Abstract
Blends of polyimides XU-218 and PEI were investigated using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis and adhesive bond testing. The thermal stability of the blends increased as the proportion of PEI increased while the α-relaxation of the blends occurred at a slower rate and was broader and more cooperative in some blends, compared with the pure polymers. Physical aging of the pure polymers and blends in the glass state revealed changes in relaxation rate and lost enthalpy that were also consistent with blends not behaving as simple mixtures. The dynamic mechanical and physical aging behaviour was attributed to an increase in density on blending which decreased the unoccupied volume and increased the constraints on molecular mobility, as well as to the presence of concentration fluctuations. The adhesive properties of the blends were also investigated and bond strength was found to vary with blend composition and test temperature.
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