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

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 (TrDA) 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 TrDAvalues, 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.