Hierarchical multiscale analysis of polyimide films by molecular dynamics simulation: Investigation of thermo-mechanical properties

The molecular dynamics simulations are adopted to investigate the thermo-mechanical properties of pyromellitic dianhydride(PMDA)/2-(4-aminophenyl)-1H-benzimidazole-5-amine(BIA), PMDA/p-phenylene diamine(PDA), PMDA/4,4'-oxidianiline(ODA), 3,3',4,4'-biphenyldianhydride(BPDA)/BIA, BPDA/PDA, and BPDA/ ODA polyimide films in hierarchical multiscale level. The results indicate that the properties follow the order of BIA > PDA > ODA. At a small scale, the hydrogen bonding in the BPDA/BIA polyimide strengthens the chain interactions and results in a coiling-shaped chain conformation, endowing the polyimide with superior properties. But the ODA increases the helical-shaped segments conformation, therefore possessing large elongation under small tension. At the scale of the entire polymeric chain, the chain mobility was discussed by the ratio of < Ree(2) > to < s(2) > and MSD. And higher chain mobility corresponds to lower tensile modulus. At a large scale, the torsion angle distribution changes apparently before and after stretching, which increases the d-spacing and elongates the entire molecular chain simultaneously, serving as the main cause of polyimide tensile deformation.