Preparation of biocompatible sterically stabilized latexes using well-defined poly(2-(methacryloyloxy)ethyl phosphorylcholine) macromonomers

Article abstract of DOI:10.1021/la903567q

A range of well-defined methacrylic macromonomers based on the biomimetic monomer 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) were synthesized by atom-transfer radical polymerization (ATRP) in alcoholic media using 2-(dimethylamino)ethyl-2-bromoisobutyrylamide. This tertiary amine-functionalized initiator was used to produce homopolymer precursors of various chain lengths via ATRP. These polymerizations were relatively well controlled (M_w/M_n ≤ 1.30), provided that the target degree of polymerization (DP) did not exceed 30. For higher target DPs, polymerization was only poorly controlled and characterized by broad molecular weight distributions (M_w/M_n = 1.50-2.31). The tertiary amine end-group of each nearly monodisperse homopolymer precursor was then quaternized using 4-vinylbenzyl chloride (4-VBC) to afford the corresponding styrene-functionalized macromonomers. PMPC₃₀ macromonomer proved to be an effective reactive steric stabilizer for the formation of polystyrene latexes when employed at 10 w/w % on the basis of the styrene monomer. Nearly monodisperse submicrometer-sized and micrometer-sized latexes were prepared by aqueous emulsion and alcoholic dispersion polymerization, respectively, as judged by scanning electron microscopy and dynamic light scattering studies. In contrast, attempted alcoholic dispersion polymerization conducted either in the presence of the PMPC₃₀ homopolymer precursor or in the absence of any macromonomer always resulted in macroscopic precipitation. Such control experiments confirmed the importance of the terminal styrene groups on the macromonomer chains for successful latex formation. FTIR spectroscopy indicated the presence of the PMPC₃₀ macromonomer within the polystyrene latex, and XPS studies indicated that these stabilizer chains are located at (or very near) the latex surface, as expected. Using PMPC₂₀ and PMPC ₁₀ macromonomers for the alcoholic dispersion polymerization of styrene led to latexes with substantially broader size distributions compared to those produced using the PMPC₃₀ macromonomer under the same conditions. Finally, these new sterically stabilized latexes exhibit excellent freeze-thaw stability and salt tolerance.

Full text of DOI:10.1021/la903567q

pubs.acs.org/Langmuir
© 2009 American Chemical Society
Preparation of Biocompatible Sterically Stabilized Latexes Using
Well-Defined Poly(2-(methacryloyloxy)ethyl phosphorylcholine)
Macromonomers
Kate L. Thompson,† Iveta Bannister,‡ Steven P. Armes,*,† and Andrew L. Lewis§
†Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.,
‡Department of Chemistry, University of Sussex, Falmer, Brighton, East Sussex BN1 9QJ, U.K., and
§Biocompatibles UK Ltd., Chapman House, Farnham Business Park, Weydon Lane,
Farnham, Surrey GU9 8QL, U.K.
Received September 21, 2009. Revised Manuscript Received October 13, 2009
A range of well-defined methacrylic macromonomers based on the biomimetic monomer 2-(methacryloyloxy)ethyl
phosphorylcholine (MPC) were synthesized by atom-transfer radical polymerization (ATRP) in alcoholic media using
2-(dimethylamino)ethyl-2-bromoisobutyrylamide. This tertiary amine-functionalized initiator was used to produce
homopolymer precursors of various chain lengths via ATRP. These polymerizations were relatively well controlled
(Mw/Mn e 1.30), provided that the target degree of polymerization (DP) did not exceed 30. For higher target DPs,
polymerization was only poorly controlled and characterized by broad molecular weight distributions (Mw/Mn
=
1.50-2.31). The tertiary amine end-group of each nearly monodisperse homopolymer precursor was then quaternized
using 4-vinylbenzyl chloride (4-VBC) to afford the corresponding styrene-functionalized macromonomers. PMPC30
macromonomer proved to be an effective reactive steric stabilizer for the formation of polystyrene latexes when
employed at 10 w/w % on the basis of the styrene monomer. Nearly monodisperse submicrometer-sized and
micrometer-sized latexes were prepared by aqueous emulsion and alcoholic dispersion polymerization, respectively,
as judged by scanning electron microscopy and dynamic light scattering studies. In contrast, attempted alcoholic
dispersion polymerization conducted either in the presence of the PMPC30 homopolymer precursor or in the absence of
any macromonomer always resulted in macroscopic precipitation. Such control experiments confirmed the importance
of the terminal styrene groups on the macromonomer chains for successful latex formation. FTIR spectroscopy
indicated the presence of the PMPC30 macromonomer within the polystyrene latex, and XPS studies indicated that these
stabilizer chains are located at (or very near) the latex surface, as expected. Using PMPC20 and PMPC10 macro-
monomers for the alcoholic dispersion polymerization of styrene led to latexes with substantially broader size
distributions compared to those produced using the PMPC30 macromonomer under the same conditions. Finally,
these new sterically stabilized latexes exhibit excellent freeze-thaw stability and salt tolerance.
Introduction
polymerization only broad molecular weight distributions can
be obtained (typically Mw/Mn > 2.0). Moreover, the terminal
vinyl group produced by CCTP does not exhibit the same
copolymerizability as conventional methacrylic monomers.6
However, CCTP has been recently combined with atom transfer
radical polymerization (ATRP) to produce low-polydispersity
macromonomers.7 Both Nagasaki and co-workers8 and Lascelles
et al.9 reported the preparation of a range of well-defined styrene-
functionalized macromonomers via anionic polymerization
of tertiary amine methacrylates using potassium 4-vinylbenzyl
alkoxide as an initiator. This approach illustrates the general
principle that vinylic macromonomers can be synthesized directly
with functional initiators provided that the terminal vinyl group
does not participate in the chain-growth reaction. Similar selec-
tivity has also been illustrated for vinyl acetate- and vinyl ether-
based ATRP initiators.10,11 ATRP has also been used to produce
macromonomers by displacing the terminal halogen atoms from
Macromonomers are polymer chains that contain at least one
polymerizable group.1 There are many literature examples of
macromonomers with terminal vinylic groups, which can be used
to prepare sterically stabilized latexes,2 graft copolymers,3 or
“bottle brush” polymers.4 There are a number of synthesis routes
to macromonomers. Commercially available macromonomers
such as methoxy-capped poly(ethylene glycol) methacrylate
are usually prepared by transesterification of monohydroxy-
terminated poly(ethylene glycol) previously prepared by anionic
polymerization. Catalytic chain-transfer polymerization (CCTP)
can be used to prepare methacrylic macromonomers,5 but
because this approach is based on conventional free radical
*Corresponding author. E-mail: s.p.armes@sheffield.ac.uk.
