(A) study on olefin polymerization over $MgCl_2$-supported ziegler-natta catalysts

Abstract

In Chapter 2, the general review for olefin polymerization study is concisely summarized with many key references in view of catalyst synthesis, polymerization process, characterization and chemistry of catalyst and polymer, and polymerization kinetics. This chapter is to be intended to help to grasp quickly in this field. In Chapter 3, recrystallization method was adapted for the catalyst preparation, which is one of the $Mgcl_2$-modification techniques for easy control of the catalyst texture compared to the ball-milling method. Detailed investigations were made on the recrystallized catalysts concerning their formation, the Lewis base effect and their kinetics in propylene polymerization, which are compared with the ball-milled catalysts. It was found that for the recrysatallized catalysts, 2-ethyl-1-hexanol was mores effective solving agent than ethanol, and $SiCl_4$ was a good recrystallizing agent. The effect of different Lewis bases in $TiCl_4$ catalysts supported on $MgCl_2$, which was modified by the recrystallization method, has been investigated in terms of activity, selectivity and morphology. ethyl benzoate(EB) and 2,2,6,6-tetramethylpiperidine (TMPip) were tested as the internal Lewis bases Propylene polymerizations were performed at 50$^\circ$C and 7 atm, using Al $(C_2H_5)_3$ as cocatalyst and TMPip as external modifier. Both supports and catalysts were characterized by BET, X-ray, SEM and other techniques. It was found that the electron donor plays an important role in the recrystallization step of $MgCl_2$ from alcoholic $MgCl_2$ solution. Ethyl benzoate(EB) was more effective internal donor leading to the porous, free-flowing and stable high activity catalyst, while TMPip was not effective as internal donor owing to its decomposition by $SiCl_4$ during the support preparation. From short time polymerization kinetics, EB was found to increase both the values of the active site concentration ([$C_p^*$]) and the propagation rate constant(kp). Co...