Topological Frustration As A New Parameter To Tune Morphology Revealed Through Exploring The Continuum Between A-B-C 3-Arm Star And Linear Triblock Polymers

Block polymers assemble into a variety of phase-separated morphologies based on volume fraction (phi) and interactions (chi) of the respective blocks. The arrangement of three different polymer blocks could either be a 3-arm star, with each block having one terminus attached to a common junction point or a linear A-B-C architecture. A versatile strategy is reported to synthesize a series of well-defined graft polymers that lie along the unexplored continuum between a 3-arm star and an A-B-C linear triblock polymer architecture. Using the technique of single-molecule insertion, precise control over the position of graft arm C along the B chain was achieved. A series of discrete graft polymers (PMMA-b-PS-g-PEO) with fixed phi and prescribed. values that lie on the continuum between a 3-arm star (omega= 0) and linear triblock polymer (omega= 1) were synthesized. Morphological studies using small-angle X-ray scattering and conventional and energy-filtered transmission electron microscopy reveal the transition between lamellae, perforated lamellae, and cylindrical morphologies with systematic variation in the. values, a trend attributed to the topological frustration and the associated. values between the three blocks. Molecular dynamic simulations of coarse-grained models were found to predict phase diagrams that are consistent with the experimentally observed morphologies. Our results suggest that changes in. lead to topological frustration which is an important additional new design parameter that can be used to tune the morphology of multiblock polymers in addition to phi and chi.