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Metal-Free Ring-Opening Metathesis Polymerization with Hydrazonium Initiators
Phong K Quach1, Jesse H Hsu1, Ivan Keresztes1
1Department of Chemistry and Chemical Biology, Cornell University, 122 Baker Laboratory, Ithaca, NY 14853, USA.
Angewandte Chemie (International Ed. in English)
|March 18, 2022
Summary
New hydrazonium initiators enable ring-opening metathesis polymerization (ROMP) of cyclopropenes, producing short polyolefin chains. This method shows efficiency comparable to established catalysts for specific monomers.
Area of Science:
- Polymer Chemistry
- Organic Synthesis
Background:
- Ring-opening metathesis polymerization (ROMP) is a versatile method for polymer synthesis.
- Cyclopropenes are strained cyclic olefins suitable for ROMP, but require specific initiators.
- Hydrazonium compounds offer a novel class of initiators for olefin polymerization.
Purpose of the Study:
- To describe the synthesis and application of novel hydrazonium initiators for cyclopropene ROMP.
- To investigate the polymerization mechanism and characteristics of the resulting polyolefins.
- To compare the efficiency of hydrazonium initiators with existing ROMP catalysts.
Main Methods:
- Condensation of 2,3-diazabicyclo[2.2.2]octane with aldehydes to form hydrazonium initiators.
- Polymerization of cyclopropene monomers using the synthesized initiators.
- Characterization of polyolefins using NMR spectroscopy to determine molecular weight and dispersity.
- Comparative studies with Grubbs' 2nd generation catalyst.
Main Results:
- Hydrazonium initiators successfully polymerized cyclopropenes via a [3+2] cycloaddition/cycloreversion mechanism.
- Short-chain polyolefins with molecular weights up to 9.4 kg/mol and low dispersities (≤1.4) were obtained.
- Optimized conditions demonstrated polymerization efficiency comparable to Grubbs' catalyst for 3-methyl-3-phenylcyclopropene.
- NMR analysis confirmed a positive correlation between monomer-to-initiator ratio and degree of polymerization.
Conclusions:
- Hydrazonium initiators represent a new and effective class of catalysts for cyclopropene ROMP.
- The polymerization proceeds through a unique cycloaddition-cycloreversion pathway.
- This method offers a viable alternative for synthesizing short-chain polyolefins with controlled properties.
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