Polymers Large molecules atactic

In small molecules, the absence of optical activity at some wavelength for chiral molecules is almost always ascribed to the fact that the ensemble of molecules contains equal number of both enantiomers - a racemic mixture. However, in a chain longer than a hundred or so units, statistical considerations demonstrate that the presence of mirror image isomers of enantiomeric chains, and therefore for racemic states, is virtually impossible, which leaves the absence of optical activity in atactic vinyl polymers an open question. The answer turned out to be one that never arises in small molecule stereochemistry an ensemble of polymer chains of an atactic polymer is a mixture of diastereomeric chains, each one chiral but without the enantiomeric chain present in the ensemble. If a single chain could be studied by a method that could reveal chiral optical properties, optical activity should be observed. However, each chain in the ensemble (a very large number of chains) would exhibit a different optical activity, even of differing sign. The optical activity properties of a sample of an atactic polymer would arise as the sum... 

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