催化剂-4.经典实例.ppt

Three types of Ziegler-Natta catalysts are currently employed: Solid and supported catalysts based on titanium compounds used in combination with cocatalysts (organoaluminum compounds). Metallocene catalysts, combination of various mono- and bis-metallocene, in particular ansa- (or bridged) metallocene complexes of Ti, Zr or Hf. They are usually used in polymerization reactions in combination with a different organoaluminum cocatalyst, methylaluminoxane (or methylalumoxane, MAO). Post-metallocene catalysts [后茂金属催化剂 ] based on complexes of various transition metals with multidentate oxygen- and nitrogen-based ligands. These complexes are also activated with MAO. The catalyst systems can be homogeneous or heterogeneous. Structures TiCl4 and TiCl3 have four crystal structures (α，β，γ and δ-type）. Except of βtype , other three types are octahedral layer structure. The transition metal is reduced from high oxidation state to low oxidation state. Metal alkyl plays important roles in Ziegler-Natta catalyst system. Reaction mechanism Coordination polymerization (Complexing polymerization, insertion polymerization: is a form of addition polymerization in which monomer adds to a growing macromolecule through an organometallic active center. The polymers tend to be linear and not branched and have much higher molar mass. Elementary reactions of Coordination polymerization （1）Chain initiation （2）Chain growth （3）Chain transfer （i）Transfer to monomer （ii）Transfer to monomer metallorganics （iii）Transfer to H2（H2 is molecular weight modifier） （iv）Intramolecular transfer （4）Chain termination (ii) O2、CO2、CO，ketones can also result in chain termination. (i) Chemicals containing reactive hydrogen (Alcohols, arboxylic acids, amines, water, etc.) can react with active sites and thus make them deactivate: 全同立构体 Isotactic 间同立构体 Syndiotactic 无规立构体 Atactic Synthesis A typical process: (MgCl2-supported Ziegler–Natta catalyst) support preparation Dealcoholation treatmen