6FDA-DABA Polyimide – Poly(Phenylene) Homopolymer and Copolymer Synthesis, Block Compatibility, FFV, Physical Properties, X-Ray Scattering, Gas Separation Performance, and Modeled Gas Transport

Abstract

A series of 6FDA-DABA (6FD) polyimide and poly(phenylene) (PP) block copolymers and homopolymers were synthesized using a Diels-Alder and polycondensation reaction. PP and 6FD parent polymer solutions in tetrahydrofuran were immiscible. The result coincides with their large theoretical solubility parameter differences of 25.47 and 33.17 (MJ/m³)^1/2. Parent and block polymers estimated fractional free volumes (FFV) ranged between 0.162 and 0.346. 6FD and PP glass transition temperatures (Tg’s) were 285°C and 400°C. Moderate PP block length resulted in two distinct Tg’s, while large block lengths suppressed the 6FD polyimide’s glass transition temperature. A SAXS and AFM morphological analysis revealed two distinct domains, with separation lengths from 9.0 to 47.7 nm. The gas transport properties and separation performance of 6FD-PP block copolymers were investigated and found to be highly dependent upon copolymer structure, FFV, and block composition. The CO₂ permeability increased from 4.3 Barrers (pure 6FD) to 155 Barrers (pure PP), and the CO₂/CH₄ selectivity decreased from 85 (pure 6FD) to 13 (pure PP). A block copolymer of roughly equivalent 6FD -PP block molecular weights had an oxygen permeability roughly between the two parent materials, resulting in a 30% increase in O₂/N₂ selectivity. Finally, five different gas permeability models were used to study structure-transport property correlations. An empirical blend model predicted the most reasonable theoretical permeability for the 6FD-PP block copolymer system. Block copolymerization of gas selective and a highly permeable material allowed for improved gas permselectivity in select gas-pair systems.

Keywords: Polyimide And Polyphenylene Block Copolymer And Homopolymer, Block Compatibility, Fractional Free Volume (FFV), Gas Transport, Gas Transport Models