(1) Chemistry and Industry of Macromonomers; Yamashita, Y., Ed.; Huthig and
Wepf: Verlag, Basle, 1993.
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Langmuir 2010, 26(7), 4693–4702
Published on Web 10/28/2009
DOI: 10.1021/la903567q 4693

Article
Thompson et al.
the chain ends,12 although this approach presumably suffers from
reduced efficiencies under monomer-starved conditions as a result
of side reactions. Another strategy is to use functional initiators to
enable postpolymerization derivatization of the polymer chain
ends.13,14 Although this is usually a two-step synthesis, it has the
advantage of allowing the efficient incorporation of terminal
vinylic groups such as (meth)acrylates or styrene that would
otherwise participate in the chain-growth stage. This approach
has also been successfully used for anionic polymerization,
conventional free radical polymerization, and ATRP.15,16
In the present work, we have synthesized near-monodisperse
macromonomers based on 2-(methacryloyloxy)ethyl phosphoryl-
choline (MPC). This zwitterionic biomimetic monomer has been
widely used for biocompatible surface coatings in health care
applications.17 Recently, we prepared biocompatible sterically
stabilized PMPC latexes using a poly(ethylene glycol) methacry-
late stabilizer in alcohol/water mixtures.18 PMPC-based macro-
monomers have been reported previously by Ishihara and
co-workers.19,20 These macromonomers were copolymerized with
n-butyl methacrylate to produce graft copolymers19 and were also
used to prepare sterically stabilized polystyrene latexes.20 How-
ever, they were synthesized by conventional free-radical poly-
merization and hence were relatively polydisperse. In addition,
Sugiyama et al. described the copolymerization of a phos-
phorylcholine-based, azo-functionalized methacrylic monomer
with methyl methacrylate by surfactant-free emulsion polymeri-
zation.21 The resulting latexes resisted protein absorption from
aqueous solution, and this resistance could be modulated by UV
irradiation. In the present work, a tertiary amine-functionalized
ATRP initiator (Figure 1) was synthesized to homopolymerize
the MPC monomer with reasonably good control. The terminal
tertiary amine groups of these precursors were then quaternized
using excess 4-vinylbenzyl chloride to produce a series of
well-defined, low-polydispersity styrene-functionalized PMPC
macromonomers. These model macromonomers were evaluated
as new reactive steric stabilizers for the synthesis of polystyrene
latexes via both aqueous emulsion and alcoholic dispersion
polymerization. It is also shown that the zwitterionic PMPC
stabilizer chains confer excellent freeze-thaw stability and high
salt tolerance.
Figure 1. Reaction scheme for the synthesis of well-defined bio-
compatible PMPC macromonomers: atom-transfer radicalpolym-
erization of 2-(methacryloyloxy)-ethyl phosphorylcholine (MPC)
in methanol at 20 °C for 6 h, followed by quaternization of the
purified PMPC homopolymer using excess 4-vinylbenzyl chloride
at 20 °C in methanol for 48 h.
alumina to remove inhibitor and then stored at -20 °C prior to use.
2,20-Azobisisobutyronitrile (AIBN; BDH), 2,20-azobis(isobutyr-
amidine) dihydrochloride (AIBA; 97%; Aldrich, U.K.), and
ammonium persulfate (APS, Aldrich, U.K.) were used as received.
Methanol was purchased from Fisher and used as received.
Deionized water was used in all experiments. Silica gel 60
(0.0632-0.2 mm) was obtained from Merck (Darmstadt,
Germany). NMR solvents (D2O, CD3OD, and CDCl3) were pur-
chased from Fisher. A poly(vinylidene difluoride) dialysis membrane
(Spectra/Por, molecular weight cutoff = 500 000 Da) was also
purchased from Fisher.
Experimental Section
Synthesis of 2-(Dimethylamino)ethyl-2-bromoisobutyryl-
amide initiator. 2-Dimethylethylenediamine (5.95 g, 0.068 mol),
triethylamine (27.27 g, 0.27 mol), and dichloromethane (120 mL)
were placed in a 1 L three-necked, round-bottomed flask and
purged with nitrogen for 30 min. A white precipitate of triethyl-
ammonium bromide was formed on addition of 2-bromoisobu-
tyryl bromide (15.49 g, 0.067 mol) to the reaction mixture, which
was stirred for another 5 h. After filtration to remove the
precipitate, the solution was dried over MgSO4 and filtered once
more, and dichloromethane was removed under reduced pressure
to afford a pale-brown liquid. The initiator was used without
further purification because 1H NMR analysis confirmed it to be
of sufficiently high purity. 1H NMR (400 MHz, CD3OD): δ 1.88
(6H, s, 2CH3), 2.26 (6H, s, N(CH3)2), 2.45 (2H, t, J = 7.0 Hz,
(CH3)2NCH2), 3.31 (2H, t, J = 7.0 Hz, CH2NHCOO(CH3)2Br).
Homopolymerization of MPC. The polymerization of MPC
monomer to afford the PMPC30 homopolymer was conducted
as follows. 2-(Dimethylamino)ethyl-2-bromoisobutyrylamide ini-
tiator (0.134 g, 0.56 mmol), bpy (0.177 g, 1.12 mmol), and MPC
(5.00 g, 16.8 mmol; target DP = 30) were weighed into a 25 mL
round-bottomed flask and degassed using three vacuum/nitrogen
cycles. Methanol (5.13 mL) was degassed separately and trans-
ferred intothe reactionflask under positivenitrogenpressure. The
Cu(I)Cl catalyst (0.055 g, 0.56 mmol) was added quickly to the
stirred solution under positive nitrogen pressure, and the reaction
Materials. 2-(Methacryloyloxy)ethyl phosphorylcholine (MPC,
99.9%) was kindly donated by Biocompatibles (Farnham, UK) and
used without further purification. 4-Vinylbenzyl chloride (4-VBC),
Cu(I)Cl (99.995%), and 2,20-bipyridine (bpy, 99%) were all pur-
chased from Aldrich and were used as received. Styrene and n-butyl
acrylate (Aldrich) were both passed through a column of basic
(12) Muehlebach, A.; Rime, F. J. Polym. Sci., Part A: Polym. Chem. 2003, 41,
3425.
(13) Haddleton, D. M.; Waterson, C.; Derrick, P. J.; Jasieczek, C. B.; Shooter,
A. J. Macromolecules 1997, 30, 683.
(14) Schon, F; Hartenstein, M.; Muller, A. H. E. Macromolecules 2001, 34, 5394.
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(15) Ishizu, K.; Tahara, N. Polymer 1996, 37, 2853.
