This study aims to investigate the influences of a combination of cocatalysts including triethylaluminum (TEA) and tri-n-octylaluminum (TnOA) for activation of a commercial Ti-based Ziegler-Natta catalyst during ethylene polymerization and ethylene/1-hexene copolymerization on the change in Ti3+ during polymerization. Thus, electron spin resonance (ESR) technique was performed to monitor the change in Ti3+ depending on the catalyst activation by a single and combination of cocatalyst. It revealed that the amount of Ti3+ played a crucial role on both ethylene polymerization and ethylene/1-hexene copolymerization. For ethylene polymerization, the activation with TEA apparently resulted in the highest catalytic activity. The activation with TEA+TnOA combination exhibited a moderate activity, whereas TnOA activation gave the lowest activity. In case of ethylene/1-hexene copolymerization, it revealed that the presence of 1-hexene decreased activity. The effect of different cocatalysts tended to be similar to the one in the absence of 1-hexene. The decrease of temperature from 80 to 70 °C in ethylene/1-hexene copolymerization tended to lower catalytic activity for TnOA and TEA+TnOA, whereas only slight effect was observed for TEA system. The effect of different cocatalyst activation on the change of Ti3+ state of catalyst was elucidated by ESR measurement. It appeared that the activation of catalyst with TEA+TnOA combination essentially inhibited the reduction of Ti3+ to Ti2+ leading to lower activity.  Furthermore, the polymer properties such as morphology and crystallinity can be altered by different cocatalysts. Copyright © 2020 BCREC Group. All rights reserved

This study focused on the effect of temperature in propylene polymerization behaviors up on different cocatalysts employed. It revealed that triethylaluminum (TEA) exhibited higher activity than tri-noctylaluminum (TnOA) with the optimal temperature of 60°C, whereas the over reduction of catalyst occurred at 70°C. However, at low temperature (ca. 50°C), the mixed cocatalysts (TEA+TnOA) gave the highest activity among the sole cocatalyst. This can be attributed to the occurrence and stabilization of proper Ti oxidation state (Ti 3+ ) form as proven by the electron spin resonance (ESR) with the combination of cocatalysts. In addition, temperatures and types of cocatalyst did not have significant effects on morphology and crystallinity of polymer.

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This research focused on effect of cocatalyst types (TEA, TnOA, and TEA+TnOA) on titanium-based Ziegler-Natta catalyst in olefin polymerization both in slurry and gas-phase systems. This study has been divided into four sections. The commercial titanium-based catalyst was selected to investigate effect of reaction temperature and oxidation state of titanium from ESR measurement on slurry ethylene and propylene polymerization in the first and the second parts, respectively. The commercial catalyst with TEA exhibited the highest activity in ethylene polymerization. However, divalent, and trivalent of titanium (Ti2+ and Ti3+) was active in ethylene polymerization to produce more polymer. Stability of Ti3+ was demonstrated to assist insertion of 1-hexene. Hence, propylene polymerization under different reaction temperatures was conducted to evaluate the titanium oxidation state (Ti3+). The ESR results revealed that TEA+TnOA at 50oC can stabilize titanium (III) state. Regarding to the third and fourth parts, different magnesium sources supported-catalyst; MgCl2 (Cat A), MgO (Cat B), and Mg(OEt)2 (Cat C); were compared in gas-phase ethylene polymerization. The modification of supported catalyst could improve the performance of catalyst and polymer. The results presented that Cat C or Mg(OEt)2 reacting with TEA showed the highest catalytic activity for both homo- and co-polymerization of ethylene. The addition of 1-hexene as comonomer could improve the activity and higher comonomer response called as “comonomer effect”. Moreover, the polymer obtained in gas-phase process exhibited remarkably better morphology than in slurry process.