Microstructured poly(2-oxazoline) bottle-brush brushes on nanocrystalline diamond

Article abstract of DOI:10.1039/b923789p

We report on the preparation of microstructured poly(2-oxazoline) bottle-brush brushes (BBBs) on nanocrystalline diamond (NCD). Structuring of NCD was performed by photolithography and plasma treatment to result in a patterned NCD surface with oxidized and hydrogenated areas. Self-initiated photografting and photopolymerization (SIPGP) of 2-isopropenyl-2-oxazoline (IPOx) resulted in selective grafting of poly(2-isopropenyl-2-oxazoline) (PIPOx) polymer brushes only at the oxidized NCD areas. Structured PIPOx brushes were converted by methyl triflate into the polyelectrolyte brush macroinitiator for the living cationic ring-opening polymerization (LCROP) of 2-oxazolines. The LCROP was performed with 2-ethyl-2-oxazoline (EtOx) as well as 2-(carbazolyl)ethyl-2- oxazoline (CarbOx) as monomers, resulting in structured bottle-brush brushes (BBB) with different pendant side chains and functionalities. FT-IR spectroscopy, fluorescence microscopy, and AFM measurements indicated a high side chain grafting density as well as quantitative and selective reactions. Poly(2-oxazoline) BBBs containing hole conducting carbazole moieties on NCD as electrode material may open the way to advanced amperometric biosensing systems.

Full text of DOI:10.1039/b923789p

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Physical Chemistry Chemical Physics
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PAPER
www.rsc.org/pccp | Physical Chemistry Chemical Physics
Microstructured poly(2-oxazoline) bottle-brush brushes
on nanocrystalline diamond
Naima A. Hutter,a Andreas Reitinger,b Ning Zhang,a Marin Steenackers,a
Oliver A. Williams,c Jose A. Garrido*b and Rainer Jordan*ad
Received 11th November 2009, Accepted 20th January 2010
First published as an Advance Article on the web 18th February 2010
DOI: 10.1039/b923789p
We report on the preparation of microstructured poly(2-oxazoline) bottle-brush brushes (BBBs)
on nanocrystalline diamond (NCD). Structuring of NCD was performed by photolithography and
plasma treatment to result in a patterned NCD surface with oxidized and hydrogenated areas.
Self-initiated photografting and photopolymerization (SIPGP) of 2-isopropenyl-2-oxazoline
(IPOx) resulted in selective grafting of poly(2-isopropenyl-2-oxazoline) (PIPOx) polymer brushes
only at the oxidized NCD areas. Structured PIPOx brushes were converted by methyl triflate into
the polyelectrolyte brush macroinitiator for the living cationic ring-opening polymerization
(LCROP) of 2-oxazolines. The LCROP was performed with 2-ethyl-2-oxazoline (EtOx) as well as
2-(carbazolyl)ethyl-2-oxazoline (CarbOx) as monomers, resulting in structured bottle-brush
brushes (BBB) with different pendant side chains and functionalities. FT-IR spectroscopy,
fluorescence microscopy, and AFM measurements indicated a high side chain grafting density as
well as quantitative and selective reactions. Poly(2-oxazoline) BBBs containing hole conducting
carbazole moieties on NCD as electrode material may open the way to advanced amperometric
biosensing systems.
