Metallocene Catalyst for High Melt Flow Polypropylene Homopolymers
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Solution Overview
Problem
The production of high melt flow polypropylene homopolymers typically requires vis-breaking techniques and peroxide additives, which are undesirable, and existing methods struggle to achieve the necessary molecular weight and melting point characteristics suitable for fiber and related applications.
Innovation Solution
A catalyst system comprising a racemic ansa-bis(indenyl)zirconocene compound, an activator-support, and an optional co-catalyst is used to produce polypropylene homopolymers with specific melt flow rates, molecular weight ratios, and melting points without the need for vis-breaking processes or peroxide additives, allowing for the creation of polypropylene homopolymers suitable for various applications, including fibers and molded products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional polymerization methods are used to produce high melt flow polypropylene homopolymers, then melt flow rate can be increased through vis-breaking techniques and peroxide additives, but the process complexity and use of harmful additives increase
Solution Approach 1:
The patent changes the fundamental parameters of the polymerization process by using a specific metallocene catalyst system with controlled hydrogen concentration to directly produce high melt flow polypropylene homopolymers with desired molecular weight characteristics, eliminating the need for post-polymerization vis-breaking treatments and peroxide additives
Solution Approach 2:
The invention extracts and eliminates the harmful vis-breaking step and peroxide additives from the conventional polymerization process by using a catalyst system that directly produces the desired melt flow characteristics during polymerization, resulting in cleaner polymer without residual peroxides or degradation products
2Productivity
If vis-breaking techniques and peroxide additives are used to increase melt flow rate, then high melt flow polypropylene can be produced, but molecular weight control and polymer purity deteriorate
Solution Approach 1:
The patent performs preliminary molecular weight control during the polymerization process itself by using hydrogen as a chain transfer agent with the metallocene catalyst system, establishing the desired molecular weight distribution before polymer isolation, thereby eliminating the need for post-processing molecular weight modification that would compromise purity
3Productivity
If peroxide additives are used to achieve high melt flow rates, then viscosity can be reduced, but polymer purity and quality decrease due to residual peroxides and degradation products
Solution Approach 1:
The invention converts the potential harm of peroxide additives and vis-breaking degradation into a benefit by using a catalyst system that naturally produces the desired low viscosity and high melt flow characteristics through controlled molecular weight distribution, transforming what was a harmful post-treatment into an inherent property of the polymerization process
Solution Approach 2:
The metallocene catalyst system with hydrogen performs self-service by automatically controlling the molecular weight and melt flow characteristics during polymerization without requiring external peroxide additives or vis-breaking treatments, producing clean polymer that is inherently suitable for fiber and film applications
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
The described catalyst system enables the production of polypropylene homopolymers with high melt flow rates, controlled molecular weight distributions, and suitable melting points, eliminating the need for vis-breaking and peroxide additives, resulting in cleaner, high-quality polymers for diverse applications.
Implementation Method 1
catalyst systems containing a bridged bis(indenyl) metallocene compound and an activator-support
Data Source
AI summary
Disclosed herein are high melt flow polypropylene homopolymers generally characterized by a melt flow rate ranging from 200 g/10 min to 3000 g/10 min, a ratio of Mw/Mn ranging from 2 to 5, and a peak melting point ranging from 138° C. to 151° C. These polypropylene homopolymers can be produced by catalyst systems containing a racemic ansa-bis(indenyl)zirconocene compound, an activator-support, and an organoaluminum co-catalyst.