Synthesis of optically active polyarylates having axially chiral binaphthylene unit

Novel optically active polyarylates having axially chiral 6,6′-binaphthylene units in the main chain have been synthesized by the reaction of (R)-or (S)-2,2′-bisalkoxy-6,6′-dibromo-1,1′-binaphthyl (1a, 1b) and aromatic diols with carbon monoxide in the presence of palladium catalyst. The resulting polyarylates had molecular weights up to 20000 and were soluble in a variety of organic solvents including N,N-dimethylformamide, 1-methyl-2-pyrrolidone, m-cresol, tetrahydrofuran, and pyridine. Circular dichroism (CD) spectra of these polyarylates showed large Cotton effects compared with those of the model compounds and were the complete mirror images of each enantiomer, suggesting the existence of an ordered conformation. The most stable structure of the optically active polyarylates indicated helical conformation by MM2 force field calculation. No change in the specific rotation of the optically active polyarylates was observed on heating at 100 °C for 5 h, suggesting thermal stability of the ordered conformation such as helix.