Miscibility and mechanical properties of tetrafunctional epoxy resin/phenolphthalein poly(ether ether ketone) blends

Phenolphthalein poly(ether ether ketone) (PEK-C) was found to be miscible w ith uncured tetraglycidyl 4,4'-diaminodiphenylmethane (TGDDM), which is a t ype of tetrafunctional epoxy resin (ER), as shown by the existence of a sin gle glass transition temperature (T-g) within the whole composition range. The miscibility between PEK-C and TGDDM is considered to be due mainly to e ntropy contribution. Furthermore, blends of PEK-C and TGDDM cured with 4,4' -diaminodiphenylmethane IDDM) were studied using dynamic mechanical analysi s (DMA), Fourier-transform infrared (FTIR) spectroscopy, and scanning elect ron microscopy (SEM). DMA studies show that the DDM-cured TGDDM/PEK-C blend s have only one T-g. SEM observation also confirmed that the blends were ho mogeneous. FTIR studies showed that the curing reaction is incomplete due t o the high viscosity of PEK-C. As the PEK-C content increased. the tensile properties of the blends decreased slightly and the fracture toughness fact or also showed a slight decreasing tendency, presumably due to the reduced crosslink density of the epoxy network. SEM observation of the fracture sur faces of fracture toughness test specimens showed the brittle nature of the fracture for the pure ER and its blends with PEK-C. (C) 2000 John Wiley & Sons, Inc.