State of Branching in Regular Polyisoprene

Fundamental data about the intrinsic viscosity in an ideal solvent of a fraction of polyisoprene with a cis unit content of approximately 85% comes from branching. Such polyisoprenes were obtained by the action of complex catalysts or by the action of lithium. We have established that the macromolecules of rubber which were obtained with a complex catalyst under the usual conditions appear on the whole to be linear. At the same time, in the samples investigated approximately 10% consists of colloidal strongly to crosslinked polymer. It can be seen that disturbance of the rate of polymerization during preparation of polyisoprene in the presence of complex catalyst brings about the formations of strongly branched polymer. Such polymer contain one branch per approximately 250 monomeric units. Knowledge of the features of the hydrodynamic behavior of macromolecules allows one to express the assumption that the trans units in the polyisoprene macromolecule obtained with a complex catalyst is not disposed in a random manner along the chain but forms a comparatively linear block of trans units. For the polymers investigated an equation for the dependence of the intrinsic viscosity in benzene on the molecular weight was obtained. For polymers which were obtained under action of a complex catalyst this was [η]=1.12×10⁻⁴×M^0.78 or ln M=5.063+1.28 ln [η] or for isoprene polymers from lithium [η]=1.33×10⁻⁴M^0.78 ln  or M=4.967+1.28 ln [η]⁠.