X-ray Diffraction, Calorimetric, and Dielectric Relaxation Study of the Amorphous and Smectic States of a Main Chain Liquid Crystalline Polymer

Abstract

Liquid crystalline polymers (LCPs) are complex systems that include features of both orientationally ordered mesophases and amorphous polymers. Frequently, the isotropic amorphous state cannot be studied due to the rapid mesophase formation. Here, a new main chain LCP, poly(triethyleneglycol methyl p,p′-bibenzoate), PTEMeB, has been synthesized. It shows a rather slow mesophase formation making possible to study independently both the amorphous and the liquid crystalline states. The structure and phase transitions of PTEMeB have been investigated by calorimetry, variable-temperature MAXS/WAXS employing synchrotron radiation, and X-ray diffraction in oriented fibers. These experiments have pointed out the presence of two glass transitions, related to the amorphous or to the liquid crystal phases. Additionally, the mesophase seems to be a coexistence of orthogonal and tilted smectic phases. A dielectric relaxation study of PTEMeB over broad ranges of temperature and pressure has been performed. The dynamic glass transition turns out to be slower for the amorphous state than for the liquid crystal. Monitoring of the α relaxation has allowed us to follow the isothermal mesophase formation at atmospheric pressure. Additionally, the dynamical behavior at high pressures has pointed out the fast formation of the mesophase induced by sudden pressure changes.

Molecular Origin of Strain‐Induced Chain Alignment in PDPP‐Based Semiconducting Polymeric Thin Films

“…While its origin was still unknown, past works attributed it to an averaged intermolecular distance of amorphous polymer chains or unoriented alkyl side‐chain packing. [ 65,66 ] A comprehensive understanding of crystallite orientation requires an analysis of all the peaks above.…”

“…While its origin was still unknown, past works attributed it to an averaged intermolecular distance of amorphous polymer chains or unoriented alkyl side-chain packing. [65,66] A comprehensive understanding of crystallite orientation requires an analysis of all the peaks above. Figure 2b showed 2D scattering patterns from wide-angle hard X-ray scattering (16.1 keV) for five PDPPT-C2C8C10 ≈100 nm thin-film samples under various strains.…”

Nanostructured Composites Based on Liquid-Crystalline Elastomers

“…LCPs may exhibit either nematic and/or smectic phases, depending on the chemical structure of the mesogenic molecules, the flexible spacers, and the polymer main chains [2]. Moreover, the mesomorphic behavior of LCPs can be influenced by external physical parameters, such as temperature and pressure [3]. Liquid-crystalline elastomers (LCEs) are a particular type of LCPs, where the polymer chains are cross-linked together via flexible or semi-flexible cross-linkers [4].…”

Dielectric properties of three liquid crystal polymers

“…Liquid crystal polymers (LCPs) are very attractive for industrial applications due to their outstanding mechanical properties, chemical stability, and high processability [1][2][3]. Many LCPs have been developed since the 1980s and have achieved practical applications in various fields such as high-speed electronic devices, circuit boards, and high-strength fibers [3][4][5][6][7].…”

“…Based on their chemical structures, LCPs can be divided into two kinds: side‐chain LCPs (SCLCPs) and main‐chain LCPs (MCLCPs) . As for the dielectric properties of SCLCPs, published papers show that α relaxation is attributable to segmental motions of the main chain, while β relaxation has been assigned to librational motion of mesogenic groups. Generally speaking, the relaxation behavior of SCLCPs is more or less similar to that of conventional polymers, while their unique chemical structures should be taken into consideration especially for MCLCPs.…”