Relief of Residual Stress in Bulk Thermosets in the Glassy State by Local Bond Exchange.

The covalently cross-linked network gives thermosets superior thermal, mechanical, and electrical properties, which, however, squarely makes the large residual stress that is inevitably induced during preparation hardly relieved in the glassy state. In this paper, an incredible reduction in residual stress is successfully achieved in bulk thermosets in the glassy state through introducing highly dynamic thiocarbamate bonds by "click" reactions of thiols and isocyanates. Due to the excellent dynamic behaviors of thiocarbamate bonds, local network rearrangement is achieved through thermal stimulation, while the strong three-dimension cross-linked network is well maintained. Ultimately, a decrease by 44% in residual stress was detected by simply annealing samples at 30 °C below glass transition temperature (T g ), during which they could well maintain more than 98.4% of the storage modulus. After the annealing, more uniform residual stress distribution was also observed, showing a 32% decline in sample standard deviation. However, the residual stress of epoxy resin, a typical thermoset as a reference, changed little even after annealing at T g . The results prove it a feasible strategy to reduce residual stress in bulk thermosets in the glassy state by introducing proper dynamic covalent bonds. This article is protected by copyright. All rights reserved.