Investigations into vinylogic addition reactions of modified polyester resins

Saturated polyester resins were modified with acetoacetate or N-substituted 3-aminocrotonate (enamine) groups. The modified vehicles were combined wit h unsaturated acrylates which are commercially available for radiation curi ng. The combinations undergo vinylogic addition reactions which were invest igated by means of differential scanning calorimetry (DSC) and other techni ques. For comparison, the curing properties of films on glass and steel sur faces were studied. The investigation of the Michael addition between aceto acetate modified resins and various acrylates showed that this reaction can occur in two steps, probably due to the reaction of the second CH-acidic H atom. However, conversion of acrylate groups and crosslinking density prov ed to be insufficient. Hence, the mechanical and chemical resistance proper ties were out of discussion for practical use in the field of coatings. Bet ter results with respect to surface properties, crosslinking density, conve rsion of acrylate groups, and reaction enthalpy were found after further tr eatment of the acetoacetate modified polyester with amines. The results, ho wever, were strongly affected both by the acrylate oligomer selected and by the amine used for the second modification step (i.e. by the individual al kyl substitution on the aminocrotonate group). Surprisingly, the n-butyl am ine derivative gave higher reactivity or better surface properties, respect ively even compared to the reaction product with ammonia (which totally fai led) and to the methyl amine derivative. (C) 1999 Elsevier Science S.A. All rights reserved.