Highly active and thermally robust pyridylbenzotriazole iron-based catalysts for preparation of polyisoprenes that feature high wet traction and low rolling resistance

A series of pyridylbenzotriazole iron (II) complexes with general formula (L2FeCl2) were synthesized and characterized by IR, ESI-MS, and elemental analysis. Determined by single-crystal X-ray crystallography, complex Fe1 adopts a distorted octahedral geometry. Upon activation with methylaluminoxane (MAO), the activity of the complex for isoprene polymerization decreased as the bulkiness of the substituent at 6-position of the pyridyl ring of the ligand increased. Notably, Fe1 exhibited excellent activity of 4.1 × 106 g/(mol (Fe)•h), affording polymers with ultra-high molecular weight (Mn = 2380 × 103 g/mol) and narrow distributions (Mw/Mn = 1.72). The resulting polyisoprenes possessed predominantly cis-1,4/3,4 alternating structure and short cis-1,4 and 3,4 sequences, irrespective of the reaction conditions, indicating high thermal stability of the catalyst. Moreover, the prepared polyisoprene composite showed higher mechanical properties compared to SSBR-2466 and SSBR-5025 which are the key components of current commercial tread rubber, and had comparable wet traction and superior rolling resistance.