Blends of epoxy resins and polyphenylene oxide as processing aids and toughening agents 2: Curing kinetics, rheology, structure and properties

Blends of poly(phenylene oxide) (PPO) with epoxy resin and amine curative can be used to enhance thermoplastic processing and thermoset toughening, while retaining high temperature performance. The curing behaviour, chemorheology, morphology and dynamic mechanical properties of epoxy-polyphenylene oxide (PPO) blends were investigated over a wide range of compositions. Two bisphenol A based di-epoxides-pure and oligomeric DGEBA - were used and their cure with primary, tertiary and quaternary amines was studied. 4,4'-methylenebis(3-chloro-2,6-diethylaniline) (MCDEA) showed high levels of cure and gave the highest exotherm peak temperature, and so was chosen for blending studies. Similarly pure DGEBA was selected for blending due to its slower reaction rate because of the absence of accelerating hydroxyl groups. For the PPO:DGEBA340/MCDEA system, the reaction rate was reduced with increasing PPO content due to a dilution effect but the heat of reaction were not significantly affected. The rheological behaviour during cure indicated that phase separation occurred prior to gelation, followed by vitrification. The times for phase separation, gelation and vitrification increased with higher PPO levels due to a reduction in the rate of polymerization. Dynamic mechanical thermal analysis of PPO:DGEBA340/MCDEA clearly showed two glass transitions due to the presence of phase separated regions where the lower T corresponded to an epoxy-rich phase and the higher T represented the PPO-rich phase. SEM observations of the cured PPO:DGEBA340/MCDEA blends revealed PPO particles in an epoxy matrix for blends with 10wt% PPO, co-continuous morphology for the blend with 30wt% PPO and epoxy-rich particles dispersed in a PPO-rich matrix for 40wt% and more PPO. © 2014 Society of Chemical Industry.