Molecular simulation of the O2 diffusion and thermo-oxidative degradation mechanism of carbon-doped boron nitride nanosheets/BTDA-ODA polyimide composites with high O2 adsorption capacity

Relevant studies have indicated that doping boron nitride nanosheets (BNNSs) into polyimide (PI) can significantly improve the thermal conductivity of composites and that the filling of inorganic nontechnical materials can inhibit the thermo-oxidative degradation of insulating polymer materials. Based on this information, three carbon-doped BNNSs models were obtained by modifying BNNSs. PI formed by the condensation of benzophenone-3,3 ',4,4 '-tetracarboxylic acid dianhydride (BTDA) and 4,4 '-diamino diphenyl ether (ODA) was used as a matrix to construct different composite models. Based on molecular simulation methods such as density functional theory (DFT) and reactive force field (ReaxFF), the diffusion of O2 through different composite systems and the inhibition of thermo-oxidative degradation of PI by different dopants were studied. The results showed that compared with pure BNNSs, the BNCB obtained by substituting carbon atoms for boron atoms on BNNSs better inhibited the thermo-oxidative degradation of PI. The adsorption of O2 and the inhibition of the O2 reaction at 2000 K with BNCB were significant improved compared with those with pure BNNSs. The content of the main products of PI thermo-oxidative degradation in the BNCB doping system was only 16% of that in the BNNSs system and the O2 consumption of the BNCB system was 34% lower than that of pure PI. By inhibiting the diffusion of O2 in PI, C-doped BNNSs reduced the contact between O2 and the PI matrix at high temperature, thus inhibiting the damage of O2 to the imide group and benzene ring in PI chains to improve the thermo-oxidative stability of composites. In this paper, a new C-doped BNNSs/PI model was designed based on the BNNS/PI composite model with high thermal conductivity, which achieved the double improvement of PI thermal conductivity and thermo-oxidative stability.