Amine-functionalized nanoporous thin films from a poly(ethylene oxide)-block-polystyrene diblock copolymer bearing a photocleavable o-nitrobenzyl carbamate junction

Article abstract of DOI:10.1039/c2sm07056a

The synthesis of a poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer bearing an o-nitrobenzyl carbamate junction is reported via a one-pot atom transfer radical polymerization (ATRP)-copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC). The accordingly obtained block copolymer was self-assembled into thin films showing, after solvent annealing, ordered PEO cylinders oriented normal to the film surface and embedded in a PS matrix. In the next step, the easy photocleavage of the o-nitrobenzyl carbamate junction and the subsequent removal of the PEO nanophase were demonstrated. This led to amine-functionalized nanoporous PS thin films as evidenced by the successful coupling of a fluorescent dye bearing a carboxylic acid group. The possibility to obtain fluorescent nanopores was then further exploited to pattern the films using a photolithographic mask.

Full text of DOI:10.1039/c2sm07056a

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PAPER
Amine-functionalized nanoporous thin films from a poly(ethylene
oxide)-block-polystyrene diblock copolymer bearing a photocleavable
o-nitrobenzyl carbamate junction†
a
Ce Guinto Gamys, Jean-Marc Schumers, Alexandru Vlad, Charles-Andre Fustin and Jean-Franc¸ois Gohy
a
b
a
a
*
ꢀ
ꢀ
Received 28th October 2011, Accepted 31st January 2012
DOI: 10.1039/c2sm07056a
The synthesis of a poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer bearing an
o-nitrobenzyl carbamate junction is reported via a one-pot atom transfer radical polymerization
(ATRP)–copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC). The accordingly obtained block
copolymer was self-assembled into thin films showing, after solvent annealing, ordered PEO cylinders
oriented normal to the film surface and embedded in a PS matrix. In the next step, the easy
photocleavage of the o-nitrobenzyl carbamate junction and the subsequent removal of the PEO
nanophase were demonstrated. This led to amine-functionalized nanoporous PS thin films as evidenced
by the successful coupling of a fluorescent dye bearing a carboxylic acid group. The possibility to obtain
fluorescent nanopores was then further exploited to pattern the films using a photolithographic mask.
copolymers have been developed. Such approaches allow the
selective cleavage of the block junction under relatively mild
conditions without altering the rest of the material and are
applicable to a wider variety of block copolymers. In this respect,
different junctions have been considered so far such as those
sensitive to chemical stimuli11–13 (e.g. metal–ligand complexes,
tritylether linkages, and disulfide bonds) or to light14 (photolabile
groups).
Introduction
Due to their ability to self-assemble at the nanoscale into well-
ordered periodic structures, block copolymers play a major role
in the field of nanotechnology.1 This self-assembly behaviour can
be described by a phase diagram indicating regions of miscibility
or immiscibility between the constituent blocks. In the immisci-
bility region, different morphologies, e.g. spheres, cylinders, and
lamellae, can be obtained depending on the block length ratio.1
The cylindrical morphology is of particular interest since it can
be transformed into an array of nanopores after elimination of
the minor component. The accordingly obtained materials
exhibit the pore size and pore topology of their parent structure
and can be used in many applications including templating,
separation, catalysis, and sensoring.2 The most widely used
methods for the removal of the minor component are ozonol-
ysis,3 chemical etching4–6 and UV degradation.7–10 However,
these methods require the use of harsh conditions such as strong
acids, strong bases or elevated temperatures. Moreover, they are
limited to a few polymers that can be degraded under conditions
that do not damage or even destroy the entire material.
Photolabile groups are indeed appealing protective tools in
organic synthesis and in life sciences because their removal
process can typically take place under neutral conditions without
using any additional chemical reagents. Among the available
photolabile groups, o-nitrobenzyl (ONB) derivatives have gained
wide acceptance and are commonly used as protecting groups for
carboxylic acids, amines and alcohols in the form of o-nitro-
benzyl esters, carbamates and carbonates, respectively.15,16
However, the use of ONB derivatives as junctions to cleave
block copolymers in order to obtain nanoporous materials is
relatively recent. Only a few recent examples based on ONB
ester groups have been reported up to now. Kang and Moon14
were the first to prepare photocleavable block copolymers based
on an ONB derivative. In their approach, a PEO-b-PS block
copolymer was synthesized by the atom transfer radical poly-
merization (ATRP) of styrene initiated by a PEO macroinitiator
bearing an ONB ester group located just beside the initiating
site of the macroinitiator. The self-assembly of the obtained
PEO-b-PS diblock copolymer led to thin films presenting a PS
matrix with well-ordered PEO cylinders, which were removed
after UV irradiation resulting in the cleavage of the ONB block
junction, by selective extraction in a methanol/water mixture.
