Production of Homogeneous Polystyrene Microparticles in a Stable Dispersion
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Dispersions of polymer particles in a liquid phase (latexes) have
many important applications in coatings technology, medical imaging, and
cell biology. A French team of researchers have now developed a method,
reported in the journal Angewandte Chemie, to produce stable
polystyrene dispersions with unprecedentedly large, and uniform,
particle sizes. Narrow size distributions are essential in many advanced
technologies, but were previously difficult to produce photochemically.
Polystyrene, often used to create expanded foam, is also well suited
to the production of latexes, in which the microscopically tiny
polystyrene particles are suspended and which are used in the
manufacture of coatings and paints, but also for calibration purposes in
microscopy as well as in medical imaging and cell biology research.
They are usually produced by thermally or redox-induced polymerization
within the solution.
To obtain an external control over the process, the teams Muriel
Lansalot, Emmanuel Lacôte, and Elodie Bourgeat-Lami at the Université
Lyon 1, France, and colleagues, have turned to light-driven processes.
“Light-driven polymerization ensures temporal control, because
polymerization proceeds only in the presence of light, whereas thermal
methods can be started but not stopped once they are underway,” Lacôte
says.
Although UV- or blue-light-based photopolymerization systems have
been established, they have limitations. Short-wavelength radiation is
scattered when the particle size becomes close to the radiation
wavelength, making latexes with particle sizes larger than the incoming
wavelengths difficult to produce. In addition, UV light is highly
energy-intensive, not to mention hazardous to the humans working with
it.
The researchers therefore developed a fine-tuned chemical initiation
system that responds to standard LED light in the visible range. This
polymerization system, which is based on an acridine dye, stabilizers,
and a borane compound, was the first to overcome the “300-nanometer
ceiling,” the size limit of UV and blue-light-driven polymerization in a
dispersed medium. As a result, for the first time, the team were able
to use light to produce polystyrene latexes with particle sizes greater
than one micrometer and with highly uniform diameters.
The team suggest applications well beyond polystyrene. “The system
could potentially be used in all areas where latexes are used, such as
films, coatings, supports for diagnostics, and more,” Lacôte says. In
addition, the polymer particles could be modified with fluorescent dyes,
magnetic clusters, or other functionalities useful for diagnostic and
imaging applications. The team says that a broad range of particle sizes
spanning the nano and micro scales would be accessible “simply by
tuning the initial conditions.”
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About the Author
Muriel Lansalot is a CNRS director of
research at the Laboratory of Catalysis, Polymerization, Processes and
Materials (CP2M) at the University Claude Bernard Lyon 1 and CPE Lyon,
France. Her research is focused on the synthesis of polymer and
nanocomposite particles using different approaches such as radical
polymerization in dispersed media, polymerization-induced self-assembly,
and photopolymerization in emulsion and dispersion.
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