Alkoxyamine-mediated Controlled Radical Polymerization in Emulsion

1
Alkoxyamine-mediated Controlled Radical
Polymerization in Emulsion Wilfred Smulders,
Christianne Göttgens, Gilles Olive, Steven van Es
Introduction
The increasing need for products with better
performance and durability requires the use of
speciality polymers with controlled composition
and architecture. However, no industrial
cost-effective process is presently available to
synthesize such polymers. Moreover, current
processes are performed in solvent media and need
recycling of solvents and thorough removal of
organic residuals. Finally, these processes are
incompatible with water, while the demand for
waterborne systems is growing fast due to
environmental concerns. Controlled Radical
Polymerization (CRP), especially when applied
directly in emulsion, will be able to reconcile
these conflicting demands. In CRP all polymer
chains allow stepwise addition of monomer
throughout the whole process by limiting the
extent of chain termination. CRP thereby allows
for the sequential radical polymerization of
monomers (multi-blocks) and construction of
well-defined architectures.
Scheme of alkoxyamine-mediated controlled radical
polymerization
The main innovations to be achieved within the
project are increase in polymerization
rate at temperatures below 100 C
development of efficient process conditions and
modelling controlled radical polymerization in
emulsion synthesis of copolymers with
controlled composition and architecture targeted
to market requirements within the field of PSA
Results and discussion
Bulk polymerizations These plots show that CRP of
styrene at 90 C is possible. These results
indicate that an increase in reaction rate is
obtained by introducing catalytic groups and open
ring structures, while control is maintained.
Polydispersities are between 1.2 and 1.4 in all
cases. However reaction rates will never be
comparable to the rates of uncontrolled
polymerizations because the principle of this
technique is based on decreasing the radical
concentration and thus the polymerization rate.
results of CRP of styrene at 90 C in bulk
Emulsion polymerizations These plots show that in
principle it is possible to perform
alkoxyamine-mediated CRP in emulsion. Both a
linear increase in molecular weight and
polydispersities below 1.5 are observed. However
in this case the rate is very slow, even compared
to the same reaction in bulk. This is probably a
consequence of the cage-effect, which does not
allow the radical chain to propagate but gives
rise to immediate trapping by the nitroxide.
results of CRP of styrene at 90 C in emulsion
Conclusions
There is a considerable effect of both structure
and functional groups on kinetics. From this
field improvements can be expected. Alkoxyamine-me
diated CRP in emulsion is possible, although a
considerable increase in reaction rate is
necessary. In order to optimize CRP in emulsion
and increase the polymerization rate a full
theoretical modelling and improved nitroxides are
required.