High-Pressure Selective Topotactic Synthesis of Ordered Trans-Polymeric CS₂ in a Zeolite

Area of Science:

• Materials Science
• Polymer Chemistry
• Solid-State Chemistry

Background:

• High-pressure polymerization of carbon disulfide (CS2) typically yields disordered solids, complicating product characterization and mechanistic studies.
• The inherent multiplicity of chemical pathways for CS2 under pressure contributes to this lack of order.
• Confining the reaction within a defined space offers a strategy to control polymerization pathways.

Purpose of the Study:

• To investigate the selective polymerization of CS2 within the confined environment of a zeolite.
• To synthesize and characterize an ordered form of Bridgman's black polymer.
• To elucidate the reaction mechanism of CS2 polymerization under confinement.

Main Methods:

• Insertion of liquid CS2 into the one-dimensional pores of the all-siliceous zeolite Theta-One.
• High-pressure and high-temperature treatment (250 °C and 14 GPa).
• Synchrotron X-ray diffraction for structural analysis.
• Ab initio calculations for structural refinement and mechanistic modeling.

Main Results:

• Selective topotactic polymerization of CS2 occurred within the zeolite pores.
• The ordered trans-isomer of Bridgman's black polymer (-(C=S)-S-)n was successfully synthesized.
• A reaction mechanism involving molecular bending followed by addition was proposed.
• Ab initio calculations indicated spontaneous formation of the trans-polymer from the confined monomer.

Conclusions:

• Confinement within zeolite Theta-One enables controlled polymerization of CS2.
• This method yields the ordered trans-isomer of Bridgman's black polymer, previously difficult to characterize.
• The study provides critical insights into the polymerization mechanism of CS2 under pressure.