Recently, our group developed a versatile strategy to synthesize
Recently, alternative strategies based on the use of cleavable
junctions between the different blocks of the precursor block
aInstitute of Condensed Matter and Nanosciences (IMCN), Bio- and Soft
Matter (BSMA), Universite catholique de Louvain, Place L. Pasteur, 1,
Louvain-la-Neuve, Belgium. E-mail: jean-francois.gohy@uclouvain.be
bInformation and Communication Technologies, Electronics and Applied
Mathematics (ICTEAM), Universiteꢀ catholique de Louvain, Place du
Levant, 3, Louvain-la-Neuve, Belgium
ꢀ
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c2sm07056a
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a wide range of diblock copolymers where the two blocks are
held together by an ONB ester junction using a one-pot
simultaneous ATRP and copper(I)-catalyzed azide–alkyne
cycloaddition (CuAAC-click reaction).17 This approach has
been adapted to a RAFT-click reaction by Theato and
coworkers18 to prepare ONB ester-based photocleavable PEO-
b-PS block copolymers used as precursors for the preparation of
nanoporous thin films.
Beyond the preparation of nanoporous materials, it can be
interesting to functionalize pores in order to perform selective
chemistry (attachment of specific molecules such as catalysts,
dyes and biomolecules) on the pore walls as well as to tune the
surface properties of the pores in terms of hydrophobicity,
charge density, etc. As a consequence, the corresponding
functionalized membranes could be used in different fields of
applications such as nano-purification, nano-catalysis and nano-
sensing. However, this concept of pore functionalization in
nanoporous films is poorly reported. The main previous works in
this field reported by Hillmyer and coworkers19,20 concern the
preparation of nanoporous polymer monoliths from ABC tri-
block copolymer precursors that assemble into a cylindrical
morphology, where the A block constitutes the matrix, C is the
removable minor component, and B provides the functionality
on the surface of the pores. Following this strategy and using
polystyrene-block-poly(dimethylacrylamide)-block-polylactide
and polystyrene-block-polyisoprene-block-polylactide as block
copolymer precursors, they prepared nanoporous polystyrene
films decorated with carboxylic acid functions and alkene groups
in the pores, respectively.
Fig. 1 General strategy for the preparation of patterned fluorescent
nanoporous thin films.
The o-nitrobenzyl carbamate-based ATRP initiator was
synthesized in three steps from a commercially available diol
(Scheme 1a). In the first step, the diol 1 is reacted with propargyl
bromide in a K2CO3/DMF mixture to selectively etherify the
phenol. The second step is the preparation of the carbamate
following a convenient procedure described by D’Addona and
Bochet.22 This procedure involves the reaction of the alcohol 2
with 1,10-carbonyldiimidazole to give an imidazolide with the
release of one equivalent of imidazole. This imidazolide inter-
mediate is easily trapped by a diamine to yield the carbamate 3
without requiring an additional base. In the last step, the pho-
tocleavable initiator 4 is obtained by coupling 3 with bromoi-
sobutyrate bromide.
Another interesting approach is the use of an ONB junction
between blocks of polymers, since ONB derivatives can provide
functionalized pores after removal of the minor phase. In the case
of ONB ester groups for example, we have recently highlighted
the presence of carboxylic acid groups on the surface of the pores
from PEO-b-PS block copolymers by coupling with a fluorescent
dye.21
As shown in Scheme 1b, the initiator 4 was then used for the
ATRP of styrene and the concomitant CuAAC with an azide
terminated PEO, which was obtained from a commercially
available mono-hydroxyl PEO. The one-pot reaction was per-
formed in DMF at 100 ꢀC, with CuBr and PMDETA as a cata-
lytic system. Those reactions were successful and the resulting
block copolymer was characterized by 1H nuclear magnetic
resonance (NMR) spectroscopy and size exclusion chromatog-
raphy (SEC) as summarized in Table 1.
In this work, we have successfully synthesized a new type of
photocleavable PEO-b-PS block copolymers bearing an ONB
carbamate block junction. Since the photoisomerization of an
ONB carbamate derivative leads to an o-nitrosobenzaldehyde
and the release of the corresponding amine, we here show the
possibility to prepare PS nanoporous thin films with nanopores
uniformly covered with primary amine groups. The presence of
these amine functions inside the pores is demonstrated by
reacting them with a fluorescent dye bearing a carboxylic acid
group. Finally, patterned fluorescent nanoporous thin films are
prepared using a photolithographic mask (Fig. 1).
The styrene conversion obtained after 24 hours of polymeri-
zation was 57.5% while the efficiency of the click coupling was
estimated to be 73% (see ESI, Fig. S1†), which implies the
presence of non-coupled blocks. After removal of the residual
non-coupled homopolymers by extraction with selective solvents
for each block (diethyl ether for PS and a mixture of methanol/
water for PEO), the accordingly obtained PEO113-hv-PS230 (the
numbers in subscript indicate the average degree of polymeri-
zation of the corresponding block) diblock copolymer displays
a narrow polydispersity index with a clear shift towards higher
molecular weight as evidenced by SEC (Fig. 3b).
