Polymer Architecture Design through Catalysis

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Polymer Architecture Design through Catalysis
www.chem.uci.edu/people/faculty/zguan/

• Christopher Levins, Christopher Popeney, Prof.
  Zhibin Guan, Department of Chemistry

Introduction
Research
The cyclophane-based catalysts we have been
focusing on making have different functional
groups which modify the electron density around
the metal center where the polymerization takes
place. Changing the electron density around the
metal center allows for control of the topology
of the polymer by controlling the rates of chain
walking and of olefin insertion. By increasing
chain walking, more highly branched polymers are
produced, whereas by decreasing the rate of chain
walking, more linear polymers are produced.
The goal of this research has been to develop
advanced transition metal catalysts for olefin
polymerization. More specifically, we have been
creating a family of cyclophane-based catalysts
based off of an existing acyclic catalyst
developed by Maurice Brookhart at UNC Chapel
Hill. The cyclophane-based catalysts show
excellent activity and high thermal stability for
olefin polymerization compared to the acyclic
catalyst at high temperatures.
Recent research of late transition metal
catalysts for polymerization of olefins has shown
an enhanced ability to control polymer topology.
The branched polymer structures produced by these
catalysts are attributed to an isomerization
mechanism, or chain walking of the catalyst
along the polymer chain. By creating catalysts
that have specific control over the rate of chain
walking, we can make target polymers with
specific topologies ranging from linear to
hyperbranched to "dendritic
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This data is from substituted acyclic catalyst.
It is clear that the functional groups have an
effect on the topology of the polymer. More
specifically, the more electron rich the metal
center is, the less branched the polymer becomes.
Polymer Radius (nm)
x
x
There are two competing reactions in these
polymerizations. They are insertion of the
olefin, and the chain walking. The insertion
is what causes the polymers to increase in
length, while the chain walking is what causes
the polymers to branch out in different
directions.
Acyclic
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Cyclophane catalyst (detailed benefits)
5x105 6x105 7x105 8x105 9x105
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Cyclophane
Molecular Weight (kg/mole)
The cyclophane design helps eliminate chain
transfer, which effectively stops the
polymerization and yields shorter polymers, by
blocking off 2 of the coordination sites on the
metal. It also has increased stability because
there is no rotation about the C-N bond, which
reduces the likelihood of decomposition.
Topology of a polymer determines most of the
physical properties of the polymer. Linear
polymers tend to be more rigid while more
branched polymers tend to be more flexible.
Linear polymers have a wide variety of uses. One
main use is in hard plastics and other materials.
Hyperbranched and dendritic polymers are mainly
used for drug delivery.
O
c
The research being done here is to successfully
synthesize a whole family of different
cyclophanes with different functional groups and
analyze to what extent the differences in
catalyst design will affect the polymers they
produce.
X-ray diffraction structure of cyclophane catalyst
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