Temperature Dependent Stress Relaxation in a Model Diels–Alder Network

The effect of temperature on the complex shear modulus (G*(?)) of a model reversible covalent network formed by the Diels–Alder reaction was studied. The gel temperature of 119°C and the functional group conversion at this temperature were determined by the Winter–Chambon criterion. The complex modulus of the cross-linked network was measured from 110°C to 121°C, near the gel temperature, to determine the frequency ranges over which stress relaxation could occur. The crossover time was found to have a strong dependence on temperature (Ea ~ 260 kJ mol–1); greater than would be expected from a typical thermally-activated retro-Diels–Alder process. Low frequency scaling of G*(?) over the experimental frequency and temperature range was interpreted to be a result of the existence of a distribution of transient clusters in these thermoreversible covalent gels.