Design of Functional Polymeric Microspheres for Living Radical Polymerizations
Background:
There has been an intense effort in recent years to fabricate core-shell colloidal particles with tailored structural and surface properties, particularly in the shell component. Because core-shell particles can be designed to have superior chemical and physical properties to homogeneous particles, they are potentially useful in a wide variety of applications including coatings, electronics, catalysis, separations and diagnostics. Synthesis of nanocomposite materials where the particle structural can be controlled down to the nanometer-submicron scale promises to significantly advance many areas in nanotechnology. The key to realizing these potential advantages lies in the ability to synthesize well-defined shells, i.e. the ability to design shell polymers with excellent control over the most important structural and chemical features, typically the molecular weight (chain length), the polydispersity of the molecular weight distribution, the "density" of the shell chains on the particle surface, and the chemical composition of the shell polymer (e.g. random copolymer, block copolymer, tapered copolymers in which the composition is gradually changed along the chain length, and polymers incorporating a desired functionality for future reaction).
Conventional techniques for making submicron core-shell particles, using for example emulsion polymerization, allow only crude control of the critical shell properties (molecular weight distribution, thickness, composition). The stochastic nature of free radical polymerization prevents effective control of the molecular weight distribution and chain composition. Diffusion of the shell monomers into the particle core reduces control of the shell thickness and composition.
Living radical polymerization provides excellent control of the molecular weight distribution, as well as providing a simple route for composition control in the synthesis of structures such as block copolymers, tapered polymers and functionalized polymers. These features would provide control over all of the critical shell properties described above.
Research:
Using nitroxide-mediated living radical polymerization, core-shell particles or "polymer particle brushes" are made starting from pre-formed polymer particle seeds (~50-500 nm diameter). These latexes are then functionalized with nitroxides on their surfaces. The shell or "brush" monomer will be polymerized in a subsequent living radical polymerization to yield core-shell particles with well-defined polymeric shells or "brushes". The particles are characterized using particle size measurements (light scattering, capillary hydrodynamic fractionation), molecular weight distributions (gel permeation chromatography), SEM, FT-IR, NMR and elemental analysis.
 
Transmission electron microscope photos showing polystyrene latexes functionalized with the nitroxide SG1(60 nm) [e], latexes with a PBA brush (75 nm) [f], and latexes with a BA-b-DMAEA amphiphilic block copolymer brush (81 nm) [g].
"An expert is someone who knows some of the worst mistakes that can be made in his subject and who manages to avoid them....again."
- Werner Heisenberg
Design of Functional Polymeric Microspheres for Living Radical Polymerizations
Background:
There has been an intense effort in recent years to fabricate core-shell colloidal particles with tailored structural and surface properties, particularly in the shell component. Because core-shell particles can be designed to have superior chemical and physical properties to homogeneous particles, they are potentially useful in a wide variety of applications including coatings, electronics, catalysis, separations and diagnostics. Synthesis of nanocomposite materials where the particle structural can be controlled down to the nanometer-submicron scale promises to significantly advance many areas in nanotechnology. The key to realizing these potential advantages lies in the ability to synthesize well-defined shells, i.e. the ability to design shell polymers with excellent control over the most important structural and chemical features, typically the molecular weight (chain length), the polydispersity of the molecular weight distribution, the "density" of the shell chains on the particle surface, and the chemical composition of the shell polymer (e.g. random copolymer, block copolymer, tapered copolymers in which the composition is gradually changed along the chain length, and polymers incorporating a desired functionality for future reaction).
Conventional techniques for making submicron core-shell particles, using for example emulsion polymerization, allow only crude control of the critical shell properties (molecular weight distribution, thickness, composition). The stochastic nature of free radical polymerization prevents effective control of the molecular weight distribution and chain composition. Diffusion of the shell monomers into the particle core reduces control of the shell thickness and composition.
Living radical polymerization provides excellent control of the molecular weight distribution, as well as providing a simple route for composition control in the synthesis of structures such as block copolymers, tapered polymers and functionalized polymers. These features would provide control over all of the critical shell properties described above.
Research:
Using nitroxide-mediated living radical polymerization, core-shell particles or "polymer particle brushes" are made starting from pre-formed polymer particle seeds (~50-500 nm diameter). These latexes are then functionalized with nitroxides on their surfaces. The shell or "brush" monomer will be polymerized in a subsequent living radical polymerization to yield core-shell particles with well-defined polymeric shells or "brushes". The particles are characterized using particle size measurements (light scattering, capillary hydrodynamic fractionation), molecular weight distributions (gel permeation chromatography), SEM, FT-IR, NMR and elemental analysis.
Transmission electron microscope photos showing polystyrene latexes functionalized with the nitroxide SG1(60 nm) [e], latexes with a PBA brush (75 nm) [f], and latexes with a BA-b-DMAEA amphiphilic block copolymer brush (81 nm) [g].
"An expert is someone who knows some of the worst mistakes that can be made in his subject and who manages to avoid them....again."
- Werner Heisenberg
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