Synthesis and properties of transparent polyimides derived from trans- and cis-1,4-bis(3,4-dicarboxyphenoxy)cyclohexane dianhydrides

To get a transparent polyimide and investigate the isomeric effect of trans and cis configuration, two novel dianhydrides, trans-and cis-1,4-bis(3,4-dicarboxyphenoxy)cyclohexane dianhydrides were synthesized (trans-2 and cis-2), and polycondensations of the dianhydrides with different aromatic diamines containing trifluoromethyl group or meta-substituent were carried out by two-step procedure. The resulting polyimides had glass transition temperature (T-g) in the range of 203262 C, and exhibited good mechanical properties with tensile strengths of 53-102 MPa, tensile moduli of 2.1-3.3 GPa, and elongations at break of 1.9-16.5 %. All semi-aromatic polyimide films showed high optical transparency in the visible region along with the cut-off wavelength of 369-375 nm due to the introduction of cyclohexane moiety into the main chain. Furthermore, compared with cis-2-based polyimides, the polyimides derived from trans-2 had higher T-g, better chemical solvent resistance and mechanical properties. It could be attributed to the relatively denser polymer chain packing in trans-2 based polyimides, which was confirmed by wide-angle X-ray diffraction.