Method for preparing polymer

Abstract

The invention provides a method for preparing polymer; a polymerization temperature in a reactor is set to change circularly between a high temperature point and a lower temperature point; the cycle has at least one period within 6 hours; the high temperature point is higher than the low temperature point by more than 10 DEG C. Polymer prepared by the method of the invention has a ratio of flow index MI 21.6 to melt index MI 21.6 being more than 60, which indicates that the polymer has excellent processability; in addition, the polymer obtained in the invention has improved yield strength, breaking strength, and falling dart impact values when compared with the prior art, which indicates that the polymer has excellent physical properties.

Description

technical field [0001] The invention relates to a method for preparing a polymer, which is realized by controlling the reaction temperature in a reactor at different times. Background technique [0002] As we all know, olefin polymers are widely used in various fields. Its rigidity, toughness, and lightness are irreplaceable for many materials. Improving and improving the performance of olefins is also the goal that researchers are constantly pursuing. In the well-known process of producing olefin polymers in the art, the traditional polymerization method is to catalyze the polymerization of olefins by Ziegler-Natta, metallocene or chromium catalysts in a single reactor. In this process, certain characteristics of the polymer are controlled by changing the combination of some polymerization parameters, so as to realize the application of the polymer in different fields. Practice has shown that no matter what kind of olefin polymer material is used, it is required to have go...

AI Technical Summary

Problems solved by technology

However, due to the different sensitivity of different components in the composite catalyst to the reaction conditions, it is often difficult to achieve the balance of large and small molecules in the olefin polymer, so it has not been commercialized so far.

Another approach is to use a single Ziegler-Natta catalyst to catalyze the production of olefin polymers in multiple reactors in series, where hydrogen concentration is increased in one reactor to produce small-molecule polymers and in the other reactor no hydrogen is added. Hydrogen produces macromolecular polymers. This process method is used to achieve the mixing of large and small molecules in a certain proportion, so as to achieve the purpose of improving processing performance and mechanical and physical properties at the same time. However, the disadvantage of this method is that the process investment is expensive, the operation is complicated, and the product huge cost

[0005] The present invention provides a kind of operation method that changes polymerization temperature cyclically within a certain period of time, and it is surprising to find that the molecular weight can be produced in a single polymerization reactor by using Ziegler-Natta catalyst or Ziegler-Natta and metallocene composite catalyst. Olefin polymers with a wide distribution and ultra-high molecular weight, that is, the produced polymers have excellent processability and mechanical physical properties at the same time, which cannot be achieved with a single polymerization reactor in the prior art

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