Gradient Modulation of Ansa-Metallocenes for Syndiotactic Propylene Polymerization: Multi-Stage Remote Substituent...

Area of Science:

• Polymer Chemistry
• Materials Science
• Catalysis

Background:

• Economical and sustainable thermoplastic all-polyolefin composites are challenging to produce.
• Polypropylene (PP) has a favorable life cycle assessment but requires modification for desired properties.
• Syndiotactic polypropylene (sPP) offers improved impact resistance, processability, transparency, and elasticity.

Purpose of the Study:

• To develop and evaluate a gradient modulation strategy for cyclopentadienyl-fluorenyl ansa-zirconocenes in propylene polymerization.
• To control polymerization activity, molecular weight, syndiotacticity, unsaturated chain ends, and mechanical properties of sPPs.
• To explore a novel pathway for sustainable polypropylene production.

Main Methods:

• Synthesis and evaluation of three substituted zirconocene catalysts (Zr1, Zr2, Zr3).
• Propylene polymerization using the developed catalysts.
• Analysis of polymer properties including molecular weight, syndiotacticity, chain ends, tensile strength, and elasticity.

Main Results:

• Catalyst substituents (2,6-, 3,5-, and 4- phenyl groups) were correlated with specific sPP properties: high molecular weight, high activity, and high syndiotacticity, respectively.
• The dominant pathway for sPP formation was identified as 1,2-insertion followed by rapid β-H elimination.
• Selected sPP samples exhibited high tensile strength (26.14 MPa) and high elastic properties (SR = 49.2%).

Conclusions:

• Gradient modulation of zirconocene catalysts provides control over sPP properties.
• The developed catalytic system enables the production of sPP with enhanced mechanical performance.
• Incorporating sterically hindered phenyl rings onto fluorenyl ligands offers a promising route to more sustainable polypropylene.