Side-chain 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. 

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

Morphology and Thermotropic Behavior of Side-Chain Liquid Crystalline Block Copolymers... 

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. 

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. 

Kishore KT, Chen X, Li CY, Shen Z, Wan FX, Zhou QF, Rong L, Hsiao BS (2009) Influence of Ic content on the phase stmctures of side-chain liquid crystalline block copolymers with hent-core mesogens. Macromolecules 42 3510-3517... 

Verploegen E, Zhang T, Jung YS, Ross C, Hammond PT. ControUmg the morphology of side chain liquid crystalline block copolymer thin films through variations in liquid crystalline content. Nano Lett 2008 8 3434-40. 

Properties have been determined for a series of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and poly [3,3-bis(methoxymethyl)oxetane]-(ro-tetrahydrofuran. The block copolymers had properties suggestive of a thermoplastic elastomer (308). POX was a good main chain for a well-developed smectic liquid crystalline state when cyano- or fluorine-substituted biphenyls were used as mesogenic groups attached through a four-methylene spacer (309,310). Other side-chain liquid crystalline polyoxetanes were observed with a spacer-separated azo moiety (311) and with laterally attached mesogenic groups (312). 

Liquid crystallinity can be attained in polymers of various polymer architectures, allowing the chemist to combine properties of macromolecules with the anisotropic properties of LC-phases. Mesogenic imits can be introduced into a polymer chain in different ways, as outhned in Fig. 1. For thermotropic LC systems, the LC-active units can be connected directly to each other in a condensation-type polymer to form the main chain ( main chain liquid crystalline polymers , MCLCPs) or they can be attached to the main chain as side chains ( side chain liquid crystalline polymers , SCLCPs). Calamitic (rod-Uke) as well as discotic mesogens have successfully been incorporated into polymers. Lyotropic LC-systems can also be formed by macromolecides. Amphiphihc block copolymers show this behavior when they have well-defined block structures with narrow molecular weight distributions. 

Komiya et al. described the living ROMP synthesis of AB-type block copolymers that contain side chain liquid crystalline polymer blocks and amorphous blocks [62]. Norbornene (NBE), 5-cyano-2-norbornene (NBCN) and methyl-tetracyclododecene (MTD) were used for the amorphous polymer blocks, while I-n (n=3,6) were used for the SCLCP block (see Fig. 9). Initiator 1 was used for the ROMP. Block copolymers with monomer ratios from 75/25 to 20/80 (amor-... 

Block Copolymer-Based Hydrogen-Bonded Side-Chain Liquid-Crystalline Copolymers... 

The synthesis and some thermal properties of three series of block copolymers comprising both main-chain and side-chain liquid-crystalline (LC) blocks in the same macromolecular structure are described. The former block is a semiflexible LC polyester (block B), and the latter is an LC polymethacrylate (block A) containing a variously substituted mesogenic unit. The two structurally different blocks were partly phase-separated within the glassy and LC states and underwent distinct phase transitions. Significant deviations of the transition enthalpies relative to those of the corresponding homopolymers suggest the occurrence of a more or less diffuse interphase which may depend on the nature of the mesophase formed. 

Fig. 2. Selected architectures of block copolymers (a) diblock (b) triblock (c) comb copolymer consisting of flexible chains (d) rod-coil diblock copolymer consisting of a rodlike block and a coil-like block (e) hairyrods, i.e., comb-block copolymers consisting of rodlike backbone and coil-like side chains and (f) LC coil with a side-chain liquid crystalline (LC) block and a flexible block. Many other variations have been introduced, such as multiblock copolymers, block copolymers consisting of several rodlike blocks, or star-shaped block copolymers. Comb-coil block copolymers with dense packing of side chains are also denoted as molecular bottle brushes, as is illustrated in (g) by a simulated structure of an isolated molecule dissolved in a solvent. (Courtesy of Mika Saariaho.)...

The possibilities are not restricted to flexible polymers. One of the blocks can be rigid rodlike, in which case a rod-coil block copolymer [54-57] is formed if the architecture is of the diblock type (see Section 2.3.1 for another example [15]). Other interesting cases comprise diblock copolymers where one of the blocks is a side-chain liquid-crystalline polymer [4, 58-62]. Finally, we mention the important class of hairy rods obtained for a comb copolymer architecture consisting of a rigid backbone and flexible side chains [4, 58-61, 63-66], to be discussed in more depth later in this review. 

Hao X, Stenzel MH, Bamer-Kowolhk C, Davis TP, Evans E. Molecular composite materials formed from block copolymers containing a side-chain liquid crystalline segment and an amorphous styrene/maleic anhydride segment. Polymer 2004 45 7401-15. 

Strange enough, so far there are no books entirely devoted to condensation TPEs and the latter are considered only in chapters of more general works. The most important TPEs prepared by polycondensation are the subject of several chapters of this book polyester-based TPEs, poly(amide-6-ethers), polyurethanes, etc. However, some less known condensation TPEs are described in Chapter 2 metal-containing macrocycles as monomers, liquid crystalline side chains, metallo-supramolecular block copolymers, as well as the use of enzymatic catalysis or of microorganisms. 

Figure 8.16 Block copolymers comprising both side-chain and main-chain liquid-crystalline (LC) blocks.

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