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Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization
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DFT and ONIOM Simulation of 1,3-Butadiene Polymerization Catalyzed by Neodymium-Based Ziegler-Natta System
Alexey N Masliy1, Ildar G Akhmetov2, Andrey M Kuznetsov1
1Department of Inorganic Chemistry, Kazan National Research Technological University, K. Marx Street 68, 420015 Kazan, Russia.
Polymers
|March 11, 2023
Summary
Neodymium-based Ziegler-Natta catalysts achieve high cis-stereospecificity in 1,3-butadiene polymerization. This is due to the lower activation energy for cis-1,3-butadiene insertion, not its initial coordination.
Area of Science:
- Polymer Chemistry
- Organometallic Chemistry
- Quantum Chemistry
Background:
- Neodymium-based Ziegler-Natta systems are crucial for stereospecific polymerization of dienes.
- Understanding the mechanism of cis-stereospecificity in 1,3-butadiene polymerization is key to controlling polymer microstructure.
- Previous studies suggest coordination preference influences stereochemistry, but the exact role in neodymium catalysis requires clarification.
Purpose of the Study:
- To theoretically investigate the origin of high cis-stereospecificity in 1,3-butadiene polymerization using neodymium-based Ziegler-Natta catalysts.
- To elucidate the role of monomer coordination and insertion in determining the stereochemical outcome of the polymerization process.
Main Methods:
- Employed modern quantum chemistry methods, including Density Functional Theory (DFT) and ONIOM simulations.
- Utilized the most cis-stereospecific active site model of the catalytic system for all simulations.
- Analyzed total energy, enthalpy, and Gibbs free energy of active centers and modeled the π-allylic insertion mechanism.
Main Results:
- Coordination of trans-1,3-butadiene is energetically more favorable (11 kJ/mol) than cis-1,3-butadiene.
- However, the activation energy for cis-1,3-butadiene insertion into the growing chain is significantly lower (10-15 kJ/mol) than for trans-1,3-butadiene.
- Activation energies were consistent for both cis- and trans-1,4-butadiene monomers, indicating insertion pathway dictates stereochemistry.
Conclusions:
- The high cis-stereospecificity is primarily governed by the lower activation energy barrier for the insertion of cis-1,3-butadiene.
- This contradicts the notion that stereoregulation solely depends on the initial coordination preference of the monomer.
- The study clarifies the mechanism behind the exceptional cis-stereospecificity achieved by neodymium-based Ziegler-Natta polymerization systems.
Keywords:
1,3-butadiene polymerizationDFTONIOMcis-1,4-polybutadieneneodymium-based Ziegler–Natta systemstereospecificityMore Related Videos
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