Amorphous-smectic glassy main-chain LCPs, 1 -: Poly(ether esters) derived from hydroxybibenzoic acid and (R,S)- and (R)-2-methylpropane-1,3-diol

The synthesis and the characterization of mainchain liquid-crystalline poly(ether esters), derived from hydroxybibenzoic acid and (R,S)- and (R)-2-methylpropane-1,3-diol, are reported. These polymers show an interesting thermal behavior. They develop mesophases with a slow rate of formation, allowing the easy quenching of the melt into: a) the glassy amorphous state, b) the glassy liquid-crystalline state, or c) a mixture of both, depending on the thermal treatment. The extent of the transformation and the symmetry of the different phases have been determined by means of calorimetric and X-ray diffraction methods. Dielectric spectroscopy results provide additional evidence for the detection of distinct glass transitions. The results show that the racemic polymer forms a low-ordered SmCalt mesophase, while a more ordered phase is obtained in the case of the enantiomerically pure polymer. The comparison of the properties of the different states evidences the special behavior and properties of the glass transition (Tg) in these polymers. Emphasis is paid to the location of the Tg of the liquid-crystalline state in comparison to the Tg of the amorphous state. It is found that the glass transition of the SmCalt glass in R,S-PBO3 (the poly(ether ester) derived from hydroxybibenzoic acid and (R,S)-2-methylpropane-1,3-diol) appears at lower temperatures than the glass transition of the amorphous state. However, in R-PBO3 (the poly(ether ester) derived from hydroxybibenzoic acid and (R)-2-methylpropane-1,3-diol), where the more ordered phase is present, the glass transition follows the classical and tendency of semicrystalline polymers.