Gas transport in membranes based on polynorbornenes with fluorinated dicarboximide side moieties

摘要

This work reports a comparative study of gas transport in membranes based on polynorbornenesudand polyoxanorbornenes containing fluorinated dicarboximide side moieties,udspecifically, poly(N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide), poly(exo-Npentafluorophenyl-ud7-oxanorbornene-5,6-dicarboximide), poly(N-3,5-bis(trifluoromethyl)phenylexo-udendo-norbornene-5,6-dicarboximide) and a random copolymer of N-pentafluorophenyl-exo-endonorbornene-ud5,6-dicarboximide-co-N-phenyl-exo-endo-norbornene-5,6-dicarboximide with 50/50Mudcomposition. The gases studied were hydrogen, oxygen, nitrogen, carbon dioxide, methane, ethane,udethylene and propylene. The presence of fluorine atoms in the membranes increases their permeabilityudin slight detriment of the permselectivity, the increase being higher for F–C bonds with carbonudhybridization sp3 than sp2. The substitution of the CH2 groups of the norbornene moieties decreasesudthe permeability as a consequence of the decrease of the solubility. A thorough study is carried out onudthe variation of the permeability coefficient and concentration of condensable gases, such as carbonuddioxide and propylene, in the poly(N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide) andudpoly(N-3,5-bis(trifluoromethyl)phenyl-exo-endo-norbornene-5,6-dicarboximide) membranes findingudthat the values of the effective diffusion coefficient are similar to those obtained by the dual-modeudmodel but significantly higher than those estimated by the time-lag from permeation results. The resultsudalso show that conditioning the membranes with condensable gases under high pressure increases theuddiffusivity.