Chain Model for Polyelectrolytes. IV. Skeletal Distribution Effects in Equimolar Polyampholytes

The chain model for polyelectrolytes developed in the preceding papers of this series is extended to equimolar polyampholytes of general skeletal structure. The present development differs from that for copolymers consisting of a regular alternation of acidic and basic groups in that the environments of the individual groups will depend upon the local skeletal distribution. This inhomogeniety affects both the titration and configurational properties, primarily through a displacement of the acid‐base equilibria. In addition, locally inhomogeneous skeletal structure can cause either an expansion or contraction at the isoelectric point, although strong deviation from random copolymerization is necessary to realize a large effect. No experimental data are available with which to compare the theory, but a calculated titration curve and expansion ratio are presented for a hypothetical polyampholyte of random skeletal structure. It is found that the titration curve of the random copolymer exhibits more buffer action near the isoelectric point than does a similar regularly alternating copolymer, but that the configurational properties and the effect on the titration curve of increased ionic strength are quite similar to the corresponding effect for the regularly alternating copolymer. It is pointed out that substantial change in titration properties may be realized by alterations in the skeletal structure of a copolymer.