Three kinds of nickelbased complexes bearing o-hydroxyaryl N-heterocyclic carbenes ［C

O］ bidentate ligands were prepared via facile synthesis method. The polymerizations of norbornene were carried out using these complexes activated with methylalminoxane (MAO). The polynorbornenes obtained are soluble at room temperature in the solvents such as cyclohexane

chlorobenzene and so on. The influence of the catalyst structure on the catalytic activity

molecular weight and molecular weight distribution of the polynorbornene was investigated.The steric and electronic effects of nickel-based complexes bearing o-hydroxyaryl N-heterocyclic carbenes ［C

O］ bidentate ligands made the resultant polymers possess high molecular weight and narrow molecular weight distribution. Under the conditions such as the reaction temperature of 0℃

the reaction time of 10 min

molar ratio of aluminum to nickel of 2000 and molar ratio of norbornene to nickel of 75000

the complexes 1

2 and 3 activated with MAO show relatively high catalytic activity as 7.6×106 g PNBE/(molNi.h)

13.4×10.6 g PNBE/(molNi.h) and 8.8×106 g PNBE/(molNi.h)

respectively.The weight-average molecular weights of polymers attained are varied from 20.0×105 to 2.0×105

and molecular weight distributions ranged from 3.3 to 1.5.The complexe 2 was investigated in detail for the influence on the catalytic activity

molecular weight and molecular weight distribution as well.The catalytic activity was decreased from 8.1×106 g PNBE/(molNi.h) to 4.6×106 g PNBE/(molNi.h) when the polymerization temperature was varied from 0℃ to 90℃

which revealed that the catalyst is stable.The weight-average molecular weights of polynorbornenes were decreased obviously from 2.1×106 to 2.9×105 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. Norbornenes were polymerized rapidly when the molar ratio of aluminum to nickel was from 1000 to 3500.However

the molecular weight and molecular weight distribution were changed hardly which indicated that chain transfer reaction to MAO did not occur. Thermo-gravimetric analysis signified that all of the polymers were stable at about 400℃ under nitrogen. Attempt to determine the glass transition temperature of polynobornene from DSC was failed

and DSC studies did not give an endothermic signal upon heating to the decomposition temperature. The polynobornenes were characterized by GPC

13C-NMR

FTIR

TG

DSC and WAXD. All of the resultant polymers showed similar FTIR and 13C-NMR spectra.The FTIR spectrum revealed no traces of double bonds

ensuring the occurrence of vinyl-type polymerization rather than ring-opening metathesis. 13C-NMR spectrum also further confirmed that the polymerization occurred via viny1-addition type polymerization (i.e. a 2

3-linked polymer); no ring-opened product was observed.Partial information on the conformation for the polynobornenes obtained by all the nickelbased complexes was obtained by means of wide-angle X-ray diffraction (WAXD).According to WAXD spectra

no traces of Bragg reflection were appeared. The polynobornenes

therefore

are non-crystalline

but similarly the polymers had short-range order and with high packing density.