some of us demonstrated that proteins can be covalently
Introduction
immobilized on NCD surfaces without losing their biological
functionality.8,9
Doped diamond substrates, including single-, poly-, nano-
crystalline (NCD) and ultrananocrystalline diamond (UNCD),
have gained tremendous interest as electrode materials due to
their unique properties. The large electrochemical potential
window, chemical inertness, physicochemical stability,
and biocompatibility make diamond especially suitable for
amperometric biosensing applications.1–4 Recent developments
in diamond growth by chemical vapor deposition (CVD), give
access to large-area synthetic diamond surfaces at reasonable
costs. However, the defined chemical functionalization of
diamond surfaces as mediating layers between the electrode
material and biological systems is still a subject of intense
research. Two different approaches have been developed
for the controlled attachment of organic molecules to
H-terminated diamond. We reported on the spontaneous
grafting of aromatic diazonium salts on hydrogenated
UNCD resulting in densely packed and homogeneous self-
assembled monolayers5 while Hamers et al.6,7 reported on the
photochemical functionalization of polycrystalline diamond
surfaces with terminal alkenes. Using the second approach,
In contrast to SAMs that allow defined but only monolayer
functionalization, the surface coupling of redox active
moieties, biomolecules or recognition sites via polymer brushes
bearing multiple functions on a single grafted chain are very
promising. They allow the design of biosensors with significant
higher loading capacities per unit area and thus, potentially
enhanced sensitivity. Even densely grafted polymer chains
that extend from the surface into the adjacent liquid
phase are accessible by large organic molecules. Due to the
flexibility of the grafted chains, the liquid phase penetrates the
polymer layer and molecules can interact with binding
partners deep within the layer. Compared to the direct
immobilization of molecules on flat surfaces, this three
dimensional arrangement of binding sites allows a modular
design modeling of biomimetic systems.10 Furthermore, the
soft polymer interface typically stabilizes biomolecules better
than two dimensional self-assembled monolayers (SAMs) and
proteins can maintain their native conformation, selectivity and
enzymatic activity.11–15
The preparation of polymer brushes on diamond surfaces
has been the subject of only a few studies.16–18 Existing
approaches are based on the pre-modification of the diamond
substrate with an organic monolayer, followed by surface-
initiated polymerization. Recently, we have shown that
polystyrene (PS) brushes could be prepared directly on
OH-terminated diamond by the self-initiated photografting
and photopolymerization (SIPGP) of styrene.19 The SIPGP
process is a straightforward synthetic route to obtain dense
a Wacker-Lehrstuhl fur Makromolekulare Chemie, Department
¨
Chemie, TU Munchen, Lichtenbergstraße 4, 85747 Garching,
¨
Germany. E-mail: Rainer.Jordan@tu-dresden.de
b Walter Schottky Institut, TU Munchen, Am Coulombwall 3,
¨
85748 Garching, Germany. E-mail: Jose.Garrido@wsi.tum.de
c Fraunhofer Institute for Applied Solid State Physics, Tullastraße 72,
79108 Freiburg, Germany
d Professur fur Makromolekulare Chemie, Department Chemie,
¨
TU Dresden, Zellescher Weg 19, 01069 Dresden, Germany
ꢀc
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4360 | Phys. Chem. Chem. Phys., 2010, 12, 4360–4366

and well defined polymer brush layers without the introduction
of specific surface-bonded initiators.20,21 However, glassy
hydrophobic PS brushes are not suitable for the immobilization
of biomolecules. Instead, more hydrophilic, biocompatible
and multifunctional polymers are desirable. Up to now,
poly(ethylene glycol) (PEG) has been the most widely used
polymer,22–25 but current PEG systems have major limitations
for long-term applications. It has been reported that PEG
coatings lose their function when placed in vivo and can
undergo oxidative degradation.4,26,27 Poly(2-oxazoline)s
(POx) have recently come into focus as a potential alternative
to the well established PEG systems.28–32 It has been
shown that POx is non-toxic and that proteins as well as
drugs can be coupled to the polymer without losing their
activity.28–29,31,33 POx show a great variability due to possible
terminal as well as pendant functionalization.34–39 We recently
reported on the preparation of homogeneous and very
stable poly(2-isopropenyl-2-oxazoline) (PIPOx) brushes on
polished glassy carbon by the SIPGP of 2-isopropenyl-
2-oxazoline (IPOx).40 The pendant oxazoline ring of the
PIPOx brushes was used to perform a consecutive living
cationic ring-opening polymerization (LCROP) with different
2-alkyl-2-oxazoline monomers resulting in so-called bottle-
brush brushes (BBBs). Such bottle-brush structures show
striking resemblance to the molecular architecture of various
polyglycans located on nearly every living cell41,42 and
are regarded as biomimetic moieties that may have high
potential for tailoring the interface between semiconductors
and biological systems. Based on our recent work on the
preparation of BBBs on glassy carbon, we here report on the
synthesis of structured poly(2-oxazoline) BBBs on nano-
crystalline diamond surfaces. As the grafting reaction is
similar, we now take advantage of the reactivity difference
between hydrogenated and oxidized diamond for a selective
SIPGP19 which allows an area specific grafting and thus
results in microstructured polymer brushes on patterned
H-/OH-terminated NCD samples. The consecutive LCROP
forming the polymer brush pendant chains was performed
with 2-ethyl-2-oxazoline (EtOx) as well as 2-(carbazolyl)-
ethyl-2-oxazoline (CarbOx) as the monomers. The interest
of the functionalization of BBs with pendant carbazole
units in the side chain is twofold. First, polymers containing
carbazole side chains are of special interest, as they are
known to be electrically conductive. Such polymers are
Experimental section
Materials
Chemicals were purchased from Sigma-Aldrich (Steinheim,
Germany) or Acros (Geel, Belgium) and used as received
unless otherwise stated. Methyl triflate (MeOTf), 2-ethyl-2-
oxazoline (EtOx) and acetonitrile (ACN) were dried by
refluxing over CaH2 under a dry argon atmosphere and were
freshly distilled prior to use.
