Trans-1,4-polybutadiene: Influences of Lewis bases on polymerization of butadiene with supported titanium catalyst systems

Abstract

Three MgCl2 supported TiCl4 pro-catalysts; Cat-A, Cat-B and Cat-C were synthesized. Cat-A was synthesized without any internal Lewis base (ILB); while Cat-B and Cat-C were synthesized using diisobutyl phthalate and ethyl benzoate as ILBs respectively. The effect of ILBs on stereoregularity and the microstructure of polybutadiene (PBD) was investigated. The vast differences in the amount of trans-1,4-structure of PBD by Cat-A, Cat-B and Cat-C systems were correlated with the nature of ILBs used by studying their polymerization kinetics. The energy barriers for polymerization reactions were calculated for all three catalysts systems using Arrhenius equation. Cat-B, has shown the highest energy barrier (23 kJ/mol) due to DIBP as ILB in its structure. Cat-A has given the lowest trans-1,4-PBD as it does not contain any ILB and has the minimum energy barrier (12 kJ/mol) while Cat-C has shown medium energy barrier (17 kJ/mol). We have also studied the effect of suitable external Lewis bases during polymerization. The effect of polymerization parameters like Al/Ti molar ratio, Al/LB molar ratios and the temperatures on PBD microstructure were studied. Based on the polymerization kinetics studies and the effect of LBs on PBD microstructure, a possible reaction mechanism has been proposed.