Light‐scattering measurements on solutions of natural and synthetic polyisoprenes

The light‐scattering behavior of solutions of natural and synthetic cis ‐1,4 polyisoprene is described. For milled natural rubber values of M̄ w increase as the solvent power of the solvent is increased and, at the same time, the second virial coefficient tends to zero. These effects may be due to compact (e. g., branched) structures. With unmilled natural rubber there is evidence for the existence of microgel. Synthetic polyisoprene shows the behavior expected of a linear polymer.