Abstract
Several methods for obtaining the size of macromolecules in dilute solution were applied to a series of linear polyisoprenes in the thermodynamically good solvent cyclohexane. The polymers, prepared by anionic polymerization, cover a wide range in molecular weight (1.5 X 104< M < 3.4 X 106) and have narrow molecular weight distributions (Mw/Mn< 1.1). The viscometric radius RVfthe radius of gyration Rg, the hydrodynamic radius RH,and the thermodynamic radius RTwere determined by viscometry and by static and dynamic light scattering. The molecular weight dependences of all four size measures are well-described by power laws (R ∞ Ma). The exponents obtained for RH, RV and RTagree fairly well with the predicted value of 0.588 for good solvents. The exponent obtained for RGis smaller, although RG/RH in fact changes rather little over the range of available data. The values ofRG/RH,RV/RH andRT/RHare in reasonable accord with the theory for self-avoiding coils and with results for polystyrene and poly (α-methylstyrene) in good solvents. © 1987, American Chemical Society. All rights reserved.