Cross-Linked Polymer−Ionic Liquid Composite Materials

A series of composites, some with permanent porosity, comprising polymers and ionic liquids have been prepared by in-situ polymerization. The characteristics of both composites and isolated polymers have been investigated. Slow mass and phase transfer characterize the interaction with a range of polymers ( 1 − 17 ) in the N,N ‘ -dialkylimidazolium ionic liquids, [emim]BF 4, [bmim]PF 6, or [omim]N(SO 2 CF 3 ) 2 . Free-radical homopolymerization of 1-vinyl-2-pyrrolidinone in [bmim]PF 6 or of 4-vinylpyridine in [omim]N(SO 2 CF 3 ) 2 gave viscous solutions from which polymer ( M w = 162 500 and 71 500 g mol -1, respectively) could be isolated. Detectable ionic liquid residues were retained in the isolated polymers despite five reprecipitations from methanol. Copolymerization of 4-vinylpyridine (VP) with >5% divinylbenzene (DVB) or trimethylolpropane trimethacrylate (TRIM) in [omim]N(SO 2 CF 3 ) 2, and homopolymerizations of the cross-linking monomers on their own, led with 90−100% monomer conversion to a series of gel-like composite materials, B − H, from which cross-linked polymers, B ‘ − H ‘, could be isolated by Soxhlet extraction of the ionic liquid. Copolymers of VP with 5−30% DVB ( E ‘, F ‘) showed a low degree of permanent porosity in the dry state. However, poly(DVB) ( G ‘) and poly(TRIM) ( H ‘) have bulk densities (<0.6 g cm -3 ), intrusion volumes (>0.9 cm 3 g -1 ), BET surface areas (70−320 m 2 g -1 ), and morphology (from SEM studies) which demonstrate the porogenic character of the ionic liquids used. Comparisons with the related products I and J obtained in toluene reveal the sensitivity of these systems both to the properties of the porogen solvent and to the monomer used.