Network structure of bimodal epoxies—a small angle X-ray scattering study

Small angle X-ray scattering measurements were performed on epoxies to determine their network structure. To provide the necessary scattering contrast the epoxy monomer used was a partially brominated diglycidyl ether of bisphenol A and the cross-linking agents were linear, low polydispersity, amine terminated poly(propylene oxide)s. Samples with both single and bimodal molecular weight distributions of cross-linking agent were prepared. A pronounced scattering maximum was observed in all networks and it can be interpreted in terms of correlation holes. Networks cured with a mixture of two cross-linking agents with different molecular weights, i.e. bimodal networks, exhibited scattering maxima at significantly lower scattering vector (q) than was observed for any single amine networks. In model bimodal epoxy graft copolymers with nearly identical chemical structure as the networks the shift to low q was barely perceptible. Experimental results from both epoxies and model graft copolymers are compared to a model calculation in order to establish a methodology to reduce molecular structure information from X-ray results.