Hyperbranched liquid-crystalline

Fig. 26. Percec s AB2 monomers for the synthesis of hyperbranched liquid crystalline den-drimers... 

Fig. 27. Percec s hyperbranched liquid crystalline dendrimer that forms isotropic and nematic phases based on monomeric gauche and anti conformations...

Scheme 6.9. Ringsdorf et al. s[434 preparation of hyperbranched liquid crystalline polymers possessing chiral capping units.

Scheme 7.6. Preparation of a hyperbranched liquid crystalline polymer possessing mesogenic building blocks and chiral termini.

Keywords Liquid crystalline polyester, liquid crystalline polymer blend, liquid crystalline polymer composite, hyperbranched liquid crystalline polymer, mechanical stability, thermal stability, reactive liquid crystalline polymer... 

Macromolecules dendritic, 285 hyperbranched, 284-286 Main-chain liquid crystalline polymers, 49 Main-chain polyester LCP mesogenic units, 50... 

Dendritic polymers are most often reported to be amorphous, which can be anticipated from their highly branched architecture. However, some exceptions are presented in the literature. Percec et al. [34,35] reported on liquid crystalline (LC) hyperbranched polymers where the LC-phase was achieved by conformational isomerism. Various repeat units of A2B type have been used where a flex-... 

Kim reported on liquid crystalline properties observed for hyperbranched aromatic amides obtained from 3,5-diaminobenzoic acid and derivatives thereof. The resulting polymers exhibited nematic liquid crystalline phases [89]. 

Branching in polymers generally reduces the crystallization tendency for conventional polymers. Therefore, hyperbranched polymers were first believed to behave as amorphous polymers due to the highly branched backbone. Several papers have, however, shown that both liquid crystalline and crystalline hyperbranched polymers can be made from some special A B monomers or by attachment of crystallizable end groups. 

Percec et al. have described the possibility of making hyperbranched polymers which exhibit liquid crystalline phases [34, 35]. They made hyperbranched polyethers based on an A B monomer having both a spacer and a... 

Hyperbranched polymers are often referred to as amorphous polymers since the branching of the backbone reduces the ability to crystallize in the same manner as linear polymers. Some exceptions have, however, been presented where the polymers have been modified to induce liquid crystallinity [34,35] or crystallinity [36] (Sect. 3.6.1). 

Side-chain liquid-crystalline polymers with controlled molecular weights have been obtained by the polymerization of FM-25 with 1-22 (X = Br)/CuBr/ L-3 in the bulk at 100 °C, to examine the thermotropic transition as a function of the MWD.324 Second-order nonlinear optical materials with branched structure were prepared by the copper-catalyzed radical polymerization of FM-26 and FM-27 using hyperbranched poly[4-(chloromethyl)styrene] as a multifunctional initiator.325... 

Ujiie S, Osaka M, Yano Y et al (2000) Ionic liquid crystalline systems with branched or hyperbranched polymers. Kobunshi Ronbimshu 57 797-802... 

Marcos M, Alcala R, Barbera J et al (2008) Photosensitive ionic nematic liquid crystalline complexes based on dendrimers and hyperbranched polymers and a cyanoazobenzene carboxylic acid. Chem Mater 20 5209-5217... 

The first thermotropic liquid-crystalline dendrimer, 15, shown in Fig. 17, was reported by Percec and Kawasumi for a hyperbranched polyether structure that consisted of an AB2 monomer, with a mesogenic unit based on confer-... 

Fig. 9.14 Chemical structures of oxetane-functionalized low-molecular-weight hole conductors a) derivatives ofTPD [34, 35, 36], b) hyperbranched triarylamine [35], and c) liquid-crystalline bisbenzthiazole derivative [64].

The units giving rise to the liquid-crystalline behavior can be in the side chains. Although most of the polymers studied have been linear, there has been some work on hyperbranched or comb-like structures. The orientation of the mesogenic groups is important. " Frequently backbones include siloxanes and acrylates, " but a variety of other structures... 

It could be envisioned that one of the future trends in development of TPEEs will continue to be modification of chemical structure of these copolyesters. Continuation of the development of advanced materials with various molecular structures is important from a fundamental and industrial perspective. It can be expected that one of the future trends could be the introduction of hyperbranched and dendritic segments into these block copolymers. Also, some progress has been achieved in incorporation of liquid crystalline sequences into the backbone or as side chains. 

Chen, Y., Shen, Z., Gehringer, L., Frey, H. and Stiriba, S.-E. (2006) Supramolecular thermotropic liquid crystalline materials with nematic mesophase based on methylated hyperbranched polyethylenimine and mesogenic carboxylic acid , Macromol. Rapid Comm., 21,69-75. 

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