Melting and recrystallization during mesophase transitions of a thermotropic liquid crystalline polymer

Abstract

Wide-angle X-ray diffraction (WAXD), polarized optical microscopy, and differential scanning calorimetry (DSC) have been employed to elucidate the mesophase transitions in a thermotropic liquid crystalline polymer (LCP) prepared by copolymerization of Bisphenol E diacetate, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. A single glass transition temperature (T,) and double endotherms were discerned in the DSC scans of the neat LCP. The dual melting peaks, commonly attributed to the fast and slow melting transitions, manifest strong dependence on thermal history. Annealing slightly above the Tg transition temperature has shown the occurrence of a solid-solid crystal transformation. However, annealing in the vicinity of melting temperatures exhibits a loss of positional ordering of solid crystals, then reorganization occurs due to the large anisotropy of rod-like macromolecules. Finally, the terminal melting transition takes place. This kind of order-disorder transition of mesophase structures is similar to the phenomenon of meltingrecrystallization in some flexible chain crystals and will be discussed based on new evidence from isothermal WAXD studies.

Effect of thermal history on the rheological behavior of a thermotropic liquid-crystalline polymer

“…Using the 73/27 HBA/HNA copolyester Lin and Winter42-43 reported that Tm 1 was higher than Tm2 in the range of annealing temperatures employed, whereas using the 58/42 HBA/ HNA copolyester Butzbach and co-workers46 observed that at low annealing temperatures, Tm 1 was lower than Tm2, but the value of Tm 1 increased rapidly with increasing annealing temperature and eventually exceeded the value of Tm2, yielding a cross-over. By examining the results reported in a paper by Kyu and co-workers45 (refer to Figure 1 in ref 45), we have noted that a cross-over between Tmi and Tm2 also occurred in their TLCP. A cross-over between Tm 1 and Tm2 seems to suggest that the location of Tmi, regardless of whether it is a high-temperature melting peak or low-temperature melting peak, depends on annealing conditions.…”

Synthesis, characterization, and in vitro degradation of liquid‐crystalline terpolyesters of 4‐hydroxyphenylacetic acid/3‐(4‐hydroxyphenyl)propionic acid with terephthalic acid and 2,6‐naphthalene diol

“…At still higher temperatures during annealing, the shift of the low‐temperature endotherm is much more than that during low‐temperature annealing. Nam et al17 observed that the premelting transition is a melting–recrystallization process. It is possible that during high‐temperature annealing near the melt transition, the positional ordering of the solid crystals might be disturbed so that the rigid macromolecules reorganize to form a new crystal structure and finally terminal melting to form a mesophase.…”

Synthesis and Properties of Polyamides and Polyesters On the basis of 2,2‘-Bipyridine-5,5‘-Dicarboxylic Acid and the Corresponding Polymer−Ruthenium Complexes

“…It is generally not suitable for diols having aromatic or tertiary hydroxyl groups because of the poor nucleophilicity, competitive elimination reactions, and steric hindrance. In our studies, those polyesters derived from rigid aromatic diols (22)(23)(24)(25)(26)(27)(28)(29) were synthesized by the reaction with 2,2′-bipyridine-5,5′-dicarbonyl chloride (20) in the presence of pyridine. Polyesters with a flexible main chain or side chain were synthesized by transesterification reaction between diethyl-2,2′-bipyridine-5,5′-dicarboxylate (21) and the corresponding diols (30-38) with a catalytic amount of titanium(IV) isopropoxide.…”

“…4′-dihydroxybiphenyl(22), bisphenol A (23), 4,4′-dihydoxybenzophone(26), dihydroxypropiophenone(27), 2,7-dihydroxynaphthalene (28), 1,n-dihydroxyalkane (33a-i, n ) 2, 4, 5, 6, 7, 8, 9, 10, 12), 2,2-dimethyl-1,3-propanediol (36), 2,5-dihydroxybenzoquinone, and 6-chloro-1-hexanol were purchased from Lancaster Synthesis Ltd. 4,4′-(Hexafluoroisopropyliene)dianiline 6, 4,4′-ethylenedi-m-toluidine (15), 4,4′-(hexafluoroisopropyliene)-diphenol (24), 2,2-dimethyl-1,3-propanediol (35), 2-methyl-2-propyl-1,3-propanediol (37), and 2-butyl-2-ethyl-1,3-propanediol (38) were purchased from Aldrich Chemical Co. Inc. 2,2′-Bipyridine-5,5′-dicarboxylic acid (1), 2,2′-bipyridine-4,4′-dicar-…”