Formation of interpolymer complexes

Abstract

Interpolymer complex formations of poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) with oligocations as well as poly(ethylene oxide) (PEO), and poly-(N-vinyl-2-pyrrolidone of various chain lengths were studied. For the case of complexation between PMAA and oligocations, the standard free energy change for the complexation ΔG° was found to be linearly dependent on the number of interacting sites, n. The stability constant K for complex is expressed as K = Ae^Bnwhere A and B are constants which depend on the chemical structure of the polyelectrolytes. For the case of complex formation through hydrogen bonding, the degree of linkage Θ, defined as the ratio of the binding groups to the total of potentially interacting groups, and the stability constant K of the polymer-polymer complexes both in aqueous and aqueous-alcoholic media were determined as a function of temperature by means of potentiometric titration. It was found that Θ and K were strongly dependent on chain length, temperature, and medium, and that hydrophobic interaction was a significant factor for the stabilization of the complexes. The enthalpy and entropy changes as well as the cooperativity parameter of the complex formation, derived by use of a one-dimensional Ising model, were also calculated. Both of these two types of interpolymer complexes were found to be in a nonequilibrium state for a considerable period of time, and they grow to an interesting morphological structure after successive aggregation. A mechanism for the complexation process was proposed in terms of the cooperative interaction.