Siloxane Containing Liquid Crystalline Polymers

Finkelmann et al. 256 274,2781 have also investigated the synthesis and the characteristics of siloxane based, crosslinked, liquid crystalline polymers. This new type of materials displays both liquid crystallinity and rubber elasticity. The synthesis of these networks is achieved by the hydrosilation of dimethylsiloxane-(hydrogen, methyl)siloxane copolymers and vinyl terminated mesogenic molecules in the presence of low molecular weight a,co-vinyl terminated dimethylsiloxane crosslinking agents156  

Covalently crosslinked siloxane containing liquid crystalline networks with elastic properties were prepared 349). In all of the networks liquid crystalline phases of the linear precursors were retained. For low degrees of crosslinking the phase transition temperatures remained nearly unchanged, whereas higher degrees of crosslinking reduced the phase transition temperatures. 

Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351 . The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

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Racks, C., Siloxane-Containing Liquid Crystalline Polymers (LCPs). In Advances in Functional Heterochain Polymers, Cazacu, M., Ed. Nova Science New York, 2008 pp 33-66. 

Electrical properties have been reported on numerous carbon fiber-reinforced polymers, including carbon nanoflber-modified thermotropic liquid crystalline polymers [53], low-density polyethylene [54], ethylene vinyl acetate [55], wire coating varnishes [56], polydimethyl siloxane polypyrrole composites [50], polyacrylonitrile [59], polycarbonate [58], polyacrylonitrile-polycarbonate composites [58], modified chrome polymers [59], lithium trifluoromethane sulfonamide-doped polystyrene-block copolymer [60], boron-containing polyvinyl alcohols [71], lanthanum tetrafluoride complexed ethylene oxide [151, 72, 73], polycarbonate-acrylonitrile diene [44], polyethylene deoxythiophe-nel, blends of polystyrene sulfonate, polyvinyl chloride and polyethylene oxide [43], poly-pyrrole [61], polypyrrole-polypropylene-montmorillonite composites [62], polydimethyl siloxane-polypyrrole composites [63], polyaniline [46], epoxy resin-polyaniline dodecyl benzene sulfonic acid blends [64], and polyaniline-polyamide 6 composites [49]. 

Percec V, Heck J (1990) Liquid crystalline polymers containing mesogenic units based on half-disc and rod-Uke moieties. 2. Synthesis and characterization of poly 2-[3,4,5-tri p-(n-dodecan-1 -y loxy)benzy loxy ]benzoate]-7 - p-11 -undecan-1 -y loxy )benzoate]naphtha-lenejmethyl siloxane. Polym Bull 24(3) 255—262. doi 10.1007/BF00306572... 

The study by Percec, Tomazos and Willingham (15) looked at the influence of polymer backbone flexibility on the phase transition temperatures of side chain liquid crystalline polymethacrylate, polyacrylate, polymethylsiloxane and polyphosphazene containing a stilbene side chain. Upon cooling from the isotropic state, golymer IV displays a monotropic nematic mesophase between 106 and 64 C. In this study, the polymers with the more rigid backbones displayed enantiotropic liquid crystalline behavior, whereas the polymers with the flexible backbones, including the siloxane and the polyphosphazene, displayed monotropic nematic mesophases. The examples in this study demonstrated how kinetically controlled side chain crystallization influences the thermodynamically controlled mesomorphic phase through the flexibility of the polymer backbone. 

Pandey, S. Kolli, B. Mishra, S. P. Samui, A. B., Siloxane Polymers Containing Azo Moieties Synthesized by Click Chemistry for Photo Responsive and Liquid Crystalline Applications. J. Polym. Sci., Part A Polym. Chem. 2012,50, 1205-1215. 

Class jS, orthogonal liquid crystal polymers. As class a, they also contain liquid crystal groups in the main chain however, these groups are here approximately perpendicular to the backbone. Two kinds of such polymers are obtained by Ringsdorf and coworkers, based on the siloxane chain and also polyesters. In this second series it appears that crystalline and liquid crystalline regions coexist until isotropization at the clearing temperature occurs. 

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