To develop the polyimide (PI) which is closely matched to the coefficient of the thermal expansion (CTE) of copper, a series of PIs are prepared from 5,4′-diamino-2-phenyl benzimidazole (DAPBI), 4,4′-diaminodiphenyl ether (ODA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) using a sequential copolymerization, blade coating, and thermal imidization process. The physical properties of the PIs are effectively regulated and optimized by adjusting the ratio of the rigid DAPBI and flexible ODA components. By increasing the DAPBI content, thermal stability, dimensional stability, and mechanical properties, the resultant polymer is enhanced. PI-80 exhibits an excellent comprehensive performance, a glass transition temperature of 370 °C, and a tensile strength of 210 MPa. Furthermore, the CTE as calculated in the range 50–250 °C is ca. 19 ppm/K, which is equal to that of copper. A highly dimensionally stable, curl-free, and high T-style peel strength (6.4 N/cm) of copper/PI laminate was obtained by casting the polyamic acid onto copper foil (13 μm) and thermally curing at 360 °C, which indicates that it has the potential to be applied as an electronic film for flexible displays and flexible printed circuit boards. A structural rationalization for these remarkable properties is also presented.
An ilmenite-like monoclinic phase of HgMnO 3 with space group P2 1 /c was prepared using high-pressure and hightemperature methods at 18 GPa and 1473 K. The MnO 6 octahedra form a two-dimensional (2D) network in the bc plane, leading to a longrange antiferromagnetic ordering with a low Neél temperature of T N ∼ 32 K. As the synthesis pressure increases to 20 GPa, a new perovskitelike rhombohedral phase with space group R3̅ c was found to occur. The rhombohedral phase exhibits a three-dimensional (3D) network for the MnO 6 octahedra, giving rise to an antiferromagnetic ordering at T N ∼ 60 K. X-ray absorption spectroscopy confirms the invariable Mn 4+ charge state in these two polymorphic phases, in agreement with the Curie−Weiss and bond valence sum analysis. HgMnO 3 provides an interesting example to study the magnetic properties from 2D to 3D by varying synthesis pressure.
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