Liquid crystalline comb-like polyimides with biphenyl-based side groups

We have synthesized series of comb-like polyimides with mesogenic units in their side groups. Such comb-like polyimides were obtained by polycondensat ion of aromatic diamines bearing biphenyl-based mesogenic moieties with bic ycle [2,2,2] oct-7-ene 2,3,5,6-tetracarboxylic dianhydride (BCDA). The diff erent diamines, with two lengths of spacer (with 6 and 11 methylene groups) , were synthesized in three steps using as mesogenic groups: biphenyl, 4-cy anobiphenyl and 4-(2-methyl-1-butoxy)biphenyl. The synthesis of the polyimi des was performed in two steps: polycondensation of a dianhydride with a di amine in N-methyl-2-pyrrolidone at room temperature giving the correspondin g polyamic acid, followed by thermal cyclization into the corresponding pol yimide. The comb-like polyimides were studied by X-ray diffraction between room temperature and 250 degrees C. Two types of smectic structure were est ablished: SmA(1) for the long spacer and SmC1 for the short spacer.