RIGID-ROD POLYESTERS WITH FLEXIBLE SIDE-CHAINS .4. THERMOTROPIC BEHAVIOR AND PHASE STRUCTURES IN POLYESTERS BASED ON 1,4-DIALKYL ESTERS OF PYROMELLITIC ACID AND 4,4'-BIPHENOL

A series of rigid-rod polyesters with long alkyl side chains, denoted as B-Cn, have been prepared by condensing 1,4-dialkyl esters of pyrome llitic acid with biphenol. The alkyl side-chain lengths were varied fr om hexyl (n = 6) to octadecyl groups (n = 18), and the thermotropic tr ansition behavior and mesophase structure of these materials were exam ined by optical microscopy, DSC, and X-ray measurements. An increase i n the length of the side chain decreases remarkably the melting point of the crystalline phase, giving rise to a liquid crystalline phase. T wo types of liquid crystalline phases with layerlike modifications, LC -1 and LC-2, have been observed. The transition behavior of these liqu id crystalline phases is described as a function of the side-chain len gth. In addition, the structural characteristics of the liquid crystal line phases as well as the crystalline phase are described as based up on X-ray data collected for oriented specimens.