Results and discussion
The synthesis of the photocleavable PEO-b-PS block copolymer
investigated in the present study was conducted using a previ-
ously reported strategy17 which consists of the simultaneous
ATRP of styrene and CuAAC-click reaction of the ATRP
initiator bearing the photocleavable junction to the PEO block.
This strategy directly results in a PEO-b-PS block copolymer
bearing a photocleavable junction between the PS and the PEO
block. Since both reactions are catalyzed by the same copper(I)
catalyst a one-pot reaction becomes possible.
The next step is the self-assembly of this copolymer in order to
generate a cylindrical morphology with the cylinders oriented
normal to the film surface. As abundantly reported in the liter-
ature,23–25 a better control of both the orientation and the lateral
ordering of the nanoscopic domains during the self-assembly of
block copolymers requires the use of external fields, such as
electric fields, shear, temperature gradients, chemically patterned
substrates, controlled interfacial interactions or solvent evapo-
ration. Among those methods, solvent annealing has attracted
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Scheme 1 (a) Synthesis of the o-nitrobenzyl carbamate-based initiator, (b) ATRP and CuAAC-click one-pot reaction and (c) photoisomerisation of the
o-nitrobenzyl carbamate junction.
increasing interest since it is a simple and versatile process to
produce highly ordered thin films. For example, Russell and
coworkers26,27 have shown for thin films prepared from PS-b-
PEO diblock copolymers that highly ordered arrays of nano-
scopic cylindrical domains oriented normal to the surface of the
film and spanning the entire film thickness can be obtained by
solvent annealing.
the PEO113-hv-PS230 diblock copolymer in benzene (a good
solvent for both PEO and PS blocks) onto silicon substrates and
annealed in benzene/water vapours at room temperature for four
hours. Using these conditions, ordered cylinders oriented normal
to the film surface were obtained as evidenced by atomic force
microscopy (AFM) in Fig. 2. In this AFM picture PS constitutes
the matrix while PEO, the minor component, forms the cylindrical
domains with an average centre-to-centre distance between the
cylinders of 32.3 nm and an average cylinder diameter of 21.5 nm.
Inspired by these studies and previous works reported by our
group,11,28 thin films were prepared by spin-coating solutions of
Table 1 Synthesis of the PEO113-hn-PS230 block copolymer using ATRP and CuAAC-click one-pot reaction. The starting PEO113-N3 block is char-
acterized by Mn ¼ 5000 g molꢁ1 and PDI ¼ 1.05
Copolymera
Styrene conversionb (%)
Mn,RMN/g molꢁ1
Mn,SEC/g molꢁ1
PDIc
PEO113-hn-PS230
57.5
28 900
45 900
1.30
a
Reaction conditions: initiator 4/PEO113-N3/CuBr/PMDETA ¼ 1 : 1 : 2 : 3 at a temperature of 100 ꢀC for 24 hours. b Determined by 1H NMR. c PDI:
polydispersity index.
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The photocleavage of the PEO113-hv-PS230 diblock copolymer
was initially investigated by exposing solutions of this copolymer
in CH2Cl2 to UV irradiation (lmax ¼ 300 nm, I ¼ 38.5 mW cmꢁ2
)
without semicarbazide hydrochloride. The evolution of the UV-
visible absorption spectrum with the irradiation time is shown in
Fig. 3a. The intensity of the band located at 310 nm and asso-
ciated with the nitro-aromatic moiety decreases with irradiation
time, while additional bands appear between 350 and 500 nm due
to the formation of the nitroso compound. Furthermore, SEC
analysis of the irradiated product (after 55 minutes) shows the
disappearance of the peak associated with the copolymer while
two new peaks appear on the chromatogram (Fig. 3b), corre-
sponding to the freed PS and PEO blocks. These results clearly
demonstrate the efficiency of the cleavage under UV light irra-
diation, allowing thereby the further preparation of nanoporous
structures.
Fig. 2 AFM height image (2 ꢂ 2 mm) of a film of PEO113-hv-PS230 spin-
coated from a benzene solution (10 g Lꢁ1) and annealed in benzene–water
vapours for 4 hours.
The preparation of nanoporous films from solvent annealed
PEO113-hv-PS230 thin films was performed by exposing them, in
the solid state, to UV light at 300 nm for 60 min in order to cleave
the o-nitrobenzyl carbamate junction, followed by the extraction
of the PEO nanophases with a mixture of methanol/water (9/1,
v/v). The removal of the PEO cylinders and the subsequent
formation of nanopores were investigated by transmission elec-
tron microscopy (TEM). Fig. 4a and b show the TEM images of
stained films (staining in RuO4 vapours for 45 min) before and
after PEO extraction, respectively. A homogeneous staining of
the TEM specimen is observed before removal of the PEO
cylinders (Fig. 4a) while bright circles corresponding to the
nanopores are visible after PEO extraction as demonstrated in
Fig. 4b. Scanning electron microscopy (SEM) was also per-
formed on the cross-section of a thin film, after extraction of the
PEO nanophases (Fig. 4c). This SEM image clearly evidences the
formation of a nanoporous thin film.
