. The process of claim 12, wherein the alkyl is of 1 to 4 carbon atoms or R 1 and R 2 form an alkylene radical of 4 to 5 carbon atoms.