Phase and orientational behaviors in liquid crystalline main-chain/side-group block copolymers (original) (raw)
Related papers
Macromolecular Symposia, 1997
Liquid crystalline block copolymers are new materials in which multiple molecular interactions can provide the driving force for complex phase behaviors and states. of order. Block copolymers containing both liquid crystalline main-chain polyester and side-group polymethacrylate blocks were investigated. They phase separated in the liquid crystalline state and their individual mesophases coexisted. The copolymers responded very differently when either a mechanical or a magnetic field was used for alignment. In the fibers the orientations of the side-group and main-chain smectic planes with respect to the fiber axis depended critically on the block lengths and on their distinct tendencies to align, whereas under a magnetic field the mesogens aligned collectively with their long molecular axis parallel to the field, independent of the copolymer structure.
Macromolecules, 2009
We report the phase structures of a series of poly(styrene-block-{3′-[4-(4-n-dodecyloxybenzoyloxy)benzoyloxy]-4-(12-methacryloyloxydodecyloxy)benzoyloxybiphenyl}) (PS-b-PMAC) side-chain liquid crystalline block copolymers (SC LCBCP). The SC liquid crystalline polymer was formed by side attaching a bentcore mesogen to the polymer backbone using a 12-carbon spacer. The phase structure of the high and low f PMAC samples were investigated using differential scanning calorimetry, small-angle and wide-angle X-ray scattering, and transmission electron microscopy techniques. The PS coil block and PMAC LC block phase separate into a lamellar morphology in all of the samples investigated (volume fraction of PMAC f PMAC ∼ 0.31-0.65). However, both the LC phase and the orientation of the hierarchical structure under mechanical shear showed strong dependence on the LC content. Samples having a high f PMAC (0.5-0.65) showed a SmC 2 LC phase (Smectic C denotes the LC molecules are tilted with respect to the layer normal, and 2 represents a bilayered structure), similar to that observed in PMAC homopolymers. Upon mechanical shear, these smectic layers oriented parallel to the shear plane and the BCP lamellae oriented perpendicular to the shear plane with the layer normal parallel to the vorticity direction. In samples having a lower f PMAC , the BCP lamellae laid parallel to the shear plane and the LC phase structure in these samples was columnar rectangular. A detailed structural and morphological study will be reported.
Macromolecular Chemistry and Physics, 1994
A novel type of block copolymers comprising both side-chain and main-chain liquid-crystalline (LC) blocks in the same macromolecular structure was synthesized and studied. The former block was either one of two LC polymethacrylates containing an azobenzene mesogen with different substituents (block A), and the latter was a semiflexible LC polyester block (block B). Thermal, dynamic-mechanical, and X-ray diffraction data indicated that the two structurally different blocks were at least partly phase-separated within the glassy and LC states. The thermodynamic phase transition parameters of block A were not affected by copolymer composition. However, significant deviations of the thermodynamic parameters of block B were observed relative to those of the corresponding homopolymers. In particular, the normalized transition enthalpies of block B were much lower, suggesting the occurrence of a more or less diffuse interphase. An increase in the nematic-isotropic temperature was found at variance with previous results on most of the LC block copolymers, in which only one block was an LC component. a) Systematic IUPAC nomenclature: 6-[4-(4-hexyloxyphenylazo)phenoxy]hexyl methacrylate (6a) and 6-[4-(4-decyloxyphenylazo)phenoxy]hexyl methacrylate (6 b).
Orthogonal Crystal Orientation in Double-Crystalline Block Copolymer
Macromolecules, 2011
Block copolymers are attractive building blocks for constructing nanostructures by self-assembly. 1À3 Their structural formation occurs through a microphase separation between incompatible constituting chains, and the morphology of the microdomains thus formed is governed by the strength of interblock repulsion and volume fraction. 4 The spatial arrangement of the microdomains is characterized by certain macrolattices, including 1-D array for lamellar microdomains, 2-D hexagonal lattice for cylindrical domains, and 3-D BCC lattice for spherical domains. At the molecular level, the block chains within the microdomains are typically liquid-like without distinct molecular order. Incorporation of crystallization into the self-organization mechanism of block copolymers to generate a hierarchically ordered structure may enrich their morphology and properties. 5À8 The presence of molecular order, which may be mesomorphic or crystalline in nature, leads to a structural hierarchy in the system; namely, the copolymer displays a long-range ordered arrangement of microdomains on a larger length scale and another characteristic ordering of chains at the molecular level. "Structure-within-structure" or "order-within-order" are the appropriate terms to describe such a morphological feature. Crystalline molecular order, in particular, can be accessed conveniently by introducing one or more crystallizable polymers into the block copolymer architecture to yield interesting directional control of mechanical, thermal, and optical properties from the anisotropic nature of polymer chains forming the crystals.
Macromolecules, 2004
Large area microdomain alignment in a ferroelectric liquid crystalline diblock copolymer (LCBCP) poly(styrene)-block-poly(isoprene-LC), (PS-PILC), incorporating a biphenyl 3-nitro-4-alkoxybenzoate LC mesogenic group and a non-LC block hexagonally packed cylinder microstructure, was successfully accomplished by application of a magnetic field at elevated temperatures. Small-and mediumangle X-ray scattering demonstrated that the PS cylinders in the LC matrix orient over large areas with their long axes perpendicular to the applied magnetic field. Correspondingly, the smectic layers of the LC mesophase in the matrix are also perpendicular to the field as the anchoring of the mesogens at the intermaterial dividing surface (IMDS) between the cylindrical microdomains and the matrix is planar (homogeneous) in this material. A negative diamagnetic anisotropy for the LC mesogens is inferred from the data. A lamellar sample was also studied and found to exhibit no preferred microstructural orientation when subjected to the magnetic field. This result is consistent with the orientational state degeneracy of planar anchoring of mesogens at the flat lamellar IMDS and closely parallels our prior results obtained by orientation of nonferroelectric LCBCPs using oscillatory shear.
Liquid crystalline side group block copolymers with a uniform polymer backbone
European Polymer Journal, 1996
Liquid crystalline triblock copolymers with LC inner block and amorphous outer blocks have been synthesized by "living" anionic polymerization and investigated using DSC, TEM, and small-angle x-ray diffraction. All samples of poly[styrene-block-2-(3-cholesteryloxycarbonyloxy) ethyl methacrylate-block-styrene] (PS-b-PChEMA-b-PS) show liquid crystalline behavior and phase separation between the blocks. Compared to triblock copolymers with PS inner block (PChEMA-b-PS-b-PChEMA) and diblock copolymers (PSb-PChEMA) the LC block copolymers with PS outer blocks have the same properties. The LC behavior and the morphology do not depend on the block arrangement; they are only influenced by the volume fractions of the blocks. Those samples in which the liquid crystalline subphase is not continuous (spheres) only a nematic phase was found, whereas in all samples with a continuous liquid crystalline subphase, the smectic A phase of the homopolymer was observed. 0 1996 John Wiley & Sons, Inc.