# An Elastocaloric Polymer with Ultra‐High Solid‐State Cooling via Defect Engineering

## TL;DR

This paper introduces a new method to improve cooling performance in polymers by engineering defects, achieving a record temperature change of over 8°C.

## Contribution

The study introduces a defect-engineering strategy in polymers that enhances elastocaloric cooling performance.

## Key findings

- Defect engineering in end-linked star polymers achieves an adiabatic temperature change of up to 8.14 ± 1.76°C.
- Dangling-chain defects nonmonotonically affect cooling performance due to competing crystallization effects.

## Abstract

Elastocaloric polymers, whose performance typically relies on phase transformation between amorphous chains and crystalline domains, offer a promising alternative to traditional refrigeration technologies. 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 reports a defect‐engineering approach in end‐linked star polymers (ELSPs) that enables an adiabatic temperature change of up to 8.14 ± 1.76 °C at an ambient temperature above 65 °C, showing an enhancement of 39% compared to ELSPs with negligible defects. This defect‐regulated solid‐state cooling is attributed to two competing effects of dangling‐chain defects on strain‐induced crystallization (SIC) and temperature‐induced crystallization (TIC), synergistically regulating the adiabatic temperature change. Specifically, 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.

This work reports a defect‐engineering strategy that enables a record‐high adiabatic temperature change of up to 8.14 ± 1.76 °C in elastomers at an elevated temperature above 65 °C. Combined experimental and theoretical efforts reveal that increasing dangling‐chain defects nonmonotonically impacts the elastocaloric cooling performance of polymers due to the competition between suppressed strain‐induced crystallization and enhanced temperature‐induced crystallization.