Prepolymerized Ziegler-Natta Catalyst for Polyolefin Transparency
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Solution Overview
Problem
Existing methods for improving the rigidity and transparency of propylene polymers, such as using nucleating agents or prepolymerizing vinyl saturated cyclic hydrocarbons, often result in reduced bulk density, reduced polymerization reactivity, or decreased catalytic activity, which limits their effectiveness in achieving high crystallization temperatures and isotactic indices.
Innovation Solution
Sequential prepolymerization of a Ziegler-Natta catalyst with α-olefin and vinyl saturated cyclic hydrocarbon without an external electron donor, followed by polymerization of olefin using the prepolymerized catalyst, to produce a highly crystalline and transparent polyolefin with maintained catalytic activity and isotactic index.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If nucleating agents are used to improve crystallization rate and transparency, then transparency and rigidity are improved, but shrinkage anisotropy and warpage defects occur
Solution Approach 1:
The patent uses vinyl saturated cyclic hydrocarbon as an intermediary substance that acts as a built-in nucleating agent within the polypropylene matrix. This intermediary approach eliminates the need for separate external nucleating agents, thereby maintaining transparency and rigidity improvements while avoiding shrinkage anisotropy and warpage defects associated with conventional nucleating agents
2Temperature
If vinyl saturated cyclic hydrocarbon is prepolymerized to improve rigidity and transparency, then crystallization temperature is improved, but bulk density is greatly reduced
Solution Approach 1:
The patent optimizes the preparation parameters including controlling the molar ratio of vinyl saturated cyclic hydrocarbon to propylene at 0.01-0.1, preparing the catalyst at specific temperatures (0-50°C), and controlling the prepolymerization time. These parameter changes enable achieving high crystallization temperature (120-135°C) while maintaining acceptable bulk density (0.35-0.45 g/mL)
3Productivity
If polymerization is performed at high temperature to increase polymerization rate, then productivity is improved, but catalytic activity is reduced
Solution Approach 1:
The patent performs preliminary action by pre-coordinating the Ziegler-Natta catalyst with vinyl saturated cyclic hydrocarbon before the main propylene polymerization. This preliminary coordination activates the catalyst and creates active sites that maintain high catalytic activity even at elevated polymerization temperatures (50-100°C), thereby achieving both high productivity and maintained catalytic activity
4Manufacturing precision
If external electron donor is used to improve Isotactic index, then Isotactic index is improved, but polymerization reactivity is reduced
Solution Approach 1:
The patent uses vinyl saturated cyclic hydrocarbon as an intermediary that coordinates with the Ziegler-Natta catalyst to form active sites with appropriate steric environment. This intermediary approach achieves high isotactic index (90-98%) through controlled coordination geometry while maintaining high polymerization reactivity, avoiding the reactivity reduction problem associated with conventional external electron donors
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves a polyolefin with high yield, isotactic index, bulk density, and crystallinity, while maintaining high catalytic activity and improving transparency and crystallization temperature, without the drawbacks of reduced reactivity or bulk density seen in previous methods.
Implementation Method 1
a) first prepolymerizing a Ziegler-Natta catalyst and α-olefin; and b) second prepolymerizing the Ziegler-Natta catalyst by adding vinyl saturated cyclic hydrocarbon
Implementation Method 2
polymerizing an olefin using the prepolymerized Ziegler-Natta catalyst, a highly crystalline and transparent polyolefin having a high crystallization temperature
Implementation Method 3
a vinyl saturated cyclic hydrocarbon polymer has a melting point of about 370° C., which is much higher than that of general propylene (melting point of pure isotactic polypropylene is 176° C.), and thus can function as a nucleating agent
Data Source
AI summary
The present invention relates to a prepolymerized catalyst for olefin polymerization, a process for polymerizing an olefin by using the catalyst and a polyolefin produced by the process, in which a Ziegler-Natta catalyst is prepolymerized sequentially using α-olefin and vinyl saturated cyclic hydrocarbon, and then an olefin is polymerized using the prepolymerized Ziegler-Natta catalyst, thereby producing a polyolefin with high yield. Therefore, the polymerized polyolefin has high Isotactic index, bulk density, and crystallinity.