In order to demonstrate the presence of amine functions inside
the pores, we then used Coumarin 343, a fluorescent dye bearing
a carboxylic acid group. The reaction between the carboxylic
acid groups of the dye and the amines on the pore walls was
Fig. 3 Cleavage of the PEO113-hv-PS230 block copolymer in CH2Cl2
(without semicarbazide hydrochloride). (a) Evolution of the UV-visible
absorption spectra as a function of irradiation time and (b) SEC traces of
the azide-functionalized PEO block and the PEO113-hv-PS230 block
copolymer before and after UV irradiation at 300 nm for 55 minutes.
As mentioned previously, the mechanism of photo-
isomerisation15 of an o-nitrobenzyl carbamate derivative is well
known and leads to the corresponding o-nitrosobenzaldehyde with
the release of a free primary amine group and CO2 (Scheme 1c).
However,apossibleside-reactionwhichconsistsintheformationof
an imine, resulting from the reaction of the released amine with the
aldehyde photoproduct, can decrease the yield in the obtained free
amine groups. This can be avoided by adding a carbonyl scavenger,
such as semicarbazide hydrochloride, to the reaction mixture.29
Fig. 4 Microscopy images of PEO113-hv-PS230 thin films after annealing
in benzene–water vapours. (a) TEM image of the annealed film stained
with RuO4, (b) TEM image of the annealed film stained with RuO4, after
extraction of the PEO nanophases and (c) SEM image of the cross-section
of a nanoporous thin film (after PEO extraction).
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performed by a classical approach30–32 using 1-ethyl-3-(3-dime-
thylaminopropyl) carbodiimide (EDAC) and hydroxybenzo-
triazole (HOBt) as peptide coupling reagents.
Fig. 5 shows the fluorescence emission spectra (lex ¼ 410 nm)
of the nanoporous film before and after coupling with Coumarin
343. As a reference, we used this dye without peptide coupling
reagents. A typical coupling procedure is described as follows.
Nanoporous thin films were immersed for 17 hours at room
temperature in a methanol solution containing Coumarin 343
and the appropriate peptide coupling reagents (EDAC/HOBt).
Then, the films were abundantly washed and rinsed in pure
methanol for 18 hours in order to remove unreacted dyes. As
shown in Fig. 5, there is almost no difference in the fluorescence
signal between the untreated nanoporous films and those soaked
in a solution of Coumarin 343 without peptide coupling reagents.
However, an intense and characteristic spectrum appears after
treatment with Coumarin 343 in the presence of EDAC and
HOBt that clearly proves the success of the coupling between the
amine groups located on the pore walls and the carboxylic acid
groups of the fluorescent dye.
Furthermore, in order to evaluate the impact of the side-
reaction leading to the formation of an imine just after photo-
cleavage of the o-nitrobenzyl carbamate junction, the yield of the
released amine groups was estimated on thin films prepared from
the PEO113-hv-PS230 copolymer exposed to UV light with and
without addition of semicarbazide hydrochloride as an o-nitro-
sobenzaldehyde scavenger. The accordingly obtained nano-
porous films were then treated with Coumarin 343 (in the
presence of EDAC and HOBt) and characterized by fluorescence
spectroscopy. The results do not show any significant differences
in fluorescence between films irradiated in the solid phase and
those irradiated in methanol with or without semicarbazide
Fig. 6 (a) Optical microscopy image of the photolithographic mask and
(b) fluorescence microscopy image of the corresponding pattern trans-
ferred to a thin film from the PEO113-hn-PS230 block copolymer.
hydrochloride (see ESI, Fig. S2†). This means that the side-
reaction leading to the formation of an imine is minimized,
probably due to a steric effect of polymer chains and/or the lack
of mobility.
Finally, the possibility to graft a fluorescent dye on the pore
walls was utilized to pattern thin films from the PEO113-hv-PS230
diblock copolymer. To this end, the nanostructured films were
exposed to UV irradiation (lmax ¼ 365 nm) for an hour through
a photolithographic mask before being washed in a methanol/
water solution to remove the cleaved PEO nanophases and then
treated with Coumarin 343. The aim here was to elaborate
fluorescent nanoporous thin films with non-porous domains
corresponding to the pattern of the photolithographic mask.
