Phase behavior, morphology and interfacial structure in thermoset/thermoplastic elastomer blends of poly(propylene glycol)-type epoxy resin and polystyrene-b-polybutadiene

Thermoset/thermoplastic elastomer (TPE) blends of poly(propylene glycol) (P PG)-type epoxy resin (ER) and a diblock copolymer, polystyrene-b-polybutadi ene (SB, with 30% styrene content), were prepared using 4,4'-diaminodipheny lmethane (DDM) as curing agent. The miscibility and thermal transition beha vior of DDM-cured ER/SB blends were investigated by differential scanning c alorimetry (DSQ and dynamic mechanical analysis (DMA). The existence of thr ee separate glass transitions, which are independent of the blend compositi on, indicates that SB is immiscible with DDM-cured ER. Neither the PS block nor the PB block exhibits miscibility with the cured ER. There exist three phases in the blends: a PS microphase, an ER-rich phase and a PB microphas e. The phase structure and morphology of the ER/SB blends were studied usin g both scanning and transmission electron microscopy (SEM and TEM); a varie ty of morphologies were observed, depending on the blend composition. For t he blends with 5 and 10 wt% SB, SB domains with irregular shapes and broadl y distributed sizes are dispersed in a continuous cured ER matrix. For the blends with 20-60 wt% SB, interpenetrating bicontinuous phase structures ar e observed. For the blends with 70 wt% and more SB, a dispersion of cured E R particles in the SB matrix is obtained. The TEM observation showed that t he two phases in the blends exhibit a good interfacial adhesion. The interf acial layer between the ER and SB phases varies from 100 to 300 nm for the blend with 20 wt% SB content, SB micelles are formed surrounding the SB dom ains in the ER matrix. Small-angle X-ray scattering (SAXS) experiments reve al that the SB diblock polymer still exhibits a lamellar microphase structu re within the SB phase and the long spacing of larnellae nearly does not ch ange in the blends. The SB diblock copolymer is microphase separated in the macroscopically phase separated ER/SB blends. (C) 2001 Elsevier Science Lt d. All rights reserved.