Abstract
A series of pH-responsive all-methacrylic ABC triblock copolymer vesicles were prepared from precursor diblock copolymer vesicles via RAFT seeded emulsion polymerisation. Microphase separation between the two hydrophobic membrane-forming B and C blocks produced a distinctive framboidal morphology, for which the mean globule size can be tuned by adjusting the triblock copolymer composition. These vesicles remain intact at neutral pH, but undergo irreversible dissociation on addition of acid as a result of protonation of the tertiary amine groups located within the third block. Small-angle X-ray scattering (SAXS) was utilised to characterise the morphologies formed at pH 8 and pH 3. According to time-resolved SAXS studies, the acid-induced dissociation of these pH-responsive framboidal vesicles involves appreciable membrane swelling within 50 ms and is complete.
Highlights
It is well-known that amphiphilic block copolymers undergo spontaneous self-assembly in aqueous solution.[1,2,3,4] For example, many variations on the vesicular morphology have been reported in the literature, including stomatocyte-like,[5] Janus-type[6] and framboidal vesicles.[7,8,9] Recent advances in polymerisationinduced self-assembly (PISA)[10,11,12] have enabled a wide range of block copolymer nanoparticles to be prepared directly in concentrated aqueous solution via reversible additionfragmentation chain transfer (RAFT) aqueous dispersion polymerisation.[13,14] Such one-pot syntheses are much more convenient than traditional post-polymerisation processing techniques, which typically involve a solvent or pH switch[15,16,17,18] or thin lm rehydration,[19,20] and are invariably restricted to dilute solution
Edge Article to prepare a 100 gram batch of G58H300 diblock copolymer vesicles, see Fig. 1. These G58H300 precursor vesicles were diluted to 10% w/w and subsequently chain-extended using varying amounts of DPA via reversible additionfragmentation chain transfer (RAFT) seeded emulsion polymerisation to prepare a series of G58H300Dz triblock copolymers, where z was adjusted from 86 to 460. 1H NMR studies indicated that more than 99% hydroxypropyl methacrylate (HPMA) conversion was achieved within 2 h at 70 C, while DPA conversions of 82–92% were achieved within 24 h at 70 C. 1H NMR studies of the nal G58H300Dz triblock copolymers were conducted in CD3OD containing 4% deuterium chloride (DCl), which is a good solvent for all three blocks
dimethyl formamide (DMF) Gel permeation chromatography (GPC) studies conducted using a series of poly(methyl methacrylate) (PMMA) calibration standards indicated that a near-monodisperse G58H300 diblock copolymer precursor (Mw/ Mn 1⁄4 1.12; see Fig. S2 in Electronic supplementary information (ESI)†) was obtained with a relatively high blocking efficiency
Summary
It is well-known that amphiphilic block copolymers undergo spontaneous self-assembly in aqueous solution.[1,2,3,4] For example, many variations on the vesicular morphology have been reported in the literature, including stomatocyte-like,[5] Janus-type[6] and framboidal vesicles.[7,8,9] Recent advances in polymerisationinduced self-assembly (PISA)[10,11,12] have enabled a wide range of block copolymer nanoparticles to be prepared directly in concentrated aqueous solution via reversible additionfragmentation chain transfer (RAFT) aqueous dispersion polymerisation.[13,14] Such one-pot syntheses are much more convenient than traditional post-polymerisation processing techniques, which typically involve a solvent or pH switch[15,16,17,18] or thin lm rehydration,[19,20] and are invariably restricted to dilute solution. DMF GPC studies conducted using a series of poly(methyl methacrylate) (PMMA) calibration standards indicated that a near-monodisperse G58H300 diblock copolymer precursor (Mw/ Mn 1⁄4 1.12; see Fig. S2 in ESI†) was obtained with a relatively high blocking efficiency.
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