Thermophysical characterization of a reversible dynamic polymer network based on kinetics and equilibrium of an amorphous furan-maleimide Diels-Alder cycloaddition

The equilibrium and kinetics of the furan-maleimide Diels-Alder (DA) reaction for the formation of a reversible network were studied by calorimetry between 25 degrees C and 90 degrees C using an amorphous bismaleimide eliminating solvent use. The relationship between the equilibrium conversion x(eq) with temperature and the effect of dilution were simulated. The glass transition-conversion relationship of the reversible network was established. The thermophysical properties of the reversible network were linked to the kinetics and equilibrium of the DA system, and studied by dynamic mechanical analysis (DMA), dielectric analysis (DEA) and rheometry. Below T-g the reversible network behaves like an irreversible network; however, above T-g, a decrease in the rubber tensile storage modulus was observed due to a reduction of cross-link density caused by the retro DA reaction. DEA revealed that above T-g, an interface is formed between released bismaleimide molecules and the remaining network. The rheological behavior is related to x(eq) and the lifetime of the reversible covalent bonds. When x(eq) is higher than the gelation conversion x(gel) (below 90 degrees C), the system gels at constant x(gel). An elastic strengthening effect is observed in a transition region between 90 degrees C and 115 degrees C. Above 115 degrees C the system is reaching a viscous melt behavior. These observations are important for the application of this network as a self-healing material and as a recyclable elastomer or thermoset. (C) 2017 Elsevier Ltd. All rights reserved.