# Transparent Polyurethane Elastomers with Excellent Foamability and Self-Healing Property via Molecular Design and Dynamic Covalent Bond Regulation

## TL;DR

Scientists created self-healing, lightweight foam materials using special chemical bonds and carbon dioxide, suitable for biomedical and wearable applications.

## Contribution

A new self-healing polyurethane foam with multiple dynamic covalent bonds and controlled cellular structure is developed using scCO2 foaming.

## Key findings

- PU-S5 shows hydrophobicity with a 97.5° water contact angle and high light transmission of 70.6%.
- The material achieves a high expansion ratio of ~10 folds and damage recovery at 60 °C.
- It has low temperature flexibility (Tg = −30.1 °C) and a low density of 0.12 g/cm³.

## Abstract

Microcellular thermoplastic polyurethane (TPU) foams with dynamic covalent bonds demonstrating exceptional self-healing capabilities, coupled with precisely controlled micron-scale cellular architectures, present a promising solution for developing advanced materials that simultaneously achieve damage recovery and low density. In this study, a series of self-healable materials (named as PU-S) with high light transmittance possessing two dynamic covalent bonds (oxime bond and disulfide bond) in different ratios were fabricated by the one-pot method, and then the prepared PU-S were foamed utilizing the green and efficient supercritical carbon dioxide (scCO2) foaming technology. The PU-S foams possess multiple dynamic covalent bonds as well as porous structures, and the effect of the dynamic covalent bonds endows the materials with excellent self-healing properties and recyclability. Owing to the tailored design of dynamic covalent bonding synergies and micron-sized porous structures, PU-S5 exhibits hydrophobicity (97.5° water contact angle), low temperature flexibility (Tg = −30.1 °C), high light transmission (70.6%), and light weight (density of 0.12 g/cm3) together with high expansion ratio (~10 folds) after scCO2 foaming. Furthermore, PU-S5 achieves damage recovery under mild thermal conditions (60 °C). Accordingly, self-healing PU-S based on multiple dynamic covalent bonds will realize a wide range of potential applications in biomedical, new energy automotive, and wearable devices.