(A) study on the correlation between active site of catalyst and polymerization mechanism in olefin polymerization

Abstract

In order to understand the nature of active site, the correlation between active site of catalyst and polymerization mechanism was investigated over different types of catalyst systems. Ethylene homopolymerization, propylene homopolymerization and ethylene-propylene copolymerization were carried out to understand the nature of active site at the initial state of catalyst and fully activated state of catalyst over three different $MgCl_2$-supported catalysts with two reaction schemes; i.e., stopped-flow polymerization (SFP) and continuously-purged polymerization (CPP) respectively. The kinetic parameters of ethylene and propylene homopolymerization were obtained by SFP. The active site concentration varied depending on the catalyst preparation method in propylene polymerization but not in ethylene polymerization. The activity of ethylene and propylene homopolymerization was also compared with SFP and CPP. From those results, a plausible model for active site distribution in olefin polymerization was proposed. More detailed studies on the proposed model were carried out by the effects of aging time and Al/Ti mole ratio in ethylene-propylene copolymerization with SFP and CPP. The catalytic behavior was in good correlation with the proposed model. From DSC and $^{13}\!C$ NMR spectra, the crystallinity of copolymer was affected by its configuration in the copolymer chain as well as its content. Those seem to be attributed to the different extent of interaction between catalytic titanium sites and aluminum alkyls; i.e., active site formation, its over-reduction and extraction of ethyl benzoate. $TiCl_3/2.5MgCl_2(0.5MgEt_2$)/THF catalyst(R) was prepared by the reduction of $TiCl_4$ with EtMgCl. The effect of diethyl aluminum chloride(DEAC) addition on the catalytic activity in ethylene-propylene copolymerization was investigated. It was suggested from FT-IR that the catalyst R formed similar bimetallic (Ti-Mg-THF) complexes to the $TiCl_3(AA)/3MgCl_2$/THF catalyst (T3...