Transformation of the bromine end group into thiol in (Meth)acrylic polymers synthesized by atom transfer radical polymerization

Article abstract of DOI:10.1021/ma102829s

The halogen end group of polymers prepared via atom transfer radical polymerization (ATRP) can be converted into other functional groups by different chemical modifications. Herein, a new method to modify the bromine end group into a thiol functionality in (meth)acrylic polymers synthesized by ATRP is reported for the first time. Thus, the bromine end group of several poly(methyl methacrylate)s was successfully converted into a thioacetate and then in a mercapto group by a controlled hydrolysis. This end-functionalization was confirmed introducing in situ a fluorescent group by thiol-ene "click" reaction with a synthetic alquene tethered to a 4,4-difluoro-4-bora-3a,4a- diaza-s-indacene (BODIPY) fragment. In addition, two model reactions in which bromide ATRP initiators were transformed into new thiol-functionalized molecules proved that this methodology can be applied to either methacrylic or acrylic polymers synthesized by ATRP.

Full text of DOI:10.1021/ma102829s

ARTICLE
pubs.acs.org/Macromolecules
Transformation of the Bromine End Group into Thiol in (Meth)acrylic
Polymers Synthesized by Atom Transfer Radical Polymerization
M. Liras,† O. García,† I. Quijada-Garrido,‡ and R. París*,‡
†Departamento de Química y Propiedades de Materiales Polimꢀericos and ‡Departamento de Química-Física de Polímeros, Instituto de Ciencia
y Tecnología de Polímeros (ICTP), Consejo Superior de Investigaciones Científicas (CSIC), c/Juan de la Cierva 3, E-28006 Madrid, Spain
ABSTRACT: The halogen end group of polymers prepared via atom transfer radical
polymerization (ATRP) can be converted into other functional groups by different
chemical modifications. Herein, a new method to modify the bromine end group into a
thiol functionality in (meth)acrylic polymers synthesized by ATRP is reported for the
first time. Thus, the bromine end group of several poly(methyl methacrylate)s was
successfully converted into a thioacetate and then in a mercapto group by a controlled
hydrolysis. This end-functionalization was confirmed introducing in situ a fluorescent
group by thiol-ene “click” reaction with a synthetic alquene tethered to a 4,4-difluoro-
4-bora-3a,4a-diaza-s-indacene (BODIPY) fragment. In addition, two model reactions
in which bromide ATRP initiators were transformed into new thiol-functionalized
molecules proved that this methodology can be applied to either methacrylic or acrylic
polymers synthesized by ATRP.
’ INTRODUCTION
establishes specific interactions with metals as gold, silver, and
cadmium.13,34-40 Moreover, the development of the thiol-ene
“click” chemistry14,41,42 has improved the potential of this kind
of polymers because this reaction shows nearly quantitative yield,
short reaction times, mild conditions, and high selectivity, which
allows obtaining easily innovative functionalized polymers and
macromolecular structures.
