Complexation between poly(acrylic acid) and poly(vinylpyrrolidone): Influence of the molecular weight of poly(acrylic acid) and small molecule salt on the complexation

Poly(acrylic acid) (PAA) with different molecular weight and poly(vinylpyrrolidone) (PVP) were prepared by free radical polymerization using 2,2′-azoisobutyronitrile (AIBN) as initiator in anhydrous methanol for PAA, and in distilled water for PVP. Then, the complexation between PAA and PVP in aqueous solution was studied by UV transmittance measurement and fluorescence probe technique. The result shows that (1) at low pH, the formation of complexation between PAA and PVP bases on the intermacromolecular hydrogen bond and the composition of the formed complex is around 3:2 (the unit molar ratio of PAA to PVP) at pH 2.60 over the range of pH investigated. (2) The cooperative interaction through the formation of hydrogen bond among active sites plays an important role in complex formation, and depends on the pH of solution, the required minimum chain length of poly(acrylic acid). (3) The hydrogen bond is not affected by small molecular salt, which only affects those carboxylic groups without forming hydrogen bond on the PAA chain.