Please
cite
this
article
in
press
as:
Richez
AP,
et
al.
Dispersion
polymerization
in
non-polar
solvent:
Evolution
toward
emerging
applications.
Prog
Polym
Sci
(2012),
http://dx.doi.org/10.1016/j.progpolymsci.2012.12.001
ARTICLE IN PRESS
G
Model
JPPS-774;
No.
of
Pages
35
A.P.
Richez
et
al.
/
Progress
in
Polymer
Science
xxx (2013) xxx–
xxx 7
Fig.
4.
Confocal
microscopy
image
of
a
colloidal
crystal
constituted
of
flu-
orescent
PMMA
particles
stabilized
by
PHSA
and
synthesized
through
dispersion
polymerization
(scale
bar,
10
m).
Oppositely
charged
par-
ticles
(1.08
m,
loaded
with
rhodamine
isothiocyanate;
and
0.99
m,
loaded
with
7-nitrobenzo-2-oxa-1,3-diazol)
irreversibly
assemble
at
high
concentrations
into
a
cubic
lattice
[47].
Source:
Reproduced
with
permission,
Copyright
2005,
Nature
Publishing
Group.
[42–45,47],
and
more
recently
in
clusters
of
controlled
number
of
particles
[46]
and
in
structures
assembled
upon
applying
an
electric
field
[48].
2.2.4.
New
applications
driving
current
and
future
developments
As
mentioned
previously,
the
development
of
new
technologies
has
recently
increased
the
interest
in
latex
particles
prepared
by
dispersion
polymerization.
This
is
because
some
of
these
applications
require
the
preparation
of
smart,
designed
particles
in
a
range
of
solvents,
depend-
ing
on
the
application.
Particulate
systems
prepared
by
this
technique
are
being
used
or
considered
for
inkjet
printing,
lubricant
additives
or
electronic
displays,
for
example.
The
use
of
such
particles
in
electronic
displays
is
exemplified
in
the
next
paragraphs
since
it
is
of
particular
relevance
as
the
particles
are
suspended
in
non-polar
solvents
within
the
display
pixels.
This
particular
application
has,
for
example,
motivated
an
increased
interest
in
the
research
studying
charge
in
non-polar
liquids,
with
some
academic
studies
utilizing
latex
particles
prepared
from
dispersion
polymerization
as
model
colloids
[49].
Charge
dissociation
at
the
particle
sur-
face
in
non-polar
solvents
in
most
of
these
cases
is
achieved
by
the
use
of
inverse
micelles
that
are
able
to
carry
the
counterions
away
from
the
particle
surface.
However,
this
method
suffers
from
drawbacks
as
the
surfactants
can
des-
orb
from
the
particle
surfaces
and
the
presence
of
excess
micelles
in
the
continuous
phase
drives
electrohydrody-
namic
instabilities
that
reduce
the
lifetime
of
a
display.
Therefore,
there
is
great
interest
in
using
dispersion
poly-
merization
to
prepare
particles
that
are
inherently
charged
in
non-polar
dispersants.
A
first
example
from
Sanchez
and
Bartlett
has
recently
used
this
technique
to
produce
latex
particles
with
oleophilic
ionic
groups
covalently
linked
to
the
particle
core
[50].
In
addition,
dispersion
polymeriza-
tion
also
offers
the
possibility
of
encapsulating
pigment
particles
or
organic
dyes
within
the
particle
core,
which
provide
the
reflective
properties
of
the
displays
[51–53].
Developments
driven
by
such
fast-moving
applications
will
stem
from
the
current
knowledge
of
the
non-polar
disper-
sion
polymerization
particle
synthesis
route,
reviewed
in
the
subsequent
chapters.
3.
Dispersion
polymerization
of
methacrylate-based
monomer
in
non-polar
solvent
Radical
dispersion
polymerizations
of
MMA
and
MMA-
based
monomers
are
discussed
in
this
section.
As
in
a
polar
solvent
(water,
alcohol,
etc.),
radical
dispersion
polymer-
ization
in
a
non-polar
solvent
(Fig.
5)
follows
five
stages
[54].
Initially,
the
reaction
medium
is
a
single
homoge-
neous
phase
(stage
1).
Stage
2
is
characterized
by
the
initiation
and
early
stages
of
reaction
propagation
(soluble
oligomers).
Then,
stage
3
is
the
precipitation
of
oligomer
chains
upon
reaching
a
critical
length
at
which
they
are
not
soluble
anymore,
and
the
coagulation
of
these
oligomer
chains
into
particle
nuclei.
Coagulation
of
these
oligomer
chains
continues
until
steric
stabilization
of
the
latex
parti-
cles
starts.
The
particle
stabilization
phase
is
started
when
enough
stabilizer
chains
cover
the
particle
surface
(stage
4).
At
this
stage
no
further
coagulation
of
oligomers
occurs.
Finally,
the
sterically
stabilized
latex
particles
keep
grow-
ing
until
nearly
complete
monomer
consumption
(stage
5).
Initially
considered
as
a
complex
system
due
to
the
lack
of
appropriate
characterization
techniques,
MMA
disper-
sion
polymerizations
in
non-polar
solvent
have
been
more
extensively
studied
over
the
years
thanks
to
the
emer-
gence
of
improved
characterization
techniques
(particle
sizing,
electron
microscopy,
etc.).
In
addition,
progress
in
synthetic
approaches
(silicone
chemistry,
controlled
poly-
merization,
etc.)
and
the
emergence
of
a
range
of
new
applications
(inkjet
printing,
electrophoretic
displays,
.
.
.)
has
also
driven
renewed
interest.
The
chemistry
of
the
non-
polar
dispersant
medium
has
also
developed
further
in
recent
years;
initially
mostly
based
on
dodecane
and
hex-
ane
solvent,
dispersion
polymerizations
have
recently
been
performed
in
more
“exotic”
solvents,
such
as
supercritical
carbon
dioxide
(scCO
2
)
(see
Section
6).
In
this
section,
the
discussion
will
focus
on
methacrylate-based
(essentially
MMA)
monomer
dis-
persion
polymerization
in
non-polar
solvents
using
various
stabilizers.
Initially,
the
discussion
is
centered
around
poly(12-hydroxystearic
acid)
(PHSA)-based
poly-
mers,
as
they
were
the
first
successful
class
of
stabilizers
used.
Section
3.2
will
focus
on
the
stabilizers
developed
as
a
result
of
the
emergence
of
silicon
chemistry,
such
as
methacryloxypropyl
terminated
polydimethylsiloxane.
Section
3.3
will
subsequently
discuss
new
stabilizers
developed
through
the
use
of
new
controlled
radical
polymerization
approaches
(RAFT,
ATRP,
and
NMP).
3.1.
Using
poly(12-hydroxystearic
acid)-based
stabilizer
The
first
widely
reported
stabilizers
for
the
synthesis
of
PMMA
latex
particles
in
non-aqueous
solvents
were
based
upon
poly(12-hydroxystearic
acid)
(PHSA).
Despite
being
a
non-commercial
material,
PHSA-based
copoly-
mers
have
been
widely
studied
over
many
years.
It
is
important
to
note
that
PHSA
has
never
been
used
as
a
homopolymer,
but
rather
as
the
major
component
(sol-
uble
part)
of
various
copolymers.
PHSA-based
stabilizers
are
always
synthesized
using
multi-step
methodologies.
Three
PHSA-based
stabilizers
can
be
found
in
the
academic