(16) (a) Ishizu, K.; Yamashita, M.; Ichimura, A. Polymer 1997, 38, 5471. (b)
Ishizu, K.; Yamashita, M.; Ichimura, A. Macromol. Rapid Commun. 1997, 18, 639. (c)
Uchida, T.; Furuzono, T.; Ishihara, K. J. Polym. Sci., Part A: Polym. Chem. 2000, 38,
3052. (d) Bon, S. A. F.; Morsley, S. R.; Waterson, C.; Haddleton, D. M. Macromolecules
2000, 33, 5819.
(17) Iwasaki, Y.; Ishihara, K. Anal. Bioanal. Chem. 2005, 381, 534.
(18) Ahmad, H.; Dupin, D.; Armes, S. P.; Lewis, A. L. Langmuir 2009, 25,
11442.
(19) Ishihara, K.; Tsuji, T.; Sakai, Y.; Nakabayashi, N. J. Polym. Sci., Part A:
Polym. Chem 1994, 32, 859.
(20) Uchida, T.; Furuzono, T.; Ishihara, K.; Nakabayashi, N.; Akashi, M. J.
Polym. Sci., Part A: Polym. Chem. 2000, 38, 3052.
(21) Sugiyama, K.; Shiraishi, K.; Ohga, K.; Shirahama, H.; Tamai, H.;
Kikukawa, K.; Yasuda, H. Polym. J. 1993, 25, 521.
4694 DOI: 10.1021/la903567q
Langmuir 2010, 26(7), 4693–4702

Thompson et al.
Article
solution turned dark brown, indicating the onset of polymeri-
zation. After 6 h, the reaction solution was diluted with methanol
and became blue/green in color, indicating aerial oxidation of
the catalyst. The solution was passed through a silica column
to remove the spent Cu(II) catalyst. The homopolymer was
then dried on a vacuum line overnight to obtain a white powder
(93% yield). Syntheses of the PMPC10, PMPC20, PMPC40, and
PMPC50 homopolymers were each conducted using the same
protocol. The target degree of polymerization was adjusted by
varying the monomer/initiator molar ratio. The relative molar
ratios of [monomer]/[initiator]/[bpy]/[CuCl] in the reaction mix-
ture were n:1:2:1, where n is the target degree of polymerization.
Quaternization of the PMPC Homopolymer. The PMPC30
homopolymer (4.23 g, 0.47 mmol) was dissolved in methanol
(13 mL) to afford a 25 wt % solution. To this solution, 4-VBC
(0.237 g, 1.41 mmol; 4-VBC/polymer molar ratio = 3:1) was
added and stirred at room temperature for 48 h. The excess
solvent was removed by rotary evaporation, and the resulting
solid was then dissolved in water. The excess 4-VBC was extracted
three times with cyclohexane. The aqueous phase was then freeze-
dried from water overnight to afford a white powder. The purified
macromonomer was characterized by 1H NMR (91% yield). The
mean degree of quaternization was calculated by comparing the
aromatic styrene signals at δ 7.55-7.70 to the two azamethylene
protons due to PMPC at δ 3.61-3.77.
Kinetics of Quaternization of PMPC10 for Kinetic Stu-
dies. 1H NMR spectroscopy was used to monitor the kinetics of
quaternization for various 4-VBC/polymer molar ratios. PMPC10
(250 mg, 0.08 mmol) was weighed into a sample vial and dissolved
in d4-methanol (0.75 mL, 25 wt %). 4-VBC (0.037 mL, 0.24 mmol,
3 mol equiv based on tertiary amine end-groups) was added to this
stirred solution using a micropipet. This reaction solution was
transferred to an NMR tube, and 1H NMR spectra were recorded
at hourly intervals. Reactions were also monitored using either
2 or 1 mol equiv of 4-VBC. Degrees of quaternization were
calculated by comparing the integrated signal at δ 2.0-2.5 arising
from the 2-(dimethylamino)ethyl end-group with the two
azamethylene protons at δ 3.6-3.8 due to the MPC repeat
units.
drying in plastic molds at room temperature. These films were
characterized by XPS measurements.
PMPC30-PS Latex Syntheses via Alcoholic Dispersion
Polymerization. PMPC30 (or PMPC20 or PMPC10) macromo-
nomer (1.00 g) was weighed into a 250 mL three-necked, round-
bottomed flask fitted with a condenser and a nitrogen inlet and
dissolved in methanol (100 mL). This solution was purged with
nitrogen for 30 min before being heated to 70 °C under a nitrogen
blanket. The AIBN initiator (0.100 g) was dissolved in styrene
(10.0 g) and purged with nitrogen before being injected into the
reaction vessel. The polymerizing solution turned milky white
within 1 h and was stirred at 70 °C for 24 h. The above protocol
was also used for PMPC10 and PMPC20 macromonomers and for
examining the effect of varying the PMPC30 macromonomer
concentration. The resulting latexes were purified by three
centrifugation/redispersion cycles. Ineachcase, the latexdiameter
was assessed by DLS (before purification) and SEM (after
purification). These latexes were also analyzed by 1H NMR,
FTIR, and XPS.
Freeze-Thaw and Salt Stability Experiments. Selected
PMPC-PS latexes (10.0 w/v % solids content) were frozen at
-20 °C and then allowed to thaw at room temperature. Floccula-
tion was judged by visual inspection and confirmed by DLS
measurements. Various PMPC30-PS latexes (1.0 mL; 2.0 w/v %
solids content) were transferred via a pipet into sample vials to
which 1.0 mL aliquots of various aqueous MgSO4 solutions were
added (0.02-1.00 M). This dilution produced 1.0% aqueous latex
dispersions in 0.01-0.50 M MgSO4. Colloidal (in)stability
was judged by visual inspection and confirmed by DLS mea-
surements.
Macromonomer and Latex Characterization. 1H NMR
Spectroscopy. All 1H NMR spectra were recorded in either
CDCl3, D2O, or CD3OD using a 400 MHz Bruker Avance-400
spectrometer. Dried PMPC-PS latexes were dissolved in 7:1 v/v
CDCl3/CD3OD for 1H NMR analysis. The integrated intensity of
the two azamethylene protons at δ 3.5-3.7 due to the PMPC
stabilizerwascomparedtothatofthe fivearomaticprotons due to
the styrene residues at δ 6.1-7.2. The dried PMPC-P(S-nBuA)
latex was dissolved in 3:1 v/v CDCl3/CD3OD, and the integrated
intensity of the nine trimethylammonium protons at δ 2.98-3.14
was compared to that of the five aromatic protons due to the
styrene residues at δ 6.1-7.2.
