Highly Permeable Polyimides

Polyimides are polymers produced by cycloimidization (formation of an imide linkage) between di-anhydrides and diamines via step-growth polymerization (Koros and Fleming 1993; Ghosh and Mittal 1996). Among other useful applications such as materials for electronics, coatings, foam, and fibers, because of their excellent solubility in common low boiling point solvents, thermal stability, and physical properties, they have been extensively studied as gas separation membranes. A typical limitation for their use in this field is due to the fact that they often exhibit high selectivity but low permeability for important gas pairs such as O₂ and CO₂, usually far below 100 Barrer (1 Barrer = 10⁻¹⁰ cm³(STP) cm cm⁻² s⁻¹ cmHg⁻¹). The low permeability is strongly related with the lack of fractional free volume of the material (FFV) because of the free rotation around the imide linkage that allows the polymer to pack densely, limiting the mass transport. Initial successes in enhancing the...