Synthesis of novel polypyromellitimides with n-alkyloxy side chains and their liquid-crystal aligning property

New well-defined brush polypyromellitimides with n-octyloxy and n-dodecyloxy side chains were prepared by two-step polycondensations of 3,6-di(n-alkyloxy)-pyromellitic dianhydrides with various conventional aromatic diamines. Their structures and properties were investigated and compared with those of polyimides without the side chains. The alkyloxylated poly(amic acid)s had inherent viscosities of 0.45-1.09 dL/g. The polyimides showed enhanced solubility in organic solvents and had layered structures in the solid state. As the side-chain length increased from n-octyloxy to n-dodecyloxy, the extent of layered structure formation increased, whereas the glass-transition temperature and thermal resistance decreased. As for the liquid-crystal (LC) aligning ability measured with 4-n-pentyl-4'-cyanobiphenyl on rubbed thin-film surfaces, all the side-chain polyimides revealed homogeneous LC alignment parallel to the rubbing direction with distinctively higher pretilt angles than those of the polyimides without the side chains. (C) 2004 Wiley Periodicals, Inc.