Macromolecular asymmetry

PROPERTIES OF SPECIAL INTEREST CiystaUine material with mechanical properties comparable to engineering plastics with rigid backbone of 4 helix similar to that of isotactic polyacetaldehyde, completely isotactic nature, and clean degradation to monomer at elevated temperature. Optical activity of polychloral based on macromolecular asymmetry is a new development the values of optical activity of these polymers is in the thousands of degrees. 

Conjugated polymers substituted by optically active groups, potentially useful as materials for enantiose-lective modified electrodes, have been prepared [174]. Some polymers have been synthesized by electropolymerization of enantiomeric monomers [175]. The polymers exhibited high stability and conductivity. The specific rotations are anomalously high, which has been interpreted by a macromolecular asymmetry arising from an helical polymer structure [176]. Electropolymerization of (S)-( -I- )-3-(2-methylbutyl)-thiophene provided another example of chiral polythiophene [177]. 

The properties of the optically active polymers are similar to other compounds except characteristics chain dimension and stmctural or conformational changes. Optically active polymers are very important due to its specific properties and attractive applications like creating of complex optical devices, enantiomeric separations as occurred in chromatographic methods as well as dispersion of the specific rotation provides the information regarding Cotton effect or conformational changes of the polymers. Similarly, configurational chirality also offers various kinds of information in terms of asymmetric carbon atom, macromolecular asymmetry and of the asymmetrical centres etc. 

Polymers that possess ordered or well defined helical structures are a subject of considerable experimental and theoretical interest [6]. Helical order is encountered among a wide variety of naturally occurring and synthetically derived macromolecules and is often responsible for the physical and biological properties of these systems. Isotactic polypropylene/ for example/ crystallizes in a 3/1 helical array with a repeat unit of 6.65 X. This structure is comprised of a racemic mixture of left- and right-handed helical forms. Consequently/ polypropylene lacks macromolecular asymmetry and is optically inactive in the solid state. 

B. Optically Active Helical Polymers with Macromolecular Asymmetry... 

Helical polymers with optical activity arising entirely from macromolecular asymmetry are a relatively new development and represent an exciting area for future study. From our oligomer studies. 

For a polydisperse solution—the hallmark of solutions of polysaccharides—s (and s ) will be a weight average [30,38,39]. If the solution contains more than one discrete (macromolecular) species—e.g. a mixture of different polysaccharides, the polydispersity will be manifested by asymmetry in the sedimenting boundary or, if the species have significantly different values for S2o,w. discrete boundaries are resolved (Fig. 2b [29]). 

Indeed, the existence of purely conformational optical activity is not a unique macromolecular requisite, being well known in low molecular weight atro-pisomerism. However, in polymers it assumes a very specific characteristic connected with the occurrence of cooperative effects which allow transmittance of molecular asymmetry along the chain to very long distances [3]. 

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