Characterization of Chain Flexibility Theory

Polymers exhibit conformations ranging from tight coils to highly extended structures such as rigid rods and rigid helical chains. The parameters and, to some extent, the methods utilized for evaluating the degree of chain flexibility are usually different for flexible versus stiff chains. 

For flexible polymers the most common parameter in use is Flory s [1,10] characteristic ratio defined as 

The relative contributions of fixed bond angles and hindered rotation can be elucidated by modification of the freely jointed chain model. Eyring [13] showed that when N is very large R can be calculated as 

In light of the above, an alternative chain flexibility parameter, which is commonly used, is the conformation (steric) factor ct 

As Flory has pointed out [14], the use of Coo is to be preferred over ct. This is because small changes in bond angles can lead to large changes in a, and bond angles are rarely known to within more than a few degrees. 

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