Optimization of the polymerization parameters for syndiotactic polymerization of styrene using supported catalysts

摘要

The two catalytic systems Ti(OBu)(4) and CpTiCl3 in combination with methylaluminoxane (MAO) were tested and compared in syndiotactic polymerization of styrene. In homogeneous conditions, CpTiCl3 gives higher productivities than Ti(OBu)(4). The productivity of CpTiCl3 increases continuously with the Al/Ti ratio. On the contrary, confirming previous results, the productivity of Ti(OBu)(4) presents an optimum for an Al/Ti ratio of about 230. To optimize the syndiotactic polymerization of styrene using these supported catalysts, different parameters were examined: we show that a high concentration of MAO for heterogeneous conditions is necessary to ensure a good reproducibility of the polymerization, the role transfer agent of the MAO was then demonstrated. Polymerizations carried out at different temperatures show that 50 degreesC is a good compromise: when the temperature is raised the productivity increases but the syndiotacticity drops. At 50 degreesC, the productivity is high enough and the syndiotacticity is above 90, at 60 degreesC, the productivity is a little higher but the syndiotacticity drops below 90. Increasing the temperature does not influence the molecular weights showing that supporting Ti(OBu)(4) or CpTiCl3 will stabilize the active species. As hydrogen behaves as a transfer agent for the conventional Ziegler catalysts, we carried out some experiments adding hydrogen during the polymerization. Indeed, the molecular weights are lowered. The melting points of the polymers depend as expected on the syndiotacticity and in a lower extent on the molecular weights. References: 22