Aqueous GPC. Molecular weights and polydispersities of the
PMPC homopolymers were determined by aqueous GPC using
two Polymer Laboratories Aquagel-OH 8 mm columns (type
40 first, followed by type30) in series with a Polymer Laboratories
ERC-7515A refractive index detector. The eluent was a solution
containing 0.2 M NaNO3 and 0.05 M Trisma buffer at pH 7.0
using a flow rate of 1.0 mL min-1. The GPC columns were
calibrated using 10 poly(ethylene oxide) (PEO) homopolymer
standards. Data were analyzed using PL Cirrus GPC software
(version 2.0) supplied by Polymer Laboratories.
PMPC30-PS Latex Syntheses via Aqueous Emulsion
Polymerization. PMPC30 macromonomer (0.50 g) was weighed
into a 100 mL round-bottomed flask containing a magnetic flea
and dissolved inwater (45.0g), and thenstyrene (5.0 g) wasadded.
This solution was degassed by five evacuation/nitrogen purge
cycles and then heated to 70 °C. Separately, the ammonium
persulfate (APS) or AIBA initiator (0.050 g) was dissolved in
water (5.0 g) and purged with nitrogen. This solution was then
injected into the reaction vessel once the temperature had reached
70 °C (or 60 °C for AIBA). The polymerizing solution turned
milky white within 30 min and was stirred for 24 h. The resulting
latexes were purifiedbythree centrifugation/redispersioncycles to
remove excess macromonomer and any unreacted styrene mono-
mer. In each case, the latex particle diameter was assessed by DLS
(before purification) and SEM (after purification). These latexes
were also analyzed by 1H NMR, FTIR, XPS, and zeta potential
measurements.
FTIR Spectroscopy. Each sample (1.0 mg) was ground up
with 150 mg of KBr to afford a fine powder and compressed into
a pellet by applying a pelletization pressure of 8 tonnes for
10 minutes. The FTIR spectra were recorded using a Nicolet
Magna (series II) spectrometer at 4.0 cm-1 resolution, and
64 scans were recorded per spectrum.
PMPC30-P(S-BuA) Latex via Aqueous Emulsion Poly-
merization. PMPC30 macromonomer (0.50 g) wasweighed intoa
100 mL round-bottomed flask containing a magnetic flea and
dissolved in water (45.0 g), and then styrene (2.50 g) and
n-butyl acrylate (2.50 g) were added. This mixture was degassed
via five evacuation/nitrogen purge cycles and subsequently heated
to 70 °C. Separately, the APS initiator (0.050 g) was dissolved in
water (5.0 g), purged with nitrogen, and then injected into the
reaction vessel at 70 °C. The polymerizing solution was stirred for
24 h, and the resulting latex was purified by dialysis against water.
The latex was assessed by DLS (before purification) and by both
SEM and aqueous electrophoresis (after purification). The puri-
fied latex was cast into films of approximately 50 μm thickness by
DLS. Dynamic light scattering (DLS; Malvern Zetasizer
NanoZS instrument) was used to obtain intensity-average
hydrodynamic latex diameters using the Stokes-Einstein equa-
tion, which is valid for dilute, noninteracting, perfectly mono-
disperse spheres. Aqueous 0.01 w/v % latex dispersions were
analyzed using disposable cuvettes, and the data were averaged
over three consecutive runs. The deionized water used to dilute
each latex was ultrafiltered through a 0.20 μm membrane so as to
remove extraneous dust.
Disk Centrifuge Photosedimentometry. The weight-average
diameter Dw of the polystyrene latexes was measured using
Langmuir 2010, 26(7), 4693–4702
DOI: 10.1021/la903567q 4695

Article
Thompson et al.
Table 1. ATRP Synthesis of PMPC Homopolymer Precursors with
Differing Target Degrees of Polymerization at 20 °C in Methanola
entry target conversion
(%)
DP
(1H NMR)
Mn
(GPC)
Mw/Mn
(GPC)
no.
DP
1
2
3
4
5
6
7
8
10
20
30
35
100
98
100
99
100
99
100
100
12
22
30
45
60
75
8400
1.21
1.28
1.29
1.30
1.97
1.87
2.31
2.01
11 600
13 100
15 100
17 500
19 400
18 900
19 100
40
50
50b
50c
a GPC data were obtained using poly(ethylene oxide) calibration
standards. b Reaction conducted at 50 °C. c Reaction initiated at 0 °C
and then warmed to 20 °C.
a Brookhaven BI-DCP instrument operating in line-start mode.
Samples were prepared by the addition of one drop of latex
dispersion to a 3:1 water/methanol mixture (total volume
10 mL). A 15:1 deionized water/methanol mixture was used as
the spin fluid. The density of the polystyrene latex particles was
taken to be 1.05 g cm-3. This is a reasonable assumption for
micrometer-sized latexes, where the thickness of the steric stabi-
lizer layer is negligible compared to the particle diameter. For
smaller latexes (typically for diameters of less than 200 nm), the
stabilizer layer thickness becomes significant, resulting in a
reduction in the effective particle density. Because an accurate
particle density is required when calculating the weight-average
particle diameter Dw, any uncertainty in the former parameter
produces an associated error in the latter.22
Figure 2. Representative aqueous GPC curves obtained for
PMPC10, PMPC20, and PMPC30 homopolymer precursors prepared
by ATRP at 20 °C (vs poly(ethylene oxide) calibration standards).
The inset compares the GPC trace obtained for the PMPC30 homo-
polymer precursor to that of the corresponding macromonomer.
1.87 to 2.31, and the actual DP is substantially higher than that
targeted. Varying the reaction temperature failed to improve the
final polydispersities of these higher DP homopolymers (entries 7
and 8 in Table 1). However, a linear evolution of the number-
average molecular weight with conversion was observed for the
PMPC30 synthesis, suggesting that reasonably good living char-
acter is obtained under these specific conditions (Figure 3).
Although this data set does show a nonzero intercept that may
indicate reduced control early in the polymerization, we empha-
Aqueous Electrophoresis. Zeta potentials were determined
using a Malvern Zetasizer NanoZS instrument equipped with
an autotitrator (MPT-2 multipurpose titrator, Malvern Instru-
ments). The solution pH was varied from 2 to 9 in the presence of
1 mM KCl using either dilute NaOH or HCl as required.
SEM. SEM studies were performed using an FEI Sirion field-
emission scanning electron microscope. Samples were dried onto
adhesive carbon disks and sputter-coated with a thin layer of gold
prior to examination using a beam current of 244 μA and a typical
operating voltage of 20 kV.
1
size that the H NMR data confirms that the actual mean DP
values are in good agreement with those targeted for the PMPC10,
PMPC20, and PMPC30 precursors. In contrast, the corresponding
data set obtained for a PMPC50 synthesis (Figure S1 in Support-
ing Information) shows a nonlinear evolution of molecular weight
with conversion and the high final polydispersities suggest that
only poor control is achieved for this higher DP homopolymer.
