LIQUID-CRYSTALLINE POLYETHERS BASED ON CONFORMATIONAL ISOMERISM .16. HEXAGONAL COLUMNAR PHASE (PHI-H) IN A NONDISCOTIC COPOLYETHER BASED ON 1,2-BIS(4-HYDROXYPHENYL)ETHANE, 1,8-DIBROMOOCTANE, AND 1,12-DIBROMOOCTANE, AND THE NOVEL 2-DIMENSIONAL-3-DIMENSIONAL PHI-H-SB TRANSITION

The copolyethers based on 1,2-bis(4-hydroxyphenyl)ethane (BPE) and a 1/1 molar ratio of 1,8-dibromooctane and 1,12-dibromododecane [BPE-8/12(1/1)] was characterized by a combination of techniques consisting of differential scanning calorimetry (DSC), simultaneous X-ray diffraction/DSC (XDDSC), and thermal optical polarized microscopy. On cooling from the isotropic phase, BPE-8/12(1/1) exhibits a hexagonal columnar (PHI-h) followed by a smectic-B (s(B)) phase. Both mesophases are enantiotropic. To our knowledge this represents the first example of a flexible nondiscotic liquid-crystalline polymer that displays a hexagonal columnar mesophase. The new PHI-h-s(B) transition represents an almost ideal case of a 2-dimensional-3-dimensional transition where longitudinal long-range order is established without significantly affecting the in-plane order. The PHI-h phase of BPE-8/12(1/1) [which can be viewed as a copolymer containing structural units derived from polyethylene and poly(p-xylylene)] bridges the gap between the columnar phases of polyethylene and of poly(p-xylylene). The present new addition to the list of columnar phases in flexible nondiscotic polymers is particularly significant as the phase occurs above the temperature range of a smectic phase. A further proof is thus provided that this class of "hexagonal" phases is liquid crystalline in nature.