Titanium Tetrabutoxide-Organoaluminum -Bromine Catalysts for cis-1, 4-Polymerization of Isoprene

Abstract

The polymerization of isoprene catalyzed by Ti(0Bu)₄-AlEt₃ or AlEt₂C1-Br₂ was studied. High cis-1, 4 polymers are obtained in excellent yield by using the catalyst formed by adding Ti(0Bu)₄ to the mixture obtained by the reaction of Br₂ with AlEt, or AlEt₂Cl. The optimum molar compositions are 1: 8 : 10 for Ti(OBu)₄-AlEt₃-Br₂ catalyst and 1 : 8 : 3.2 for Ti(0Bu)₄ AlEt₂Cl-Br₂ catalyst.
The obtained cis-1, 4 polymer by using the former catalyst has higher M_v, lower M_n and wider M_w/M/_n ratio than some commercial polyisoprene or the polymer previously obtained by using Ti(OBu)₄-AlEt₃-AlBr₃ catalyst.
The reaction of AlEt₃ with Br₂ affords C₂H₅Br and a part of AlEt₃ would convert to AlEt₂Br and AlEtBr₂, and the mixtures of these organoaluminum compounds would be effective for the complexing of Ti(OBu)₄.