Synthesis of High Isotactic and High Melt Flow Polypropylene in Liquid Propylene

Abstract

This is a report on the study of high melt flow, highly isotactic polypropylene homopolymer synthesized in liquid monomer using a fifth generation Ziegler-Natta catalytic system. At highest catalyst productivity, the response of thecatalyst to hydrogen as chain transfer is studied. Melt flow rate is controlled by hydrogen as chain transfer from 0.4 to 300 g/10min with changing the amount of hydrogen from 0 to 1400 ppm. Results show that the melt flow rate of homopolymer is increased linearly with increasing the amount of hydrogen in polymerization. The effect of external electron donor on catalyst productivity and stereoregularity of the final product has been studied. The external electron donor on the catalyst caused an increase in polymer isotacticity, but led to decrease in catalyst productivity andits response to hydrogen (i.e., requiring relatively more hydrogen for molecular weight control). This new generation of Z-N catalyst system containing 1,3-diether as internal electron donor has the ability to produce very high MFR polymers (for thin wall parts) in combination with narrow molecular weight distribution. These reactor grades of polypropylene have many advantages compared to visbroken (controlled rheology) grades such as lower cost and better processability. These resins can be used as homopolymer matrix in sequential polymerization to obtain impactcopolymers (heterophasic copolymers).

Keywords

• bulk polymerization
• polypropylene
• ziegler-natta catalyst
• high isotactic
• high melt flow