Additional MPC homopolymerizations using 2-(dimethylamino)-
ethyl-2-bromoisobutyrylamide targeting DPs of 30, 40, and 50
were performed several times, and the GPC data proved to be
reproducible; the PMPC30 precursor was always near-monodis-
perse (Mw/Mn = 1.2 to 1.3), whereas the PMPC40 and PMPC50
precursors were invariably polydisperse (Mw/Mn = 1.6 to 2.0).
There is some evidence for a high molecular weight tail in the GPC
trace for the PMPC50 homopolymers, possibly suggesting some
termination by combination (Figure S2 in Supporting Infor-
mation). Currently, we have no convincing explanation for the
dramatic loss of living character observed for the higher target DP
syntheses, although we note that other workers have reported some
difficulties in using amide-based ATRP initiators.23 Nevertheless,
we have shown that near-monodisperse PMPC homopolymers can
be obtained for a target DP of up to 30. As we shall see later, this is
sufficient to obtain well-defined PMPC macromonomers that
allow the preparation of sterically stabilized latexes with enhanced
colloidal stabilities.
XPS. X-ray photoelectron spectra (XPS) were acquiredusing a
Kratos Axis Ultra DLD X-ray photoelectron spectrometer
equipped with a monochromatic Al KR X-ray source (hν =
1486.6 eV) and operating at a base pressure of 10-8 to 10-10 mbar.
Latex particles were dried onto a silicon wafer and evacuated to
ultrahigh vacuum prior to XPS measurements.
Results and Discussion
A summary of the target degrees of polymerization, conver-
sion, molecular weight, and polydispersity of the various PMPC
homopolymer precursors synthesized in this study is shown in
Table 1. Reasonably good control was achieved for the poly-
merization of MPC with target DPs of 10, 20, and 30 because the
polydispersities of these homopolymers were 1.29 or less and the
actual degree of polymerization agreed well with that of the
targeted DP, as judged by 1H NMR. GPC traces of these
PMPC30, PMPC20, and PMPC10 homopolymer precursors are
shown in Figure 2, confirming that the differing degrees of
polymerization can easily be distinguished. However, it is clear
from Table 1 that there is a marked increase in polydispersity and/
or a loss of control if the target DP is greater than 30. For a target
DP of 35, the final polydispersity is still relatively low at 1.30, but
the actual DP is significantly higher than that targeted, suggesting
relatively poor initiation efficiency under these conditions.
For higher target DPs, the final polydispersities range from
Macromonomers were synthesized by quaternizing the tertiary
amine end-groups of the three well-defined homopolymer pre-
cursors (PMPC10, PMPC20, and PMPC30) using excess 4-VBC, as
shown in Figure 1. Assigned NMR spectra for the 2-(dimethyl-
amino)ethyl-2-bromoisobutyrylamide initiator, PMPC30 homo-
polymer precursor, and corresponding PMPC30 macromonomer
(22) Cairns, D. B.; Armes, S. P.; Bremer, L. G. B. Langmuir 1999, 15, 8052.
(23) Limer, A.; Haddleton, D. M. Macromolecules 2006, 39, 1353.
4696 DOI: 10.1021/la903567q
Langmuir 2010, 26(7), 4693–4702

Thompson et al.
Article
Figure 4. 1H NMR spectra recorded in CD3OD for (a) 2-(dimethyl-
amino)ethyl-2-bromoisobutyrylamide, (b) PMPC30 homopolymer
precursor before quaternization, and (c) PMPC30 macromonomer
after quaternization and purification using a 4-VBC/amine molar
ratio of 3:1.
reaction by 1H NMR spectroscopy. The PMPC10 homopolymer
was used in these kinetic experiments because its relatively low
degree of polymerization ensures that its initiator signals are
prominent, which aids quantification. The three 4-VBC/PMPC10
molar ratios (3:1, 2:1, and 1:1) investigated each allowed full
quaternization to be achieved, albeit on differing time scales
(Figure 5). The 3:1 molar ratio led to complete quaternization
within 14 h, whereas using a 1:1 molar ratio required 72 h at 20 °C.
A control experiment was conducted to examine the possible side
reaction of 4-VBC with the solvent. No changes were observed in
Figure 3. Homopolymerizationof MPC in methanol via ATRP at
20 °C: (A) conversion and semilogarithmic plot of monomer
concentration vs time data; (B) evolution of the number-average
molecular weight and polydispersity with monomer conversion.
The solid line represents the theoretical Mn evolution with conver-
sion. Reaction conditions: MPC (10.0 g, 1.13 mmol), methanol
(11.0 mL), target DP = 30, relative molar ratios of [I]/[Cu(I)]/[L]
= 1:1:2. Aqueous GPC data were obtained using poly(ethylene
oxide) calibration standards.
1
the H NMR spectrum of 4-VBC in CD3OD for up to 72 h at
20 °C, thus confirming that no reaction occurs between 4-VBC
and CD3OD under these conditions. Another possibility is that
the 4-VBC might esterify the anionic phosphate groups on the
PMPC homopolymer, in addition to quaternizing the desired
tertiary amine end-group. Thus, a PMPC30 homopolymer con-
taining no terminal tertiary amine group was synthesized using
m-methylphenyl bromoisobutyrate (MPBr) initiator and mixed
with a 3-fold excess of 4-VBC for 72 h in CD3OD. Again, no
change in the 1H NMR spectrum was observed, confirming that
no reaction occurs in the absence of terminal tertiary amine
groups.
Table 2 summarizes the GPC data obtained for the PMPC
homopolymers before and after quaternization, and the inset in
Figure 3 compares the GPC molecular weight distributions before
and after quaternization of the PMPC30 precursor. Quaterniza-
tion resulted in essentially no difference in the molecular weight
distribution, as expected. Moreover, there was essentially no
difference between the aqueous GPC curves recorded using UV
and refractive index detectors (data not shown), thus confirming
that each PMPC chain contained a UV chromophore (i.e.,
a terminal polymerizable styrenic unit).
are shown in Figure 4. On quaternization with 4-VBC, NMR
shifts are observed for the six dimethyl protons and the two
azamethylene protons. The original positions of these two proton
signals are shown in the initiator NMR spectrum (Figure 4a), and
those of the corresponding homopolymer precursor (Figure 4b)
are shown as peaks a and b, respectively. The new positions of
these two signals for the quaternized PMPC30 macromonomer
are shown in Figure 4c. These NMR observations allow the extent
of quaternization to be conveniently monitored: the complete
disappearance of these initiator end-group signals in the δ 2.2-
2.8 region indicates that full quaternization has been achieved.
