邻-酚羟基取代N-杂环卡宾[C,O]螯合双配体镍/MAO催化降冰片烯加成聚合的研究

3种邻-酚羟基取代的N-杂环卡宾[C,O]螯合双配体镍配合物在甲苯中以甲基铝氧烷(MAO)为助催化剂,催化降冰片烯(NBE)聚合.考察了反应温度、时间、n(Al)/n(Ni)以及n(NBE)/n(Ni)等因素对催化活性和所得聚降冰片烯相对分子质量及其分布的影响.结果表明,0℃时催化体系的聚合活性可达,1.34×107gPNBE/(molNi.h);所得聚降冰片烯(PNBE)重均相对分子质量(Mw)可达2.0×106,相对分子质量分布(Mw/Mn)为3.3~1.5,热分解温度在440℃附近,且在室温下可溶于环己烷和三氯苯.通过对聚合产物FTIR,13C-NMR和WAXD分析表明,该聚合反应以烯烃加成聚合方式进行,且聚合物是非晶态结构.

Polymerization of Norbornene via Nickel-based Complexes Bearing o-Hydroxyaryl N-Heterocyclic Carbenes [C,O] Bidentate Ligands/MAO

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 7.6×10~6 g PNBE/(molNi·h),13.4×10~6 g PNBE/(molNi·h) and 8.8×10~6 g PNBE/(molNi·h), respectively.The weight-average molecular weights of polymers attained are varied from 20.0×10~5 to 2.0×10~5, 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 8.1×10~6 g PNBE/(molNi·h) to 4.6×10~6 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 2.1×10~6 to 2.9×10~5 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, ~ 13 C-NMR, FTIR,TG,DSC and WAXD.All of the resultant polymers showed similar FTIR and ~ 13 C-NMR spectra.The FTIR spectrum revealed no traces of double bonds,ensuring the occurrence of vinyl-type polymerization rather than ring-opening metathesis. ~ 13 C-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.