A Simulation Study on the Effect of Tailoring Molecular Architectures on the Mechanical Behaviors of Lamella-Forming BABCB Linear Multiblock Copolymers

Multiblock copolymers consisting of rubbery/glassy blocks possess highly designable architectures for improving the mechanical properties. However, the underlying mechanism for the influence of the molecular architecture on the mechanical behaviors of the multiblock copolymers is not well understood, and thus, the potential of tailoring chain architectures to modulate the performance is not fully exploited. Herein, we investigated the mechanical properties of lamella-forming BABCB multiblock copolymers using coarse-grained molecular dynamics simulations coupled with self-consistent field theory, focusing on the effect of the architecture on the mechanical properties. We have considered two cases, glassy B-blocks and rubbery A/C-blocks in one case, while in the other case it is the other way around. It is found that the mechanical performance can be largely modulated by adjusting the ratio τ of the middle B-block in both cases. For the BABCB pentablock architecture, the central factor is that the stretching degree of the middle bridging B-block can be altered by changing τ and implanted into the equilibrium structure while consequently affecting the stress–strain behavior. Specifically, the modulus during the hardening stage increases as τ decreases in the case of glassy B-blocks, whereas the softening–hardening transition becomes faster in the other case. The largely tunable stress–strain behavior enables significant mechanical enhancement of the BABCB pentablock copolymer samples in comparison to the ABC triblock copolymer counterpart, nearly a 120% improvement in the toughness. In brief, our work demonstrates that multiblock copolymer materials are expected to meet different application requirements by rationally designing the chain architecture.