Creep-Suppressed and Tough Triblock Copolymer Vitrimer Elastomers Enabled by Confined Polystyrene Microphases and Heterogeneous Dynamic Networks

Incorporating dynamic covalent networks into thermoplastic elastomers has emerged as a promising strategy for developing recyclable rubbery materials, yet such systems still suffer from pronounced creep and permanent deformation. Moreover, in most reported systems, the polystyrene(PS)microphase-separated morphology is inherited from conventional block copolymer architectures and remains largely uncontrolled, allowing thermoplastic domains to reorganize or relax under stress and elevated temperatures. Here, we report a series of asymmetric poly(myrcene)-poly(isoprene)-poly(styrene-isoprene) (PMIS) triblock copolymers that integrate vitrimer networks with deliberately constrained PS microphases. Epoxidation of both side chains and backbone segments followed by dynamic ester crosslinking generates a heterogeneous distribution of exchangeable bonds, while partial incorporation of polyisoprene (PI) segments into PS-rich blocks restricts PS microphase separation and domain mobility. This molecular design enables cooperative regulation of PS phase stability and dynamic network rearrangement, rather than treating them as independent structural elements. As a result, the resulting elastomers exhibit significantly suppressed creep over a broad temperature range (30-120 °C) while maintaining stress relaxation and recyclability characteristic of vitrimer systems. By systematically varying PS content, this work elucidates how constraining thermoplastic microphase separation within dynamic covalent networks provides an effective pathway to regulate viscoelastic behavior and dimensional stability, offering molecular-level insight into the design of recyclable elastomers beyond conventional vitrimer-modified thermoplastic elastomers.