After purification to remove excess 4-VBC, new aromatic and
benzylic peaks due to the conjugated 4-vinylbenzyl group are
observed in the 1H NMR spectrum (Figure 4c, δ 5.4-7.9). It is
perhaps worth emphasizing that the amide-based ATRP initiator
is essential for ensuringthat these PMPC macromonomers exhibit
good hydrolytic stability: our preliminary studies (data not
shown) using the corresponding ester-based ATRP initiator
indicated that extensive hydrolysis of the quaternized chain ends
occurs, even on storage at below ambient temperature.
Polystyrene latexes were prepared using the PMPC-based
macromonomers as reactive steric stabilizers, as illustrated in
The amount of 4-VBC required to quaternize the PMPC
homopolymer precursors fully was assessed by monitoring this
Langmuir 2010, 26(7), 4693–4702
DOI: 10.1021/la903567q 4697

Article
Thompson et al.
Figure 5. Quaternization of a 25 w/v % PMPC10 homopolymer conducted in CD3OD at 20 °C using 4-VBC/amine molar ratios of 3:1, 2:1,
and 1:1.
Table 2. Comparison of GPC Data (vs Poly(ethylene oxide) Cali-
bration Standards) Obtained before Quaternization and after Qua-
ternization (and Purification)
all of the macromonomer chains are located on the outside of the
latex, this corresponds to an adsorbed amount, Γ, of roughly
1.2-1.3 mg m-2. These adsorbed amounts are approximately
constant for all three latexes, as expected.
before quaternization
after quaternization
Alcoholic dispersion polymerization was also used to prepare
polystyrene latexes (Table 4). The dispersion polymerization of
styrene in alcoholic solution is well documented.25 Various vinyl-
functionalized macromonomers have been used to ensure effec-
tive steric stabilization, which is normally a prerequisite for
colloid stability under these conditions.26,27 In the present study,
we conducted several control experiments to demonstrate that the
macromonomer architecture is essential for producing colloidally
stable latex particles. Polymerization of styrene in methanol at
70 °C using an AIBN initiator in the absence of any polymeric
stabilizer simply led to macroscopic precipitation, as expected (see
entry 10 in Table 4 and also Figure 7). A similar experiment
conducted in the presence of the PMPC30 homopolymer precur-
sor (i.e., each chain merely has a terminal tertiary amine group,
rather than a polymerizable styrene group) also led to precipita-
tion, with little or no colloidal latex being formed (entry 11 in
Table 4). In contrast, the polymerization of styrene in the presence
of 10 w/v % of the corresponding PMPC30 macromonomer led to
the production of a near-monodisperse, micrometer-sized poly-
styrene latex under the same conditions. These results confirm
that the presence of a reactive terminal styrenic group is essential
for successful latex formation and also suggests that negligible
chain transfer to the PMPC precursor occurs (i.e., in situ stabilizer
grafting via chain transfer to polymer is not sufficient to ensure
colloid stability in this case). However, lowering the stabilizer
concentration to 5 w/v % failed to produce a stable latex. This is
perhaps understandable given the relatively massive MPC repeat
units: a mean DP of 30 corresponds to an Mn of approximately
9000, which means that there are relatively few stabilizer chains
per unit mass compared to conventional macromonomers such as
commercially available poly(ethylene glycol) monomethacrylates
(for which Mn = 1000 or 2000).22 Syntheses conducted using
either the PMPC20 or the PMPC10 macromonomer at 10 w/v %
yielded latexes that were significantly more polydisperse than that
target conversion
(%)
DP
Mn (g mol-1
)
Mw/Mn Mn (g mol-1
)
Mw/Mn
10
20
30
100
98
100
8400
11 600
13 900
1.21
1.28
1.29
8400
11 500
14 000
1.22
1.30
1.32
Figure 6. A summary of the various latex syntheses conducted
using aqueous emulsion polymerization is provided in Table 3.
Entries 1, 3, and 5 were prepared using the PMPC30 macromono-
mer, and in each case, very high conversions and narrow particle
size distributions were obtained. It is perhaps worth emphasizing
that such results are not always observed for surfactant-free
macromonomer-only syntheses: in some cases only rather poly-
disperse latexes are obtained under these conditions.24 It is also
noteworthy that entries 5 and 6 involve the synthesis of film-
forming styrene/n-butyl acrylate copolymer latexes rather than
polystyrene latex. Depending on the precise formulation, it is often
possible to obtain colloidally stable latexes via aqueous emulsion
polymerization even in the absence of any polymeric or surfactant
stabilizer. This proved to be the case in the present study. Thus,
polystyrene latexes could be obtained in the absence of any
polymeric stabilizer when using the anionic persulfate or cationic
AIBA initiators at 70 or 60 °C, respectively. However, these latexes
are significantly larger and more polydisperse than those prepared
in the presence of the PMPC30 macromonomer. This supports the
hypothesis that the latter particles are sterically stabilized by the
chemically grafted PMPC30 macromonomer chains. Latexes pre-
pared in the absence of macromonomer are merely charge-stabi-
lized, with the surface charge originating from the initiator
fragments. Given their larger latex diameter and significantly
higher polydispersity, this is clearly a much less effective stabiliza-
tion mechanism under the stated conditions. 1H NMR analysis of
the dried latexes allows the calculation of the amount of PMPC30
macromonomer incorporated into the latex particles. In the case of
aqueous emulsion polymerization, the PMPC30 macromonomer
comprises 3.7-7.3% of the latex by mass (Table 3). Assuming that
(25) Arshady, R. Colloid Polym. Sci. 1992, 270, 717.
(26) Lascelles, S. F.; Malet, F.; Mayada, N. C.; Billingham, N. C.; Armes, S. P.
Macromolecules 1999, 32, 2462.
(27) Fujii, S.; Iddon, P. D.; Ryan, A. J.; Armes, S. P. Langmuir 2006, 22, 7512.
(24) Dupin, D.; Armes, S. P.; Fujii, S. J. Am. Chem. Soc. 2009, 131, 5386.
4698 DOI: 10.1021/la903567q
Langmuir 2010, 26(7), 4693–4702

Thompson et al.
Article
Figure 6. Reaction scheme for the synthesis of sterically stabilized polystyrene latexes by either aqueous emulsion or alcoholic dispersion
polymerization using the PMPC-based macromonomer.
