Helical rigidity

Research Focus Preparation of materials having a helical rigid-rod shape that exhibit cholesteric or nematic crystal-phase behavior. 

Formation of a helical rigid rod Selective polymerization of CH over BH... 

In contrast to the zigzag formation of linear hydrocarbons, long perfluoroalkyl chains are helical, rigid and rod-like structures [49, 52]. This structure, due to the steric repulsion between fluorine atoms, consists of a full helical twist every 13 carbon atoms [49,52]. Short... 

This approach can also be extended to the preparation of multiple rotaxanes down a single, flexible, filamentous ligand. However, as with helicates, rigid or semiflexible spacers are needed... 

The helical rigid-rod polymers have a high DP even in very dilute solution (10 6 M in hexane), due to their large association constant (5 108 L/mol). When... 

Paramyosin behaves as an extremely asymmetric a-helical rigid rod in solution, as shown by its hydrodynamic and light-scattering properties 22, 36), its dynamic viscoelastic behavior 1,2), the hypochromicity of its far-ultraviolet absorption spectrum 50), and its optical rotatory properties 12, 56). 

PROPERTIES OF SPECIAL INTEREST Chiral-helical rigid-rod structure and yields liquid crystals in solution. Potentially useful as models for the understanding of the structure and properties of biological molecules. Unreachve toward hydrogenation at ambient temperature and pressure and resistant toward acid hydrolysis. One of the few soluble polyisocyanides of high molecular weight. ... 

A unique but widely studied polymeric LB system are the polyglutamates or hairy rod polymers. These polymers have a hydrophilic rod of helical polyglutamate with hydrophobic alkyl side chains. Their rigidity and amphiphilic-ity imparts order (lyotropic and thermotropic) in LB films and they take on a F-type stmcture such as that illustrated in Fig. XV-16 [182]. These LB films are useful for waveguides, photoresists, and chemical sensors. LB films of these polymers are very thermally stable, as was indicated by the lack of interdiffusion up to 414 K shown by neutron reflectivity of alternating hydrogenated and deuterated layers [183]. AFM measurements have shown that these films take on different stmctures if directly deposited onto silicon or onto LB films of cadmium arachidate [184]. 

Top entering mixers are heavy duty equipment. They are usually fixed to a rigid structure or tank mounting. Either radial flow or axial flow turbines may be used. Speeds vary from 50 to 100 rpm and usually require a double set of helical gearing or a single set of worm gears to achieve these low speeds. Therefore, they are more expensive than single reduction mixers. 

Fig. 2.47 The (P)-2.5-helical structure of N.N -linked oligoureas as determined by NMR meaurements in pyridine-c/5. (A) Stereo-view along the helix axis of a low energy conformer of nonamer 178 generated by restrained molecular dynamics calculations. (Adapted from [274]). The helix is characterized by (i) a rigid +)-SYnclinal arrangement around the C(a)-...

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