Cyclic Bridged Metallocene Catalyst for Bimodal Polymerization
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Solution Overview
Problem
Metallocene catalysts used in olefin polymerization, particularly those with cyclic bridges, face challenges in processability due to low productivity and narrow molecular weight distribution, leading to difficulties in producing polymers with improved mechanical and optical properties.
Innovation Solution
A cyclic bridged metallocene catalyst system activated by aluminoxane and supported on a porous material, such as silica, is used for gas-phase polymerization of ethylene and other olefins, enhancing productivity and allowing for broad molecular weight distribution, which improves film haze and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallocene catalysts are used for polymerization, then superior physical properties are achieved, but processability deteriorates due to narrow molecular weight distribution and lower melt strength
Solution Approach 1:
The invention uses a mixture of two different metallocene catalysts (first and second metallocene catalysts) to produce a polymer with bimodal molecular weight distribution. This segmentation of the catalyst system allows simultaneous production of high molecular weight chains (for mechanical strength) and low molecular weight chains (for processability), resolving the contradiction between superior physical properties and ease of processing
Solution Approach 2:
The invention creates a composite catalyst system combining two distinct metallocene catalysts with different ligand structures (e.g., cyclopentadienyl-based and indenyl-based). This composite approach produces a polymer with combined characteristics: narrow overall distribution but with both high and low molecular weight fractions present, achieving both strength and processability
2Strength
If metallocene catalysts are used for polymerization, then superior physical properties are achieved, but productivity deteriorates due to lower output compared to conventional catalysts
Solution Approach 1:
The invention merges the functions of two different metallocene catalysts into a single polymerization system. The first metallocene catalyst produces high molecular weight polymer contributing to mechanical strength, while the second metallocene catalyst produces low molecular weight polymer enhancing flow and processing. This merging of catalyst functions simultaneously achieves superior physical properties and maintained productivity
3Strength
If molecular weight distribution is narrowed to improve physical properties, then mechanical strength increases, but processability deteriorates due to difficulty in processing
Solution Approach 1:
The invention segments the molecular weight distribution into two distinct populations (bimodal) through using two different metallocene catalysts. The high molecular weight fraction provides mechanical strength while the low molecular weight fraction provides processability. This segmentation resolves the contradiction by having different molecular weight populations serve different functional requirements
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 catalyst system achieves higher productivity and broad molecular weight distribution, resulting in polymers with improved melt strength, film haze, and mechanical properties, making them easier to process and suitable for various applications.
Implementation Method 1
a cyclic bridged metallocene catalyst system activated by aluminoxane and supported on a porous material, such as silica, is used for gas-phase polymerization of ethylene and other olefins
Data Source
AI summary
A process for polymerizing olefin(s) utilizing a cyclic bridged metallocene catalyst system to produce polymers with improved properties is provided. The catalyst system may include a cyclic bridged metallocene, LA(R'SiR')LBZrQ2, activated by an activator, the activator comprising aluminoxane, a modified aluminoxane, or a mixture thereof, and supported by a support, where: LA and LB are independently an unsubstituted or a substituted cyclopentadienyl ligand bonded to Zr and defined by the formula (C5H4-dRd), where R is hydrogen, a hydrocarbyl substituent, a substituted hydrocarbyl substituent, or a heteroatom substituent, and where d is O, 1, 2, 3 or 4; LA and LB are connected to one another with a cyclic silicon bridge, R' SiR', where R' are independently hydrocarbyl or substituted hydrocarbyl substituents that are connected with each other to form a silacycle ring; and each Q is a labile hydrocarbyl or a substituted hydrocarbyl ligand.