Miscibility, crystallization kinetics and real-time small-angle X-ray scattering investigation of the semicrystalline morphology in thermosetting polymer blends of epoxy resin and poly(ethylene oxide)

Thermosetting polymer blends of poly(ethylene oxide) (PEO) and bisphenol-A- type epoxy resin (ER) were prepared using 4,4'-methyl-enebis(3-chloro-2,6-d iethylaniline) (MCDEA) as curing agent. The miscibility and crystallization behavior of MCDEA-cured ER/PEO blends were investigated by differential sc anning calorimetry (DSC). The existence of a single composition-dependent g lass transition temperature (T-g) indicates that PEO is completely miscible with MCDEA-cured ER in the melt and in the amorphous: state over the entir e composition range. Fourier-transform infrared (FTIR) investigations indic ated hydrogen-bonding interaction between the hydroxyl groups of MCDEA-cure d ER and the ether oxygens of PEO in the blends. which is an important driv ing force for the miscibility of the blends. The average strength of the hy drogen bond in the cured ER/PEO blends is higher than in the pure MCDEA-cur ed ER. Crystallization kinetics of PEO from the melt is strongly influenced by the blend composition and the crystallization temperature. At high conv ersion, the time dependence of the relative degree of crystallinity deviate d from the Avrami equation. The addition of a non-crystallizable ER compone nt into PEO causes a depression of both the overall crystallization rate an d the melting temperature. The surface free energy of folding rr, displays a minimum with variation of composition. The spherulitic morphology of PEO in the ER/PEO blends exhibits typical characteristics of miscible crystalli ne/amorphous blends, and the PEO spherulites in the blends are always compl etely volume-filling. Real-time small-angle X-ray scattering (SAXS) experim ents reveal that the long period L increases drastically with increasing ER content at the same temperatures. The amorphous cured ER component segrega tes interlamellarly during the crystallization process of PEO because of th e low chain mobility of the cured ER. 4 model describing the semicrystallin e morphology of MCDEA-cured ER/PEO blends is proposed based on the SAXS res ults. The semicrystalline morphology is a stack of crystalline lamellae, th e amorphous fraction of PEG, the branched ER chains and imperfect ER networ k are located between PEO lamellae. (C) 2001 Elsevier Science Ltd. All righ ts reserved.