THE SYNTHESIS AND CHARACTERIZATION OF THERMOTROPIC POLYESTERS WITH SUBSTITUENTS ON THE MESOGENIC UNITS

The syntheses of a series of new thermotropic liquid crystalline homopolymers, copolymers, and polymer blends, as well as their monomers were discussed. These polymers were prepared from 1,10-decane bisterephthaloyl chloride and substituted hydroquinones, and had a general structure as follows: where X = (CH(,2))(,(eta)) -H; n = 0, 1, 2, 3, ......, 10. or X = Br, -CN, -NO(,2), -OCH(,3). In the copolymers, X was either -CN or -OCH(,3) of different ratios. The structures and the thermotropic properties of these polymers were characterized by inherent viscosity measurements, gel permeation chromotagraphy, (\u2713)C-NMR, differential scanning calorimetry, and polarizing microscopy observations. All of the polymers had fairly low melting temperatures, which were desirable for thermotropic liquid crystalline polymers, and most of them had a mesophase (very likely nematic) above the melting point. As an example, the ethyl-substituted polymer had a melting point of 71(DEGREES)C and an isotropization temperature of 127(DEGREES)C. The substituent effects on the thermotropic behavior of these polymers were systematically studied in terms of both steric and polar effects. Increasing the size of the substituents resulted in the decrease of the thermal stability of the mesophase, while the higher polarity of the substituents resulted in a higher stability. With some success a theoretical treatment was developed which partly answered the questions which arose from the different behavior of polymers with different substituents; for example, why the methoxy-substituted polymer was (to the author\u27s suprise) non-liquid-crystalline. The copolymerization of monomers with different substituents was found to be a good way to lower the melting point of the polymers. Copolymerization also caused a steady change in the mesophase thermal stability with changing composition of the copolymers. Observations on the optical microscopy revealed that no phase separation occurred in the mesophases of the blends formed from two different thermotropic polymers. However, the liquid crystalline polymers were immiscible with a non-liquid-crystalline polymer, and consequently both phase separations and phase inversions were observed with changing combination of the two components of these blends