A thermotropic main-chain random copolyester containing flexible spacers of differing lengths .1. Synthesis and characterization

A thermotropic main-chain random copolyester containing flexible spacers of differing lengths (hereafter referred to as PSHQ6-12) was synthesized, via condensation polymerization in solution, by first preparing 2-(phenylsulfonyl)-1,4-hydroquinone (A), 4',4 ''-bis(chloroformyl)-1,6-diphenoxyhexane (B6), and 4',4 ''-bis(chloroformyl)-1,12-diphenoxydodecane (B12). Using differential scanning calorimetry we found that PSHQ6-12 exhibits only two thermal transitions: (i) a glass transition at ca. 90 degrees C and (ii) a nematic-isotropic transition at ca. 192 degrees C. The absence of crystalline structure in PSHQ6-12 at room temperature, which was also confirmed by wide-angle X-ray diffraction (WAXD), is attributable to the lack of an orderly packed structure, which originated from the large differences in the length of CH2 units between monomer B6 having 6 CH2 units and monomer B12 having 12 CH2 units. That is, the coexistence of CH2 units of greatly differing lengths apparently prevented the crystallization of PSHQ6-12, forming only a glassy nematic phase. This is in contrast with the situations for homopolyesters, poly[(phenylsulfonyl)-p-phenylene 1,6-hexamethylenebis(4-oxybenzoate)] (PSHQG) and poly[(phenylsulfonyl)-p-phenylene 1,12-dodecamethylenebis(4-oxybenzoate)] (PSHQ12), which were found via WAXD to have highly ordered structure at room temperature and undergo three thermal transitions: (i) a glass transition, (ii) a crystalline-nematic transition, and (iii) a nematic-isotropic transition. Using polarized optical microscopy we found that both copolyester PSHQ6-12 and homopolyesters PSHQ6 and PSHQ12 exhibit Schlieren texture' in the nematic region. PSHQ6-12 enabled us to prepare, using p-chlorophenol as solvent, lyotropic solutions at concentrations of 60 wt % and higher until the solution becomes a glassy state. The lyotropic solutions were also found to exhibit Schlieren texture under quiescent conditions and form banded structure under shear.