Chemomechanics in the Moisture-Induced Malleability of Polyimine-Based Covalent Adaptable Networks

The moisture-induced malleability of polyimine-based covalent adaptable networks (CANs) enables the thermosets to be reprocessed and recycled at ambient temperature using only water, which leads to an energy-neutral green processing of the materials. This paper provides both experimental and theoretical studies to understand the effects of temperature and moisture content on the kinetics of bond exchange reactions (BERs), malleability, in situ softening, and damping effects of polyimine-based CANs. The study shows that the temperature and moisture content are equivalent in affecting the time scale of network stress relaxation. A time–temperature–moisture superposition principle is therefore established. The modeling theory identifies the critical thicknesses when the network relaxation is dominated by the moisture diffusion or the intrinsic BER kinetics. It also probes the transition region of polyimine CANs underwater, in which the glassy solid samples gradually transform into the malleable state with an enhanced damping ratio.