Molecular engineering of side-chain liquid crystalline polymers by living polymerizations (original) (raw)
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Thermotropic liquid-crystalline polymers: A new type of mesomorphic macromolecular system
1980
A new approach to the synthesis of thermotropic liquid-crystalline (LC) polymers is described based on the polymerization of monomers containing various mesogenic groups attached to the backbone chain by flexible polymethylene spacer groups. Dozens of new LC polymers are described, including derivatives of polymethacryloyl L-lysine, cholesteric esters of long-chain aminocarboxylic acids, and other aromatic polymers. Phase transition temperatures, heats of fusion, and x-ray structural analysis were evaluated. Polymers exhibiting spontaneous optical anisotropy in the glasslike, elastic, and fluid states are described, and schemes of molecular packing in the LC phase are proposed. We show the possibility of realizing smectic, nematic, and cholesteric types of structures in these thermotropic LC polymers. A n LC structure for various comblike copolymers not having mesogenic groups at every monomeric unit was detected. The role of specific interactions in side groups and their mobility in allowing for the LC structure are discussed, and the necessity of having particular conformations of the macromolecules is shown to provide the LC structure in films made from various solutions.
Liquid crystalline block and graft copolymers
Acta polymerica, 1996
Since the first reports on the combination of liquid crystalline polymers in block (1985) and graft (1986) copolymers with amorphous and semi-crystalline polymers, the scientific interest has been focused on understanding how the size and type of the mesophase displayed by the liquid crystalline part(s) affects the LC + isotropic transition and the order in the LC domains themselves with respect to the morphology displayed. An overview of the work that has been done so far will be given, as well as a closer discussion of the interaction between morphology and LC phase behavior as evaluated on a large number of very well defined LC side group block copolymers. Furthermore, applications and results of mechanical and optical investigations are discussed.
Phase and orientational behaviors in liquid crystalline main-chain/side-group block copolymers
Journal of Polymer Science Part B: Polymer Physics, 1998
The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field.
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.
Side-chain liquid-crystalline alternating copolymers of mesogenic monomers: synthesis and properties
Macromolecules, 1993
Seven new vinyl ether and fumarate monomers containing different mesogenic groups were synthesized and copolymerized to obtain three series of side-chain liquid crystalline copolymers. The freeradical copolymerization of the monomers led to copolymers with nearly alternating structures, although a preferential incorporation of fumarate units was always observed. Alternating tendency and composition behavior of the copolymers were interpreted in terms of a penultimate unit effect model. By appropriately adjusting the stoichiometry of the feed mixture, copolymers with a random distribution of mesogenic groups were also prepared. Comparison of the nematic-to-isotropic transition temperature and entropy (Tm,A,Sm) of alternating copolymers revealed that the randomization of mesogenic groups produces a moderate but definite increase in both the stability (TN) and degree of order (A&) of the nematic mesophase.
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.
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).