Isoprene Polymerization: Catalytic Performance of Iminopyridine Vanadium(III) Chloride versus Vanadium(III) Chloride

A series of vanadium complexes bearing iminopyridine bidentate ligands with various electronic and steric properties:V1[CH2Ph],V2[CMe2CH2CMe3],V3[Ph] andV4[2,6-iPr2Ph] were prepared and characterized by IR spectroscopy and microanalytical analysis. The catalytic capacity of all the complexes has been investigated for isoprene polymerization and was controlled by tuning the ligand structure with differentN-alkyl andN-aryl groups. Activated by methylaluminoxane (MAO), the aryl-substituted complexV3[Ph] exhibited highcis-1,4 selectivity (75%), and the resultant polymers had high molecular weights (Mn= 6.6 × 104) and narrow molecular weight distributions (PDI = 2.3). This catalyst showed high activity up to 734.4 kg polymer (mol V)−1h−1with excellent thermostability even stable at 70 °C. Compared to the traditional VCl3/MAO catalytic system, iminopyridine-supported V(III) catalysts displayed higher catalytic activities and changed the selectivity of monomer enchainment fromtrans-1,4 tocis-1,4.Keywords:polyisoprene;iminopyridine ligands;vanadium complexes;VCl3/MAO;Ziegler-Natta polymerization