Macromolecular size of polyelectrolytes containing ammonium and sulfonic acid groups, as determined by light scattering

The macromolecular dimensions of fractionated polyelectrolytes poly(4-vinylpyridine) quaternized (PVPyQ), poly[(3-methacryloylamino) propyltrimethyl ammonium chloride] (PMPTA), poly(diallyl dimethyl ammonium chloride) (PDDA), and poly[(3-methacryloylamino) propyltrimethyl ammonium chloride-co-2-acrylamido-2-methyl-1-propanesulfonic acid] P(MPTA-co-APSA), were determined by light scattering, using aqueous electrolyte as solvent. PVPyQ, PMPTA, and P(MPTA-co-APSA) of various comonomer compositions were synthesized by radical polymerization. All polymers were fractionated by membrane ultrafiltration. Light scattering measurements on dialyzed solutions give good Zimm plots from which the average molecular weight, Mw, mean squared radius of gyration, 〈s2〉, and second virial coefficient, A2, were determined. No significant selective sorption of the electrolyte by the polyelectrolytes was detected. Positive A2 values are obtained in all cases, corresponding to good solvent conditions, however, the interpenetration function, Ψ, has low values (0.01–0.10), showing that the excluded volume effect is relatively low. In PDDA, the dependence of 〈s2〉 on Mw suggests that the coil of this polyelectrolyte is contracted by branching. In the ammonium–sulfonic copolymers, the comonomer stoichiometric feed 1:1 yields an insoluble copolymer (possible complex formation between amino and sulfonic groups). The soluble copolymers (with unbalanced comonomer compositions) have dimensions similar to the homopolymers, and not appreciably dependent on composition; hence no contraction due to complex formation is detected in these copolymers.