Gas-phase polymerization of 1,3-butadiene with supported half-sandwich-titanium-complexes

Abstract

Using half-sandwich-titanium-complexes polybutadiene (BR) can be produced with a particular microstructure of about 81% cis, 18% 1,2, and 1% trans units. A stirred bed reactor and a fluidized bed reactor were constructed for gas-phase polymerization of 1,3-butadiene by cyclopentadienyltrichlorotitanium (CpTiCl3) on MAO (methylaluminoxane) impregnated silica (MAO/SiO2). The major determinant of polymerization activity and molecular weight is the AlMAO/Ti-ratio on the carrier. Polymerization activity increases to 14 500 kg BR/(mol Ti*h) with a molecular weight of 1.9×106 g/mol and the catalyst becomes noticeably more stable. Activity further increases when the CpTiCl3 catalyst is prealkylated with small quantities of TIBA (triisobutylaluminium). Systematic methodological experimentation of the heterogenization suggests that a Ti(III)-species is responsible for polymerization. The gas-phase polymerization of 1,3-butadiene reveals a rate of polymerization which is considerably greater than the equivalent rate in the homogeneous system. The polymers all have similar characteristics, pointing to the same active species. The microstructure of the polybutadiene produced was investigated by spectroscopic measurements and by hydration; a preference to block structures of 1,2-units could not be established.