Molecular Dynamics Simulations of Self-Healing Topological Copolymers with a Comblike Structure

Y Fang and TK Yue and S Li and ZY Zhang and J Liu and LQ Zhang, MACROMOLECULES, 54, 1095-1105 (2021).

DOI: 10.1021/acs.macromol.0c02056

Topological copolymers with a comblike structure have been found to have the ability to recover without the need for extraneous material components and the use of external stimuli; however, a systematic and fundamental understanding at the molecular level is still lacking. In this work, coarse-grained molecular dynamics (CGMD) simulation and noncovalent interaction (NCI) analysis were employed to investigate a model system of self-healing comblike copolymers consisting of methyl methacrylate (MMA) and n-butyl acrylate (n-BA). Specifically, the different interactions of neighboring macromolecules were analyzed by NCI. Then, the influence of the following three parameters on the mechanical properties and interpenetration of side chains was probed: (1) a spacer between side chains l(g), (2) average molecular weight per backbone bond m(b), and (3) the flexibility of side chains k(s). Based on the optimum of the three parameters, self-healing simulations were performed to examine the mechanical behavior of the system at different healing temperatures and healing times. The NCI results reveal that the sectional backbone chains are forced to stretch due to the steric repulsion and the side chains of neighboring molecules are interpenetrated due to the attraction of van der Waals force. Favorable steric repulsion and a spacer between side chains allow for interpenetration of side chains of neighboring macromolecules, leading to optimal mechanical properties with the graft polymer composition phi = l(g)/(l(g) + R-sc) congruent to 3/7, where R-sc and l(g) are the length of side chains and the spacer separating two consecutive side chains along the polymer backbone, respectively. Interpenetration of side chains is negatively correlated with the average molecular weight per backbone bond (m(b)) for graft chains. Comblike copolymers with stiff side chains tend to form lock-and-key structures, which are conducive to closer interpenetration and better mechanical properties.

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