Tröger's Base Polyimide Membranes with Enhanced Mechanical Robustness for Gas Separation

Area of Science:

• Polymer Chemistry
• Materials Science
• Chemical Engineering

Background:

• Tröger's base (TB) units enhance microporosity in polyimides (PIs), improving gas permeability and selectivity for separations.
• TB-based PIs often suffer from poor mechanical properties due to low molecular weight from sterically hindered and less reactive TB diamines.

Purpose of the Study:

• To develop a novel polymerization strategy for creating high-performance TB-based polyimides.
• To overcome the limitations of traditional TB diamine polymerization for enhanced mechanical and gas separation properties.

Main Methods:

• Synthesis of a novel diamine containing a bisimide linkage (BIDA).
• Polymerization of BIDA with paraformaldehyde using a "TB polymerization" strategy to form TB-PIs.
• Incorporation of a meta-methyl substituent into BIDA to create m-MBIDA for improved polymer properties.

Main Results:

• The m-MBIDA-derived m-MTBPI achieved high molecular weight with good tensile strength (90.4 MPa) and fracture toughness (45.1 MJ/m³).
• The m-MTBPI membrane showed significantly enhanced gas separation capabilities, approaching the 1991 Robeson upper bound.
• The m-MTBPI membrane exhibited no plasticization under high-pressure CO₂/CH₄ separation (up to 20 bar), nearing the 2018 upper bound.

Conclusions:

• The novel "TB polymerization" strategy successfully produced high-performance polyimides with improved mechanical strength and gas separation efficiency.
• The m-MTBPI material demonstrates excellent potential for industrial gas separation applications, particularly for CO₂/CH₄ mixtures.
• This approach offers a viable route to overcome previous limitations in TB-based polyimide development.