Stereochemistry of Polymers
When a polymer has stereochemical isomerism within the chain, its properties often depend on the stereochemical structure. Thus, the analysis of the Stereo-Chemistry of polymers is important and NMR spectroscopy has been the most valuable tool for this purpose. It is a general rule that for a polymer to crystallize, it must have highly regular polymer chains. Highly irregular polymers are almost inevitably amorphous. Polymer chains can have isomeric forms that decrease the regularity of the chains.
There are three important forms of isomerism in polymers.
·Sequence Isomerism (Head-to-Tail or Head-to-Head)
Stereochemical formulae for polymer chains are shown as Fischer projections rotated through 90o i.e. displayed horizontally rather than vertically, or as hypothetical extended zigzag chains the latter occasionally give a clearer indication of the three-dimensional arrangement.