Impact of Topological Defects on Strain-Induced Crystallization in Elastocaloric Polymers

Elastocaloric polymers, whose performance typically relies on phase transformation between amorphous chains and crystalline domains, offer a promising alternative to traditional refrigeration technologies due to their solid-state characteristics and environmental benefits. While engineering polymer-network architecture has shown the potential to boost elastocaloric performance, the role of topological defects remains unexplored despite their prevalence in real polymers. This study investigates strain- and temperature-induced crystallization in a series of model end-linked star polymers (ELSPs) with controlled dangling-chain defects, focusing on their effects on mechanical properties and elastocaloric performance. Our findings reveal two competing effects: suppression of strain-induced crystallization (SIC), which hinders amorphous chain alignment and crystalline domain orientation, and promotion of temperature-induced crystallization (TIC), which enhances polymer network flexibility. Increasing dangling-chain defects monotonically lowers ELSPs’ mechanical performance at high temperatures due to suppressed SIC, but nonmonotonically impacts the mechanical performance at low temperatures due to the competition between suppressed SIC and enhanced TIC. Additionally, elastocaloric experiments show an intriguing defect-dependent adiabatic temperature change, highlighting the critical role of topological defects in maximizing the cooling performance of elastocaloric polymers.