# Regiochemical Control of Shape Morphing in Diels–Alder Covalent Adaptable Networks

## TL;DR

This paper shows how changing the position of a chemical group in a polymer network can significantly affect its thermal and shape-morphing properties.

## Contribution

The study introduces regioisomerism in Diels–Alder networks as a novel design parameter for shape-morphing materials.

## Key findings

- 3-substituted DAP networks showed higher thermal stability with retro-DA dissociation temperatures of ∼150 °C compared to 120 °C for 2-substituted networks.
- 3-DAP networks enabled shape morphing in a wider and higher-temperature window (80–140 °C) compared to traditional DA-based networks.
- Stress relaxation rates differences were used to achieve controlled bending in bilayer structures.

## Abstract

We demonstrate that
regioisomerism in Diels–Alder (DA) reactions
offers a subtle yet powerful way to tune the thermomechanical and
shape morphing behavior of dynamic polymer networks. Here, we directly
compare DA polymer (DAP) networks built from linear polymers with
identical backbones but containing either 2- or 3-substituted furan
pendant groups. For a wide range of cross-linking degrees, the 3-substituted
DAP (3-DAP) networks exhibited higher thermal stability, with retro-DA
dissociation temperatures (T

rDA
) of ∼150 °C versus 120 °C for the 2-substituted
counterparts, higher elastic moduli and significantly slower temperature-dependent
stress relaxation rates. The difference in the stress relaxation rates
of 2- and 3-DAP elastomers was leveraged to demonstrate controlled
bending in a bilayer structure via selective network plasticization.
Moreover, due to the higher T

rDA
values, the use of 3-DAP elastomers in the single-material
constructs opened a wider and a higher-temperature window (i.e., between
80 and 140 °C) for shape morphing, which is more practical compared
to the traditionally employed DA-based networks such as 2-DAP elastomers
which could be morphed only between 60 and 90 °C. These findings
establish regioisomerism in the furan ring as a powerful parameter
for designing DA-based shape morphing materials.