2ND VIRIAL-COEFFICIENT OF ARBORESCENT POLYSTYRENES AND ITS TEMPERATURE-DEPENDENCE

The solution behavior of arborescent (highly branched) polymers was ex amined in terms of Az variation with polymer structure, solvent type, and temperature. Two series of graft polymers in three successive gene rations were examined, with side chains of either 5000 (S05 series) or 30 000 (S30 series). Scaling relationships A(2) proportional to M-w(a ) were found for both series, with a = -0.94 or -0.97, consistent with rigid-sphere behavior. Temperature-dependent measurements were carrie d out in cyclohexane and in toluene, to allow decomposition of A(2) in to its enthalpy (A(2,H)) and entropy (A(2,S)) components. In cyclohexa ne, the magnitudes Of A(2,H) and A(2,S) were mainly affected by the br anching functionality of the polymers, and less significantly by the m olecular weight of the side chains. Furthermore, the temperature depen dence of A(2) in bath solvents was found to be more strongly influence d by branching functionality than by the molecular weight of the polym ers. Variations in the Theta temperature for polymers of low branching functionality in cyclohexane are consistent with the trends observed in star-branched polymers. However, no measurable Theta temperature wa s observed for a polymer with a branching functionality f(w) = 180.