Synthesis of polyamides from rigid and sterically hindered dicarboxylic acids and diamines under mild conditions

The rate of polycondensation of piperazine with the 2,4-dinitrophenyl, succinimido, phthalimido, and 4-nitrophenyl esters of bicyclo2.2.2]octane-trans-2,3-dicarboxylic acid was measured and found to decrease in this sequence. In the reaction of two moles of piperazine with one mole of diester, the reactivity of both ester groups was equal. In equimolar mixtures, the second ester group reacts with the second group about ten times slower because of steric hindrance. In the reaction of the esters with N,N′-dimethylethylenediamine no such effects were observed. The aminolysis of the N-hydroxyphthalimido ester stops at low conversions unless a very large excess of triethylamine is added. The catalytic effect of 1,2,4-triazole on the aminolysis was proportional to the triazole concentration. From the rate of ester consumption in the presence of pure triethylamine, the extent of possible racemization of the optically active dicarboxylic acid was estimated. In view of the rate data, the extent of polycondensation, and side reactions, only 2,4-dinitrophenyl and N-hydroxysuccinimido diesters are suitable for the synthesis of polyamides derived from rigid and sterically hindered dicarboxylic acids.