Nanocrystalline diamond (NCD)
NCD was grown by microwave plasma enhanced chemical
vapor deposition. Prior to growth, prime grade 100 silicon
wafers were cleaned with standard SC1 solution and seeded
with a colloid of monodisperse diamond nanoparticles known
to realize nucleation densities in excess of 1011 cmÀ2 57
The
.
growth conditions were 3% CH4 diluted in hydrogen at a
pressure of 50 mbar. The microwave power was 3500 W and
the film was grown to 150 nm thickness in around 25 min; the
temperature was 700 1C.
Clean NCD surfaces were hydrogenated in a commercial
microwave plasma reactor (AX5010) using a hydrogen flow
100 sccm, hydrogen pressure 50 mbar and microwave power of
750 W during 15 min. The structuring was performed using a
Shipley S1818 photoresist that was spin-coated at 6000 rpm
with a MicroTec MJB 3 mask aligner (Suss, Garching,
¨
Germany). After exposure (Mercury i-line) and development,
the samples were oxidized in a Technics Plasma 100-E plasma
system (oxygen pressure 1.4 mbar, microwave power 200 W,
5 min). The photoresist was removed by ultrasonication in
acetone and 2-propanol.
2-Isopropenyl-2-oxazoline (IPOx)
IPOx was synthesized according to Seeliger et al.36
2-(Carbazolyl)ethyl-2-oxazoline (CarbOx)
CarbOx was synthesized following a route described by Hsieh
and Litt.45 Bromopropionitrile was added dropwise to a
suspension of carbazole (1 eq.) and tert-butylammoniumbromide
(0.03 eq.) in NaOH (50%) and benzene at room temperature
(RT). After 2 h, the reaction was quenched with hot water.
The resulting yellow precipitate was filtered and washed with
hot water. After recrystallization in ethanol, the obtained
N-propionitrile-carbazol was dissolved in aminoethanol
(1.4 eq.) and n-butanol. Cadmium acetate dihydrate (0.03 eq.)
was added and the reaction mixture stirred under reflux for
24 h at 140 1C. After evaporation of the solvent the residue
was purified by recrystallization in hexane to give CarbOx as a
colorless solid.
hole transporting materials by
a hopping mechanism
involving adjacent carbazole units.43,44 For the fabrication
of electrically conductive, hydrophilic, and biocompatible
polymer brushes on diamond for amperometric biosensors,
poly(2-oxazoline) BBBs with carbazole moieties constitute
an intriguing system. Secondly, the fluorescence of the
carbazole unit offers a direct way to determine if a sterically
demanding oxazoline monomer (CarbOx) can be introduced
effectively into a BBBs by means of surface-initiated living
cationic polymerization using grafted macroinitiators.
1H NMR: d ppm 8.10 (m, 2H), 7.45 (m, 4H), 7.24 (m, 2H),
4.65 (m, 2H), 4.18 (t, J = 9.43 Hz, 2H), 3.80 (t, J = 9.63 Hz,
2H), 2.81 (m, 2H); 13C NMR: d ppm 27.32, 39.70, 54.41,
67.36, 108.45, 119.10, 120.42, 123.01, 125.71, 139.95, 165.68;
IR (KBr): 3047 (m), 2952 (m), 1669 (s).
The combination of the unique properties of NCD as
electrode material and the biocompatibility as well as variability
of the poly(2-oxazoline) layer may open the way to stable
biosensing systems with enhanced biocompatibility.
Self-initiated photopolymerization and photografting (SIPGP)
Freshly prepared and structured NCD substrates were
submerged in approximately 2 mL of distilled and degassed
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Phys. Chem. Chem. Phys., 2010, 12, 4360–4366 | 4361

IPOx in a photoreaction tube under dry argon atmosphere.
