Heesub Kim

Cubic and Columnar Supramolecular Architectures of Rod–Coil Molecules in the Melt State

The liquid crystalline behavior of compounds 1 (n = 7, 12, 15) differs significantly from that exhibited for conventional rodlike molecules. They organize into layered smectic, bicontinuous cubic or hexagonal columnar mesophases depending on the temperature or the volume fraction of coil segments.

Structure and phase behaviour of polyazomethines having flexible (n-alkyloxy)methyl side chains

Abstract Structure and phase behaviour of a series of thermotropic polyazomethines having ( n -alkyloxy)methyl side chains (-CH 2 O- n -C m H 2m+1 , m = 4, 6, 8, 12) have been studied by wide-angle X-ray scattering, differential scanning calorimetry (d.s.c.) and polarizing optical microscopy. In d.s.c. thermograms the samples showed basically three transitions. The first transitions were ascribed to solid-solid transitions resulting from a large increase in disorder of the side chains. The second ones were assigned to crystal-mesophase transitions arising from melting of the side chain crystals. The third ones were attributed to mesophase-isotropic melt transitions. All the samples showed layered structures in the mesophase as well as in the crystalline phase, in which the side chains were fully interdigitated. In the crystalline phase the repeat units of rigid main chain were found not to align parallel with those of neighbouring main chains, but slipped by 49°. In the mesophase the side chain crystals were molten and the layer spacings increased proportionally with increasing side chain length. The structural regularity in the slipped repeat unit disappeared in the polymers bearing long side chains, whereas it was retained in those having short side chains. A unidirectional shearing made the layer plane align parallel on the surface.

Solubilization of n-alkanes into polyazomethines having flexible (n-alkyloxy)methyl side chains

Abstract Solubilization behavior of n-alkanes (Ck, k = 15, 20, 32, 40 and 50) into polyazomethines (Cm-PAM) having flexible (n-alkyloxy)methyl side chains (CH2OCmH2m−1, m = 4, 6, 8, 12) was studied by measuring layer spacings of the layered structures with wide-angle X-ray scattering (WAXS) and effects of side chain lengths of the polymers and chain lengths of n-alkanes were discussed. Liquid n-alkanes were miscible with the side chains of the polymers only when the side chains were molten to form mesophase. In mesophase the layered structure was not disrupted by adding Ck and on adding excess n-alkanes the presense of solubility limits was confirmed. With increasing side chain length of Cm-PAM and chain length of Ck the solubility limit of n-alkane increased and decreased, respectively.

Solubilization of n-alkanes into polyazomethines having flexible (n-alkyloxy)methyl side chains: 2. Theoretical model for the estimation of solubility limit

In a previous paper (H. Kim et al., Polymer, 1996, 37, 2573), the solubility limit of n-alkanes in blends of n-alkane/polyazomethine having flexible (n-alkyloxy)methyl side chains was reported as a function of side chain lengths of the polymer and chain lengths of n-alkanes. This paper proposes a theoretical model for estimating the solubility limit of n-alkanes. The model assumes that n-alkanes solubilize only into the layered side chain domain and that the side chain has a hyperbolic tangent function profile due to very high grafting density and density uniformity. The calculated solubility limit of n-alkane increases and decreases with increasing chain length of the side chain and chain length of the n-alkane, respectively. The model predictions are in qualitative agreement with experimental results (H. Kim et al., Polymer, 1996, 37, 2573) although the former are much lower than the latter.

Formation of Columnar and Cubic Liquid Crystalline Phases in the Complex of Coil-Rod-Coil Molecule Containing Poly(Ethylene Oxide) with LiCF3SO3

Abstract The preparation and thermotropic phase behavior of coil-rod-coil triblock molecule of docosyl 4-(4-oxy-4′-biphenylcarbonyloxy)-4′-biphenyl carboxylate with poly(ethylene oxide) of twelve ethylene oxide subunits (E-12–22) and the complexes of the triblock molecule with LiCF3SO3 are presented. E-12–22 appears to be only a smectic liquid crystalline. However, the complexation of E-12–22 with LiCF3SO3 induces a rich variety of enantiotropic liquid crystalline phases. The complexes of E-12–22 with 0.10–0.30 mol of LiCF3SO3 per ethylene unit of a molecule exhibit successively cubic, columnar and smectic A mesophases on heating. The thermal stability of the mesophase exhibited by the lithium complexes based on each triblock molecule increases with increasing salt concentration.

Preparation and Properties of Hairy-Rod Molecular Composites

Molecular composites are polymer blends, in which rigid rod-like “fiber” polymers are molecularly dispersed in flexible polymer matrix1,2. To obtain excellent mechanical properties of the composites, fiber polymers must be so isotropically dispersed in the blend system that no phase separation can be observed3,4. Once phase separation has taken place, the molecular composite transforms to a macroscopic composite, and this phase separation is a serious problem in most of molecular composites. In polymer systems containing rigid-rod polymers a phase separation is particularly facile to occurr, since between the rigid backbones a strong van der Waals attraction is present to form a separate phase. To overcome this phase separation problem a number of novel methods has been introduced for making molecular composites with satisfactory properties.

RIGID-ROD POLYMERS WITH FLEXIBLE n-ALKOXYMETHYL SIDE BRANCHES

In recent years, rigid-rod polymers with regularly substituted flexible side branches have drawn a lot of attention, since they exhibit both high thermal resistance and excellent solubility1. In addition, these polymers, if properly designed, can become even fusible. In structure, most of them are crystalline2,3 and form sanidic liquid crystallinity4, even though they are strongly branched. This new crystal structure is called layered crystal structure.3