Influence of reaction conditions on catalytic properties of rac-Et(2-MeInd)2ZrMe2/(2,6-tBu2PhO-)AliBu2 in ethylene-propylene copolymerization

Ethylene-propylene copolymerization reactions were carried out using rac-Et(2-MeInd)2ZrMe2 catalyst and (2,6-tBu2PhO-)AliBu2 as activator under varying reaction conditions. We demonstrate that reaction conditions such as monomer concentration, Al/Zr molar ratio and solvent type (toluene and heptane) all have significant effect on activity of the system and copolymers composition. The decrease in reaction pressure from 11 to 3 atm leads to: a) 1.6-fold increase in specific activity (from 3030 to 4840 kg copolymer/(mol Zr•h•atm)), b) increase of Mn value from 38 to 89 kg/mol, and c) increase of ethylene content in copolymer from 87 to 92 mol %. The increase of ethylene/propylene molar ratio from 0.7 to 2 does not significantly affect activity but leads to the rise in the ethylene content in copolymer from 92 to 97 mol % and, correspondingly, to the increase of copolymer crystallinity from 43 to 48%. As a result, thermal and mechanical properties of the obtained polymers also change, according to the shifts in copolymers composition. The change in Al/Zr molar ratio is confirmed to have great effect on the catalytic activity of our systems. In a row of Al/Zr= 100, 150, 200, 300 mol/mol, the lowest activity of 80 and the highest one of 8550 kg copolymer/(mol Zr•h•atm) are observed at 100 and 150 molar ratios correspondingly. We have also demonstrated the ability of catalytic systems with isobutylaluminum aryloxide activators to operate in aliphatic medium (heptane). On another note, during the reaction quenching, aryloxide activator hydrolyzes the polymer infused with 2,6-di-tert-butylphenol antioxidant. This results in the increased resistance of copolymers to the thermal-oxidative degradation. The presence of 4 wt% phenol in the copolymer leads to an increase in the 5% mass loss temperature by 67°C. Moreover, increasing the residual phenol content from 2 to 4 wt% affects the mechanical properties of the copolymers: the elongation-at-break increases from 500 to 600%, and the tensile strength decreases from 10 to 8 MPa.

Influence of reaction conditions on catalytic properties of rac-Et(2-MeInd)2ZrMe2/(2,6-tBu2PhO-)AliBu2 in ethylene-propylene copolymerization Keywords:

metallocene , alkylaluminum aryloxide , ethylene-propylene copolymerization , Properties