Modeling of copolyimide chain microstructure formation in a course of the one-pot copolycondensation in molten benzoic acid

Mathematical modeling was has been developed for the chain microstructure formation in the synthesis of copolyimides (CPI) by the one-pot high-temperature catalytic polycondensation from two diamines A and B (comonomers) and one dianhydride C (intermonomer) in molten benzoic acid at 140°C accomplished with different regimes of intermonomer loading. The kinetic scheme including the acylation of the amino group of both diamines with the anhydride fragment, decomposition, and imidization of two intermediate amido acid fragments was examined. The kinetic parameters of the acylation and imidization stages necessary for calculations were determined previously in independent experiments. 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, the 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 and the chain microheterogeneity parameter (K _m = 0.5) for the first three comonomer pairs at gradual intermonomer loading correspond to the multiblock microstructure of the chain. These values are in good agreement with the experimental values obtained from 13C NMR data for CPI based on the indicated diamines and 2,2-propylidenebis(1,4-phenyleneoxy)diphthalic dianhydride.