Table 3. Emulsion Polymerization of Styrene Showing Initiator and Stabilizer Type and Mean Latex Diameter Determined by DCP, DLS, and
SEMa
particle diameter (nm)
initiator
type
latex
conversion (%)
stabilizer content by
NMR (wt %)
entry no.
stabilizer
SEM
170
560
95
DCP
DLS (PDI)
Γ (mg m-2
1.2c
)
1
2
3
PMPC30 macromonomer
no added stabilizer
PMPC30 macromonomer
no added stabilizer
PMPC30 macromonomer
no added stabilizer
APS
APS
AIBA
AIBA
APS
92
48
85
70
86
37
180 ( 17
580 ( 29
118 ( 10
670 ( 88
191 (0.03)
667 (0.05)
114 (0.02)
1060 (0.10)
119 (0.04)
650 (0.07)
3.7
7.3
5.4
1.3c
4
200, 750
5b
1.2d
6b
APS
a Reactions were conducted at 60 °C (AIBA) and 70 °C (APS) in water for 24 h using 1.0 wt % initiator and 10 w/v % macromonomer based on the
styrene monomer. b These two entries are film-forming 1:1 styrene/n-butyl acrylate copolymer latexes. c Calculated using the SEM diameter. d Calculated
using the DLS diameter because of the film-forming nature of the copolymer latex.
Table 4. Effect of Stabilizer Type on the Mean Particle Diameter as Determined by DCP, DLS, and SEM for Polystyrene Latexes Prepared via
Alcoholic Dispersion Polymerization in Methanol at 70 °C for 24 h Using 1.0 wt % AIBN Initiator Based on the Styrene Monomer
stabilizer
(w/v %)
latex
conversion (%)
stabilizer content
by NMR (wt %)
entry no.
stabilizer type
SEM
DCP
DLS
Γ (mg m-2
)
7
8
9
10
11
12
PMPC30 macromonomer
PMPC20 macromonomer
PMPC10 macromonomer
no added stabilizer
PMPC30 homopolymer
PMPC30 macromonomer
10
10
10
0
10
5
100
100
100
0
0
0
1020
1090
930
1080 ( 96
1120 ( 140
900 ( 100
1140 (0.05)
1450 (0.30)
1120 (0.16)
0.7
0.4
0.6
1.3
0.8
1.0
Figure 7. SEM images of selected polystyrene latexes prepared in the presence of PMPC30 (A, B, and D), PMPC20 (E), and PMPC10 (F)
macromonomers and a charge-stabilized PS latex control (C) prepared by aqueous emulsion polymerization in the absence of any
macromonomer.
produced using the PMPC30 macromonomer, but there is no
obvious trend between mean latex diameter and macromonomer
chain length. 1H NMR spectroscopy was again used to calculate
the stabilizer content of the latex. Since alcoholic dispersion
polymerization produces much larger latexes (with corres-
pondingly lower specific surface areas), the stabilizer contents
were somewhat lower than those prepared by emulsion polymeri-
zation (0.4-0.7%, Table 4). This leads to Γ values of between
Langmuir 2010, 26(7), 4693–4702
DOI: 10.1021/la903567q 4699

Article
Thompson et al.
Figure 8. FTIR spectra recorded for the PMPC30 macromonomer, a charge-stabilized polystyrene latex prepared by emulsion polymeri-
zation in the absence of macromonomer, a polystyrene latex prepared by emulsion polymerization using the PMPC30 macromonomer and
APS initiator, and a polystyrene latex prepared by alcoholic dispersion polymerization using the PMPC30 macromonomer and AIBN
initiator.
0.8 and 1.3 mg m-2, which are comparable to those calculated for
the three smaller latexes (Table 3). This suggests that our
assumption that all of the macromonomer chains are located at
the surface of these latexes is likely to be valid.
FTIR spectra were recorded for the PMPC30 macromonomer
and selected polystyrene latexes (Figure 8). The ester carbonyl
stretch due to the PMPC macromonomer is observed at around
1730 cm-1. Characteristic bands also appear at 1260 and
1090 cm-1 due to the PdO and P-O-C stretches, respectively,
and also at 970 cm-1 due to the antisymmetric stretches of the
three C-N bonds in the trimethylammonium group,28 which are
consistent with previous FTIR studies of PMPC.19,20,29 All of
these bands are also observed in the spectrum obtained for the
polystyrene latex prepared by aqueous emulsion polymerization.
This confirms the presence of the PMPC stabilizer (but not its
spatial location) in this latex. In contrast, no carbonyl band
was observed for the micrometer-sized PMPC30-PS latex pre-
Figure 9. Zeta potential vs pH curves obtained for polystyrene
and poly(styrene-co-n-butyl acrylate) latexes prepared in the pre-
pared by alcoholic dispersion polymerization. However, this
negative result was not unexpected; the much lower specific
surface area of this latex means that its stabilizer content is less
than 1% by mass (Table 4), which precludes the detection of the
carbonyl band.
Aqueous electrophoresis curves obtained for a charge-stabi-
lized polystyrene latex and several sterically stabilized latexes
prepared using the PMPC30 macromonomer are shown in
Figure 9. As expected, the bare polystyrene latex prepared in
the absence of any stabilizer using the cationic AIBA initiator
exhibits a positive zeta potential for most of the pH sweep
(pH 2-7). In contrast, all of the PMPC30-stabilized latexes exhibit
much shallower electrophoretic curves with zeta potentials
of approximately (5 mV (and hence very low surface charge).
sence of the PMPC30 macromonomer and also a charge-stabilized
polystyrene latex control synthesized in the absence of a macro-
monomer.
This is not surprising given that the PMPC chains are zwitterionic
in nature and therefore have no net charge. Provided that the
PMPC stabilizer layer is sufficiently thick, the underlying cationic
surface charge (due to the initiator fragments and quaternized
macromonomer end-groups) is effectively screened. Therefore,
these electrophoretic results are consistent with the PMPC30
macromonomer being located at the particle surface. Further
evidence is provided by XPS analysis (Table 5). XPS is very
surface-specific, with a typical analysis depth of around 2-5 nm.
Hence only the near surface of the particles is interrogated.
Therefore, if the PMPC30 macromonomer lies at the surface of
the latex, then XPS should exhibit characteristic N 1s and P 2p
signals due to its nitrogen and phosphorus atoms, respectively.
These features are indeed observedinthe XPS spectra, with the N/
(28) Meyre, M. E.; Lambert, O.; Desbat, B.; Faure, C. Nanotechnology 2006, 17,
1193.
(29) Furuzono, T.; Ishihara, K.; Nakabayashi, N.; Tamada, Y. Biomaterials
2000, 21, 327.
4700 DOI: 10.1021/la903567q
Langmuir 2010, 26(7), 4693–4702

Thompson et al.
