Preparation method of propylene copolymer with low ethylene content and wide molecular weight distribution

Abstract

The invention provides a preparation method of a propylene copolymer with ethylene content lower than 0.5% (wt) and wide molecular weight distribution. The method comprises a catalyst system and a two-step polymerization process. The catalyst system comprises a Ziegler-Natta catalyst with organosilane with extremely high hydrogen sensitivity. With the catalyst system, extremely high molecular weight can be produced in first step polymerization, and extremely low molecular weight can be produced in the second step. Polymerization products obtained in the two steps are mechanically mixed, wherein melt flow rate ratio (2.16kg, 230 DEG C) of the fist step and the second step is higher than 400, such that the propylene copolymer with wide molecular weight distribution can be obtained.

Description

technical field [0001] The invention relates to a preparation method of a propylene copolymer, in particular to a preparation method of a propylene copolymer with low ethylene content and wide molecular weight distribution. The propylene copolymer can be used in the field of polypropylene foaming, but not limited to this field. Background technique [0002] Polypropylene is one of the most widely used and fastest growing synthetic resins in the world. However, due to poor toughness and low melt strength of ordinary polypropylene, its application in extrusion coating, blow molding and foam molding is greatly limited, so high melt strength polypropylene technology has a bright future, theoretical research shows , a wide molecular weight distribution can greatly enhance the melt strength of polypropylene, so the method of manufacturing polypropylene with a wide molecular weight distribution is an area of ​​interest to the theoretical and industrial circles. [0003] The wide d...

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Problems solved by technology

[0004] Chinese patents US2009023881A1, CN1266066A, US2011034649A1, CN102159594A, CN101213249A, and CN1163621 disclose methods for manufacturing polypropylene with a wide molecular weight distribution. The technology for manufacturing polypropylene with a wide distribution is based on catalyst composition or process control. The catalyst synthesis technology is complicated and costly. The universality of polymerization process control is poor, and the molecular weight distribution of the obtained polymer is not wide enough, etc.

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