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 behavior (UCST ≈ 145°C). The system was cured by organic peroxide just above the UCST. A light scattering peak and its growth at an early stage of curing suggested the reaction-induced spinodal decomposition caused by elevation of the UCST with the polymerization of DAP. Transmission electron 154microscopy showed that, even in the case of low PPE content (e.g., 20 wt%), PPE-rich phase could be the matrix of phase-decomposed material. Furthermore, it was shown that fine polyDAP domains of 10 nm diameter are dispersed in the matrix, and in the polyDAP-rich dispersed particles of μm diameter, fine PPE domains of 10 nm scale are occluded. The fine domains in both the dispersed particles and the matrix could be formed by successive spinodal decomposition under very deep quench after the micrometer-scale particle/matrix morphology had been arrested by partial cure. Tensile modulus, elongation at break, and fracture toughness (GIC, KIC) of the fully cured blends increased almost linearly with increasing PPE content. The toughening seems to be realized mostly by the unique morphology via the two-step spinodal decomposition to render the PPE-rich matrix even for the low PPE content system. Dynamic mechanical analysis, Fourier transform infrared spectroscopy, and solvent extraction experiment showed that polyDAP significantly grafted on PPE chains to yield a network matrix.
