Liquid-crystalline block copolymers

Lee KM, Han CD. Microphase separation transition and rheology of side-chain liquid-crystalline block copolymers. Macromolecules 2002b 35 3145-3156. 

Osuji C, Chao CY, Bita 1, Ober CK, Thomas EL. Temperature-dependent photonic bandgap in a self-assembled hydrogen bonded liquid-crystalline block copolymer. Adv Funct Mater... 

Scheme 14 Chemical structure of hydrogen-bonded side-chain liquid-crystalline block copolymer [28]...

ADAMS GRONSKI Amorphous—Liquid-Crystalline Block Copolymers 175... 

The critical thicknesses are thus in the range of the dimensions of lamellar, cylindrical or spherical mesophases in block copolymers with ordered morphologies. The question is whether the phase boundary between the amorphous and the liquid-crystalline phase in a block copolymer will exert an ordering effect as assumed in the original theory or rather a disordering influence. The latter case and transitions between the two cases have also been treated recently by an extension of the theory (5). Therefore a theoretical framework exists, within which the transition behaviour of amorphous / liquid-crystalline block copolymers can be described. 

ADAMS GRONSKI Amorphous—Liquid- Crystalline Block Copolymers... 

Xiang, M.L. et al., Surface stability in liquid-crystalline block copolymers with semifluorinated monodendron side groups, Macromolecules 33, 6106-6119, 2000. 

Figure 2. Structure of liquid crystalline block copolymers (LC-BCPs) (A) rod-coil diblock copolymer (B) rod-coil diblock copolymer with flexible spacer in the rod block (C) side group liquid crystal-coil (SGLC- coil) diblock copolymers (D) coil -rod-coil ABC triblock copolymers (predicted to be novel ferroelectric fluid by R. G. Petschek and K. M. Wiefling, Phys. Rev. Lett., 1987, 59(3), 343-346) (E) rod-rod diblock copolymer (one example of well-defined po-ly(n-hexyl isocyanate-fc-n-butyl isocyanate) rod-rod diblock copolymer was given by Novak et al. [68], however, no morphology studies were reported) (F) dendritic liquid crystal-coil (DLC-coil) diblock copolymer (not reported).

Table 3. Comparison of different synthetic methods for liquid crystalline block copolymers.

The field of liquid crystalline block copolymers has undergone great development in the last 10 years showing increasing attraction for both polymer chemists and polymer physicists. More work needs to be carried out in order to fully explore this class of materials. Novel architectures such as LC-BCP with a dendritic LC block, rod-rod block with different rod diameters, and other novel structures will prove to be very interesting. 

However, understanding the thermodynamics of phase separation in liquid crystalline block copolymers is in its infancy. The morphology of such block copolymers will be influenced by the competition between... 

Block copolymers of butadiene and styrene are therefore readily synthesized an-ionically, with either of the two monomers polymerized first. Precursor copolymers of poly(styrene-h/oc -butadiene) have been used to prepare well-defined liquid crystalline block copolymers by the same polymer analogous reaction described in Sec. 2.5 of this chapter (Scheme 21) [201-203]. Following anionic polymerization by sequential monomer addition, the polymer analogous reactions of the cholesterol (PS-PBCh) [201] and azobenzene (PS-PBAz) [203] derivatives were essentially quantitative, while that of the phenyl benzoate (PS -PBBz) block went to up to 94% conversion [202]. The polydispersities of the liquid crystalline copolymers (pdi= 1.13-1.23) were nearly as narrow as those of their precursor copolymers (pdi = 1.08 -1.21, M =8.09-9.2xl0 ) [201, 203]. 

The amorphous segment of microphase-separated amorphous/liquid crystalline block copolymers may influence the ordering of the mesogens at the interface, as well as the size and discreteness of that interface. Living copolymerizations are therefore being used to determine the effect of the morphology and domain size on the thermotropic behavior of side-chain liquid crystalline block copolymers. 

As summarized in Table 14, block copolymers of methyl methacrylate and 6-[4 -(4"- -butoxyphenoxycarbonyl)phenoxy]hexyl methacrylate (PMMA-PMOB) [90, 91] or 6-[4 -(4"-cyanophenylazo)phenoxy]hexyl methacrylate (PMMA-PMAC) [90] demonstrate that liquid crystalline block copolymers behave similarly to standard block copolymers. That is, entry 1 shows that short blocks are miscible, such that this PMMA-PMOB copolymer exhibits a... 

Tian YQ, Watanabe K, Kong XX, Abe J, lyoda T. 2002. Synthesis, nanostructure, and functionality of amphiphilic liquid crystalline block copolymers with azobenzene moieties. Macromolecules 35 3739 3747. 

Chao C, Li X, Ober C, Osuji C, Thomas EL. 2004. Orientational switching of mesogens and microdomains in hydrogen bonded side chain liquid crystalline block copolymers using AC electric fields. Adv Funct Mater 14 364 370. 

Han YK, Dufour B, Wu W, Kowalewski T, Mat qaszewski K. 2004. Synthesis and characterization of new liquid crystalline block copolymers with p cyanoazobenzene moieties and poly(n butyl acrylate) segments using atom transfer radical polymeriza tion. Macromolecules 37 9355 9365. 

Watanabe K, Yoshida H, Kamata K, lyoda T. 2005. Direct TEM observation of perpendicularly oriented nanocylinder structure in amphiphilic liquid crystalline block copolymer thin films. Trans Mater Res Soc Jpn 30 377 381. 

Amorphous-Side-Chain Liquid Crystalline Block Copolymers. 52... 

Other alignment methodologies have been cited [82], including optical alignment of liquid crystalline block copolymers, and temperature gradients [83, 84], but are less general or practical. 

He Xiao-Hua., Wang Xia-Yu. (2002). Synthesis and Properties of Thermotropic Liquid-Crystalline Block-Copolymers Containing Links of Polyaiylate and Thermotropic Liquid-CtystaUine Copolyester (HTH-6) Natur. Sci. J. Xiangtan Univ, 23(1), 49-52. 

FTIR polarisation spectroscopy was used to study the orientational behaviour of the different constituents of a liquid crystalline block copolymer (copolyester-imide) during uniaxial elongation at different temperatures. Differences in the degree of alignment (as well as in the response to the application of the mechanical load) were observed. With increasing temperature, the level of the applied stress and the induced degree of orientation decreased, while the differences in the orientational behaviour of the mesogen and the flexible spacer were retained (243). 

Time-resolved FTIR is used to study the structure and dynamics of ferroelectric liquid crystalline block copolymers. From analysis of the dynamic dichroism of the FTIR spectra, it was concluded that the components in the PS microphase are oriented randomly while the liquid aystalline groups form an ordered phase. The switching is of an electroclinic type, in which the tilt angle and the mesogenic motion increase with temperature, especially if the PS block is heated above Tg. The orientation of the liquid crystalline block after... 

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