Fig. 6a and b show, respectively, the optical microscopy image
of the photolithographic mask and the fluorescent microscopy
image of a PEO113-hv-PS230 thin film after successive patterning
and functionalization with Coumarin 343. As shown by Fig. 6b,
one can observe a successful replica of the pattern with blue
regions corresponding to parts of the film functionalized with
Coumarin 343 since this colour is characteristic of the maximum
emission wavelength of Coumarin 343 (430 < lem < 450 nm).
Conclusion
We have shown for the first time the possibility to prepare amine-
functionalized nanoporous thin films from a PEO-b-PS diblock
copolymer bearing an o-nitrobenzyl carbamate junction. The
synthesis of this photocleavable block copolymer was performed
Fig. 5 Grafting of a functionalized fluorescent dye on the pore walls.
Fluorescence spectra of: starting nanoporous thin film (black curve),
nanoporous thin film soaked in a Coumarin 343 solution without
coupling reagents (red curve) and nanoporous thin film soaked in
a Coumarin 343 solution with EDAC and HOBt coupling reagents (blue
curve).
using
a combined ATRP–click chemistry approach. The
accordingly obtained block copolymer was self-assembled into
thin films that were further annealed in benzene/water vapours
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affording a cylindrical morphology oriented normal to the film
surface. After UV exposure and removal of the PEO nanophases,
nanoporous PS thin films were obtained with nanopores covered
by primary amine groups. As a potential application, these
functionalized nanoporous films could be used as membranes for
selective separation at the nanoscale. Indeed, primary amine
groups on the pore walls are interesting anchoring sites for
further chemical reactions including peptide coupling or imine
formation with biomolecules.
15 hours. The staining step was performed by exposing the
samples to RuO4 vapours for 45 minutes. Scanning electron
microscopy (SEM) was performed on a Zeiss LEO 982
microscope operating at an acceleration voltage of 10 kV.
Cross-sectional analyses were performed at a tilt angle of 15ꢀ.
Fluorescence spectroscopy measurements were performed on
a SPEX-Fluorolog spectro-fluorometer (Horiba-Jobin Yvon) in
a front face (FF) mode with an excitation wavelength (lex) of
410 nm. Fluorescence Microscopy (FM) was performed on an
Olympus AX70 microscope operated in the reflection mode. The
fluorophore was excited (lex ¼ 290–400 nm) with a UV lamp
(Hamamatsu LC5) equipped with a 150 W xenon lamp (L8253).
A band pass filter (LOT-Oriel, 360 nm, FWHM ¼ 40 nm) was
placed in the excitation path. The fluorescence images were
captured through a long working distance objective (ꢂ50, NA
0.45) using an Olympus Color View III camera (2576 ꢂ 1932
pixels resolution). Ellipsometry was performed using an SE 800
PV spectroscopic ellipsometer (Sentech). The photolithography
was performed using a contact aligner (K&W) equipped with an
Hg lamp.
Finally, the amine functionality inside the nanopores has then
allowed the grafting of a fluorescent dye. The possibility to
functionalize a predetermined area of the film has been demon-
strated by irradiating the film through a photolithographic mask.
Only the exposed areas have been functionalized with a fluores-
cent dye demonstrating the success of the patterning.
Experimental part
Materials and instrumentation
Poly(ethylene oxide) monomethylether (PEO113-OH, Mn ¼ 5000
g molꢁ1, PDI ¼ 1.05) was purchased from Polymer Source Inc.
and was dried by azeotropic cycles with toluene prior to use.
Styrene (Aldrich, 99%) was passed through an activated basic
alumina column before use. 5-Hydroxy-2-nitrobenzyl alcohol
(Aldrich, 97%) was dried in vacuo. Potassium carbonateꢀ(K2CO3,
99%) was dried for 24 hours in a vacuum oven at 100 C. Trie-
thylamine (Et3N) was dried over KOH. N,N-Dimethylforma-
mide (DMF) was distilled on CaH2. Tetrahydrofuran (THF) was
distilled on sodium/benzophenone. Propargyl bromide (Aldrich,
8 wt% in toluene), CuBr (Aldrich, 99.999%), N,N,N0,N00,N00-
pentamethyldiethylenetriamine (PMDETA, Aldrich, 98%), tosyl
chloride (TsCl, Fluka, 99%), ethyl 2-bromoisobutyrate (Acros,
98%) and all other chemicals were used as received. Flash chro-
matography was performed on a silica gel (0.040–0.063 mm
grade).
1H and 13C NMR spectra were recorded on a 300 MHz or 500
MHz Bruker Avance II spectrometer. Molecular weights and
polydispersity indices of the polymer were measured on a Waters
SEC system equipped with a Waters 510 pump and a 410
differential refractometer (40 ꢀC; eluent: DMF; flow rate of
0.5 mL minꢁ1). The calibration was performed using polystyrene
standards. Atomic force microscopy (AFM) was performed on
a Digital Instruments Nanoscope V scanning force microscope in
tapping mode using NCL cantilevers (Si, 48 N mꢁ1, 330 kHz,
Nanosensors). Irradiation intensities have been measured with
Synthesis of 5-propargylether-2-nitrobenzyl alcohol (2)
This synthesis was previously described.17
Synthesis of 5-propargylether-2-nitrobenzyl carbamate (3)
1,1-Carbonyldiimidazole (120 mg, 0.74 mmol) was dissolved in
anhydrous THF (2 mL) and the solution was cooled to 0 ꢀC.