Atom transfer radical polymerization (ATRP) is one of the
most powerful techniques to obtain polymers with high control
over composition, topology, and functionality.1-8 A further
feature of polymers obtained by ATRP is that they preserve a
ω-halogen end group that can be converted into other functional
groups. Thus, formation of azides, amines, hydroxyl, double
bonds, and so on have been shown to be feasible.1 However,
studies aimed to provide efficient routes to transform the halogen
into thiol are scarce, and until now, they have been restricted to
the case to polystyrene [P(St)].9-12
Taking into account the actual importance of thiol-functiona-
lized polymers and the contrasted versatility of ATRP, in this
contribution we show a new and easy methodology to convert
the bromine end group into a thiol group in (meth)acrylic
polymers synthesized by ATRP. To the best of our knowledge,
this is the first time that this transformation is reported. There-
fore, in the first place, two reactions using ATRP initiators as
model molecules were carried out to show that this strategy
can be applied to acrylic and methacrylic compounds without
hydrolysis of the ester group. Then, several bromine end-
functionalized homopolymers of poly(methyl methacrylates),
P(MMA)s, synthesized in a controlled way by ATRP, were
modified in two steps to obtain thiol end-functionalized
P(MMA)s. Nevertheless, it is well-known that this thiol end
group tends to cyclize through “backbiting” to form a thiolactone
end group in P(MMA)s.18 Therefore, and in order to prove the
unequivocal existence of thiol end group in the polymers, the
second reaction was done in the presence of an alquene-
fluorescent molecule synthesized previously and a source of
radicals. This in situ thiol-ene “click” reaction14 is almost
quantitative and therefore colored, and fluorescent end-function-
alized P(MMA)s are going to be obtained. As a result, it is
In a pioneer work, Garamszegi et al.9 converted the bromine
end group of P(St) into an isothiouronium salt by reaction with
thiourea. Subsequently, they treated this salt with a NaOH
solution at 110 °C for 24 h, obtaining the corresponding thiol
end-functionalized polymers. Unfortunately, a main drawback of
this methodology is that this second reaction needs a high basic
conditions, and therefore, it cannot be used for (meth)acrylic
polymers since the ester groups would be hydrolyzed. Then, the
use of ATRP for the preparation of mercapto end-functional
polymers is limited to this polymer or when thiol-precursor
ATRP initiators are used.13,14 In this sense, reversible addition-
fragmentation radical controlled polymerization (RAFT) could
be advantageous over ATRP, since it allows obtaining thiol end-
functionalized polymers by modification of the usual initiator
fragment incorporated in the macromolecular chain.15-17 Thus,
several groups have investigated this thiol functionalization of
RAFT polymers by aminolysis,18-23 hydrolysis,24-26 or metal
hydrides reduction27,28 in order to obtain new both functional
polymers and macromolecular architectures.29-33
The demand of well-defined polymers with thiol functional-
ities has increased in different areas, such as optics, micro-
electronics, and biotechnology, since the mercapto group
Received: December 13, 2010
Revised:
January 25, 2011
Published: February 14, 2011
r
2011 American Chemical Society
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Table 1. Experimental Synthetic Conditions and Characterization of P(MMA)s Synthesized by ATRP and Their Corresponding
BODIPY End-Modified Polymers
P(MMA)-Br
P(MMA)-BODIPY
entry
time (min)
convn (%)
M
n,theor (g mol-1
)
Mn,SEC (g mol-1
)
Mw/Mn
ε (M-1 cm-1
)
1
2
3
4
2
10
15
20
11.6
35.3
44.5
52.8
7 150
21 375
26 900
31 880
7 944
21 560
30 224
32 900
1.19
1.06
1.05
1.05
2560
1370
900
870
possible, on the one hand, to verify the formation of thiol groups
in the polymers and quantify them by absorption measurements
and, on the other hand, to demonstrate that this methodology
can be use together with a thiol-ene “click” reaction to construct
a new range of advanced polymers.
up, the reaction mixture was quenched with chloroform. Then, the
solution was passed through a neutral alumina column to remove the
catalyst. The solution was concentrated by rotary evaporation, and the
polymer precipitated by pouring the solution into a large excess of
n-hexane (600 mL). The precipitated products were filtered and dried
until an invariable weight was reached. Total monomer conversions
were measured gravimetrically. 1H NMR (300 MHz, CDCl3): δ (ppm)
0.69-1.30 (3H, CH3) 1.68-2.18 (2H, CH2), 3.46-3.88 (3H, OCH3).
13C NMR (75 MHz, CDCl3): δ (ppm) 16.34-17.47 and 18.84-19.57
(CH3), 44.51-45.72 (C), 51.93-52.58 (OCH3), 52.74-55.17 (CH2),
178.80-177.14 (COO). IR: ν (cm-1) 3000, 2963, 1740, 1490, 1455,
1445, 1390, 1280, 1245, 1195, 1155, 1060, 990, 845, 755.
