Influence of Stereochemical Composition on an Asymmetrically Substituted Polysilylenemethylene

摘要

Polymer science presents numerous examples of chains for which important physical properties depend on the stereochemical composition and stereochemical sequence. The polypropylenes, constructed from –CH2CH(CH3)-, present important examples. Upon cooling to a sufficiently low temperature from a one-component melt, the isotactic and syndiotactic samples become crystalline (with markedly different unit cells), but the atactic chain becomes an amorphous glass. Important differences are apparent at temperatures above the melting points of the crystals, where the miscibility of the two-component PP melts depends on the stereochemical composition of the chains. The binary mixture of atactic polypropylene and isotactic polypropylene is miscible in the melt, but replacement of either species with syndiotactic polypropylene can lead to immiscibility in the melt [1-4].