Syntheses and properties of new aromatic polybenzoxazoles bearing ether and phenylethylidene or 1‐phenyl‐2,2,2‐trifluoroethylidene linkages

Two new bis(ether acyl chloride)s, 1,1‐bis[4‐(4‐chloroformylphenoxy)phenyl]‐1‐phenylethane and 1,1‐bis[4‐(4‐chloroformylphenoxy)phenyl]‐1‐phenyl‐2,2,2‐trifluoroethane, were prepared from readily available reagents. Aromatic polybenzoxazoles with both ether and phenylethylidene or 1‐phenyl‐2,2,2‐trifluoroethylidene linkages between phenylene units were obtained by a conventional two‐step procedure including the low‐temperature solution polycondensation of the bis(ether acyl chloride)s with three bis( o ‐aminophenol)s, yielding poly( o ‐hydroxyamide) precursors, and subsequent thermal cyclodehydration. The intermediate poly( o ‐hydroxyamide)s exhibited inherent viscosities of 0.39–0.98 dL/g. All of the poly( o ‐hydroxyamide)s were amorphous and soluble in polar organic solvents such as N , N ‐dimethylacetamide, and most of them could afford flexible and tough films via solvent casting. The poly( o ‐hydroxyamide)s exhibited glass‐transition temperatures ( T g 's) of 129–194 °C and could be thermally converted into corresponding polybenzoxazoles in the solid state at temperatures higher than 300 °C. All the polybenzoxazoles were amorphous and showed an enhanced T g but a dramatically decreased solubility with to respect to their poly( o ‐hydroxyamide) precursors. They exhibited T g 's of 216–236 °C through differential scanning calorimetry and were stable up to 500 °C in nitrogen or air, with 10% weight‐loss temperatures being recorded between 538 and 562 °C in nitrogen or air.