Junhan Cho

Effects of morphology on toughening of tetrafunctional epoxy resins with poly(ether imide)

Abstract Tetraglycidyl-4,4′-diaminodiphenyl methane based resin with 30 phr diaminodiphenyl sulfone as curing agent was toughened with poly(ether imide) (PEI). The effects of morphology on the fracture toughness of modified epoxy resins were investigated. Morphology was controlled by changing the curing conditions. The co-continuous structure and morphology of the PEI spherical domain dispersed in the epoxy matrix were obtained. Phase-inversed morphology with PEI matrix was also obtained with 30 phr PEI content. The cured resin with phase-inversed morphology showed the highest fracture toughness. The modified epoxy resins with enhanced fracture toughness exhibited other improved mechanical properties such as flexural strength, flexural modulus and strain at break.

Phase Behavior of a Weakly Interacting Polystyrene and Poly(n‐hexyl methacrylate) System: Evidence for the Coexistence of UCST and LCST

The phase behavior of a weakly interacting binary system composed of deuterated polystyrene (dPS) and poly(n-hexyl methacrylate) (PnHMA) was investigated by the turbidity measurement for the binary blend, and by small angle X-ray scattering (SAXS) and depolarized light scattering for the block copolymers. For the binary dPS/PnHMA blend, a new phase diagram involving both the upper critical solution transition (UCST) and lower critical solution transition (LCST) was observed by the delicate control of molecular weights between dPS and PnHMA. Whereas for the block copolymers such as dPS-block-PnHMA and PS-block-PnHMA, an order-to-disorder transition (ODT) on heating was observed within the experimental temperature range depending on the molecular weight. This coexistence of both a UCST and LCST in the dPS/PnHMA blend consequently represents the experimental evidence that the corresponding (d)PS-b-PnHMAs possess not only ODT, but also lower disorder-to-order transition (LDOT) character driven by a compressibility difference, although the latter is hindered by thermal degradation.