Investigations into vinylogic addition reactions of modified polyester resins

Abstract

Saturated polyester resins were modified with acetoacetate or N-substituted 3-aminocrotonate (enamine) groups. The modified vehicles were combined with unsaturated acrylates which are commercially available for radiation curing. The combinations undergo vinylogic addition reactions which were investigated by means of differential scanning calorimetry (DSC) and other techniques. For comparison, the curing properties of films on glass and steel surfaces were studied. The investigation of the Michael addition between acetoacetate 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 proved to be insufficient. Hence, the mechanical and chemical resistance properties were out of discussion for practical use in the field of coatings. Better results with respect to surface properties, crosslinking density, conversion of acrylate groups, and reaction enthalpy were found after further treatment of the acetoacetate modified polyester with amines. The results, however, were strongly affected both by the acrylate oligomer selected and by the amine used for the second modification step (i.e. by the individual alkyl substitution on the aminocrotonate group). Surprisingly, the n-butyl amine derivative gave higher reactivity or better surface properties, respectively even compared to the reaction product with ammonia (which totally failed) and to the methyl amine derivative.