Synthesis of Thio-Ester End-Functionalized P(MMA)s,
[P(MMA)-SCOCH3]. The bromine end-functionalized P(MMA)s (1
g) and potassium thioacetate (3 equiv) were stirred in acetone (25 mL)
and refluxed for 4 h. Then, the acetone was removed, and the crude was
redissolved in dichloromethane, washed with water, and dried with
sodium sulfate. The resulting thio-ester end-functionalized P(MMA)s
were obtained as a pale-yellow solids. Yield: 99%.
Synthesis of BODIPY End-Functionalized via Thiol End-
Functionalized P(MMA)s, [P(MMA)-BODIPY]. The former thio-
ester end-functionalized P(MMA)s (1 g), sodium methoxide (3 equiv),
2,20-azobis(2-methylpropionitrile (AIBN) (10 equiv), and alquene-
BODIPY (5) (1.1 equiv) were stirred in anhydrous dichloromethane
(25 mL) and refluxed overnight. The crude of reaction was precipitate
into cold n-hexane (250 mL), and the solid was filtered and washed with
n-hexane. The resulting BODIPY end-functionalized P(MMA) was
obtained with high yields as pink solids.
’ EXPERIMENTAL DETAILS
Materials. For the preparation of the polymers: MMA (99%,
Fluka) was passed through an alumina column and distilled prior to
use to remove the inhibitor. N,N,N0,N0,N00-Pentamethyldiethylenetria-
mine (PMDETA, 99%, Aldrich) was purified by vacuum distillation.
Ethyl 2-bromoisobutyrate (EBrIB, 99%, Aldrich), CuBr (99.999%,
Aldrich), and the solvents n-hexane and chloroform (99.6%, Panreac)
were used as received. For the model reactions: EBrIB, methyl 2-bromo-
propionate (MBrP, 99%, Aldrich), potassium thioacetate (98%,
Aldrich), and sodium methoxide (95%, Aldrich) were employed without
previous modification. For the synthesis of the BODIPY-alquene com-
pound and the “click” reaction with the thiol end-functionalized polymers
pentenoyl chloride (98%, Aldrich), 3-ethyl-2,4-dimethylpyrrole (97%,
Aldrich), triethylamine (99%, Fluka), boron trifluoride diethyl etherate
(Fluka), and 2,20-azobis(2-methylpropionitrile) (AIBN, 98%, Across) were
employed as received. The BODIPY derivate 4,4-difluoro-1,3,5,7,8-penta-
methyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (PM567, laser grade from
Exciton, Dayton, OH) used as reference in the measurement of the photo-
physical properties was also used without previous purification.
Methods. 1H and 13C NMR spectra were recorded on a Bruker
300 MHz spectrometer in CDCl3 at room temperature. Infrared spectra
were recorded using KBr pellets on a Perkin-Elmer Spectrum One FT-
IR spectrophotometer. Mass spectroscopy was made in an Agilent
HPLC/MS 1100. UV-vis absorption and fluorescence spectra were
recorded on a Perkin-Elmer Lambda-16 and on a Perkin-Elmer LS5OB
spectrophotometer, respectively. The fluorescence quantum yield (Φ)
was evaluated relative to the PM567 dye in ethanol solution (Φ =
0.86).43 Molecular weights (Mn) and molecular weight distributions
(MWD) were determined by SEC with a GPC Perkin-Elmer (DMF with
LiBr (0.1 wt %) as mobile phase at 0.3 mL min-1 and 70 °C using
P(MMA) standards for the calibration) provide with a Waters 410
differential refractometer detector.
