| Polyolefin material is a variety with largest yield and widest applications amongpolymers, which plays more and more important roles in human progress anddevelopment. Moreover catalysis is a core technology for production of polyolefin.Novel catalytic systems involving mono-anionic or neutral, bidentate or tridentate,oxygen-, nitrogen-, or phosphorus-containing chelating ligands have recently beendescribed for ethylene polymerization and are still being investigated. In fact， thereaction mechanism will play a vital role in catalyst designing, andimprovement the performance of polyolefin material. In this article, we wouldexplore reaction mechanism at molecular and electron level as well as key factors thateffect catalytic activity by combining experimental and theoretical methods..1. Styrene was polymerized by using bis (b-ketoamino) nickel (II) complex asthe catalyst precursor and methylaluminoxane (MAO) as the cocatalyst. At same time,styrene polymerization using (2Z,4E)-4-(methylimino)-pent-2-en-2-ol Ni (MPNi)catalyst has been studied using density functional theory at the B3LYP/6-31g (d, p)level. In particular, the reaction mechanisms have been investigated in detail. Theresults indicate that the reaction involves a four-mamboed cyclic transition state withan energy barrier of21.63kcal mol-1. In addition, the analysis indicates that strongp-d interactions between styrene and Ni2+are very important for the activation ofstyrene.2. Norbornene polymerizations proceeded with bis(b-ketoamino)-nickel(II){Ni[CH3C(O)CHC(NR)CH3]2[R=phenyl (1) or naphthyl (2)]} complexes as thecatalyst precursors and the organo-Lewis compound tris(pentafluorophenyl)borane[B(C6F5)3] as a unique cocatalyst. From our calculations, comparing with phenyl assubstituent group of ligand, the naphthyl has strong electron delocalization ability.Because the positive charge of central ion will increase sharply, it possesses strongelectrophilic capacity and the catalyst activity is also high. The study also shows thatwhen substituent group of phenyl is electrondrawing group, the catalyst activitywould be enhanced greatly. 3. In this part, we have studied bimetallic effects in the reaction of ethylenepolymerization for enhanced polar comonomer enchainment selectivity. The studiedshowed the hydrogen bond between H atom of alkane and Ni atom is that thebimetallic catalysts exhibit significantly higher activities than the monometalliccatalysts. Mechanistic studies confirm that, polymerizations follow a coordinativeinsertion process, with enhanced monomer enchainment facilitated by the secondcatalytic center4. The molecular structure and electronic structure of Ar′SnSnAr′andAr*SnSnAr*as well as their reaction activity with ethylene were studied by usingB3LYP DFT calculations in the present paper. The results show that Ar′SnSnAr′andAr*SnSnAr*have different stable spin state. For Ar’SnSnAr’, the singlet state isground state with a planar structure (PL) that the plan of two central aryl rings areparallel and almost in a plane. However, for Ar*SnSnAr*, the triplet state is groundstate with a perpendicular structure (PE), the plan of two central aryl rings areperpendicular with each other. The result shows that the singlet and triplet statestabile stations are able to transfer to each other by crossing points of PES. Ourcalculation also indicates that both Ar’SnSnAr’ and Ar*SnSnAr*reacts withethylene to via a concert reaction channel of triplet state via3TS3that was followedby a potential energy surfaces crossing point to reach to the product of singlet state.For the stepwise channel, both triplet and singlet potential energy surfaces holdhigher energy barrier than their in the concerted reactions. |
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