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 ( T g ) 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 T g due to the phase separation of the former blends. The blends of MCDEA and PPO were miscible over the concentration range investigated and T g of the blends decreased with increasing MCDEA concentration. © 2013 Society of Chemical Industry