Limitations of Diels–Alder Dynamic Covalent Networks as Thermal Conductivity Switches

Abstract

Creating polymers that exhibit a switchable thermal conductivity requires a fundamental understanding of how polymer structure and inter- and intramolecular interactions influence thermal transport. To develop this fundamental understanding, we synthesize a series of precursor un-cross-linked statistical copolymers with varying mole fractions of furan functional groups via reversible-addition fragmentation chain transfer (RAFT) polymerization. These precursor polymers, containing the furan diene, were then cross-linked using a reversible Diels–Alder cycloaddition to form dynamic covalent networks of varying cross-link densities. Furthermore, two separate dienophile cross-linkers were used to investigate how the molecular weight and length of the cross-linker influence the mechanical and thermal properties of the network. Counter to some recent theoretical studies, we found that both the elastic modulus and thermal conductivity were largely unaffected by the extent of cross-linking and the structure of the cross-linker. For this system, the Diels–Alder reaction was also found to be slow in the solid state, further limiting its utility as a thermal conductivity switch.