STUDIES ON A MISCIBLE POLYIMIDE BLEND

Blends of polyimides XU-218 and PEI were investigated using differenti al scanning calorimetry, dynamic mechanical analysis, thermogravimetri c analysis and adhesive bond testing. The thermal stability of the ble nds increased as the proportion of PEI increased while the alpha-relax ation 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 cha nges in relaxation rate and lost enthalpy that were also consistent wi th blends not behaving as simple mixtures. The dynamic mechanical and physical aging behaviour was attributed to an increase in density on b lending which decreased the unoccupied volume and increased the constr aints on molecular mobility, as well as to the presence of concentrati on fluctuations. The adhesive properties of the blends were also inves tigated and bond strength was found to vary with blend composition and test temperature.