STUDY ON STRUCTURE-PROPERTY RELATIONSHIP OF POLYIMIDE BLENDS .2. STRUCTURE AND MISCIBILITY OF POLYIMIDE PBPI-E/PTI-E BLENDS

The structure and miscibility of polyimide PBPI-E/PTI-E blends were studied by wide- and small-angle X-ray scattering and dynamic mechanical analysis, where PBPI-E is a biphenyl-dianhydride-based polyimide, and PTI-E is a polyimide from 4,4'-thiodiphthalic anhydride and 4,4'-oxydianiline. The results obtained show that there exists a paracrystalline structure in the blends with high content of PBPI-E, but this does not affect the miscibility of the blends. The blends are miscible over the entire composition range, since only one T(g) was observed for each blend. Meanwhile, the segregation of PTI-E during crystallization of PBPI-E in the blends is interlamellar.

Chemical bond characteristics, thermal expansion property and compressibility of AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths)

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY2O4 and BaY2O4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.