A light scattering study of alfin polybutadiene

The weight average molecular weights, M u , of some unfractionated Alfin polybutadienes ranged from 5 to 20 million. The ratio of the mean‐square radius of a linear polybutadiene molecule to its molecular weight in a thermodynamically neutral solvent is estimated to be R 2 / M = 2.2 (±0.3) × 10 −17 cm. 2 g. −1 mole. The relationship [η] = 0.125 M v 0.77 between intrinsic viscosity and molecular weight is estimated for linear polybutadiene in cyclohexane at 25°. The average value of Φ′, the parameter in the Flory‐Fox theory of intrinsic viscosity, is found to be 3.6 × 10 24 mole −1 (or Φ = 2.5 × 10 23 mole −1 ) for linear molecules and appears to increase with branching. Branching is found to decrease with increasing conversion for this polymer. Values of the osmotic second virial coefficient, A 2 , are discussed in connection with theoretical predictions. Various corrections to measured quantities required because of polydispersity in polymer samples are presented.