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

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 13 C 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 T g 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 132-134and 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. KEY WORDS Liquid Crystalline Polymer / Liquid Crystalline Glass / Cold Crystallization / Nematic Phase / Solid-State 13 C NMR / Polyether / Conformation / Various main-chain thermotropic liquid crystalline (LC) polymers have been developed for more than these two decades, and their phase transitions and structures in possible phases have extensively been investigated by calorimetry, microscopy, diffractometry, spectroscopy, and so on. 1-6 However, the structure and dynamics at a molecular level are not fully understood in the respective phases and the detailed information is still limited about the relationship between the chemical structure and properties for the main-chain thermotropic LC polymers. The main reason of such difficulties may be due to thermal instability in the LC phase mostly appearing at higher temperatures and a lack of systematic investigations directly associated with the LC phase.Recently we synthesized a new type of main-chain thermotropic LC polyether EDMB-10 (Scheme 1) with a simple chemical structure and found that the phase transitions associated with the nematic phase appear in the range of temperature less than 150 • C where most of analytical methods can be employed without any thermal changes in chemical structure of the sample. 7,8 For example, we could investigate in detail the liquid crystallization and crystallization pr...

Solid-State 13C NMR Studies of the Structure and Chain Conformation of Thermotropic Liquid Crystalline Polyether Crystallized from the Liquid Crystalline Glassy Phase

“…The sample was brought to the LC glassy state by quenching from the melt to ice-water and then the form sample was obtained by annealing the quenched sample at 130 C for 30 min in a silicone bath and rapidly quenching to ice-water. 8 …”

“…This fact suggests that the spacer conformation in the LC glassy phase may be nearly the same as in the noncrystalline component. 8 The broken lines indicate the results of the line shape analysis carried out by assuming that each constituent line is described as a Lorentzian.…”

“…For comparison, the spacer conformation of each component in the form sample is also shown in Figure 4. Figure 5 shows the CP/MAS 13 C NMR spectra of the crystalline and noncrystalline components of the form sample in the mesogen carbon region, which 8 Broken lines indicate the results of the line shape analysis carried out by assuming that each constituent line is described as a Lorentzian.…”

“…8 Since the noncrystalline component corresponds to the supercooled LC component in each sample crystallized from the LC phase, the structure of the mesogen and spacer groups in the LC phase may be preserved in the supercooled LC component which is left without crystallization in each sample. Therefore, the N and N phases must have also different structures in the mesogen and spacer units as described above for the supercooled noncrystalline components in the form and samples.…”

“…7 By evaluating the results thus obtained, we have found that the LC glassy phase is readily produced by quenching the LC polymer from the melt to ice-water as a result of the suppression of crystallization after rapid liquid crystallization in this system. 8 Moreover, cold crystallization from the LC glassy phase is allowed to occur above the glass transition temperature, and another type of crystal form, form , is produced, which is evidently different in wideangle X-Ray diffraction profile from form that is ordinarily crystallized by slowly cooling from the melt through the nematic phase. In particular, a form sample with much higher crystallinity is obtained by annealing the LC glassy specimen at 130 C for a certain period and then quenching it to 0 C. This fact leads to an interesting proposal that another stable nematic phase may appear at about 130 C on rapid heating from the LC glassy phase although the ordinary unstable nematic phase appearing on cooling from the melt is readily transformed to form crystals without significant time delay in this system.…”