Abstract
Non-metallocene oxovanadium(V) complexes bearing either [ONNO]-type amine pyridine bis(phenolate) ligands or [ONN]-type amine pyridine phenolate ligands were employed as efficient catalysts to copolymerize ethylene with several unsymmetrical norbornene-containing dienes, such as 5-vinyl-2-norbornene (VNB), 5-ethylidene-2-norbornene (ENB) or dicyclopentadiene (DCPD), producing copolymers with high comonomer incorporations (VNB: 33.0 mol %; ENB: 30.4 mol %; DCPD: 31.6 mol %, respectively) and high molecular weight (VNB: 86.4 kDa; ENB: 256 kDa; DCPD: 86.4 kDa, respectively). The enchainment of the dienes was proven to be exclusive of vinyl-addition via the C=C double bond of the norbornene ring while the other double bond was retained near the backbone without crosslinking. During the copolymerization of ethylene with ENB, a positive ‘comonomer effect’ was observed. The catalytic activities of the catalysts as well as the molecular weights and comonomer incorporations of the resultant copolymers could be tuned within a wide range by varying the structures of the catalysts and copolymerization conditions. The [ONN]-type oxovanadium(V) complexes showed higher catalytic activities than those of [ONNO]-type oxovanadium(V) complexes, irrespective of the structure of the dienes. In addition, the dominant chain transfer pathway of the non-metallocene oxovanadium(V) catalytic system promoted copolymerization was proven to be transfer to aluminum compounds.
Highlights
The synthesis of well-defined polyolefin with reactive pendent vinyl group, which can be converted into functional groups by further chemical transformations, has drawn much attention over recent decades [1,2,3,4,5,6,7,8,9,10]
All the resultant copolymers exhibited unimodal molecular weight distribution, suggesting the single site catalytic behaviors of these catalysts. Among these three [ONNO]-type oxovanadium(V) complexes, complex b showed the highest catalytic activities in both homopolymerization of ethylene and copolymerization because of its less steric hindrance originated from the longer bridge between the pendant pyridine donor and the ligand skeleton, and produced copolymers with moderate molecular weights (MWs)
Polymerization conditions: the copolymerizations were carried out in 50 mL of toluene at 50 °C under 4 atm of weight and polydispersity index of the copolymers were determined by high temperature GPC at 150 ◦ C; c The glass ethylene pressure, polymerization for 10 min, Ethyl trichloroacetate (ETA) (300 equiv. to vanadium complexes) was employed as transition temperatures of the copolymers were determined by DSC; d The number of polymer chains produced by a DCPD incorporation were calculated by 1H NMR spectra; b Weight-average reactivating agent
Summary
The synthesis of well-defined polyolefin with reactive pendent vinyl group, which can be converted into functional groups by further chemical transformations, has drawn much attention over recent decades [1,2,3,4,5,6,7,8,9,10]. The cyclic olefin copolymers (COCs), which are usually synthesized from copolymerization of ethylene with cyclic olefin, are kinds of materials have higher modulus than high density polyethylene (HDPE) and PP, and exceptional moisture barrier for a clear polymer along with low moisture absorption rate. High density polyethylene (HDPE) and PP, and exceptional moisture barrier for a clear polymer along with low moisture absorption rate. In. In our previous work, the high-oxidation synthesized [ONNO]-type and [ONN]-type oxovanadium(V) complexes showed high catalytic activities and promising stabilities in copolymerization copolymerization of ethylene with norbornene (NBE), and copolymerswith with high high NBE. E/NBE copolymers to further investigate their capability of copolymerizing ethylene and norbornene derivatives with an additional C=C double bond, including 5-vinyl-2-norbornene (VNB), 5-ethylidene-2-norbornene (ENB), and and DCPD.
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