Polysiloxane, liquid crystalline

The side chain polysiloxane liquid crystalline polymers PI, P2 and P3 composed of the above three ferroelectric liquid crystals as the side groups exhibit the ferroelectric liquid crystal phase, their chemical formulae being respectively. 

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

A number of polyphosphazenes of repeat unit [-PRR N-] also exhibit liquid-crystalline phases [166-168]. It is certainly intriguing that apparently the only classes of flexible chains that extensively exhibit liquid-crystalline phases are the polysiloxane and polyphosphazene semi-inorganic polymers. 

Kumar U, Kato T, Frechet JMJ. Use of intermolecular hydrogen bonding for the induction of liquid crystallinity in the side chain of polysiloxanes. J Am Chem Soc 1992 114 6630-6639. 

Other crystalline inorganic polymers such as poly(dichlorophosphazene), poly(aryloxyphosphazenes), liquid crystalline polysiloxanes and poly(dichloro-silane) have also been studied by X-ray diffraction methods, enabling the conformations in the crystallites in the solid state to be established. 

Finkelmann, H. and Rehage, G. Investigations on liquid crystalline polysiloxanes, I, Synthesis and characterization of linear polymers. Makromol. Chem. Rapid Commun. 1, 31 (1980)... 

Scheme 12 Synthesis of crown-containing liquid crystalline polysiloxane poly (23)...

Some polysiloxanes form liquid-crystalline phases because of the presence of relatively stiff side chains.168-176 They have been much studied, particularly with regard to the effect of deformation of the elastomeric polysiloxane phase on the mesomorphic behavior exhibited by the side chains. 

Jones, B.A., Bradshaw, J.S., Nishioka, M., and Lee, M.L., Synthesis of smectic liquid-crystalline polysiloxanes from biphenylcarboxylate esters and their use as stationary phases for high-resolution gas chromatography, J. Org. Chem., 49, 4947, 1984. 

K. Markides, M. Nishioka, et al., Smectic biphenylcarboxylates ester liquid crystalline polysiloxane stationary phase for capillary gas chromatography, Anal. Chem., 57 1296-1299(1985). 

Liquid Crystalline Polysiloxane Surfaces and Edges of a Smectic Layered Ferroelectric... 

Beside the synthesis of linear polysiloxanes, hydrosilylation was also nsed to obtain liquid crystalline elastomers. This can be performed in two ways, either a one pot reaction involving a diolefln together with the functionalized mesogen or a two step process involving first the synthesis of a linear polysiloxane, bearing adequate functions for a further crossfinking. For example, a photosensitive group such as benzophenone could be introduced (Fig. 5, x and y are theoretical values). In order to ensure a full conversion in silane, the time of reaction was increased here to 65 h [17]. 

Petn, A., Kummer, S., Anneser, H., Eeiner, E, and Btauchle, C. Photoinduced reorientation of cholesteric liquid crystalline polysiloxanes and applications in optical information storge and second harmonic generation. Ber. Bunsenges. Phys. Chem. 97, 1281 (1993). 

The concept of a side chain liquid crystal polymer has been demonstrated in a number of laboratories and is well documented in the literature (J ). Most of the side chain liquid crystalline polymers reported to date contain polysiloxane, polyacrylate or polymethacrylate main chains. More recent studies on the effect of backbone flexibility now include the use of flexible poly(ethylene oxide) or more rigid poly( a-chloroacrylate) chains. 

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