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

J Morthomas and V Viola and V Vallejo-Otero and GP Baeza, MACROMOLECULES, 56, 4800-4813 (2023).

DOI: 10.1021/acs.macromol.3c00619

We use coarse-grained molecular dynamics simulationsto study theimpact of the chain topology on the structure and thermal and mechanicalproperties of crystallizable multiblock copolymers. We investigatelinear, star, comb, and ring topologies for which we vary in a systematicway the content in crystallizable units through the length of theso-called "hard segments" while keeping the overallmolecular weight constant. Our results emphasize that the crystallizationtemperature is driven by the hard-segment length, regardless of thechain 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 forma high number of small and well-distributed crystallites, their linearand star counterparts result in much coarser clusters from 12% ofcrystallizable units. This trend is further enhanced for higher hard-segmentcontents until ca. 20% where ring molecules start to form wormlikeclusters. The shear modulus at rest is systematically computed byfollowing the Green-Kubo method, which demonstrates the roleof (i) the average cluster's size and (ii) the network connectivity.Beyond contributing to the understanding of the structure- propertyrelationship of thermoplastic elastomers, the peculiar nature of themolecules investigated in this work also extends the fundamental knowledgeof polymer crystallization.

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