Polymerization was allowed to complete within 20 h under
constant irradiation with UV light (300–400 nm; lmax = 350 nm)
at RT. After SIPGP, the samples were immediately cleaned by
sequential ultrasonication with ethanol, ACN, ethyl acetate
(all HPLC grade) for 5 minutes each.
Results and discussion
The preparation of microstructured bottle-brush brushes
(BBBs) on nanocrystalline diamond (NCD) is outlined in
Fig. 1. First, a hydrogenated NCD substrate was patterned
by conventional photolithography. The exposed areas were
oxidized in an oxygen plasma. After removal of the photoresist
and thorough cleaning, the partially oxidized NCD substrate
was submerged in bulk 2-isopropenyl-2-oxazoline (IPOx) and
irradiated under UV light (lmax = 350 nm) for 20 h for the
Living cationic ring-opening polymerization (LCROP)
The poly(2-isopropenyl-2-oxazoline) (PIPOx) modified NCD
substrates were submerged in a solution of 2 mL dry and
freshly distilled acetonitrile (ACN) with an excess amount of
methyl trifluoromethane sulfonate (MeOTf) at approximately
À35 1C under a dry argon atmosphere. After stirring for 3 h at
0 1C, the mixture was allowed to equilibrate to RT and stirred
for 60 min before EtOx or CarbOx was added under argon
atmosphere. In the case of the side chain LCROP with
CarbOx, 2 mL of dry ACN were added at this point. The
reaction solution was stirred at 80 1C for 16 h. Finally, an
excess of piperidine was added to selectively terminate the
LCROP. After 60 min, the sample was removed from the
reaction solution and thoroughly washed with a saturated
solution of potassium carbonate in deionized water (Millipore).
Final cleaning was performed by sequential ultrasonication in
deionized water, ethanol, ACN and ethyl acetate for 5 min each.
self-initiated
(SIPGP).40
photografting
and
photopolymerization
After SIPGP, the substrate was again thoroughly cleaned by
ultrasonication in acetonitrile, ethyl acetate, and ethanol for
5 minutes each to remove only physisorbed material. AFM
measurements revealed that
a dense and homogeneous
polymer brush layer with a thickness of 79 Æ 8 nm was
selectively formed on the oxidized NCD areas (Fig. 2). Data
analysis of the AFM scans gave a surface roughness on
polymer coated regions with an rms of 5.4 nm, which is
significantly lower as compared to the bare NCD surface
regions (rms 9.6 nm). The change of the layer surface
morphology shows the formation of a homogeneous and
continuous brush that completely screens the oxidized NCD
substrate. The reactivity contrast between the H- and
OH-terminated surface areas during the SIPGP process is in
agreement with our recent account on the SIPGP of styrene on
ultrananocrystalline diamond (UNCD).19 In the SIPGP
mechanism, the monomer acts as a photosensitizer, activating
a surface functional group by hydrogen abstraction to start a
free radical surface-initiated polymerization.21 The selective
formation of polymer brushes on the OH-terminated areas can
be explained by the difference in bond dissociation energy
Infrared spectroscopy (FT-IR)
Infrared spectroscopy (FT-IR) was performed on an IFS 55
Bruker instrument equipped with a diffuse reflectance Fourier
transform infrared (DRIFT) setup from SpectraTech and a
mercury–cadmium–telluride (MCT) detector. For each spectrum,
500 scans were accumulated with a spectral resolution of
(BDE) of C–H (401.5 kJ mol ) )
À1 46 and O–H bonds (71 kJ molÀ1 19
4
cmÀ1
. Background spectra were recorded on freshly
on diamond. The measured brush height is in good agreement
with our recently reported kinetic studies on the SIPGP of
IPOx on polished glassy carbon substrates.40
prepared hydrogenated NCD samples.
Atomic force microscopy (AFM)
The formation of PIPOx brushes was confirmed by FT-IR
measurements (Fig. 3). The strong bands at 1650 cmÀ1 (amide
I) and 1193 cmÀ1 can be assigned to the stretching vibration
modes of CQN and C–O in the 2-oxazoline ring.40
AFM scans were obtained with a Nanoscope IIIa scanning
probe microscope from Veeco Instruments using standard tips
in tapping mode (driving amplitude of B1.25 V at a scan rate
of 0.5 Hz). The average roughness (rms) was calculated from a
representative 2 mm2 large area.
