Molecular composites formed by solutions of a rodlike polymer (PBT) in polyphosphoric acid

Nematic solutions of the rodlike poly(1,4-phenylene-2,6-benzobisthiazole), PBT, in polyphosphoric acid, PPA, have been aligned in a shear flow to form a molecular composite. The tensile creep and recovery behaviour are studied to reveal a solidlike behaviour (no viscous flow) with a substantial Young's modulus E. X-ray diffraction studies show PBT to be aligned in the flow direction, and suggest that PPA oligomers may be oriented orthogonal to the PBT. The latter may reflect specific solvation of PBT by PPA. Values of E are compared with predictions from composite theory.