TIME CURE SUPERPOSITION DURING CROSS-LINKING

Using a dynamic scaling theory for the viscoelasticity of cross-linking polymers near the gel point, we predict the superposition of viscoelastic functions at differing extents of reactions. For example, to superpose the stress relaxation modulus, a vertical shift is needed to account for the increase in the equilibrium modulus with cure, G∞ ~ ϵ8/3, and a horizontal shift for the divergence of the characteristic relaxation time, Tz ~ ϵ~4, where ϵ is the critical extent of reaction. Experiments on model epoxies show excellent superposition both below and above the gel point and give G∞ ~ ϵ2-8±0.2 and Tz ~ ϵ-3.9±0.2. The critical regime where this superposition is valid is surprisingly wide, encompassing over half of the reaction. © 1990, American Chemical Society. All rights reserved.