Syndiotactic Selectivity Of Metallocene Catalysts And Syndiotactic Polypropylene Preparation

In this thesis. Cs-symmetric syndiospecific metalloncene catalyst, i-Pr(Cp-Flu)ZrCl2. was synthezied and was used for preparing not only the syndiotactic polypropylene (sPP) but also several other kinds of syndiotactic a - olefin. The influence of polymerization conditions on the properties of sPP was investigated and the thermal behaviors of sPP were studied.The important role of the solvent during the course of preparation of catalyst complex was deeply studied. It was found that the ether was much more suitable solvent for the preparation of catalyst than other solvents. By using this complex and the cocatalyst. methylalumoxane(MAO), syndiotactic polypropylene (sPP) with syndiotacticity index (SI) >80%, melt point 130℃was prepared in the condition of low pressure. The metalloccne complex and sPP have been characterized by means of IR. 'II NMR. EI-MS spectra, element analysis and DSC.The different conditions such as temperature, solvent and [Al]/[Zr] have a great influence upon the process of polymerization. With the increase of the temperature. SI and molecular weights would go down and the activity of the catalyst would reach to its top value at 70℃. Increasing the polarity of the solvent would lead to sPP with lower SI and a higher activity of the catalyst. Meanwhile molecular weights showed a minimal value because of the decrease of the monomer solubility. The increase of [Al]/|Zr| would cause the decrease of the SI and the molecular weights. And the activity of catalyst reached the maximum value at the ratio of 2500:1.Through the kinetic curves, it was showed that the intensity of the reaction could be controlled by decreasing the temperature of the polymerization reaction.The thermal behaviors included thermal stability and the double melting peak phenomena were studied based on the sPP. It was confirmed that sPP was quite stable in air and the double melting peak was related to the different crystal of sPP. Furthermore the nonisothermal and the isothermal crystallization were investigated by DSC.By using the catalyst i-Pr(Cp-Flu)ZrCl2, the snydiotactic poly( 1-butene), the snydiptactic poly(l-pentene). the snydiotactic poly(l-hexene), the snydiotactic poly( 1 -octene) the snydiotactic were synthesized. Determined by the I3C NMR, they possessed with SI 92%, 70%. 65% and 68% respectively.