Neighbor Interactions and Internal Rotations in Polymer Molecules. II. Polyelectrolytes

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Abstract
The influence of the interaction between neighboring ionizable groups of a polyelectrolyte molecule on the internal rotations around its skeletal bonds is considered. It is found that the repulsion between neighboring groups tends to contract the molecule by twisting the molecular chain, and acts therefore against other forces which tend to extend the molecular dimensions. The quantitative analysis is based on calculating a grand partition function of the polyelectrolyte molecule, in which both the energy of interactions within each bond and the energy of interaction between neighboring ionizable groups are expressed as functions of the internal rotation angles. The grand partition function is used in obtaining the various averages of the trigonometric functions of the internal rotation angles which determine 〈h 2〉 according to the results of the previous paper (Part I). These averages are given as functions of the degree of ionization of the macromolecule. The effect of the internal rotation of the skeletal bonds on the potentiometric titration and buffering capacity of polyelectrolyte solutions is discussed.