Branching in isoprene polymers of regular structure

Branching in isoprene polymers with cis‐1,4 content of ∼85% obtained by polymerization in the presence of a complex catalyst and under the action of lithium was determined by studying intrinsic viscosity of polymer fractions in an ideal solvent. It was established that macromolecules of polyisoprenes obtained with a complex catalyst under polymerization conditions commonly used are essentially linear. At the same time, in the polymers studied, there is a fraction (∼10% of the polymer weight) consisting of colloidal size particles formed by highly crosslinked polymer molecules. A rubber sample of the above type prepared with uncontrolled dosage of catalyst components and at elevated temperature proved to be a highly branched polymer. The discovered features in hydrodynamic behavior of macromolecules in benzene solutions suggest that trans units in the macromolecules of polyisoprenes obtained in the presence of the complex catalyst are not randomly distributed along the chain but form comparatively long blocks. The intrinsic viscosity—molecular weight relation in benzene solutions was determined for both types of polymers studied.