Under argon, 5-propargylether-2-nitrobenzyl alcohol (2, 152.5
mg, 0.74 mmol) was added dropwise as a solution in THF
(2 mL). The mixture was stirred at room temperature for 3 hours.
This mixture was slowly added via a cannula to a solution of 1,3-
diaminopropane (138.5 mL, 1.66 mmol) in THF (4 mL) previ-
ously cooled to 0 ꢀC. The obtained solution was then slowly
brought to room temperature and stirred overnight. THF was
removed under reduced pressure and the residue was dissolved in
ethyl acetate. The mixture was washed four times with 10% HCl,
and twice with brine. The organic layer was dried over MgSO4,
filtered and evaporated to give the carbamate 3 as a yellow
crystalline solid (164 mg, 72%).
1H NMR (300 MHz, CDCl3): d(ppm) 8.20 (d, 1H, 3J ¼ 9.1 Hz,
3
H
Ar), 7.15 (s, 1H, HAr), 6.98 (d, 1H, J ¼ 9.1 Hz, HAr), 5.65 (s,
1H, –NH–), 5.54 (s, 2H, –CH2–OCO–), 4.79 (d, 2H, 4J ¼ 2.3 Hz,
C^C–CH2–), 3.34 (q, 2H, 3J ¼ 6.2 Hz, 3J ¼ 12.4 Hz, –NH–CH2–),
3
4
2.83 (t, 2H, J ¼ 6.4 Hz, –CH2–NH2), 2.60 (t, 1H, J ¼ 2.3 Hz,
–C^CH), 1.67 (m, 2H, –CH2–), 1.44 (s, 2H, –NH2).
13C NMR (75 MHz, CDCl3): d(ppm) 161.7 (CAr–O–), 157.4
(C]O), 141.6 (CAr–NO2), 137.8 (CAr–CH2–), 126.0 (H–CAr),
115.8 (H–CAr), 114.7 (H–CAr), 79.2 (H–C^C–), 78.5 (H–C^C–),
64.2 (–CH2–OCO–), 59.3 (C^C–CH2–), 39.4 (–NH–CH2–), 38.0
(–NH–CH2–), 31.3 (–CH2–).
€
a radiometer RM12 from Dr Grobel UV-electronik GmbH
equipped with UVA (315–400 nm) and UVB (280–315 nm)
sensors. UV-vis spectra were recorded on a Varian spectrometer
(Cary, 50 Conc). Transmission electron microscopy (TEM) was
performed on a LEO 922 microscope, operating at 200 kV
accelerating voltage in bright field mode. Samples for TEM
experiments were prepared by spin-coating the polymer solution
onto a silicon substrate with a large silicon oxide top layer
(400 nm). The samples were then floated on a HF solution
(5 wt%). After about 90 seconds, they were transferred onto pure
water and they were detached from their support, floating on
water. Parts of the films were then picked up on TEM grids (pure
copper, mesh: 300). The grids were then dried in a vacuum for
Synthesis of 5-propargyl-2-nitrobenzyl carbamate
bromoisobutyrate (4)
Under argon, a solution of bromoisobutyrate bromide (53.6 mL,
0.43 mmol) in 1 mL of THF was added dropwise to a stirred
solution of 5-propargylether-2-nitrobenzyl carbamate 3 (120.9
mg, 0.39 mmol) and triethylamine (60.3 mL, 0.43 mmol) in THF
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ꢀ
(1.5 mL) at 0 C. The mixture was gradually brought to room
ellipsometry (film thickness of 69 nm for a polymer concentra-
tion of 10 g Lꢁ1). To cleave the PEO phase, the block copolymer
films were placed under three UV lamps (Rayonet photochemical
reactor) emitting at a wavelength (lmax) of 300 nm with an
intensity of 38.5 mW cmꢁ2. After 1 hour of exposure, the films
were immersed in a methanol/water (9/1, v/v) solution for 18
hours.
temperature and stirred overnight. THF was removed under
reduced pressure. The residue was dissolved in ethyl acetate and
washed with water. The organic phases were combined, dried
over MgSO4, filtered and evaporated in vacuo. The residue was
purified on flash chromatography (eluent: chloroform/acetone,
93/7, v/v) affording a yellow viscous product (95 mg, 53%).
