Miscibility, crystallization and real-time small-angle X-ray scattering investigation of the semicrystalline morphology in thermosetting polymer blends

The results of the study of a completely miscible thermosetting polymer ble nd containing a crystallizable component are reported. Blends of poly(epsil on -caprolactone) (PCL) and bisphenol-a-type epoxy resin (ER) cured with 4, 4'-methylenebis(3-chloro-2,6-diethylan (MCDEA) were prepared and compared w ith blends of PCL with uncured bisphenol A-type epoxy resin, i.e. diglycidy lether of bisphenol A (DGEBA). The miscibility, crystallization behavior an d spherulitic morphology of both uncured DGEBA/PCL blends and MCDEA-cured E R/PCL blends were investigated by differential scanning calorimetry (DSC), optical microscopy, and Fourier-transform infrared (FTIR) spectroscopy. It was found that PCL is completely miscible with both DGEBA and MCDEA-cured E R in the melt and in the amorphous state over the entire composition range, as shown by the existence of a single composition-dependent glass transiti on temperature (T-g). The overall crystallization rate and crystallinity of PCL in the MCDEA-cured ER/PCL blends decrease much more rapidly with incre asing amorphous content than those of the DGEBA/PCL blends. The spherulitic morphology of PCL in both the uncured and the cured blends is characterist ic of miscible crystalline/amorphous blends. and the PCL spherulites in the se blends are always completely volume-filling. The miscibility of the uncu red DGEBA/PCL blends is considered to be due predominately to the entropic contribution, whereas that of the cured ER/PCL blends is due to the enthalp ic contribution. FTIR investigations indicated hydrogen bonding interaction between the hydroxyl groups of MCDEA-cured ER and the carbonyl groups of P CL in the cured system, which is an important driving force for the miscibi lity of the cured ER/PCL blends. Real-time small-angle X-ray scattering (SA XS) experiments revealed that the amorphous cured ER segregated interlamell arly during the crystallization process of PCL, which is considered to resu lt from the low chain mobility of the cured ER in the ER/PCL blends. On the basis of the SAXS results, a model describing the semicrystalline morpholo gy of MCDEA-cured ER/PCL. blends is proposed. The amorphous fraction of PCL , the branched ER chains and imperfect ER network are located between PCL l amellae in the crystallized blend. (C) 2001 Elsevier Science Ltd. All right s reserved.