A Model for Phase Separation During a Thermoset Polymerization

A model was developed to predict the fraction and composition of the dispersed phase segregated during a thermoset polymerization (e.g., a rubber-modified epoxy system). This model can also be used to predict the mean radius and volumetric concentration of the dispersed particles. The location of equilibrium and spinodal curves is described by a Flory-Huggins equation that includes the thermoset conversion. Equations for nucleation, coalescence, and growing rates were derived and analyzed. The morphology development is assumed to be arrested by gelation of the thermoset matrix. The dispersed-phase fraction and the concentration of dispersed particles decrease with an increase in the curing temperature; however, the mean radius goes through a maximum. Accelerating the polymerization by adding a catalyst has the same effect as a temperature increase. Conditions leading to spinodal demixing are discussed.