SOLUBLE POLYIMIDES WITH POLYALICYCLIC STRUCTURE .1. POLYIMIDES FROM BICYCLO[2.2.2]OCT-7-ENE-2-EXO,3-EXO,5-EXO,6-EXO-TETRACARBOXYLIC 2,3/5,6-DIANHYDRIDES

Bicyclo[2.2.2]oct-7-ene-2-exo,3-exo,5-exo,6-exo-tetracarboxylic 2,3:5,6-dianhydride (3a) and its 1-methyl analogue (3b) were synthesized by a one-pot Diels-Alder (DA) reaction from maleic anhydride, and 4,5-dibromocyclohexane-1,2-dicarboxylic anhydride (2a) and 3-methyl-4,5-dibromocyclohexane-1,2-dicarboxylic anhydride(2b), respectively. Each tetracarboxylic dianhydride was also prepared directly without isolation of the bromine adduct (2a or 2b) from the reaction product of bromine with 4-cyclohexene-1,2-dicarboxylic anhydride (1a) or 3-methyl-4-cyclohexene-1,2-dicarboxylic anhydride (1b). The polyimides prepared from 3a and 3b with aromatic diamines were soluble in aprotic and protic polar solvents and possessed molecular weights in the range from 1.6 X 10(4) to 4.6 X 10(4). The polyimide films were revealed to be almost colorless. Thermal gravimetric analysis gave an indication that these polyimides had good thermal stability with no significant weight loss up to approximately 360-degrees-C. A thermal decomposition mechanism is proposed on the basis of GC-MS analysis on the pyrolyzed products of the model compounds 6a and 6b, and it is concluded that the decomposition in nitrogen was a consequence of the retro-DA reaction of polymer chains.