| Summary: | Small-angle neutron and X-ray scattering (SANS and SAXS) coupled with thermal analysis, optical microscopy and FTIR have been employed to probe the phase behavior, crystallization kinetics and crystalline morphologies of PCL/PC blends. The composition dependence of the glass transition temperature T$\sb{\rm g}$ exhibited a discontinuity and was critically analyzed using the classical equations of Gordon-Taylor and Fox, and the free volume theory of Kovacs. Results derived from the random phase approximation (RPA) analysis of the SANS profiles measured at 30$\sp\circ$C for the deuterated PC-rich blends and those obtained from the melting point depression analysis of the PCL-rich blends suggested favorable blend interactions. The effects of composition, crystallization temperature and PC crystallinity on the athermal and isothermal crystallization kinetics of PCL in PCL-rich blends have been examined. Combination of the overall crystallization rate measurements and the radial growth rate results unequivocally demonstrated that PC is an effective nucleating medium for PCL crystallization. Evolution of the PCL lamellar growth was monitored by synchrotron SAXS. The interlamellar spacing initially varied with time and then approached a plateau value at the later stage of crystallization. An insertion mechanism is proposed in which PCL is crystallized in the amorphous intralamellar phase of PC. Crystalline morphologies of deuterated PC/PCL blends were studied by SANS and SAXS in the semicrystalline/amorphous state (above T$\sb{\rm m}$ of pure PCL). A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. The long range correlation length ($\sim$10$\sp2$ A) and the short range correlation length ($\sim$10 A) derived from this model were inferred to be associated with the crystalline PC domain and the local cluster in the amorphous phase, respectively. Quantitative SAXS analysis suggested that random mixing of PCL and PC lamellae occurred in the semicrystalline/semicrystalline state. Two distinct regions of incorporation were identified in the semicrystalline/amorphous state. It was found that PCL was rejected from the interlamellar region in the PCL-rich blends. In contrast, PCL was incorporated into the amorphous phase between the crystalline lamellae in the PC-rich blends.
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