Liquid crystalline coumarin polymers, 1. Synthesis and properties of side‐group liquid crystalline polymers with coumarin moieties

This paper deals with two series of novel side‐group liquid crystalline polymers containing coumarin (2H‐1‐benzopyran‐2‐one) moieties. Several kinds of polymethacrylates of Series I (Fig. 1) containing a 7‐benzoyloxycoumarin unit in the side group with or without substituent at 3 or 4 position of coumarin ring were prepared, in order to study the influence of spacers, tail groups and the positions of the tail groups on their liquid crystalline properties. Three polymethacrylates (Series II, Fig. 1) containing a phenyl 7‐octyloxycoumarin‐3‐carboxylate unit, which consisted of a turned ester group between the aromatic rings in the central unit of side group as compared to Series I, were also prepared. The investigation of the thermal behavior of the two series indicated that the structure of the side‐group significantly affected the liquid crystalline properties of the polymers. It was found that the polymers in Series I with substituents at the 3 position of the coumarin ring exhibited mesophase with a wide temperature range, whereas the polymers with substituents at the 4 position showed no mesophase. In addition, each polymer of Series I tended to exhibit a glassy state, whereas each polymer of Series II tended to exhibit a crystalline state. This would be due to the different interactions of side groups of the polymers in Series I and II. It was also revealed that the UV‐Vis absorption and fluorescence spectra were influenced by their mesogenic structures and chromophore aggregations. Furthermore, the preliminary results about the emission spectra suggested that the annealing of the polymer film had a great influence on its fluorescence property.