Abstract
Until now, the leading polymer of intrinsic microporosity PIM-1 has become quite famous for its high membrane permeability for many gases in gas separation, linked, however, to a rather moderate selectivity. The combination with the hydrophilic and low permeable poly(ethylene glycol) (PEG) and poly(ethylene oxides) (PEO) should on the one hand reduce permeability, while on the other hand enhance selectivity, especially for the polar gas CO2 by improving the hydrophilicity of the membranes. Four different paths to combine PIM-1 with PEG or poly(ethylene oxide) and poly(propylene oxide) (PPO) were studied: physically blending, quenching of polycondensation, synthesis of multiblock copolymers and synthesis of copolymers with PEO/PPO side chain. Blends and new, chemically linked polymers were successfully formed into free standing dense membranes and measured in single gas permeation of N2, O2, CO2 and CH4 by time lag method. As expected, permeability was lowered by any substantial addition of PEG/PEO/PPO regardless the manufacturing process and proportionally to the added amount. About 6 to 7 wt % of PEG/PEO/PPO added to PIM-1 halved permeability compared to PIM-1 membrane prepared under similar conditions. Consequently, selectivity from single gas measurements increased up to values of about 30 for CO2/N2 gas pair, a maximum of 18 for CO2/CH4 and 3.5 for O2/N2.
Highlights
Polymers of intrinsic microporosity have been and continue to be the objects of many research papers since Budd and McKeown launched their first publication aboutPIM-1 in 2004 [2].PIM-1 is a hydrophobic polymer formed as a molecular ladder; the polymer chains cannot pack tightly because of their contorted molecular structure, provided by spiro fused rings in the polymer chain
Permeability was lowered by any substantial addition of poly(ethylene glycol) (PEG)/poly(ethylene (or higher equivalents) oxide) (PEO)/PPO regardless the manufacturing process and proportionally to the added amount
Within Path 3, we combined small PIM-1 blocks with different PEO-containing co-monomers (PEG di-substituted by esterification with dihydroxybenzoic acid (DHBA)) to form multiblock copolymers (PIM1-b-PEO)
Summary
Polymers of intrinsic microporosity have been and continue to be the objects of many research papers (see, e.g., citations in [1]) since Budd and McKeown launched their first publication about. Within Path 3, we combined small PIM-1 blocks (at least smaller blocks than in Paths 1 and 2) with different PEO-containing co-monomers (PEG di-substituted by esterification with dihydroxybenzoic acid (DHBA)) to form multiblock copolymers (PIM1-b-PEO) This approach increased the influence of PEO further by avoiding large parts/blocks of pure PIM-1. PEG/PEO chains tend to crystallize with increasing molecular weight and crystallites do not contribute to permeability At elevated temperature, these crystallites will melt, influencing diffusivity and solubility favorably [10]. We include measurements of gas permeability at elevated temperatures to inquire the influence of melting PEO chains
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