Bimodal Polypropylene Polymerization for Impact Strength
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Solution Overview
Problem
Current metallocene catalysis technologies for producing polypropylene materials face challenges in achieving a balance between toughness and stiffness, with limitations in porosity and rubber content, leading to suboptimal impact strength and molecular weight distribution.
Innovation Solution
A bimodal polypropylene polymerization process using a catalyst system with a support having a specific particle size, surface area, and pore volume, allowing for a matrix phase with high propylene content and a fill phase that partially fills the matrix, enhancing porosity and rubber loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If metallocene catalysts are used to produce polypropylene copolymers, then copolymers have narrow composition distributions and favorable properties, but the iPP matrix has low porosity and is unable to hold sufficiently high rubber content required for toughness and impact resistance
Solution Approach 1:
The patent applies segmentation by using a sequential two-catalyst polymerization process where the first catalyst (metallocene) produces the iPP matrix with controlled narrow composition distribution, and the second catalyst (Ziegler-Natta) produces the rubber phase with high elasticity. This segmentation of function between two catalyst systems allows each to optimize its specific role, resolving the contradiction between composition precision and impact resistance.
Solution Approach 2:
The patent creates a composite heterophasic copolymer material consisting of an iPP matrix phase and a rubber dispersed phase. The matrix provides structural integrity and stiffness, while the rubber phase provides toughness and impact resistance. This composite structure allows the final material to exhibit both the manufacturing precision benefits of metallocene catalysts and the mechanical properties benefits of high rubber content.
2Manufacturing precision
If MCN catalysts are used, then copolymers have narrow MWD, but the MWD is too narrow to obtain sufficient crystalline, low molecular weight polymer required for stiffness
Solution Approach 1:
The patent segments the molecular weight distribution control between two catalysts: the metallocene catalyst produces the high molecular weight iPP matrix with narrow MWD for precision, while the Ziegler-Natta catalyst produces the lower molecular weight rubber phase with broader MWD that contributes to stiffness through crystallization. This segmentation resolves the contradiction between narrow MWD precision and sufficient stiffness.
3Volume of stationary object
If high concentration of hydrogen is used to form low molecular weight polymers for fast-crystallization shrinkage, then high porosity is achieved, but polymerization under these conditions detracts from the stiffness of the resulting ICP
Solution Approach 1:
The patent applies preliminary action by first forming the porous iPP matrix structure through controlled polymerization before introducing the rubber phase. The porosity is pre-established through the matrix formation process with optimized hydrogen concentration, and then the rubber phase is added to fill some pores and provide stiffness without requiring additional high hydrogen concentrations that would compromise stiffness.
Solution Approach 2:
The composite heterophasic structure allows the iPP matrix to provide porosity for toughness while the rubber phase provides stiffness. The rubber phase acts as a stiffening agent within the porous matrix, resolving the contradiction between achieving high porosity and maintaining stiffness.
4Quantity of substance
If the formation of rubber in a separate phase outside the matrix is allowed, then high rubber content can be achieved, but it results in severe reactor fouling
Solution Approach 1:
The patent applies the nested doll principle by forming the rubber phase within the pores and void spaces of the iPP matrix structure, rather than as a separate external phase. The rubber is nested within the matrix framework, which contains it and prevents the severe reactor fouling that would occur with external separate phase formation, while still achieving high rubber content.
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 process produces polypropylene materials with improved impact strength, stiffness, and molecular weight distribution, achieving high porosity and rubber content while maintaining economic production on a commercial scale.
Implementation Method 1
contacting propylene monomer under polymerization conditions with a first catalyst system, comprising a single site catalyst precursor compound, an activator, and a support to form a matrix phase of propylene polymer
Implementation Method 2
contacting an alpha olefin monomer selected from ethylene, C3 to C20 alpha olefins, or a combination thereof, with a second catalyst system under polymerization conditions to form a fill phase for pores of the matrix
Implementation Method 3
a support having an average particle size (PS) of more than 30 μm, a surface area (SA) of 400 m2/g or more, a pore volume (PV) of from 0.5 to 2 mL/g
Data Source
AI summary
This invention relates to heterophasic copolymers of propylene and an alpha olefin comonomer having a high fill phase content (≥15%), and heterophasic polymerization processes using a single site catalyst system with a support having high average particle size (PS≥30 μm), high surface area (SA≥400 m2/g), low pore volume (PV≤2 mL/g), and a mean pore diameter range of 1≤PD≤20 nm.