The monomer 2-isopropenyl-2-oxazoline (IPOx) has two
orthogonal polymerizable groups, namely the vinyl group used
for the SIPGP and the 2-oxazoline ring for the living cationic
ring-opening polymerization (LCROP). Very recently, we
have used this dual-functionality of IPOx to prepare defined
bottle brushes by the polymerization of IPOx by living anionic
or free radical polymerization with consecutive LCROP47 as
well as brushes of bottle brushes on polished glassy carbon
(GC).40 First, the PIPOx brushes were converted into a
polycationic macroinitiator followed by the side chain cationic
polymerization of 2-substituted-2-oxazolines. Here, an analogous
approach was employed for the preparation of micro-
structured P(IPOx-g-EtOx) and P(IPOx-g-CarbOx) BBBs
on NCD.
Fluorescence microscopy
Fluorescence microscopy images were obtained with a Leica
DMI 6000 B microscope equipped with a Hamamatsu C4742
camera. The sample was irradiated using a Leica Fluo A
filter cube (BP340-380 nm). The cross-section analysis was
performed by pixel analysis of the 256 bit black and white
fluorescence image using the public domain Image J software
package.
1H- and 13C nuclear magnetic resonance (NMR)
The conversion of the neutral PIPOx brushes into the
cationic polyelectrolyte was achieved by submerging the
modified NCD substrate in a solution of methyl triflate in
acetonitrile for 5 h. The P(IPOx+OTfÀ) brush layer was
NMR spectra were recorded on
a Bruker ARX 300
(1H, 300.13 MHz and 13C, 75.48 MHz) with tetramethylsilane
as internal standard at T = 293 K in CDCl3.
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4362 | Phys. Chem. Chem. Phys., 2010, 12, 4360–4366

Fig. 1 Preparation of structured poly(2-oxazoline) bottle-brush brushes (BBBs) on NCD. (a) An H-terminated nanocrystalline diamond (NCD)
surface was structured by photolithography and oxygen plasma. (b) PIPOx brushes were selectively formed on the oxidized NCD surface regions
by UV-induced SIPGP of IPOx. (c) Conversion of the PIPOx brush backbone to the macroinitiator salt PIPOx+OTfÀ by methyl triflate in
acetonitrile. (d) Surface initiated LCROP of EtOx or CarbOx from the PIPOx+OTfÀ macroinitiator salt and termination of the side chain
polymerization with piperidine. The reaction scheme (below) outlines the surface and side chain grafting reactions resulting in dense bottle-brush
brushes (BBBs).
characterized by FT-IR (Fig. 3). The strong C–F stretching
mode at 1268 cmÀ1 as well as a SQO stretching band at
1025 cmÀ1 of the triflate counterion are clearly visible, proving
the formation of the P(IPOx+OTfÀ) macroinitiator brush.
Successively, the side chain LCROP was performed with the
P(IPOx+OTfÀ) macroinitiator brush and EtOx and CarbOx
as the monomer to obtain BBBs. It is noteworthy that for the
LCROP, the monomer was directly added to the reaction
mixture without taking out the macroinitiator substrate (as
for the above described IR characterization) to avoid side
reactions of the reactive oxazolinium moieties. The LCROP of
EtOx and CarbOx was performed overnight at 80 1C. After
completion of the LCROP grafting, piperidine was added to
selectively terminate the side chain polymerization. The
substrate was again intensively cleaned by ultrasonication
in different solvents to ensure that only chemically grafted
polymer remains on the substrate before further analysis.
FT-IR spectroscopy confirmed the successful conversion of
PIPOx brushes into P(IPOx-g-EtOx) and P(IPOx-g-CarbOx),
respectively. The CQN (1650 cmÀ1) and C–O (1106 cmÀ1
)
stretching bands, for the pendant 2-oxazoline ring disappear
and the typical characteristic amide I band for poly(2-
substituted-2-oxazoline)s at 1627 cmÀ1 for P(IPOx-g-EtOx)
and 1623 cmÀ1 for P(IPOx-g-CarbOx) as well as the strong
CHx deformation mode around 1450 cmÀ1 appears.48 Addi-
tionally, the intensity increase of the aliphatic C–H stretching
band between 2850 and 3000 cmÀ1 resulting in the characteristic
aliphatic absorption pattern for a POx backbone indicates the
formation of POx side chains in the BBs. The IR spectrum of
P(IPOx-g-CarbOx) also exhibits an absorption band at
3041 cmÀ1 corresponding to the aromatic C–H stretching bands.
