Mesogenic Rodlike Aromatic Polyesters.

We have explored the effect of substituents on the crystal nematic and nematic isotropic transition temperatures of poly p-phenylene terephthalate. The substituents halogen, phenyl, and hexyl replaced hydrogen on the ring of hydroquinone or terephthalic acid. One gets a much larger reduction of the transition temperatures if a phenyl substituent is on terephthalic acid. We believe this substituent forces the carbonyl group out of the ring plane, and creates a more flexible link.