1H NMR (300 MHz, CDCl3): d(ppm) 8.21 (d, 1H, 3J ¼ 9.1 Hz,
H
Ar), 7.17 (s, 1H, HAr), 7.09 (s, 1H, –NH–), 6.99 (d, 1H, 3J ¼ 9.1
Grafting of Coumarin 343
4
Hz, HAr), 5.56 (s, 2H, –CH2–OCO–), 4.79 (d, 2H, J ¼ 2.4 Hz,
3
3
The nanoporous thin films were soaked in 5 mL of a solution
containing Coumarin 343 (14 mg Lꢁ1), HOBt (10 mg Lꢁ1) and
EDAC (10 mg Lꢁ1) in methanol. After 17 hours, the films were
abundantly rinsed and immersed overnight in pure methanol.
–C^C–CH2–), 3.37 (q, 2H, J ¼ 6.3 Hz, J ¼ 12.5 Hz, –NH–
CH2–), 3.27 (q, 2H, 3J ¼ 6.3 Hz, 3J ¼ 12.5 Hz, –NH–CH2–), 2.62
4
(t, 1H, J ¼ 2.4 Hz, –C^CH), 1.96 (s, 6H, CH3), 1.71 (m, 2H,
–CH2–).
13C NMR (75 MHz, CDCl3): d(ppm) 173.1 (C]O), 162.0
(CAr–O), 156.5 (C]O), 141.0 (CAr–NO2), 137.1 (CAr–CH2),
128.1 (H–CAr), 114.8 (H–CAr), 113.6 (H–CAr), 77.3 (H–C^C–),
77.1 (H–C^C–), 63.8 (CH2–OCO–), 62.6 (C–Br), 56.6 (C^C–
CH2), 37.9 (–NH–CH2), 37.1 (–NH–CH2), 32.8 (–CH3), 30.2
(–CH2–).
Acknowledgements
This work was supported by the EU FP7 SELFMEM project
(no. 228652). AV is a Post-doctoral Researcher of the FRS-
FNRS. CAF is a Research Associate of the FRS-FNRS. The
authors acknowledge Olivier Bertrand for illustrations and TEM
experiments.
Synthesis of PEO113-N3
This synthesis was previously described.17
References
1 I. W. Hamley, Angew. Chem., Int. Ed., 2003, 42, 1692–1712.
2 M. Hillmyer, Adv. Polym. Sci., 2005, 190, 137–181.
3 P. Mansky, C. K. Harrison, P. M. Chaikin, R. A. Register and
N. Yao, Appl. Phys. Lett., 1996, 68, 2586.
4 J. M. Leiston-Belanger, T. P. Russell, E. Drockenmuller and
C. J. Hawker, Macromolecules, 2005, 38, 7676–7683.
5 M. Glassner, J. P. Blinco and C. Barner-Kowollik, Polym. Chem.,
2011, 2, 83–87.
6 K. Satoh, J. E. Poelma, L. M. Campos, B. Stahl and C. J. Hawker,
Polym. Chem., 2012, DOI: 10.1039/c1py00484k.
7 C. Tang, K. Sivanandan, B. C. Stahl, G. H. Fredrickson, E. J. Kramer
and C. J. Hawker, ACS Nano, 2010, 4, 285–291.
Synthesis of PEO113-hn-PS230
Under argon, a Schlenk tube with CuBr (17.3 mg, 0.12 mmol, 2
equiv.) was filled with a solution containing styrene (2512 mg,
24.12 mmol, 400 equiv.), PMDETA (41.8 mg, 0.24 mmol, 3
equiv.), PEO113-N3 (303 mg, 0.06 mmol, 1 equiv.), and DMF
(925 mL) previously degassed by three freeze–pump–thaw cycles.
The mixture was stirred for 5 minutes and was then frozen.
Under argon, 215 mL (0.06 mmol, 1 equiv.) of a solution of the
photocleavable initiator 4 in DMF (C ¼ 100 g Lꢁ1) was added.
The mixture was degassed by three freeze–pump–thaw cycles,
filled with argon, and stirred in an oil bath at 100 ꢀC for 24 hours
(styrene conversion ¼ 57.5%). The mixture was diluted with
CH2Cl2 and washed with aqueous EDTA (0.04 mol Lꢁ1) to
remove the copper catalyst. The organic phase was dried over
Na2SO4, filtered and evaporated under reduced pressure. The
residue was precipitated twice in hexane, filtered and dried in
vacuo at 35 ꢀC for 24 hours. Residual homo-PEO and homo-PS
were removed by extraction with selective solvents (diethyl ether
for PS and a mixture of methanol/water, 90/10, v/v for PEO).
Mn (SEC) ¼ 45 900 g molꢁ1; PDI (SEC) ¼ 1.30. 1H NMR (500
MHz, CDCl3) d(ppm) 8.17 (m, 1H, HAr in the ortho position of –
NO2; junction), 7.89 (s, 1H, ]CH triazole; junction), 7.47 (s, 1H,
NH–CO; junction), 7.30–6.24 (m, 1152H, HAr; PS + junction),
5.53 (s, 2H, –CH2–OCO–; junction), 5.31–5.28 (m, 3H, CH2–O,
ether; junction + CH–Br, end chain), 3.64 (s, 452H, CH2; PEO),
3.38 (s, 3H, CH3–O, PEO), 2.4–1.2 (m, 690H, Hbackbone; PS).
