Ethylene Copolymers With Segmented Branching For Impact Resistance
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Solution Overview
Problem
Medium or high density polyethylene polymers with high molecular weight and broad molecular weight distribution often lack sufficient puncture, impact, and tear resistance, which are essential for certain end-use applications.
Innovation Solution
A catalyst composition comprising two metallocene catalyst components is used to produce ethylene-based copolymers with a specific molecular weight ratio and long chain branch distribution, resulting in polymers with improved mechanical properties, such as high puncture and impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If medium or high density polyethylene polymers with high molecular weight and broad molecular weight distribution are used, then processing ease and melt strength are improved, but puncture, impact, and tear resistance are insufficient
Solution Approach 1:
The patent segments the polymer into two distinct molecular weight components: a high molecular weight component (Mw > 100,000) providing melt strength and processing ease, and a low molecular weight component (Mw < 10,000) providing puncture, impact, and tear resistance. This segmentation allows each component to fulfill specific functional requirements that cannot be achieved by a single broad molecular weight distribution.
Solution Approach 2:
The patent applies local quality by assigning different long chain branch characteristics to different molecular weight components. The high molecular weight component has controlled long chain branching (5-20 branches per 1000 carbon atoms) for melt strength, while the low molecular weight component has higher long chain branching (20-50 branches per 1000 carbon atoms) for toughness and impact resistance. This localized differentiation optimizes performance in specific application areas.
2Strength
If dual metallocene catalyst system is used to produce polymers with specific molecular weight ratio and long chain branch distribution, then puncture and impact resistance are improved, but catalyst composition complexity increases
Solution Approach 1:
The catalyst system is segmented into two distinct metallocene catalysts, each responsible for producing a specific molecular weight component. Catalyst A (e.g., rac-ethylenebis(indenyl)zirconium dichloride) produces the high molecular weight component with controlled long chain branching, while Catalyst B (e.g., dimethylsilylenebis(phenylindene)zirconium dichloride) produces the low molecular weight component with higher long chain branching. This segmentation of catalytic function enables precise control over polymer architecture.
Solution Approach 2:
The patent utilizes parameter changes by varying the metallocene catalyst structure (different ligand systems, metal centers, and bridging groups) to control the molecular weight and long chain branch frequency of each polymer component. By adjusting catalyst composition ratios, comonomer content, and polymerization conditions, the patent achieves target molecular weight distributions and branch frequencies that optimize mechanical properties.
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 resulting ethylene copolymers exhibit enhanced puncture and impact resistance, as demonstrated by dart impact strength greater than 300 g/mil, while maintaining a balance of stiffness and physical properties.
Implementation Method 1
A catalyst composition comprising two metallocene catalyst components is used to produce ethylene-based copolymers with a specific molecular weight ratio and long chain branch distribution
Data Source
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AI summary
Disclosed herein are ethylene-based polymers produced using dual metallocene catalyst systems. These polymers have low densities, high molecular weights, and broad molecular weight distributions, as well as having the majority of the long chain branches in the lower molecular weight component of the polymer, and the majority of the short chain branches in the higher molecular weight component of the polymer. Films produced from these polymers have improved impact and puncture resistance.