The sedimentation constantss0at infinite dilution and the intrinsic viscosities [&eegr;] of five fractions of polyisobutylene have been determined in cyclohexane, a good solvent. Their osmotic molecular weights ranged from 3.1×104to 1.4×106. Under the assumption that the effective hydrodynamic radii vary as the average linear dimensions of the molecule,f0/&eegr;0=P(⟨r2⟩)½and[&eegr;]=&PHgr;(⟨r2⟩)32/M, wheref0is the frictional coefficient, &eegr;0is the viscosity of the solvent, ⟨r2⟩ is the mean‐square end‐to‐end distance of the molecule, andPand &PHgr; are constants. In confirmation,s0[&eegr;]⅓/M⅔is constant throughout the molecular weight range investigated. Furthermore, &PHgr;⅓P−1=2.5×106. The close agreement of this quantity with values for four other systems reported in the literature indicates thatP,like &PHgr;, is a universal constant for flexible chain molecules. It follows also that the observed proportionality ofs0(or ofM/f0) toM0.42instead of toM½occurs because of intramolecular interactions which cause the molecule in solution to be expanded by a factor &agr; which increases with molecular weight.The above theory accounts for both the sedimentation and intrinsic viscosity behavior of flexible chain molecules in a satisfactory manner. Neither the Kirkwood‐Riseman nor the Debye‐Bueche theories succeeds in doing so.
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