Polymerization Of Norbornene Via Nickel And Palladium Complexes Bearing O-Hydroxyaryl N-Heterocyclic Carbenes [C, O] Ligands/Mao

In this dissertation, a series of new olefin polymerization catalysts, such as nickel and palladium complexes bearing o-hydroxyaryl N-heterocyclic carbenes [C,O] quadridentate ligands (NHC₂-Ni, NHC₂-Pd), allyl palladium complexes bearing o-hydroxyaryl N-heterocyclic carbene [C,O] ligands (NHC-allyl-Pd), palladium-based complexes bearing o-hydroxyaryl N-heterocyclic carbenes [C,O] bidentate ligands (NHC-Pd), have been synthesized and characterized. Catalytic activities of these complexes for norbornene were investigated. The effects of catalyst structures, polymerization conditions on olefin polymerization behavior and polymer structure have been discussed in detail. The polynorbornenes obtained from NHC₂-Ni are soluble at room temperature in the solvents such as cyclohexane, chlorobenzene and so on. Moreover, the polynobornenes were characterized by GPC, ¹³C-NMR, FTIR, TG, DSC and WAXD. The microstructure and property of polynobornenes were characterized briefly. The relationship between structure of catalysts and property of polymer was discussed. The full dissertation was summarized as follows:1. Nickel and palladium complexes bearing o-hydroxyary N-heterocyclic carbenes [C,O] ligands (NHC₂-Ni,NHC₂-Pd,NHC-allyl-Pd and NHC-Pd) have been synthesized. After activated by methylaluminoxane (MAO), these catalytic precursors could polymerize norbornene with high catalytic activities up to 3.8×10⁷gPNBE/(molM·h) and produce narrow, unimodal molecular weights distribution (MWD) and high molecular weight polymers(Mw/Mn=1-3, 10⁵-10⁶g/mol). Herein, it is noteworthy that the steric bulk effect of the imidazole substituted group (R) on catalytic activity and molecular weight of polymers is significant to a certian extent. At the similar reaction condition, the catalytic activities rank in descending order R=Cy> Mes>^tBu. However, the molecular weight are basically same.2. For NHC₂-Ni(R=Cy), NHC-allyl-Pd(R=Cy), NHC-Pd(R=Mes), the effects of polymerization conditions such as Al/M molar ratio, monomer concentration, reaction temperature and solvent on norbornene polymerization behavior have been discussed in detail. The molecular weights of polynorbornenes were decreased obviously from 2.1×10⁶ g/mol to 2.9×10⁵ g/mol with the temperature increase from 0℃to 90℃while the molecular weight distributions were varied from 2.3 to 1.8 at the same temperature range for NHC₂-Ni(R=Cy).3. The polynobornenes were characterized by ¹³C-NMR, FT IR, TG, DSC and WAXD. The results indicated that the polymerization occurred via vinyl-addition type polymerization (i.e. a 2,3-linked polymer); All of the polymers were good thermal-resistant. The solubility of polymer from NHC₂-Ni and NHC₂-Pd was explained from chain flexibility and packing density by FTIR and WAXD. The polymerization mechanism was studied for nickel complexes bearing o-hydroxyaryl N-heterocyclic carbenes [C,O] quadridentate ligands.