Reaction induced phase separation in mixtures of multifunctional polybutadiene and epoxy

The phase behavior and separation dynamics have been investigated in blends of diglycidyl ether of bisphenol A (DGEBA), curing agent methylene dianiline (MDA), and a reactive liquid rubber (R45EPI) through application of differential scanning calorimetry (DSC), one- and two-dimensional light scattering, and optical microscopy. DSC analysis indicates that the system consists of three reactions: the self-condensations of DGEBA and R45EPI, as well as a cross-reaction between the two constituents. Observation of the dynamics of the 50/25.4/50 DGEBA/MDA/R45EPI system reveals that an initial phase separation is governed by the dominant self-curing reaction of DGEBA, followed by a phase dissolution characterized by a broadening of the interfacial regions catalyzed by a cross-reaction between the two species. A subsequent phase separation occurs at late stages since the copolymerization reaction does not proceed to completion. On the other hand, by changing the ratio of the beginning constituents to 70/25.4/30 DGEBA/MDA/R45EPI, the dissolution phenomena is not observed resulting from an even more dominant DGEBA/MDA condensation reaction. It is demonstrated that alterations in the initial compositional ratio greatly affect the phase separation dynamics of the system.