Blends of epoxy-amine resins with poly(phenylene oxide) as processing aids and toughening agents : I. Uncured systems

The effect of two different bisphenol-A-based diepoxides—nearly pure DGEBA340 and a DGEBA381 oligomer—and an aromatic diamine curative (MCDEA) on the solubility and processability of poly(phenylene oxide) (PPO) was studied. The solubility parameters of the diepoxies and the curative calculated from Fedors's method suggest miscibility of PPO with the components, and this was observed at the processing temperature; however, some of the blends were not transparent at room temperature, indicating phase immiscibility and/or partial PPO crystallization. The steady shear and dynamic viscosities of the systems agreed well with the Cox–Merz relationship and the logarithmic viscosities decreased approximately linearly with increasing amounts of DGEBA381, DGEBA340 or MCDEA, thus causing a processability enhancement of the PPO. The dynamic rheology of intermediate PPO:DGEBA compositions at 200 °C showed gel-like behaviour. Dynamic mechanical analysis of blends with varying PPO:DGEBA ratios showed that the main glass transition temperature (Tg) of the blends decreased continuously with increasing epoxy content, with a slightly higher plasticizing efficiency being exhibited by DGEBA340 compared to DGEBA381. However, blends with 50 and 60 wt% PPO had almost identical Tg due to the phase separation of the former blends. The blends of MCDEA and PPO were miscible over the concentration range investigated and Tg of the blends decreased with increasing MCDEA concentration