Hafnium Metallocene Catalysts for Propylene Polymerization
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Solution Overview
Problem
Current metallocene catalysts for propylene polymerization fail to produce high molecular weight propylene homopolymers and heterophasic copolymers with optimal melting temperatures and molecular weights, limiting their application in materials with desired tensile and impact properties.
Innovation Solution
Development of specific C1-symmetric metallocene catalysts, including hafnium-based complexes with specific ligand structures and cocatalysts, such as aluminium and boron-based compounds, which are used in a liquid/liquid emulsion system to form solid catalyst particles without external carriers, enhancing polymerization performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional metallocene catalysts are used for propylene polymerization, then the polymerization process can proceed, but the molecular weight of the resulting propylene homopolymers is insufficient and melting temperature is low
Solution Approach 1:
The patent changes the metal center from zirconium to hafnium, and modifies the ligand structure with specific substituents (tert-butyl groups at positions 3 and 5 of the indenyl rings). These parameter changes in the catalyst composition result in propylene homopolymers with melting temperature ≥160°C and molecular weight ≥200,000, simultaneously improving both temperature and reliability parameters
Solution Approach 2:
The patent creates a composite catalyst system combining hafnium metal center with specific C1-symmetric metallocene ligands and aluminoxane cocatalysts. This composite material approach enables the catalyst to produce polymers with both high melting temperature and high molecular weight, resolving the contradiction between these two properties
2Temperature
If metallocene catalysts are used for heterophasic copolymer production, then copolymerization occurs, but the melting point of the polymer matrix and molecular weight of the rubber phase are not optimal
Solution Approach 1:
The patent modifies catalyst parameters by using hafnium instead of zirconium and incorporating specific ligand structures with tert-butyl substituents. These changes enable the production of heterophasic copolymers with matrix melting point ≥160°C and rubber phase molecular weight ≥200,000, simultaneously improving both temperature and quantity parameters
3Productivity
If existing metallocene catalysts are used, then polymerization activity is achieved, but catalyst productivity and overall performance need improvement
Solution Approach 1:
The patent develops a composite catalyst system with hafnium metal center, C1-symmetric metallocene ligands, and aluminoxane cocatalysts. This composite structure achieves high catalyst activity and productivity while simultaneously producing polymers with high molecular weight and melting temperature, resolving the contradiction between productivity and reliability
Data Source
AI summary
A complex of formula (I): (I′) M is Hf; each X is a sigma ligand; L is a bridge of formula -(ER82)y—; y is 1 or 2; E is C or Si; each R8 is independently a C1-C20-hydrocarbyl, tri(C1-C20-alkyl)silyl, C6-C20-aryl, C7-C20-arylalkyl or C7-C20-alkylaryl or L is an alkylene group such as methylene or ethylene; Ar and Ar′ are each independently an aryl or heteroaryl group optionally substituted by 1 to 3 groups R1 or R1′ respectively; R1 and R1′ are each independently the same or can be different and are a linear or branched C1-C6-alkyl group, C7-20 arylalkyl, C7-20 alkylaryl group or C6-20 aryl group with the proviso that if there are four or more R1 and R1′ groups present in total, one or more of R1 and R1′ is other than tert butyl; R2 and R2′ are the same or are different and are a CH2—R9 group, with R9 being H or linear or branched C1-C6-alkyl group, C3-8 cycloalkyl group, C6-10 aryl group; each R is a —CH2—, —CHRx- or C(Rx)2- group wherein Rx is C1-4 alkyl and where m is 2-6; R5 is a linear or branched C1-C6-alkyl group, C7-20 arylalkyl, C7-20 alkylaryl group or C6-C20-aryl group; R6 is a C(R10)3 group, with R10 being a linear or branched C1-C6 alkyl group; and R6 and R7′ are the same or are different and are H or a linear or branched C1-C6-alkyl group. Invention relates also to a catalyst in solid form comprising (i) a complex of formula (I) and (ii) a cocatalyst of an aluminium compound and (iii) a cocatalyst of a boron compound.