Morphology development in a thermoset/thermoplastic blend: DAP/PPE system via apparent two-step spinodal decomposition

Abstract

A thermoset/thermoplastic system, diallyl phthalate (DAP)/poly(2,6-dimethyl-1,4-phenylene ether) (PPE), was found to show upper critical solution temperature (UCST)-type phase behaviour (UCST ≈ 145°C). The system was cured by organic peroxide just above the UCST. The morphology development during curing was studied by time-resolved light scattering, Fourier transform infrared spectroscopy (FTi.r.) and transmission electron microscopy (TEM). A light scattering peak appeared at an early stage of curing and the scattering intensity increased with time, suggesting that the reaction-induced spinodal decomposition was caused by elevation of the UCST with the polymerization of DAP. Then the intensity gradually decreased and the peak decayed. Combining the TEM analysis, the peak decay was ascribed to a disordering in the mutual arrangement of polyDAP-rich particles in the PPE-rich matrix at a late stage of spinodal decomposition. In fully cured systems, fine polyDAP domains of the order of 10 nm were found to form in the PPE-rich matrix and fine PPE domains in polyDAP-rich particles. The fine domains could be formed by successive spinodal decomposition in both the dispersed particles and the matrix, under very deep quench after the micrometre-scale particle/matrix morphology was arrested by partial cure.