Article
Table 5. XPS Data Summarizing the Near-Surface Elemental Compositions of the PMPC30 Macromonomer, Two Polystyrene Latexes Prepared
by Emulsion and Dispersion Polymerization in the Presence of This Macromonomer, and the P(S-nBuA) Film-Forming Latexes Prepared by
Emulsion Copolymerization Using This Macromonomera
% PMPC30 surface
coverage
XPS sample description
PMPC30 macromonomer
charge-stabilized polystyrene latex (prepared with APS initiator)
PMPC30-PS latex (emulsion polymerization, APS initiator)
PS precipitate (attempted dispersion polymerization, AIBN initiator)
PMPC30-PS latex (dispersion polymerization, AIBN initiator)
charge-stabilized P(S-BuA) latex film (APS initiator)
% C
% N
2.7
% P
2.7
% O
% S
N/P
1.0
0.9
1.0
73.3
95.5
84.6
97.4
83.0
89.4
90.4
21.2
4.6
13.2
2.6
14.2
10.6
9.6
0.4
0.1
1.0
1.1
37
52
1.4
1.4
PMPC30-P(S-BuA) latex film (APS initiator)
a A macroscopic precipitate of polystyrene and a charge-stabilized polystyrene latex prepared in the absence of any macromonomer are also included
as reference materials.
Table 6. Summary of the Colloidal Stabilities of Various Latexes after Being Subjected to a Single Freeze-Thaw Cycle (at 10 w/v % Solids, Frozen
at -20 °C) or the Presence of Varying Amounts of MgSO4 (2.0 w/v % Solids)a
MgSO4 concentration (mol dm-3
)
DLS latex
diameter (nm)
freeze-thaw stability
(DLS, nm)
latex type
APS-PS
PMPC30-PS
PMPC30-PS
PMPC20-PS
PMPC10-PS
APS-P(S-BuA)
PMPC30-P(S-BuA)
0.01
0.05
0.10
0.20
0.30
0.50
667
191
1140
1450
1120
650
x
x
x
x
x
x
x (precipitate)
(191)
(1140)
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
(1400)
(1190)
√
x
√
x
√
x
√
x
√
x
√
x
√
x (precipitate)
√
(precipitate)
119
√
a x - Particles are unstable and visibly aggregated. - Particles are stable and remain dispersed, with the final DLS latex diameter in nanometers
observed after thawing also reported, where applicable.
P atomic ratios being approximately unity (Table 6). Ishihara and
co-workers20 obtained similar XPS results for their PMPC-
stabilized polystyrene latexes, although in their case the N/P
atomic ratios were not reported. Surprisingly, although aqueous
electrophoresis suggests that the PMPC30 macromonomer is
present at the surface of the PMPC30-P(S-BuA) latex, XPS
analysis of the latex film does not reveal any characteristic
nitrogen or phosphorus signals due to the MPC units. Presum-
ably, this is because the hydrophilic PMPC chains can bury
themselves in the low-Tg copolymer film when subjected to the
ultrahigh-vacuum conditions required for XPS studies. Similar
findings (and conclusions) have been reported by Clarke and co-
workers for MPC-based statistical copolymers.30
Having demonstrated that the PMPC-based macromonomers
are indeed located at the latex surface and thus act as steric
stabilizers, we evaluated the latex colloid stability by two
methods: a single freeze-thaw cycle and exposure to varying con-
centrations of MgSO4 (Table 6). A charge-stabilized polystyrene
latex control flocculated substantially in just 0.01 M MgSO4 and
also failed to redisperse after a freeze-thaw cycle. However, each
latex stabilized by the PMPC-based macromonomers (DP = 10,
20, or 30) remained stable at up to 0.50 M MgSO4 and also readily
redispersed after freeze-thaw cycles, as judged by DLS. Clearly,
the PMPC chains confer substantially enhanced colloidal stabi-
lity. Good freeze-thaw stability is a typical characteristic of
sterically stabilized latexes, but the excellent salt tolerance is
presumably due to the zwitterionic nature of the PMPC chains;
it is well known that such polybetaines generally exhibit a so-
called antipolyelectrolyte effect, whereby they are “salted in” on
addition of electrolyte (rather than “salted out” like conventional
polyelectrolytes).31,32
Conclusions
Novel biocompatible styrene-functionalized macromonomers
have been synthesized using a tertiary amine-functional ATRP
initiator followed by postpolymerization quaternization using
4-vinylbenzyl chloride. Empirically, we find that there is an upper
limit for the target DP of the homopolymer precursors under
the conditions investigated in this work: above a target DP of 35,
only rather broad molecular weight distributions are obtained
(Mw/Mn > 2.0), whereas for DP = 10-30 relatively low poly-
dispersity chains are produced (Mw/Mn < 1.30) with reasonable
control over the target DP. The latter macromonomers were
evaluated as reactive polymeric stabilizers for the polymerization
of styrene using either aqueous emulsion or alcoholic dispersion
formulations. For example, near-monodisperse, sterically stabi-
lized polystyrene latexes of micrometer dimensions are obtained
via dispersion polymerization in the presence of the PMPC30
macromonomer, whereas only a macroscopic precipitate is ob-
served if a non-quaternized PMPC30 homopolymer precursor was
utilized. This illustrates the essential role played by the terminal
polymerizable styrene group in determining the final particle
morphology. Similarly, near-monodisperse polystyrene latexes
of around 100-200 nm diameter were obtained via emulsion
polymerizationusing the same PMPC30 macromonomer, whereas
only polydisperse, charge-stabilized latexes were obtained in the
absence of any stabilizer. FTIR, aqueous electrophoresis, and
XPS studies confirmed that the chemically-grafted macromono-
mer is present at (or very near) the surface of the prepared latex
particles. The highly hydrated, zwitterionic nature of these PMPC
chains confers enhanced colloid stability on these sterically
stabilized latexes compared to charge-stabilized latexes. For
example, no significant particle aggregation occurs inthe presence
of up to 0.50 M MgSO4 or after a freeze-thaw cycle at -20 °C.
(30) Clarke, S.; Davies, M. C.; Roberts, C. J.; Tendler, S. J. B.; Williams, P. M.;
O’Byrne, V.; Lewis, A. L.; Russell, J. Langmuir 2000, 16, 5116.
(31) Mahon, J.; Zhu, S. Colloid Polym. Sci. 2008, 286, 1443.
(32) Matsuda, Y.; Kobayashi, M.; Annaka, M.; Ishihara, K.; Takahara, A.
Chem. Lett. 2006, 35, 1310.
Acknowledgment. Biocompatibles is thanked for supplying
the MPC monomer and for permission to publish this work.
Langmuir 2010, 26(7), 4693–4702
DOI: 10.1021/la903567q 4701

Article
Thompson et al.
S.P.A. is the recipient of a five-year Royal Society-Wolfson
Research Merit Award.
MPC when targeting a mean degree of polymerization
of 50. Comparison of GPC curves obtained for near-
monodisperse and polydisperse PMPC homopolymer pre-
cursors. This material is available free of charge via the
Internet at http://pubs.acs.org.
Supporting Information Available: Kinetic and molecular
weight data obtained for the uncontrolled polymerization of
4702 DOI: 10.1021/la903567q
Langmuir 2010, 26(7), 4693–4702