Sedimentation analysis of 1,4‐ cis ‐polybutadiene in a theta solvent, diethyl ketone at 10.3°C

A sedimentation and viscosity study of 1,4‐ cis ‐polybutadiene (having 95% 1,4‐ cis units) in a θ‐solvent diethyl ketone (DEK) at 10.3°C. is reported. The limiting sedimentation coefficient s o and the limiting viscosity number [η]θ of the monodisperse sample of this polymer in the given θ‐solvent as functions of its molecular weight M are derived from data on polydisperse fractions by application of the method described by Homma et al. The results are: s o = 0.530 × 10 −15 M 1/2 (in sec.) and [η]θ = 1.60 × 10 −3 M 1/2 (in dl./g.). Substitution of the experimental data into the well‐known Mandelkern‐Flory equation yields 1.74 × 10 6 for the familiar parameter Φ 1/3 P −1 , which is about 30% lower than the usually accepted value (2.5 × 10 6 ).