The Effects of Sequence Structure on the Mechanical Properties of Siloxane-Containing Polyimides: Insights from Molecular Dynamics Simulations.

In order to provide a theoretical framework for the synergistic optimization of the "rigid backbone-flexible network" in the molecular design of polyimides with high Young's modulus, high toughness, and excellent creep resistance for wearable electronics applications, the effects of sequence structure on the mechanical properties of siloxane-containing polyimides were investigated by molecular dynamics simulations. A series of poly(siloxane-imide) block copolymer models with distinct sequence structures were constructed via molecular dynamics (MD) simulations based on 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFDB) as hard segment A, and 6FDA and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (SiDA) as soft segment B. The results indicate that extending hard segment length enhances Young's modulus and suppresses creep because of the enhancement of chain rigidity and formation of stable physical aggregates. Appropriately extending soft segment sequence length can improve the failure strain through rapid conformational adjustment, while excessively long soft segments lead to stress concentration, thereby reducing the failure strain. The (A5B5)2 model structure exhibits superior comprehensive performance among all systems, with a relatively high Young's modulus, failure strain, and creep recovery rate. This is attributed to the synergistic balance between the rigidity of the hard segment and the mobility of the soft segment.