New Thermotropic Copoly(keto esters) Based on 3,4'-Disubstituted Benzophenones

Two isomeric benzophenone derivatives, 3-hydroxy-4'-carboxy- and 4-hydroxy-3'-carboxybenzophenone, were synthesized and used to prepare new home-and copoly(keto esters) with some commercial comonomers. Polymerizations were performed both by solution and melt polycondensation methods which affect the inherent viscosity and solubility of the resultant products. Yields were always almost quantitative independently of the synthetic method employed. All the samples exhibited very high thermal stability. Phase behaviour and morphology of the polyesters have been investigated by differential scanning calorimetry (DSC) analysis and optical microscopy. A liquid-crystalline (LC) phase was observed in most of the specimens containing commercial hydroxy acids in percentages higher than 30 mol-%, while both homopolymers melt to an isotropic liquid. Preliminary gravimetric sorption experiments, using acetone as a penetrant, were carried out on films prepared from some of the copolymers able to give both isotropic non-crystalline and nematic LC morphologies. The penetrant sorption was strongly reduced by the presence of the frozen nematic LC phase that behaves similarly to the conventional crystalline ordered state.