Diels-Alder polymerization of some derivatives of abietic acid

The Diels-Alder polymerization reaction between a bisdiene derived from abietic acid and 4,4'-diphenylmethanedimaleimide (bismaleimide) was studied. The bisdiene was the dehydrodecarboxylation product of abietic acid, denoted here as diabietyl ketone. An insoluble and infusible polymer with high molecular weight was obtained. It is a poly(ketoimide) with hydrophenanthrene moieties in the backbone. The analyses showed that the chemical structure of the polymer was different from that expected. The polymer structural unit was found to contain bismaleimide and diabietyl ketone units not in a molar ratio of 1:1, as expected, but in a ratio of 5-6:1. The phenomenon was ascribed to the difference between the rates of the two concomitant reactions in the synthesis; the homopolymerization of bismaleimide and the proper Diels-Alder polymerization. The polymer having in structure the monomer units in 1:1 ratio was, however, obtained by both the dehydrodecarboxylation of the diacid resulted from the Diels-Alder reaction between abietic acid and 4,4'-diphenylmethanedimaleimide and the polycondensation of the ketone of maleated abietic acid with 4,4'-diaminodiphenylmethane. The monomers and the polymers were investigated by usual physical and chemical methods. The thermal stability of polymers was evaluated by TGA. The synthesized polymers were identical heat-resistant as the crosslinked polymer obtained from 4,4'-diphenylmethanedimaleimide. They were stable in air up to 360 degrees C.