Ethylene/Propylene Copolymerization Catalyzed By Vanadium-Based Catalyst In The Presence Of Electron Donors

Vanadium-based catalysts are widely used in the production of ethylene-propylene rubber(EPR). However, they exhibit low catalytic activity and low stability even at 30-50 °C. In order to improve the catalytic performance of vanadium systems, in this dissertation, VOCl3-EASC catalyst system in the presence of various phosphorus or nitrogen-containing electron donors were investigated for ethylene-propylene copolymerization. The effects of donor type and dosage, polymerization temperature and time on the polymerization were examined in detail. The main contents are as follows:1. The addition of phosphorus-containing donor, dimethyl phosphate(TMA), diethyl phosphate(DEP), dibutyl phosphate(BPP), diphenyl phosphide(TPPI), tributyl phosphate(TBP), and diphenyl phosphate(TPP) significantly improve the catalytic performance. The catalytic activity was up to 4.11 kg·g-1·h-1·bar-1 which is 3 times higher than that of donor-free system. Moreover, the catalyst system remained highly active as the polymerization proceded for more than 1 h, demonstrating the longer durability. The resultant ethylene-propylene copolymers possessed high molecular(up to 12.24 × 10-4 g/mol). Determined by NMR and DSC, the propylene units existed in a random maner along the polymer chain and incorporation levels were higher than that obtained with VOCl3-EASC catalyst.2. The catalytic activity of VOCl3-EASC catalyst could be enhanced by the addition of ethyl benzoate(EB) and diisobutyl phthalate(DIBP) and afforded polymers with high molecular weight(up to 18.80 × 10-4 g/mol) and narrow molecular weight distributions(Mw/Mn~2.0). The resulting of ethylene-propylene copolymers were characterized by means of DSC, GPC and NMR. It was shown that the obtained propylene incoporation levels were higher than that obtained with electron donor-free system and the obtained copolymers were amorphous and the Tg values lower to that with VOCl3-EASC system.3. Copolymerization of ethylene with propylene were carried out with VOCl3-EASC catalyst in the presence of 2,2’-azobisisoheptonitrile(AIHN) and 2,2’-azobis(2-methylpropionitrile)(AIBN). The addition of these donors enhanced the catalytic activity, which was about twice that of VOCl3-EASC system, while the molecular weights of polymers were about the same as that obtained with donor-free syetem,the Tg values decreased.