聚乙烯结构与催化剂 Linear low Single Site Post-Metallocene Low Density High density Density Catalyst Products Catalyst Products Phillips or Hoechst Union Carbide MITSUI Exxon Dow Du pont 1939 Unipol 1955 Tamer Exact 1970’s 1975 1991 Affinity Hyper-Branched 1993 1996 自游基 Ziegler -Natta 茂金属催化剂 后过渡金属催化剂聚乙烯结构与催化剂