Abstract: The properties of polyisoprene bulk polymerized with rare-earth catalyst (Ln-IR) are reported. The Mooney viscosity(ML) values of Ln-IR are obviously higher than that of Ln-IR obtained in solution polymerization with the same [η]. Under certain polymerization conditions, some long branching chains may occur in the molecular structure of Ln-IR. The cis-1,4 content of Ln-IR was slightly lower than that of Ti-IR and NR, but the stress-strain property and viscoelasticity were basically the same as that of Ti-IR. The bulk Ln-IR showed a good fluidity at higher shear rate. The activation energy of viscous flow was about 11.0 kJ/mol, equal to that of Ti-IR, but slightly lower than that of NR.

Key words: polyisoprene, bulk polymerization, rare-earth catalyst, synthetic rubber