8 T. Thurn-Albrecht, R. Steiner, J. DeRouchey, C. M. Stafford,
E. Huang, M. Bal, M. Tuominen, C. J. Hawker and T. P. Russell,
Adv. Mater., 2000, 12, 787–791.
€
9 T. Thurn-Albrecht, J. Schotter, G. A. Kastle, N. Emley, T. Shibauchi,
L. Krusin-Elbaum, K. Guarini, C. T. Black, M. T. Tuominen and
T. P. Russell, Science, 2000, 290, 2126–2129.
10 J. Bang, S. H. Kim, E. Drockenmuller, M. J. Misner, T. P. Russell and
C. J. Hawker, J. Am. Chem. Soc., 2006, 128, 7622–7629.
11 C. A. Fustin, B. G. G. Lohmeijer, A. S. Duwez, A. M. Jonas,
U. S. Schubert and J. F. Gohy, Adv. Mater., 2005, 17, 1162–1165.
12 M. Zhang, L. Yang, S. Yurt, M. J. Misner, J. T. Chen, E. B. Coughlin,
D. Venkataraman and T. P. Russell, Adv. Mater., 2007, 19, 1571–
1576.
13 J.-H. Ryu, S. Park, B. Kim, A. Klaikherd, T. P. Russell and
S. Thayumanavan, J. Am. Chem. Soc., 2009, 131, 9870–9871.
14 M. Kang and B. Moon, Macromolecules, 2009, 42, 455–458.
15 J. F. Cameron and J. M. J. Frechet, J. Am. Chem. Soc., 1991, 113,
4303–4313.
16 A. Patchornik, B. Amit and R. B. Woodward, J. Am. Chem. Soc.,
1970, 92, 6333–6335.
17 J.-M. Schumers, J.-F. Gohy and C.-A. Fustin, Polym. Chem., 2010, 1,
161–163.
18 H. Zhao, W. Gu, E. Sterner, T. P. Russell, E. B. Coughlin and
P. Theato, Macromolecules, 2011, 44, 6433–6440.
19 J. Rzayev and M. A. Hillmyer, J. Am. Chem. Soc., 2005, 127, 13373–
13379.
Nanoporous thin films preparation
Silicon substrates were cleaned by a piranha solution and
abundantly rinsed with ultra-pure water. Solutions of the
copolymer in benzene (10 g Lꢁ1) were spin coated onto these
substrates at 2000 rpm for 40 s. The obtained films were annealed
in benzene/water vapours for 4 hours before being evaluated by
20 T. S. Bailey, J. Rzayev and M. A. Hillmyer, Macromolecules, 2006, 39,
8772–8781.
21 J.-M. Schumers, A. Vlad, I. Huynen, J.-F. Gohy and C.-A. Fustin,
Macromol. Rapid Commun., 2012, 33, 199–205.
22 D. D’Addona and C. G. Bochet, Tetrahedron Lett., 2001, 42, 5227–
5229.
4492 | Soft Matter, 2012, 8, 4486–4493
This journal is ª The Royal Society of Chemistry 2012

View Article Online
23 S. H. Kim, M. J. Misner, L. Yang, O. Gang, B. M. Ocko and
T. P. Russell, Macromolecules, 2006, 39, 8473–8479.
24 C. Park, Y. Yoon and E. L. Thomas, Polymer, 2003, 44, 6725–6760.
25 M. Li and C. K. Ober, Mater. Today, 2006, 9, 30.
26 S. H. Kim, M. J. Misner, T. Xu, M. Kimura and T. P. Russell, Adv.
Mater., 2004, 16, 226–231.
27 Z. Q. Lin, D. H. Kim, X. D. Wu, L. Boosahda, D. Stone, L. LaRose
and T. P. Russell, Adv. Mater., 2002, 14, 1373–1376.
28 C.-A. Fustin, P. Guillet, M. J. Misner, T. P. Russell, U. S. Schubert
and J.-F. Gohy, J. Polym. Sci., Part A: Polym. Chem., 2008, 46,
4719–4724.
29 C. G. Bochet, J. Chem. Soc., Perkin Trans. 1, 2002, 125–142.
30 S.-Y. Han and Y.-A. Kim, Tetrahedron, 2004, 60, 2447–2467.
31 J. M. Humphrey and A. R. Chamberlin, Chem. Rev., 1997, 97, 2243–
2266.
32 A. Fernando, Curr. Opin. Chem. Biol., 2004, 8, 211–221.
This journal is ª The Royal Society of Chemistry 2012
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