The synthesis of polypropylene glycol based polyethers and their use in membranes for the membrane aromatic recovery system (MARS)

This study reports the syntheses of aliphatic polyethers, by cationic ring-opening photo polymerisation of oxetane functionalised polypropylene glycol (PPG), and the application of these polyethers in forming membranes for use in the membrane aromatic recovery system (MARS). The PPG was functionalised using 3-methyl-3-bromomethyl oxetane. The cationic ring-opening polymerisation of oxetane functionalised PPG was effected by UV light in the presence of onium salt photoinitiator to produce crosslinked gels. This is the first study reporting the photo-initiated cationic ring-opening polymerisation of PPG. The polyethers produced showed high affinity for phenol (partition coefficient of 58 between polyether and water) and proved chemically stable in 10 wt.% caustic solution. The membranes were prepared by impregnating the mixture of oxetane functionalised PPG and onium salt photoinitiator into the pores of a mesoporous polypropylene support and subsequently exposing them to UV light. The membrane prepared was then tested under MARS operating conditions for more than 2 months during which it was observed to be stable. The membrane exhibited mass transfer rates (3 × 10−6 m s−1) 20 times higher than that of tubular silicone rubber membranes (1.5 × 10−7 m s−1).