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

Abstract

Several polyimides derived from 3,3Ј,4,4Ј-benzophenonetetracarboxylic dianhydride (BTDA) and 3,5-diaminobenzate 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/ PP0DA, 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.

Polyimides with side groups: Synthesis and effects of side groups on their properties

“…The authors considered that this was ascribed to the strong interaction between mesogen units and LC molecules. In addition, other polyimides containing short linear alkyl side groups end‐capped with biphenyl or 4‐cyano‐biphenyl mesogen units were also reported by Liu and coworkers, Gallot and coworkers, Cheng and coworkers, Takezoe and coworkers, and Gu and coworkers . Most of them can generate high pretilt angles.…”

“…In addition, other polyimides containing short linear alkyl side groups end-capped with biphenyl or 4-cyano-biphenyl mesogen units were also reported by Liu and coworkers, 128 Gallot and coworkers, 129 Cheng and coworkers, 130,131 Takezoe and coworkers, 132,133 and Gu and coworkers. 134 Most of them can generate high pretilt angles. Besides, stilbene mesogen units were attached to the end of linear alkyl side groups too.…”

Effect of copolymerization on crystallization kinetics of semicrystalline polyimides

“…Because semicrystalline polyimides offer further advantages of increased solvent resistance and retention of mechanical properties above the glass transition temperature ( T g ), these features have made semicrystalline polyimides the focus of considerable research over these years 1–3. One of the typical examples was based on 1, 3‐ bis (4‐aminophenoxy) benzene (TPER) and 3, 3′, 4, 4′‐biphenyltetracarboxylic dianhydride ( s ‐BPDA), it displayed excellent mechanical properties, chemical resistance and electric properties 4, 5.…”