Method for determining resin cure kinetics with low-frequency Raman spectroscopy

Abstract

Characterizing resin extent of cure kinetics is critical to understanding the structure–property-processing relationships of polymers. The disorder band present in the low-frequency region of the Raman spectrum is directly related to conformational entropy and the modulus of amorphous materials, both of which change as the resin polymerizes. Normalizing the disorder band to its shoulder (∼85 cm⁻¹) provides structural conversion kinetics, which we can directly correlate to chemical conversion kinetics for methacrylate and epoxy–amine based resin systems. In addition to fitting both the structural and chemical conversion data to a phenomenological kinetic rate equation, we also demonstrate a relationship between the chemical and structural kinetics which appears to relate to the softness of the material. Lastly, we use the method to investigate a methacrylate/epoxy interpenetrating polymer network resin system. We find that the structural and chemical conversions occur simultaneously during the formation of the primary (methacrylate) network, but there is a lag between the two during the formation of the secondary (epoxy–amine) network.