Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

Abstract

Kinetics of propylene polymerization with two TiCl 4 /MgCl 2 model catalysts of different Ti load (Cat-1: Ti 0.1 wt%; Cat-2: Ti 1.0 wt%) was investigated in this work. Time-dependent variations of active centers fraction ([C*]/[Ti]) and active center distribution of the two catalysts were compared. In propylene polymerization with Cat-1, [C*]/[Ti] was only 7.8 % in the initial stage, but increased for more than three times in reaction period of 600 s. Propylene polymerization with Cat-2 had much lower [C*]/[Ti]. Active center distributions of the two catalysts were markedly different. Cat-1 has evidently higher proportion of aspecific active centers and less isospecific ones than that of Cat-2. These catalysts also showed different time-dependent variations of active center distribution. The chain propagation rate constant of isospecific centers in Cat-2 was evidently higher than that in Cat-1, but propagation rate constants of either aspecific and medium-isospecific centers were only slightly changed by enhancing Ti content of the catalyst. The results suggest that isospecific centers are mainly originated from clustered Ti species, but non-clustered Ti species are the main source of active centers with lower stereoselectivity. By considering factors like dispersion states of Ti species and release of shielded active species through disintegration of catalyst particles, active center models have been proposed to explain the different kinetic behaviors of the two model catalysts.

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure

“…In contrast to the Mt-II/borate-I/alkylaluminum systems, the Mt-I/borate-I/alkylaluminum catalysts produced PE with much higher M w and significantly broader MWD. When pure TIBA was the alkylaluminum, the M w (163,000) was very close to that of the PE produced with Mt-II/MMAO (195,000) reported in the literature [ 49 ], but the polydispersity of PE by Mt-I/borate I/TIBA (Ɖ = 10.3) was more than three times larger than that of Mt-II/MMAO (Ɖ = 3.05). Similarly, when TEA was introduced in the Mt-I/borate I catalyst, the PE molecular weight sharply decreased with increase of the TEA/TIBA ratio, and the polydispersity index first increased then decreased (see Table 1 ).…”

Comparative Analysis of Ethylene/Diene Copolymerization and Ethylene/Propylene/Diene Terpolymerization Using Ansa-Zirconocene Catalyst with Alkylaluminum/Borate Activator: The Effect of Conjugated and Nonconjugated Dienes on Catalytic Behavior and Polymer Microstructure

“…The vanadium- (VOCl 3 , VCl 4 , VO(OR) 3 and V(acac) 3 ) and titanium-based heterogeneous Zeigler‒Natta catalysts have been used in the copolymerization of ethylene with conjugated diene. Unfortunately, the copolymerization activity was significantly reduced due to the stronger coordination efficiency of the conjugated diene than ethylene [ 17 , 18 , 19 , 20 , 21 ]. It is difficult to use vanadium (V) since discoloration, ageing, and toxicity are induced by the polymer’s residual V content over 5–10 ppm.…”

Rapid kinetic evaluation of homogeneous single-site metallocene catalysts and cyclic diene: how do the catalytic activity, molecular weight, and diene incorporation rate of olefins affect each other?

“…The obtained E/ENB copolymer samples were extensively puried in a multi-step procedure before being dried under vacuum. [37][38][39]…”