Factors Influencing Curing Behavior in Phase-Separated Structures

Abstract

Using time-resolved Fourier transform infrared spectroscopy, the reaction kinetics of ternary blends consisting of crystallizable polyester [poly(hexamethylene adipate) (PHMA)], polyether [poly(propylene glycol) (PPG)], and poly(methyl methacrylate-co-n-butyl methacrylate) [P(MMA-co-nBMA)] has been characterized. As the polyester and polyether have reactive isocyanate (NCO) units, they are able to react with water vapor in the environment. A specially designed cell was constructed to obtain reaction kinetics for samples of varying thickness at different relative humidity and temperature. Without catalysts, the reaction kinetics obtained is significantly slower than expected for the diffusion-limited mechanism of a homogeneous medium, indicating that the reaction-limited mechanism controls primarily curing in these thin films. As shown previously, the miscibility behavior of these blends at various temperatures is complex. The morphological features, which have been characterized by vibrational spectroscopy, optical microscopy, and atomic force microscopy, depend on thermal history and initial phase behavior. Reaction rates were shown to be highly dependent on sample morphology, being faster with smaller phase-separated domains and lower degrees of crystallinity.