The transformation of the PIPOx brushes into BBBs was
further investigated by atomic force microscopy (AFM). AFM
measurements revealed a significant increase of the polymer
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Fig. 2 AFM600 dpi) or amend the caption accordingly.?> scans (20 Â 20 mm2), section analysis and depth analysis of the patterned polymer
brush structures on NCD. (a) The SIPGP of IPOx for 20 h (lmax = 350 nm) results in 79 Æ 8 nm thick PIPOx brushes selectively on the OH-
terminated NCD regions. The native NCD regions have a roughness of 9.6 nm rms, the PIPOx coated regions of 5.4 nm rms. (b) The side chain
LCROP using EtOx and termination with piperidine results in 385 Æ 40 nm thick P(IPOx-g-EtOx) BBBs.
increase caused by the side chain LCROP depends on the
used 2-oxazoline monomer. While a thickness increase of
393% was measured for the LCROP of EtOx, the CarbOx
side chain polymerization resulted in a thickness increase of
96%. This can be explained considering that the LCROP of
sterically demanding 2-substituted-2-oxazolines is significantly
slower as compared to EtOx or 2-methy-2-oxazoline
(MeOx).51 The difference in the LCROP kinetics was
expected and is in good agreement with our previous studies
on the copolymerization of 2-oxazoline with different
2-substitutions.52–56 However, the successful conversion of
the PIPOx brush into P(IPOx-g-CarbOx) BBBs demonstrates
that even sterically demanding 2-oxazazoline monomers can
be incorporated in dense BBBs.
Polymers containing carbazole side chains are known to
Fig. 3 FT-IR spectra of PIPOx, P(IPOx+OTfÀ) brushes as well as
exhibit hole conduction. In this respect, P(IPOx-g-CarbOx)
P(IPOx-g-EtOx) and P(IPOx-g-CarbOx) BBBs on NCD.
BBBs containing carbazole moieties are intriguing candidates
for the preparation of conductive, hydrophilic and bio-
brush thickness. For the side chain LCROP of EtOx, the
average structure height was increased from 79 Æ 8 nm for the
PIPOx brush to 385 Æ 40 nm for the P(IPOx-g-EtOx) BBBs.
This is consistent with our findings for the BBBs formation on
glassy carbon and can be explained by the strong stretching
of the bottle-brush backbone by side chain crowding.40
The almost fivefold increase in brush thickness indicates
a very high if not quantitative conversion of the pendant
2-oxazoline ring to BBBs. Furthermore, AFM measurements
show an increase of the lateral structure width of around
0.5 mm. The widening of nano- and microstructured polymer
brushes has been the subject of theoretical and experimental
studies.49,50 The widening is caused by the extension of grafted
chains toward polymer-free surface regions and is propor-
tional to the polymer chain molecular weight.
compatible polymer layers for amperometric biosensing.
Conductivity measurements of P(IPOx-g-CarbOx) layers and
the functionalization of such BBBs with redox proteins will be
the subject of future experiments.
Besides the electron donor properties, carbazole groups
are fluorescent. This allows the direct assessment of the
area selective grafting reaction of P(IPOx-g-CarbOx) BBB
structures by fluorescence microscopy. The fluorescent
microscopy image taken of the BBBs of P(IPOx-g-CarbOx)
(Fig. 4) shows a strong and selective fluorescence only at the
polymer modified and initially oxidized NCD areas. No
fluorescence could be observed on H-terminated NCD areas.
This experiment further confirms the selective grafting of
PIPOx onto the oxidized NCD areas and the successful side
chain grafting of the CarbOx by LCROP. Furthermore,
while we demonstrated recently that sterically demanding
fluorescent dyes can be attached covalently to the BBB side
chain ends, we show here that bulky fluorophores can also be
introduced within the BBB side chain by means of side chain
grafting.
The conversion of PIPOx into P(IPOx-g-CarbOx) was also
monitored by AFM. 56 Æ 10 nm thick PIPOx brushes resulted
in 110 Æ 15 nm thick P(IPOx-g-CarbOx) BBB structures after
the side chain LCROP of CarbOx. These experiments show
that under identical reaction conditions, the layer thickness
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4364 | Phys. Chem. Chem. Phys., 2010, 12, 4360–4366

frame of the international graduate school CompInt
(‘‘Materials Science of Complex Interfaces’’). M.S. is additionally
thankful for a postdoc fellowship from the Wacker-Institute
for Silicon Chemistry at the TU Munchen.
¨
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