Formation of the chain microstructure in copolyimide synthesis by high-temperature polycondensation in molten benzoic acid

Abstract

Kinetic features of chain microstructure formation in the synthesis of copolyimides with five-membered imide cycles were studied by the high-temperature polycondensation method in molten benzoic acid from two diamines A and B (comonomers) and one dianhydride C (intermonomer) at 140 ℃ using different regimes of intermonomer loading. The kinetic scheme, including (for the first and second comonomers) the acylation of the amino group with the anhydride fragment, decomposition, and imidization of intermediate amido acid fragments, was examined. The kinetic parameters of the acylation stage necessary for calculation were determined for the model reactions of 9,9-bis(4-aminophenyl)fluorene and 1,12-dodecameth-ylenediamine with phthalic anhydride in acetic acid. The numerical solution of the system of kinetic equations for different regimes of intermonomer loading gave the calculated dependences of the change in time of the average block length and current concentrations of amino and anhydride groups, amido acid fragments (unstable dyads AC1 and BC1), imide cycles (stable dyads AC2 and BC2), and triads. The calculated values of the average block length (l ≈ 4) and microheterogeneity parameter of the chain (K m ≈ 0.5) for the gradual intermonomer loading correspond to the multiblock structure of the chain. These values are in good agreement with the experimental values obtained from the data of 13C NMR spectroscopy for copolyimide based on the indicated diamines and 2,2-propylidenebis(phenyl-4-oxyphthalic acid) dianhydride.