Interpolymer complexes of a graft copolymer with polyelectrolytes and equivalent blends of binary homopolymer complexes: A comparative study of their stability and thermodynamic parameters

Interpolymer complexes of acrylamide/vinyl alcohol graft copolymers (AAm/VA) were prepared with two typical polyelectrolytes, e. g. poly(methacrylic acid) (PMA) and poly(ethyleneimine) (PEI). The equivalent blends of the same composition as the graft copolymer complexes were also prepared by mixing stoichiometric portions of binary homopolymer complexes. The stability constant (K), degree of linkage (theta) and related thermodynamic parameters (e.g. standard free energy change Delta G(0), standard enthalpy change Delta H-0 and standard entropy change Delta S-0) were determined for each system by using Osada's method. The comparative study between graft copolymer complexes and equivalent blends indicated a considerable difference in these parameters. An interpretation of this discrepancy was sought in terms of copolymer effect, neighbouring group influence, and the nature of secondary binding forces upon interpolymer complexation.