The preparation of low-polydispersity vesicles via polymerisation-induced self-assembly (PISA) in aqueous media is explored. Firstly, a binary mixture of relatively long and relatively short poly(ethylene glycol) (PEG) stabiliser blocks is evaluated for the preparation of diblock copolymer vesicles via RAFT aqueous dispersion polymerisation of 2-hydroxypropyl methacrylate (PHPMA) at 50 °C. Systematic variation of the mole fraction (x) of the longer PEG block while targeting a mean degree of polymerisation (DP) of 400 for the PHPMA block produced a series of nano-objects at 10% w/w solids. These nano-objects were studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS), but proved to be too large for conventional small-angle X-ray scattering (SAXS) studies. TEM indicated the formation of rather large, polydisperse and somewhat non-spherical vesicles for x ≥ 0.7, with the narrowest size distribution being observed when x = 0.9. However, DLS studies indicated relatively narrow size distributions for x = 0.7 - 0.9, with the lowest polydispersity being observed for vesicles with x = 0.8. Thus, a binary mixture of chemically dissimilar stabiliser blocks was examined instead. Systematic variation of the relative proportions of a short poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC28) and a long PEG113 produced a series of nano-objects, which were studied by TEM, DLS, aqueous electrophoresis and SAXS. TEM indicated that pure vesicles were obtained for x ≥ 0.6. Both DLS and SAXS indicated the lowest size polydispersities were obtained for the smallest pure vesicles (< 200 nm diameter) when x = 0.6 or 0.7 for the PEG113 stabiliser. SAXS analysis suggested a high degree of segregation of the PMPC28 stabiliser chains within the inner vesicle leaflet. Optimum segregation was achieved for x = 0.6, for which SAXS indicated the lowest size polydispersity.
The effect of varying the molecular weight of PMPC-PHPMA worms on their thermoresponsive behaviour was investigated. Thus, two PMPC precursors were synthesised (with mean DPs of 15 and 26) and chain-extended via RAFT aqueous dispersion polymerisation of HPMA at 50 °C to produce PMPC15-PHPMA150 and PMPC26-PHPMA280 worm gels. Their thermoresponsive behaviour was compared using TEM, DLS, SAXS and oscillatory rheology. TEM and DLS studies of PMPC26-PHPMA280 worms indicated no thermoresponsive behaviour on cooling to 5 °C but cooling to 2 °C for 19 h induced an irreversible worm-to-sphere transition. Conversely, PMPC15-PHPMA150 worms exhibited a reversible worm-to-sphere transition on cooling to 5 °C, with concomitant degelation being observed at 18% w/w solids. However, oscillatory rheology studies indicated some hysteresis on regelation at 28 °C, as well as a relatively high critical gelation concentration of ~15% w/w solids.
Finally, the PISA synthesis of all-acrylic poly(2-hydroxyethyl acrylate)-poly(4-hydroxybutyl acrylate) (PHEA-PHBA) diblock copolymer nano-objects was investigated. The resulting nano-objects were characterised using 1H NMR, GPC, DLS, SIPLI, variable temperature oscillatory rheology and selected formulations were crosslinked with glutaraldehyde to enable TEM studies.