Synthesis of Bromine End-Functionalized P(MMA)s,
[P(MMA)-Br]. ATRPs of MMA were carried out in bulk at 100 °C,
using EBrIB as initiator, CuBr/PMDETA as catalyst system, and a
constant monomer/initiator concentration ratio of 600:1. The poly-
merization times, shown in Table 1, were established to obtain moder-
ated conversions to ensure a high bromine end-functionalization degree
in the chains. A typical polymerization procedure was as follows: Amine
ligand (PMDETA, 80 mg, 5 ꢀ 10-4 mol) and degassed monomer (10 g,
0.1 mol) were added to dry Pyrex tube ampules with CuBr (72 mg, 5 ꢀ
10-4 mol). Next, the polymerization mixtures were carefully degassed by
bubbling dry argon for 20 min, and then the initiator (32.5 mg, 1.67 ꢀ
10-4 mol) was introduced into the sealed ampules using degassed
syringes to start the polymerization. The ampules were immediately
placed in a thermostatic oil bath at 100 °C. When the desired time was
Synthesis of 2-Acetylsulfanyl-2-methylpropionic Acid
Ethyl Ester (1). EBrIB (0.43 g, 2.2 mmol) and potassium thioacetate
(0.276 mg, 2.4 mmol) were stirred in 25 mL of acetone for 2 h at reflux.
The work-up of the reaction involved removing the acetone on a rotary
evaporator, redissolving the orange solid in dichloromethane, washing
with water several times, and drying over sodium sulfate. The resulting
thioacetate was obtained as a yellow liquid. Yield: 99%. 1H NMR (300
MHz, CDCl3): δ (ppm) 4.18 (q, J = 7.1 Hz, 2H, CH2CH3), 2.26 (s, 3H,
CH3CO), 1.57 (s, 6H, (CH3)2C), 1.25 (t, J = 7.1 Hz, 3H, CH3CH2). 13
C
NMR (75 MHz, CDCl3): δ (ppm) 194.94 (COS), 173.66 (COO),
61.66 (CH2O), 51.32 (C(CH3)2), 30.12 (CH3CO), 25.84 (CH3)2),14.01
(CH3CH2). MS (EI): m/z (%): 190 (5), 148 (26), 87 (18), 75 (44),
59 (48), 43 (100), 31 (51). IR: ν (cm-1) 3000, 2950, 2885, 1743
(COO), 1700 (COS), 1475, 1370, 1265, 1165, 1130, 1030, 960 (CS),
640 (CSC).
Synthesis of 2-Mercapto-2-methylpropionic Acid Ethyl
Ester (2). The former thioacetate (200 mg, 1.05 mmol) and sodium
methoxide (62.5 mg, 1.15 mmol) were stirred in 25 mL of methanol for
4 h at room temperature. When the reaction is completed the solvent
was removed, and the residual was dissolved in dichloromethane,
washed with water three times, and dried over sodium sulfate. The
resulting liquid, 150 mg (99%), was a mixture (1:1) of thiol and disulfide.
1H NMR (300 MHz, CDCl3): δ (ppm) 4.17 (q, J = 7.3 Hz, 2H,
CH2CH3 disulfide), 4.15 (q, J = 7.3 Hz, 2H, CH2CH3 thiol), 1.58 (s, 6H,
CH3C disulfide), 1.45 (s, 6H, CH3C thiol), 1.28 (t, J = 7.3 Hz, 3H,
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CH3CH2 disulfide) 1.26 (t, J = 7.3 Hz, 3H, CH3CH2 thiol). 13C NMR
(75 MHz, CDCl3): δ (ppm) 174.02 (COO disulfide), 172.61 (COO,
thiol), 60.46 (CH2O), 52.39 (C sulfide), 43.85 (C, thiol), 29.92
Scheme 1. Model Reactions for the Transformation of Bro-
mine Groups into Thiol Groups
((CH3)2C, sulfide), 24.51 ((CH3)2C, thiol),þ13.06 (CH3CH2). MS
þ
(ES) m/z: 147 (Mthiol - 1); 317 (Mdisulfide þ Na). IR: ν (cm-1
)
2985, 2945, 2885, 2580 (SH), 2265, 1740 (COO), 1470, 1390, 1265,
1030.
