Bin Wu,Qingyu Zhang,Hongyu Liu,Tongtong Zhang,Xiaolong Yang,Fangming Zhu
Novel half-titanocene catalysts containing fluorinated phenoxy ligands were synthesized and used for the syndiotactic polymerization of styrene in the presence of low methylaluminoxane (MAO) and triisobutylaluminum (TIBA) as cocatalysts. The influences of polymerization conditions, including temperature and Al/Ti ratio, on polymerization behaviour and the molecular weight of the resultant polymer were studied. The fluorinated half-titanocene catalysts displayed higher catalytic activity and produced syndiotactic polystyrene (sPS) with a higher molecular weight as a result of the electron-withdrawing conjugation effect of fluorinated phenoxy ligands. This effect stabilizes Ti(III) active centers and/or enhances propagation while reducing the chain transfer rate constant.
Highly efficient terpolymerizations of ethylene, propylene and 5-ethylidene-2-norbornene (ENB) using a half-titanocene containing iminoimidazolidine (T5) catalyst with a methylaluminoxane (MAO) cocatalyst could be achieved in the presence of small amounts of triisobutylaluminium (TIBA) and 2,6-ditertbutyl-4-methyl-phenol (BHT) at TIBA : BHT : Ti = 20 : 20 : 1 (molar ratio). The catalytic activity reached 2.20 × 107 g polymer per mol of Ti per h for the copolymerization of ethylene and propylene and the ethylene–propylene copolymer with a high incorporation ratio of propylene (39.1 mol%) was afforded by using the T5/TIBA/BHT/MAO catalytic system. Interestingly, the catalytic activity, the incorporation ratio of propylene into the copolymer chains and the percentage of randomly distributed sequences could be improved by an increase in the BHT/Ti molar ratio from 0 to 20. Very importantly, the ENB conversion could reach more than 95%, indicating that this T5/TIBA/BHT/MAO catalytic system exhibits excellent copolymerization ability for ENB with ethylene and propylene. The content of ENB units in the resulting ethylene–propylene–diene rubbers (EPDMs) could be increased up to 6.8 mol% (20.8 wt%) by increasing the ENB concentration in the monomer feed without sacrificing the catalytic activity and ENB conversion. The extremely high ENB conversion was significant for the highly efficient production of EPDMs with relatively low cost and short processes. The EPDM with a high content of ENB units is critical for rapid vulcanization during the processing and for the preparation of a functionalized EPDM. The CC double bonds in the ENB units in the above EPDM can be cleanly converted into carboxylic functional groups via light-mediated thiol–ene reaction, leading to the production of the functionalized EPDM with various contents of carboxylic side groups. The functionalized EPDMs exhibit enhanced hydrophilicity, which may result in good compatibility with inorganic fillers and strong interaction between inorganic fillers and organic terpolymers.
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