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Keywords:

  • cationic polymerization;
  • isoprene;
  • zinc halide;
  • polyisoprene;
  • microstructure

Abstract

The activity of ZnX2-based initiating systems (X = Cl, Br, I) in the cationic polymerization of isoprene was studied. The highest activity was achieved when co-initiator (ZnX2) was solubilized in a minimal amount of strongly coordinating solvent such as diethyl ether or acetone and when trichloroacetic acid was used as an initiator. It is shown that the polymerization rate increased in the series ZnI2 < ZnCl2 < ZnBr2. An increase of initiator concentration and temperature also led to an increase of the polymerization rate. The obtained polyisoprenes did not contain high-molecular-weight and insoluble fractions and were characterized by low number-average molecular weight and relatively narrow molecular weight distribution. Unsaturation of polyisoprene decreased with an increase of monomer conversion and reaction temperature. The unsaturated part of the polyisoprene chain possessed predominantly 1,4-trans microstructure with regular and inverse addition, whereas the 1,2- and 3,4-isomers were present as minor components. It is shown that the synthesized low-molecular-weight polyisoprenes are effective plasticizers for rubber compounds in the manufacture of tyres. © 2012 Society of Chemical Industry