Synthesis of 2-Acetylsulfanylpropionic Acid Methyl Ester
(3). Procedure described for synthesis of 1. Yield: 99%. 1H NMR (300
MHz, CDCl3): δ (ppm) 4.22 (q, J = 7.3 Hz, 1H, CHCH3), 3.71 (s, 3H,
CH3O), 2.33 (s, 3H, CH3CO), 1.48 (d, J = 7.3 Hz, 3H, CH3CH). 13
C
NMR (75 MHz, CDCl3): δ (ppm) 194.19 (CH3COS), 172.85
(COOCH3), 53.11 (CH3O), 41.12 (CH), 30.55 (CH3COS), 18.06
(CH3CH). MS (EI) m/z (%): 162 [nominal mass, Mþ] (7), 149 (2),
120 (24), 88 (8), 59 (22), 43 (100). IR: ν (cm-1) 2990, 2945, 2865,
1750 (COO), 1710 (COS), 1470, 1385, 1265, 1170, 1130, 1020, 960
(CS), 630 (CSC).
Synthesis of 2-Mercaptopropionic Acid Methyl Ester
(4). The hydrolysis of 3 was made using the procedure for compound
2 and with a similar yield. In this case, a mixture (2:1) of thiol and
disulfide was obtained. 1H NMR (300 MHz, CDCl3): δ (ppm) 3.69 (s,
3H, CH3O), 3.56 (q, J = 7.1 Hz, 1H, CH thiol), 3.55 (q, J = 7.1 Hz, 1H,
CH disulfide), 1.43 (d, J = 7.1 Hz, 3H, CH3-CH, disulfide), 1.41 (d, J =
7.1 Hz, 3H, CH3-CH, thiol). MS (ES) m/z: 119 (Mthiolþ - 1); 179
(Mthiolþ þ CH3COO-); 261 (Mdisulfideþ þ Na). IR: ν (cm-1) 2970,
2945, 2870, 1745 (COO), 1465, 1380, 1265, 1230, 1130.
Figure 1. Pictures of sample 1 before and after end-modifications.
the polymers, but it was difficult to quantify with precision the
chain end-functionality. This fact is due to the overlapping of the
signals corresponding to the protons of both the initiator
fragment and the ultimate monomeric unit in the MW range of
the obtained polymers. However, the adequate functionality of
these bromine-terminated polymers has been well confirmed in
the literature through different analysis techniques and/or by
chain extension reactions.44,45
Synthesis of 4-(20,60-Diethyl-10,30,50,70-tetramethyl-40,40-
difluoro-40-bora-30a,40a-diaza-s-indacen-80-yl)but-1-ene (5). A
mixture of 3-ethyl-2,4-dimethylpyrrole (1.0 mL, 8.1 mmol) and pentenoyl
chloride (0.45 mL, 4.05 mmol) in 1,2-dichloroethane (50 mL) was refluxed
under argon for 30 min. Triethylamine (2 mL, 15.4 mmol) was then added
at room temperature, and the mixture stirred for 30 min. Then, boron
trifluoride diethyl etherate (2 mL, 16 mmol) was added, and it was refluxed
for 2 h. The subsequent work-up yielded a red residue that was purified by
flash column chromatography (silica gel, n-hexanedichloromethane 9:1 as
A well-known method to convert an alkyl halide into a thiol
involves the reaction of a halide with postassium thioacetate to
give the corresponding thioester. Subsequent hydrolysis of this
compound establishes the formation of the corresponding
thiol.46 Before trying this methodology in the synthesized P-
(MMA)-Br polymers, two model reactions with analogues
molecular compounds (Scheme 1) were investigated in order
to corroborate this synthetic strategy. Thus, the ATRP initiators
EBrIB and MBrP were chosen as model molecules to show that,
on the one hand, the methodology can be employed for
methacrylic or acrylic polymers and, on the other hand, the
hydrolysis does not affect the ethoxy or methoxy groups of these
compounds, respectively. In both cases, the reactions yields were
nearly quantitative and the desired molecules were easily ob-
tained, as it is observed from their respective yields and char-
acterizations included in the Experimental Details section.
