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# Investigations of the miscibility, crystallization, melting, and deformation behavior of poly(ether ether ketone)/poly(ether imide) blends

Abstract (Summary)
This dissertation reports the studies of the blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI). The investigations reported encompass both the thermodynamic and kinetic aspects of this binary blend. The phase behavior of PEEK/PEI blends in the amorphous states was investigated by differential scanning calorimetry (DSC), density measurement, and Fourier-Transform Infrared (FTIR) spectroscopy. Amorphous PEEK/PEI blends were miscible over the whole composition range. The specific volume measurement and the equilibrium melting point depression analysis showed the existence of favorable interaction between PEEK and PEI. The FTIR study suggested that the oxygen lone-pair electrons of the ether groups in PEEK interact favorably with the electron-deficient imide rings in PEI. The coplanarity of the two nearest imide rings in PEI was changed by blending to accommodate the favorable interaction with PEEK. The two-stage crystallization behavior of PEEK and PEEK/PEI blends was studied by thermal mechanical analysis (TMA) and DSC. The two crystallization stages of PEEK were first time distinguished clearly by measuring the thickness change of PEEK films during isothermal crystallization. A crystallization kinetics model considering both primary and secondary crystallization was applied to extract the respective rate constants of the two crystallization stages. The results were discussed in terms of the diffusion mechanisms during PEEK crystallization. The growth of PEEK spherulites from the pure melt and from the blends with PEI was studied by hot stage optical microscopy. The spherulite growth kinetics was analyzed using a modified Lauritzen-Hoffman theory which considers the diluent effect of PEI. The regime III-II transition was observed for PEEK and PEEK/PEI blends. The side surface free energy, fold surface free energy, and the work of chain folding were calculated, and were discussed in terms of the stiffness and bulkiness of PEEK molecules. The semicrystalline morphology and the melting behavior of PEEK/PEI blends were studied by optical microscopy and DSC, respectively. The optical micrographs of PEEK spherulites grown from the blends showed that a significant amount of PEI was rejected to the interfibrillar regions of the PEEK spherulites. The melting study indicated that PEEK crystal reorganization on heating was hindered by blending with PEI, and this was attributed to the incorporation of PEI in the PEEK crystalline interlamellar regions. The amorphous and the crystalline PEEK/PEI blend films were drawn uniaxially by solid-state coextrusion. The glass transition, density, crystallization behavior, and the respective orientations were studied. The T$\sb{\rm g}$s of amorphous PEEK/PEI blends were depressed by drawing. The kinetics of crystallization of drawn PEEK/PEI blends was also reported. The orientation studies by IR dichroism showed that the orientations of both PEEK and PEI were decreased by increasing PEI content in the blends.
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