Introduction of side chains containing biphenyl unit on the crystalline morphology and properties of polyimides

摘要

Several polyimides derived from 3,3',4,4'benzophenonetetracarboxylic dianhydride (BTDA) and 3,5diaminobenzate containing various side chains with biphenyl unit through various flexible spacer were prepared by thermal imidization. By incorporating side chains, the solubility was greatly enhanced and all the polyimides with side chains showed good solubility in polar solvents. During a continuous thermal imidization procedure, the BTDA/ MPDA polyimide samples formed a novel banded spherulites with not only zigzag Maltese crosses, but also distinct extinction rings, while the polyimides with side chains revealed only fine grainy crystalline particle. X-ray diffraction of BTDA/MPDA powder showed sharp diffraction peak in the X-ray diffraction and revealed the existence of highly ordered crystalline structure in polyimide, while BTDA/PPODA, BTDA/PP2DA, and BTDA/PP6DA polyimides with side chains revealed only a broad reflection at the low angle and demonstrated the presence of low-ordered layer structure. DSC confirmed that the introduction of side chains significantly reduced the melting points of the resulted polyimide, thus it greatly enhanced its thermal plasticity. However, the heat-resistant properties such as the thermal stability were generally decreased, and all the polyimide with side chains showed a typical two-step thermal degradation behavior relating to the pyrisis of side chains and polyimide backbone. (c) 2006 Wiley Periodicals, Inc.