Therefore, it was proved that this synthetic strategy is available.
The successfully reactions used in the molecular models were
applied to the bromide end-functionalized P(MMA)s. The
formation of the thioester end functional group was easily carried
out. Initially, the bromine end-functionalized P(MMA)s were
converted into thio-ester end-functionalized P(MMA)s employ-
ing practically the same experimental conditions than in the
model reactions. However, more drastic conditions were used to
ensure complete transformation. Thus, the polymer/potassium
thioacetate ratio was 1:3, and the reaction solution was at reflux
for 4 h. Although the SEC determinations did not show evidence
of changes in the molecular weigh of the samples, the modifica-
1
eluent). Red crystals were obtained. Yield: 40%. H NMR (300 MHz,
CDCl3): δ (ppm) 6.04-5.84 (m, 1H, CHdCH2), 5.15 (dd, J = 24.7, 1.5
Hz, 1H, CH2dCH), 5.11 (dd, J = 17.9, 1.5 Hz, 1H, CH2dCH), 3.16-3.05
(m, 2H, CH2-Ar), 2.50 (s, 6H, CH3-Ar3,5), 2.35-2.45 (m, 6H, CH2CH3
and CH2-CH), 2.33 (s, 6H, CH3-Ar1,7), 1.04 (t, J = 7.6 Hz, 6H,
CH3CH2). 13C NMR (75 MHz, CDCl3): δ (ppm) 152.25 (C3/C5),
143.67 (C7a/C8a), 136.64 (CH2=), 135.66 (C1/C7), 132.64 (C2/C6),
130.84 (C8), 115.44 (CH=), 35.22 (CH2CH), 27.13 (CH2CH2), 17.15
(CH2CH3), 14.79 (CH3-Ar), 13.28 (CH3-Ar), 12.38 (CH3CH2). MS
(EI): m/z (%): 358 [nominal mass, Mþ] (100), 343 (60), 329 (14),
317 (82), 302 (39), 287 (48). IR: ν (cm-1) 3010, 1550, 1480, 1190, 980.
UV/vis (CHCl3) λmax(ε) 525 nm (59 000 M-1 cm-1).
’ RESULTS AND DISCUSSION
Several bromide end-functionalized P(MMA) were synthe-
sized in a controlled way by ATRP employing similar experi-
mental conditions as those used previously by our research
group.44 Thus, the polymerizations were carried out in bulk at
100 °C using EBrIB as initiator and CuBr/PMDETA as catalyst
system. The polymerization times, shown in Table 1, were
established to obtain moderated conversions to ensure the high
bromine end-functionalization of the chains. As expected, the
number-average MWs obtained by SEC (Mn,SEC) were very close
to those calculated theoretically from the conversion (Mn,theo).
Moreover, the polydispersity indeces (Mw/Mn) were low
(∼1.05-1.19), which indicates that the obtained polymers
1
tion could be observed by H and 13C NMR (overall in the
sample with lower Mw) with the appearance of new weak signals
at 2.01 ppm in 1H NMR and 31.32 and 206.90 ppm in 13C NMR
corresponding to the SCOCH3 group. In addition, in the IR
1
possessed well-defined structures. From the H NMR and IR
analyses, it was possible to verify the macromolecular structure of
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Scheme 2. Synthetic Route for the Formation of BODIPY End-Functionalized P(MMA)s: (a) Thio-Ester End-Functionalization,
(b) Hydrolysis and Thiol End-Functionalization (in Parentheses Possible “Backbiting” Side Reaction), and (c) Thiol-Ene “Click”
Reaction and BODIPY End-Functionalization
Figure 2. UV-vis normalized absorption (solid lines) and fluorescence
(dashed lines) spectra of sample 1 in chloroform at room temperature.
