Linear, Star, Comb, and Ring Crystallizable Multiblock Copolymers Investigated by Molecular Dynamics Simulations

Abstract

We use coarse-grained molecular dynamics simulations to study the impact of the chain topology on the structure and thermal and mechanical properties of crystallizable multiblock copolymers. We investigate linear, star, comb, and ring topologies for which we vary in a systematic way the content in crystallizable units through the length of the so-called "hard segments" while keeping the overall molecular weight constant. Our results emphasize that the crystallization temperature is driven by the hard-segment length, regardless of the chain topology and the fraction of crystallizable units in the material. The variation of the topology however leads to major structural differences. While ring molecules (and comb ones to a lesser extent) tend to form a high number of small and well-distributed crystallites, their linear and star counterparts result in much coarser clusters from 12% of crystallizable units. This trend is further enhanced for higher hardsegment contents until ca. 20% where ring molecules start to form wormlike clusters. The shear modulus at rest is systematically computed by following the Green−Kubo method, which demonstrates the role of (i) the average cluster's size and (ii) the network connectivity. Beyond contributing to the understanding of the structure−property relationship of thermoplastic elastomers, the peculiar nature of the molecules investigated in this work also extends the fundamental knowledge of polymer crystallization.