Formation of the Liquid Crystalline Glassy Phase and Cold Crystallization of a New Crystal Form from the Glassy Phase for Thermotropic Liquid Crystalline Polyether

Abstract

The formation of the liquid crystalline (LC) glassy phase and phase transitions including cold crystallization associated with this phase have been investigated for main-chain thermotropic LC polyether (EDMB-10), which is composed of 3,3’-dimethyl-4,4’-biphenyl units as mesogen and 10 methylene sequences as spacer, by mainly using DSC, wide angle X-ray diffractometry, and solid–state 13C NMR spectroscopy. When the sample is quenched from the isotropic melt to ice-water, the LC glassy phase is really produced as suggested by the previous finding that the liquid crystallization temperature is almost independent of the cooling rate whereas the crystallization temperature rapidly decreases with increasing cooling rate. The liquid crystalline glass thus formed is found to undergo cold crystallization above Tg and to produce a new type of crystal form (form β) which is significantly different in structure from form α ordinarily crystallized on cooling from the isotropic melt through the nematic phase. In particular, the highest crystallinity of form β can be obtained by annealing the LC glass at 130°C for 30 min–about 2 d and then quenching to 0°C. This fact suggests that the stable nematic phase associated with the crystallization of form β may appear on rapid heating around 130°C. In addition, form α is also crystallized even on heating when the LC glass is annealed at 132–134°C and also quenched to 0°C, implying the appearance of the stable nematic phase preferentially producing form α at this temperature range. Additional phase transitions are also observed for the form β sample with the highest crystallinity and their origins are briefly discussed.