Nanoscopic Confinement Effect Of Layered MMT On Ethylene Polymerization By Late Transitional Metal Complex

Nanoscopic confinement effect on polymerization and on the structure of polymer prepared in situ have become attractive. It is very important to learn such confinement because it is a fundamental scientific issue.In this thesis, late transitional metal catalyst for olefin polymerization and layered montmorillonite (MMT) were selected as typical system to study the nanoscopic confinment effect of layered structure of MMT on the olefin polymerization and the structure of polymer prepared in-situ.Two series immobilized catalysts based on Fe(II) and Ni(II) were prepared and characterized. These catalysts were used for ethylene polymerization. Polymers sampled at different times were measured by XRD, DSC and GPC. It was found that the layered structure of MMT affects the ethylene polymerization and the properties of polyethylene prepared in situ.When intercalated Fe(II) complex polymerizes ethylene, it produced polyethylene with higher molecular weight and melting point than corresponding homogeneous one. Such results are caused by the confinement effect of layered structure of MMT. The nanoscopic space between layers of MMT lowers the chain transfer reaction, which is the key factor determining the molecular weight of polymer prepared by Fe(II) complex.When intercalated Ni(II) complex polymerizes ethylene, it produced polyethylene with high branched, high molecular weight and low melting point at early stage of polymerization, and polyethylenes with low branched, low molecular weight and high melting point were generated latter. Such results are also caused by the confinement effect of layered structure of MMT. The nanoscopic space between layers of MMT lowers the "chain walking" rate during polymerization, resulting low branching degree of polymer. So polyethylenes with high melting point were produced.