Figure 3. Absorption extinction coefficient versus percentage in weight
of BODIPY moieties in the P(MMA).
analysis, an increment of the width of the band of the CdO
stretching occurred. Last, the change of color of the samples,
which become yellow-pale as is shown in Figure 1b, is other proof
that corroborates the modification.
528 nm and a maximum of emission at 549 nm (excited at
490 nm), which are the typical values for BODIPY-based dyes.43
The introduction of a fluorescence dye let us to quantify the
number of these groups by absorption measurements using as a
reference the absorption extinction coefficient (ε) of the com-
mercial BODIPY dye PM567 in the same solvent (ε = 80 000 M-1
cm-1). Logically, the intensity of emission (and absorption)
depends on the number of BODIPY dyes (see Table 1) and,
therefore, on the molecular weight. Thus, the shorter the
macromolecular chain is, the higher the number of BODIPY
tethered molecules per gram and the higher absorption value, as
is shown in Figure 3. From this figure, it is observed that the
experimental results fit quite well with the theoretical line
calculated from the BODIPY dye used as reference. Therefore,
and taking into account the molecular weights, it was possible to
estimate that the degree of BODIPY end-functionalization, and
subsequently, the degree of the thiol end-functionalization in the
precursor is nearly quantitative for all polymers under study.
It is well-known that thiol-polymers are susceptible to further
oxidation to disulfide, leading to bimodal polymer populations
composed of thiol and disulfide functional polymers.29 More-
over, Xu et al.18 reported that the thiol end group generated
during the aminolysis of P(MMA) synthesized by RAFT tends to
cyclize thought “backbiting” to form a thiolactone end group.
Although our hydrolysis method should be able of hydrolyze this
thiolactone, the second reaction of the proposed synthetic
methodology was made in the presence of an alquene-BODIPY
molecule (5), previously synthesized, and AIBN as radical
initiator (see Scheme 2). This in situ formation of the thiol
end-functionalized polymers in the present of thiol-reactive
compounds was done to lead simultaneous protection/function-
alization of the created thiols. The thiol-ene reaction14 is almost
quantitative, and therefore, dye end-functionalized P(MMA)s
were obtained as orange-pink powder (Figure 1c). As a result, it
was possible to verify the formation of thiol groups in the
polymers through their reactivity. As an example, Figure 2 shows
the absorption and emission spectra of a chloroform solution of
sample 1. Samples present a maximum of absorption at around
’ CONCLUSIONS
In this work, it has been demonstrated that the bromine end-
functional group of (meth)acrylic polymers synthesized by
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ATRP can be easily transformed into thiol groups in only two
steps. The methodology was applied for well-defined P(MMA)s
of different molecular weight and synthesized by ATRP. The
correct thiol end-functionalization of the polymers was corrobo-
rated by a thiol-ene “click” reaction, introducing a fluorescent
moiety that allows us to quantify the thiol functionalization.
Moreover, two model reactions were employed in order to show
that this methodology can be also applied to other methacrylic
and acrylic polymers.
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’ AUTHOR INFORMATION
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Corresponding Author
*Tel (34) 91 258 74 30 and (34) 91 562 29 00; Fax (34) 91 564
48 53; e-mail rparis@ictp.csic.es.
’ ACKNOWLEDGMENT
Authors thank the financial support of the Consejo Superior
de Investigaciones Científicas (CSIC) and Ministerio de Ciencia
e Innovaciꢀon (MICINN) through the Project CTQ2008-03229.
R.P. thanks MICINN for a Juan de la Cierva contract and M.L.
thanks CSIC for a JAE-Doc contract. Moreover, authors are very
grateful to Dr. A. Mu~noz-Bonilla for her assistance in the SEC
measurements.
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