Frequency-dependent dielectric measurements have been used to monitor and c
haracterize the phase separation process in high-performance thermoplastic-
thermoset blends of 2,6-dimethyl-1,4-phenylene ether (PPE) with an epoxy di
glycidylether of bisphenol A (DGEBA) and 4,4-methylene bis(3-chloro-2,6-die
thylamine) (MCDEA). The systems studied are 30, 45 and 60% PPE/DGEBA-MCDEA
blends. The results are compared with dynamical mechanical measurements and
the developing morphology.
Both dielectric and mechanical measurements are shown to be good techniques
to monitor the phase-separation process and the reaction advancement. Diel
ectric measurements monitor the buildup in T-g in both the PPE-rich continu
ous phase and in the epoxy-rich occluded phases. Dielectric measurements ar
e advantageous as they can be made in situ continuously on a single sample
throughout the entire cure process. The results show that the phase separat
ion process initially occurs rapidly involving a large amount of the epoxy-
amine diffusing into the occluded phase. The rate of the epoxy-amine reacti
on in the epoxy-rich 30% PPE mixture is approximately equal to that in the
neat epoxy-amine system due to two opposing effects, a slower reaction rate
due to dilution and a lower level of conversion at vitrification due to th
e presence of high T-g PPE. In the 60% PPE mixture, the dilution effect of
the PPE has a large affect on the decreasing the reaction rate and achievem
ent of vitrification. The continuous thermoplastic-rich phase is observed t
o vitrify first, followed by vitrification of the thermoset as occluded par
ticles. Finally, the results show as evidenced by the size of the occluded
particles and the composition of the continuous phase that the morphology i
s strongly influenced by the kinetics, diffusion, and viscosity conditions
during phase separation. (C) 1999 Elsevier Science Ltd. All rights reserved
.