Investigation of pH dependence of poly(acrylic acid) conformation by means of electric birefringence

Conformational transitions of polyacrylic acid with two different molecular weights (PAA100 and PAA250) have been investigated by means of electric birefringence method. The conformation of the polymer chains has been found to depend on pH, showing slight increase in the chain length up to a degree of neutralization 0.3 (ca. pH 6) and, after an almost plateau value, sharply increase to a maximum near the equivalence point. This was attributed to changes in the degree of polyelectrolyte ionization with variation of pH. A model was proposed that interprets the experimental results in the light of the counterion condensation approach.