The structure of poly(carbonsuboxide) on the atomic scale: a solid-state NMR study

Area of Science:

• Polymer Chemistry
• Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science

Background:

• Amorphous poly(carbonsuboxide) [(C3O2)x] is synthesized via polymerization of carbonsuboxide (C3O2).
• Understanding the short-range order and polymerization mechanism is crucial for characterizing this material.
• Previous structural models required further experimental validation.

Purpose of the Study:

• To elucidate the precise structure of amorphous poly(carbonsuboxide) [(C3O2)x].
• To investigate inter- and intramonomeric bonding within the polymer.
• To determine the polymerization mechanism and short-range order.

Main Methods:

• Utilized 13C solid-state NMR spectroscopy with two labeling schemes.
• Employed double-quantum and triple-quantum 2D correlation experiments for peak assignment.
• Performed double-quantum constant-time experiments to establish distance constraints for intermonomeric bonds.
• Supported experimental data with infrared spectroscopy, chemical analysis, and density functional theory (DFT) predictions.

Main Results:

• Distinguished four distinct carbon environments via 13C NMR.
• Assigned peaks using through-space and through-bond dipolar coupling.
• Established connectivity and distance constraints for polymer structure.
• DFT calculations complemented experimental findings on bond lengths.

Conclusions:

• Unambiguously excluded structural models based on gamma-pyronic units.
• Provided strong support for models featuring alpha-pyronic units.
• Discussed the potential for planar ladder- and bracelet-like alpha-pyronic structures in poly(carbonsuboxide).