Class Of Liquid Crystalline Polymers Research Articles

From liquid crystal polymers containing crown ethers to tapered building blocks containing crown ethers which self‐assemble into tubular supermolecules

Abstract : Molecular recognition directed self-assembly of supramolecular architectures or noncovalent synthesis, and molecular recognition directed self-assembly of transition states or self-synthesis, are two of the most active topics of research in the area of supramolecular chemistry. We are concerned with the use of the simplest endo-receptor i.e., crown ether in the design of two classes of systems. The first one is a system which is externally regulated by molecular recognition processes via a crown ether endo-receptor. This system is based on various classes of liquid-crystalline polymers which exhibit phase transitions that are manipulated by the reversible complexation of the crown ether present in different parts of their repeat unit with metal salts. The information gained from these experiments is then exploited in the design of the second group of systems. This consists of self-assembling building blocks containing various combinations of crown ether as endo-receptor and a tapered group as exo-receptor. Upon complexation with metal salts, these building blocks self-assemble into tubular supramolecular architectures. Therefore, while the first system exhibits molecular recognition directed phase transitions, the second one self-assembles into tubular supramolecular architectures via various molecular recognition processes. These tubular supramolecular architectures display a thermotropic hexagona columnar (phi h) liquid crystalline phase, which enables the structure of the self-assembled supramolecular architecture to be determined by X-ray diffraction experiments. jg

Degree of polymerization and dynamics in liquid crystalline poly-(1-subst.-ethylenes)

Abstract Dielectric relaxation measurements of two classes of liquid crystalline polymers with different degrees of polymerization were carried out. The only difference between the samples is that in the first case the liquid crystalline (LC) part is coupled to the polyethylene chain by a -COO group, whereas in the second case, an ether group (O) connect the same parts. Increasing the degree of polymerization increases the clearing temperatures and decreases the dielectric relaxation frequencies f R of reorientation of the LC part around both its short and long molecular axes. At higher degrees of polymerization, a saturation effect of f R is observed which is related to the chemical structure of the linking group.

The synthesis and characterization of a new class of liquid crystalline polymers based on s-triazine

Abstract The synthesis and characterization of a new class of liquid crystalline alternating copolymers based on s-triazine rings, connected by flexible alkyldiamine spacers and other selected bridging groups is reported. The propensity of the system to demonstrate liquid crystallinity as a function of the bridging group is investigated. Unexpectedly, the homopolymer of the triazine ring connected by a flexible alkyldiamine spacer is also a liquid crystalline polymer. A new polymerization technique is reported in which the alkyldiamine serves the dual role of monomer and proton acceptor. These polymers form liquid crystalline glasses which are transparent and have good mechanical properties. This suggests that they could be interesting materials to be further studied in the context of non-linear optics.

Combined main chain/side chain polymers. A new class of liquid crystalline polymers with unusual structural, thermodynamic and dynamic properties

Abstract Combined main chain/side chain polymers carry rigid rod-like mesogenic units both in the side chain and along the chain backbone. The properties of such combined systems are expected to be controlled by the competition of the interactions between the mesogenic units in the side and main chains as well as the tendency of the chain backbones to maximize their entropy. The thermodynamic, structural and dynamic properties of such combined main chain/side chain liquid-crystalline polymers were investigated for various chain architectures. The combined systems were found to display properties corresponding in many cases to a favourable superposition of properties characteristic of both main and side chain systems. These include high transition temperatures (up to 530 K) and broad ranges of stability of liquid-crystalline phases (up to about ΔT = 170 K). The orientational order parameter was found to approach values of 0.9 and it was possible to orient some of the polymers in weak external fields such a...