Heterophasic Polypropylene Catalysts for High-Viscosity Rubber Phases
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Solution Overview
Problem
Existing metallocene catalysts struggle to produce heterophasic polypropylene copolymers with high molecular weight in the rubber phase and high melting point, limiting the tensile and impact properties of the material.
Innovation Solution
The use of asymmetric hafnium bridged bisindenyl type metallocene catalysts in combination with a cocatalyst and optionally a silica support to produce heterophasic polypropylene copolymers with a high intrinsic viscosity in the soluble fraction and high melting point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional metallocene catalysts are used to produce heterophasic polypropylene copolymers, then the polymerization process is feasible, but the molecular weight of the rubber phase remains low (IV < 4 dl/g)
Solution Approach 1:
The patent changes the chemical parameters of the catalyst system by introducing asymmetric hafnium bridged bisindenyl metallocene catalysts with specific ligand structures (Formula I). This parameter change in catalyst composition enables the production of rubber phase with IV ≥ 4 dl/g, resolving the molecular weight limitation of conventional catalysts
Solution Approach 2:
The patent creates a composite catalyst system combining metallocene complex (Formula I), cocatalyst (Formula II or III), and optionally a support material. This composite approach synergistically enhances the catalyst's ability to produce high molecular weight rubber phase while maintaining heterophasic structure
2Temperature
If conventional metallocene catalysts are used for heterophasic polypropylene production, then the process is efficient, but the melting point of the homopolymer matrix is low (Tm < 155-157°C)
Solution Approach 1:
The patent modifies the catalyst structure parameters to asymmetric hafnium bridged bisindenyl type (Formula I) with specific substituent patterns. This parameter change in catalyst chemistry directly influences the crystallinity and melting point of the produced polypropylene matrix, achieving Tm ≥ 155°C
Solution Approach 2:
The patent segments the polymer structure into distinct phases: a crystalline homopolymer matrix phase and an amorphous rubber phase. This segmentation allows the matrix to achieve high melting point and stiffness while the rubber phase provides toughness, resolving the contradiction between temperature and strength
3Strength
If the molecular weight of the rubber phase is increased to improve tensile and impact properties, then the material becomes more ductile, but the processing flowability deteriorates
Solution Approach 1:
The patent applies local quality by creating distinct regions with different properties: the rubber phase particles have high molecular weight (IV ≥ 4 dl/g) for toughness, while the continuous matrix phase has optimized molecular weight for flowability. This local differentiation allows simultaneous achievement of mechanical properties and processability
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 heterophasic polypropylene copolymers exhibit improved tensile and impact properties with a high melting point and molecular weight, particularly in the rubber phase, enhancing material stiffness and performance.
Implementation Method 1
Metallocene catalysts have been used to manufacture polyolefins for many years. Countless academic and patent publications describe the use of these catalysts in olefin polymerization.
Data Source
AI summary
A heterophasic polypropylene copolymer having an MFR2 of 0.05 to 20 g/10 min (ISO 1133 at 230° C. with a loading of 2.16 kg) and a melting point (Tm) of 156 to 164° C. (measured by DSC according to ISO 11357) wherein the heterophasic polypropylene copolymer comprises at least the following components: (A) 55.0 to 95.0 wt % of a crystalline fraction (CF) having a comonomer content of 0 to 3.0 wt %; and (B) 5.0 to 45.0 wt % of a soluble fraction (SF) having a comonomer content of 12 to 45 wt %; wherein the intrinsic viscosity (IV) (in decalin at 135° C.) of the soluble fraction (SF) is 2.5 to 11 dl/g, and wherein the amount of crystalline fraction (CF) and the amount of soluble fraction (SF) are determined in 1,2,4-trichlorobenzene at 40° C.