Abstract:Two types of thermoset ( TS) / thermoplastic ( TP) blends were studied in this workꎬ including the
EP / PI and BMI/ PES systems. In ̄situ reaction ̄induced phase separation was studied by the phase contrast micro ̄
scope. In the initially homogeneous sampleꎬ uniform phase separate morphology was formed in all the samples. At cer ̄
tain concentrationsꎬ the initial bicontinuous structure gradually changed to be ununiform inside and outside the sam ̄
ples. Scanning electron microscope was used to observe the fractured cross sectional surfaceꎬ after the samples were i ̄
sothermally cured. At very low TP concentrationsꎬ sea ̄island structure is formedꎬ with the TP ̄rich particles dispersed
in the TS ̄rich matrix. At relative higher TP concentrationsꎬ a macroscopic core ̄shell structure is formed in the whole
sample. The outer areaꎬ including edge of the sample and upper and lower part close to the substratesꎬ mostly consis ̄
ted of TS ̄rich domainsꎬ with only few of TP ̄rich particles randomly located. In the inner partꎬ bicontinuous structure
formedꎬ where the TP ̄rich phase is thin and extending like a network. The current two systems have some points in
common: TS monomer and oligomers are good fluid at the experimental temperaturesꎬ as are the fast componentꎻ the
TP polymers are macromolecules and have high glass transition temperaturesꎬ as are slow component with viscoelastic
featuresꎻ with the phase separation proceedingꎬ viscoelasticity of the TP gradually showedꎬ being glassy below Tg and
elastic or viscoelastic under Tg. The entangled TP ̄rich network need much time to relaxꎬ which cannot follow the
speed of phase separation. Thusꎬ the whole entangled TP ̄rich network would inevitably shrink to promote the phaseseparation. With the strong dynamic asymmetry in such systemsꎬ the initially formed bicontinuous developed to be the
macroscopic core ̄shell structure in the whole sample.