RAFT aqueous dispersion polymerization is used to prepare poly(methacrylic acid)-poly(2-hydroxypropyl methacrylate) diblock copolymer nanoparticles, which exhibit stimulus-responsive behaviour on adjusting the solution temperature and/or solution pH.
The present study
focuses on the use of copolymer nanoparticles
as a dispersant for a model pigment (silica). Reversible addition–fragmentation
chain transfer (RAFT) alcoholic dispersion polymerization was used
to synthesize sterically stabilized diblock copolymer nanoparticles.
The steric stabilizer block was poly(2-(dimethylamino)ethyl methacrylate)
(PDMA) and the core-forming block was poly(benzyl methacrylate) (PBzMA).
The mean degrees of polymerization for the PDMA and PBzMA blocks were
71 and 100, respectively. Transmission electron microscopy (TEM) studies
confirmed a near-monodisperse spherical morphology, while dynamic
light scattering (DLS) studies indicated an intensity-average diameter
of 30 nm. Small-angle X-ray scattering (SAXS) reported a volume-average
diameter of 29 ± 0.5 nm and a mean aggregation number of 154.
Aqueous electrophoresis measurements confirmed that these PDMA71–PBzMA100 nanoparticles acquired cationic
character when transferred from ethanol to water as a result of protonation
of the weakly basic PDMA chains. Electrostatic adsorption of these
nanoparticles from aqueous solution onto 470 nm silica particles led
to either flocculation at submonolayer coverage or steric stabilization
at or above monolayer coverage, as judged by DLS. This technique indicated
that saturation coverage was achieved on addition of approximately
465 copolymer nanoparticles per silica particle, which corresponds
to a fractional surface coverage of around 0.42. These adsorption
data were corroborated using thermogravimetry, UV spectroscopy and
X-ray photoelectron spectroscopy. TEM studies indicated that the cationic
nanoparticles remained intact on the silica surface after electrostatic
adsorption, while aqueous electrophoresis confirmed that surface charge
reversal occurred below pH 7. The relatively thick layer of adsorbed
nanoparticles led to a significant reduction in the effective particle
density of the silica particles from 1.99 g cm–3 to approximately 1.74 g cm–3, as judged by disk
centrifuge photosedimentometry (DCP). Combining the DCP and SAXS data
suggests that essentially no deformation of the PBzMA cores occurs
during nanoparticle adsorption onto the silica particles.
An atom-efficient, wholly aqueous one-pot synthesis of zwitterionic diblock copolymers has been devised. Such copolymers can serve as highly effective aqueous dispersants for nano-sized transparent yellow iron oxide particles.
Two new classes of polyampholytic diblock copolymers are prepared via RAFT aqueous solution polymerization and their aqueous solution behaviour is assessed using 1H NMR spectroscopy, dynamic light scattering and aqueous electrophoresis measurements.
Well-defined doubly pH-responsive schizophrenic diblock copolymer nanoparticles with tunable isoelectric points are prepared via RAFT aqueous dispersion polymerization using an efficient one-pot protocol.
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