COMPLEXATION OF ACRYLIC-ACID COPOLYMERS WITH POLYBASES - IMPORTANCE OF COOPERATIVE EFFECTS

The formation of polymer complexes stabilized through hydrogen bonds was studied in the case of homopolymer/copolymer couples. We used two homopolymers, poly(ethylene oxide) (PEO) and poly(N-vinylpyrrolidone) (PVP), as hydrogen-bond acceptors and several copolymers of acrylic acid (AA) with vinylsulfonic acid (VS) or with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as hydrogen-bond donors. Under acidic conditions (e.g., pH congruent-to 3), the strong-acid groups (VS or AMPS) are dissociated and uncomplexable, while the carboxylic groups (COOH) can be complexed by the polybase (PEO or PVP). Potentiometric and viscometric studies were performed and it was found that the properties and the structure of the complexes formed depend on the experimental parameters: molar content of sulfonated monomers, concentration of polyacid and polybase, molecular weight of polymers, and nature of polybase. There is a dramatic influence of the content of uncomplexable groups on the complexation reaction. In some cases, the presence of even a low content of sulfonate groups in the polyacid chain prevents complex formation: for instance, a polyacid containing more than 10% of sulfonate groups cannot be complexed by PEO. Upon experimental conditions, the structure of the complex ranges from a compact form, implying a low viscosity and occasionally precipitation, to a highly branched gellike form, leading to an important increase in viscosity. The results obtained with the above polybase/copolyacid systems seem to be similar to experimental results concerning the complexation of polybases with partially neutralized poly(acrylic acid), and they are in good agreement with predictions of a theoretical model previously reported.