Effect of Thermal History on the Time Evolution of the Structure of a Main-Chain Thermotropic Liquid-Crystalline Polyester

Abstract

The effect of thermal history on the time evolution of the structure of a main-chain thermotropic liquid-crystalline polymer, poly[(phenylsulfonyl)-p-phenylene l,10-decamethylenebis(4oxybenzoate)] (PSHQ10), was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and optical microscopy. For the study, the specimens having the following thermal histories were employed: (a) fully oriented melt-spun fiber, (b) as-cast specimen, and (c) as-cast specimen followed by thermal treatment at 190 °C in the isotropic region. We found that when an as-cast specimen was annealed at 130 °C, it exhibited an intermediate endothermic peak at a temperature (Tmi) between the crystal melting temperature (Tm2) (~120 °C) and the nematic-isotropic transition temperature (Tni) (~180 °C) very soon after the annealing began, but when an as-cast specimen was first heated to 190 °C in the isotropic region followed by annealing at 130 °C, only T^a and Tni appeared until the annealing continued for ~40 h and then Tmi appeared as the annealing continued further. We found, however, that a melt-spun fiber exhibited only Tm2 and Tni until the annealing continued for ~40 h and then Tml appeared as the annealing continued further. By conducting variable heating rate DSC we have concluded

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3-bis[4-(4′-aminophenoxyl) cumyl] benzene

“…These crystals are metastable and the formation is highly dependent on annealing conditions: temperature and time. Han et al 15 and Kim and Han 16 also found an intermediate melting endotherm before normal melting in poly[(phenylsulfonyl)-p-phenylene 1,10-decamethylene bis-(4-oxybenzoate)] (PSHQ10) caused by annealing; the formation of this annealing-induced endotherm has a profound effect on the rheological properties of this polymer.…”

“…The double or multimelting phenomenon has long been observed in a number of crystalline polymers, such as flexible chain, semirigid chain, and rigid chain polymers: for instance, polyethylene (PE), 3 polypropylene (PP), 4 nylon, 5 poly(ethylene terephthalate) (PET), 6,7 poly(aryl ether ether ketone) (PEEK), 8 -10 poly(ether diphenyl ether ketone) (PEDEK), 11 and thermotropic liquid crystalline polyesters. [12][13][14][15][16][17][18] Among those polymers PET and PEEK have been extensively studied by a number of authors. A variety of explanations for the multimelting behavior have been put forward: (1) different crystal structures, which have been observed in trans-1,4-polyisoprene, 19 isotactic polypropylene 4 ; (2) different morphological characters with different lamellar thicknesses, which have been found in cis-1,4-polyisoprene 20 and PEEK; and (3) melting, reorganization, and remelting, which were observed in poly(⑀-caprolectone), 21 and PET.…”

Main-chain liquid crystalline polymers bearing periodically grafted folding elements

“…12,13 Inclusion of flexible spacers in the polymer backbone, on the other hand, leads to completely different organization of the chains in the mesophase, which is also of a smectic-type; however, the chains typically lay extended perpendicular to the layer plane, with the mesogenic units lying either perpendicular (smectic A) or at an angle (semctic C) to the plane. A variety of flexible spacers, such as polymethylene, [17][18][19][20][21][22][23][24][25][26][27] oligoethylene oxide, [28][29][30][31][32][33] and oligosiloxane segments [34][35][36] have been incorporated within the backbone of the main-chain LCPs; oligosiloxane spacers have been found to reduce the phase transition temperatures most drastically and often lead to the formation of a nematic mesophase with wide temperature stability. In the cases where the pendant substituent is installed on the flexible spacer of the backbone, folding of the chain to exclude the pendant substituent is often seen; [37][38][39][40][41][42][43] this happens especially when a bulky pendant unit, such as a ferrocenyl 38,39 or phenyl unit, [40][41][42][43] is present.…”

Revisit the crystallization mechanism of vectra,? a liquid crystal polymer

“…They conducted thin‐film solution polymerizations and found lamellar single crystals from poly(2,6‐oxynapththoate/ m ‐oxybenzoate) and from poly( p ‐oxybenzoate). Han et al21 also studied the effect of thermal history on a main‐chain thermotropic liquid‐crystalline polyester with flexible units. Nakai et al22 investigated phase‐separation processes and self‐organization of textures in the biphase region of a thermotropic liquid crystalline polyester using a polarizing light microscopy.…”