A novel route to ionogels using polymerisation-induced self-assembly in ionic liquid

Abstract

This Thesis describes the ionic liquid-directed self-assembly of block copolymers via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerisation-induced self-assembly (PISA) to conveniently generate so-called ionogels. Firstly, polymer solubility screenings were conducted in two hydrophilic ionic liquids (ILs), 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) and 1-ethyl-3-methylimidazolium ethyl sulphate ([EMIM][EtOSO3]). Subsequently, suitable polymers were identified for proceeding PISA syntheses. Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(benzyl methacrylate) (PBzMA) were identified as a suitable stabiliser block and core-forming block, respectively. Additionally, benzyl methacrylate (BzMA) monomer was shown to be miscible with both ILs, enabling the development of dispersion PISA formulations which provide the most accessible route to worm gels. A PHEMA macromolecular chain transfer agent was synthesised via RAFT solution polymerisation and subsequently chain extended via RAFT dispersion polymerisation of BzMA in [EMIM][DCA] to afford block copolymer nanoparticles, specifically spheres, worms and vesicles, as confirmed by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The presence of worms enabled the formation of free-standing gels at copolymer concentrations >4% w/w. These gels that exhibited comparable electrochemical properties and thermal stability to [EMIM][DCA] alone. Moreover, rheological studies indicated that stiffer gels were formed when an increasing proportion of worms was present. This PISA formulation in [EMIM][DCA] facilitates the in situ formation of worm ionogels without the need for crosslinkers, co-solvents or post-polymerisation processing/purification. PHEMA-b-PBzMA nanoparticle syntheses were also conducted in [EMIM][EtOSO3]. The presence of spheres and vesicles was confirmed by DLS and SAXS, however no gelation occurred for the PBzMA DP range at 15% w/w and 20% w/w copolymer, indicating the absence or an insufficient proportion of worm-like nanoparticles. This could be due to the length of the PHEMA stabiliser block being sufficiently large to prevent fusion of 2D spheres in this specific IL, thus hindering the ability to form anisotropic worms.