Silica supports for metallocene catalysts

The effect of silica supports on metallocene catalyst performance using the vacuum pore fill method has been studied. High pore volume microspherical and granular silica gel supports composed of a homogeneous matrix were studied. It was found that high pore volume silica gels give higher activity catalysts with better polymer morphology than supports with small pore sizes. Low pore volume. spray dried supports that contain voids and low pore volume, microspherical supports composed of a homogeneous matrix give poor activity catalysts. In addition these catalysts give polymers with poor morphology. Particle size does not have a significant effect on the activity and resulting polymer morphology for catalysts supported on high pore volume microspherical supports. To improve catalyst performance on the high pore volume microspherical support MS-3030 further, catalyst preparation parameters were studied. The amount of pore filling (percentage of silica gel pore volume occupied by the solution of metallocene-methylaluminoxane (MAO) in toluene that is added to the support during the catalyst preparation) was studied. An 80% pore fill gave the best combination of activity and polymer morphology. Increasing the drying temperature of the catalyst to >65 degrees C had no effect on polymer morphology although it had a detrimental effect on catalyst activity. Toluene washing the finished catalyst to remove the unsupported metallocene-MAO species resulted in a dramatic improvement in polymer morphology. Highly concentrated solutions of MAO in toluene are necessary for preparing metallocene catalysts by the pore filling method on low pore volume supports without overfilling the pores. However, these concentrated solutions of MAO in toluene give low activity catalysts with poor polymer morphology. PBCPA/1479. (C) 1998 The Institute of Materials.