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We have basically re-written the equation of how the polymerization
process can work, which can have a direct impact on the cost of the
reaction and the types of materials that we can create. said Virgil
Percec, a professor in Penns Department of Chemistry. Polymerization
is a billion-dollar-a-year industry, and the applications for the
technology are enormous, ranging from medicine to coatings, from
moldable forms of rubber to electronics and even complex organic
synthesis, all via these radical reactions.
This new technique, called Single Electron Transfer-Living Radical
Polymerization, also offers chemists greater control over the
molecular architecture of the polymers they create and allows them to
use materials that did not work with the traditional process. The
mechanism of the synthesis reaction works so well that there is very
little worry about undesirable side reactions, and the resulting
polymers do not need to be purified to remove the catalyst. Their
findings are presented in the Journal of the American Chemical
Society.
The SET-LRP mechanism can allow for a greater control over the
three-dimensional structure of the polymers being created, Percec said.
The overall process is not only more efficient, it also provides
industrial chemists a new creative tool for building consumer and
industrial.
Polymerization links individual molecules, referred to as monomers,
together to form synthetic products on a larger-scale. In the chemical
reaction to create polymers, chemists use catalysts to decrease the
amount of energy it takes to create a shared bond between individual
atoms of each monomer. The traditional method, referred to as
atom-transfer radical polymerization or metal catalyzed living radical
polymerization, demands high temperatures and a great amount of the
metal catalyst, in part, because the process depends on the energy it
takes to transfer inner-sphere electrons - which are deep within the
cloud of electrons surrounding an atom - in the act of bonding
monomers together.
The new method created by Percec and his colleagues involves the
transfer of outer-sphere electrons, which requires much lower
activation energy and, therefore, a different catalytic cycle than
atom-transfer radical addition. Both the traditional and SET-LRP
processes use copper-based catalysts to drive the reaction, but the
SET-LRP reaction uses a common, elemental form of copper - in the form
of powder or wire - in the presence of environmentally friendly
solvents, such as water, to move the reaction along. This prevents the
build up of excess amounts of copper by-products and reduces the need
to continually add more catalyst to keep the reaction going.
While this might seem like a refinement of the traditional process -
the resulting polymers, in fact, are structurally the same - this
method involves an entirely different approach to the chemical
reaction, Percec said.
Funding for the research was provided by the National Science
Foundation.
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