32 research outputs found
Synthesis of High ÏâLow N Diblock Copolymers by Polymerization-Induced Self-Assembly
Polymerizationâinduced selfâassembly (PISA) enables the scalable synthesis of functional block copolymer nanoparticles with various morphologies. Herein we exploit this versatile technique to produce soâcalled âhigh Ï âlow N â diblock copolymers that undergo nanoscale phase separation in the solid state to produce subâ10 nm surface features. By varying the degree of polymerization of the stabilizer and coreâforming blocks, PISA provides rapid access to a wide range of diblock copolymers, and enables fundamental thermodynamic parameters to be determined. In addition, the preâorganization of copolymer chains within stericallyâstabilized nanoparticles that occurs during PISA leads to enhanced phase separation relative to that achieved using solutionâcast molecularlyâdissolved copolymer chains
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Self-Assembly of Amphiphilic Statistical Copolymers and Their Aqueous Rheological Properties
A range of polyÂ(<i>n</i>-butyl methacrylate-<i>stat</i>-methacrylic acid) [PÂ(BMA-<i>stat</i>-MAA)] statistical
copolymers of various compositions and molecular weights ranging from
5 to 30 kDa were prepared using either reversible additionâfragmentation
chain transfer (RAFT) solution copolymerization or conventional free
radical polymerization in isopropanol (IPA). On dilution with water,
these amphiphilic copolymers self-assembled to form spherical nano-objects
as confirmed by small-angle X-ray scattering (SAXS) and transmission
electron microscopy. Various structural models were examined to extract
information regarding the mean nano-object size and morphology. It
is found that nano-object radii are independent of copolymer molecular
weight but depend on the copolymer composition: the smaller the amount
of MAA units in the copolymer chains, the larger the nano-objects
that are formed. Combined SAXS and aqueous electrophoretic measurements
indicated that most of the MAA units are located at the nano-object
surface. Furthermore, SAXS and rheology measurements were used to
monitor the effect of solvent composition on the copolymer morphology
both at a fixed copolymer concentration (either 1 or 25 wt %) and
also for a gradual variation in copolymer concentrations (from 1 to
40 wt %) when adding water to the initial copolymer solution in IPA.
These studies revealed that the copolymers are present in solution
as molecularly dissolved Gaussian chains when the solvent composition
is IPA-rich. However, the copolymer chains self-assemble into spherical
nano-objects when the solvent composition is water-rich. At intermediate
solvent compositions, SAXS analysis confirmed the formation of an
interconnected nano-object network, which accounts for the apparently
anomalous increase in solution viscosity on dilution indicated by
rheology measurements