A real-time study of the phase-separation process during polymerization of rubber-modified epoxy

Abstract

The phase-separation process of a rubber-modified epoxy system during curing was described in terms of a nucleation-growth mechanism. It was derived from morphological observations that spherical domains were developed during polymerization in a continuous matrix. The morphological changes were recorded in real time by means of optical microscopy. We have applied a model to predict the amount and radius of the dispersed phase that segregated during a thermosetting polymerization. The model was based on the Flory-Huggins equation for the thermodynamic description as well as constitutive equations for the nucleation and growth rates. Using this model, we could semi-quantitatively interpret and describe the phase-separation process of the second phase from a curing mixture. During the initial polymerization period, the mixture remained homogeneous; at a certain reaction extent a thermodynamically stable rubber-rich phase with critical particle size r c or larger grew spontaneously. The build-up of molecular weight in the matrix during polymerization resulted in the changing of the two-phase morphology and the fixation of the spherical domain structure. Nucleation was the controlling factor of the phase-separation process. We concluded that the nucleation and growth of spherical second phase was expected to be directly related to the interfacial tension, increase of molecular weight, thermodynamic properties and composition gradient.