Viologen based star copolymer membranes: Preparation and application in CO2/CH4 separation

Abstract

The eight-armed star copolymer of polyhedral oligomeric silsesquioxane-based poly[(n-butyl acrylate)-co-1-(2-(((2-(acryloyloxy)ethyl)carbamoyl)oxy)ethyl)-1′-methyl-viologen hexafluorophosphate] [POSS-P(BA-co-VAP)₈] containing a polyhedral oligomeric silsesquioxane (POSS) core and 8 arms of viologen based ionic P(BA-co-VAP) is prepared for carbon dioxide (CO₂) separation. In the eight-armed star copolymer, the POSS segment affords great convenience for synthesis of eight-armed star copolymer via reversible addition fragmentation chain transfer (RAFT) polymerization and helps to improve the mechanical strength of the polymer membrane. The poly(n-butyl acrylate) (PBA) segment is hydrophobic and has a low glass transition temperature (T_g), which helps to form star copolymer nano-assemblies and also helps to form membrane at room temperature. The ionic poly[1-(2-(((2-(acryloyloxy)ethyl)carbamoyl)oxy)ethyl)-1′-methyl-viologen hexafluorophosphate] (PVAP) segment is crucial to form nano-assemblies and reversibly adsorb and desorb CO₂ and to improve CO₂ permeability and CO₂/CH₄ permselectivity. By casting the star copolymer nano-assemblies, porous membrane with pore size around 0.2–3.9 μm is prepared, and the prepared membrane exhibits a CO₂ permeability of 636.3 Barrer and a CO₂/CH₄ permselectivity of 22.9, which is competitive to the previously reported polymer membranes.