Stimuli-Triggered Stereoselective Relaxations in Diels-Alder Polymer Networks

Diels-Alder polymers (DAP) networks have the unique ability to reconfigure their permanent shape through the mechanism of network plasticity with minimal macroscopic creep. Using a combination of DSC and variable-temperature FTIR techniques, we demonstrate that the rate of bond reshuffling is dependent on the stereochemistry of DA junctions and that this rate is faster for endo DA isomers as compared to their exo counterparts. We quantify the process of temperature-dependent conversion of endo to exo isomers, relate it with Young’s moduli, degree of strain recovery, and rates of stress relaxation in DAP materials, and compare the results with those obtained with permanently crosslinked networks. Temperature annealing of as-prepared DAP networks results in all-exo materials with enhanced mechanical properties and improved strain recovery. Further control of the relaxation through network rigidity and crosslinking density enables designing and constructing DAP multi-material constructs with programmable stress-induced and temperature-induced deformations.