Non-metal with metal behavior: metal-free coordination-insertion ring-opening polymerization

Area of Science:

• Polymer Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• Ring-opening polymerization (ROP) traditionally relies on metal catalysts.
• The coordination-insertion mechanism, a key ROP pathway, has been exclusively metal-mediated.
• Developing metal-free alternatives is crucial for sustainable and biocompatible polymer synthesis.

Purpose of the Study:

• To demonstrate a metal-free coordination-insertion ROP mechanism.
• To utilize N-trimethylsilyl-bis(trifluoromethanesulfonyl)imide (TMSNTf2) as a non-metallic initiator for ROP.
• To achieve sequential block copolymerization of trimethylene carbonate (TMC) and ε-caprolactone (ε-CL) without metal catalysts.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy for structural elucidation.
• Size Exclusion Chromatography (SEC) for molecular weight determination.
• Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI-TOF) mass spectrometry for polymer characterization.
• Kinetic studies to understand polymerization processes.

Main Results:

• Successful metal-free coordination-insertion ROP of TMC and ε-CL was achieved using TMSNTf2.
• The mechanism involves monomer coordination to the silicon atom and nucleophilic attack by the -NTf2 group.
• Sequential block copolymerization of TMC and ε-CL was successfully performed.
• TMSNTf2-mediated ROP yielded both linear and cyclic polymers.
• Polymerization followed a two-stage first-order kinetic process.

Conclusions:

• TMSNTf2 facilitates an unprecedented metal-free coordination-insertion ROP mechanism.
• This work expands the scope of ROP catalysts beyond traditional metal-based systems.
• The developed method offers a new pathway for synthesizing well-defined polymers, including block copolymers, without metal contamination.