DSpace at VNU: Synthesis and optical investigation of amphiphilic diblock copolymers containing regioregular poly(3-hexylthiophene) via post-polymerization modification

Synthetic Metals 217 (2016) 172–184

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Synthetic Metals
journal homepage: www.elsevier.com/locate/synmet

Synthesis and optical investigation of amphiphilic diblock copolymers
containing regioregular poly(3-hexylthiophene) via
post-polymerization modification
Thu Anh Nguyenb , Trung Thanh Nguyena , Le-Thu T. Nguyena , Thang Van Lea,c ,
Ha Tran Nguyena,c,*
a
Faculty of Materials Technology, Ho Chi Minh City University of Technology (HCMUT), Vietnam National University, 268 Ly Thuong Kiet, District 10, Ho Chi
Minh City, Viet Nam
b
National Key Lab of Polymer and Composite Materials, Viet Nam National University, Ho Chi Minh, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet
Nam
c
Materials Technology Key Laboratory (Mtlab), Vietnam National University, Ho Chi Minh City, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet Nam

A R T I C L E I N F O

Article history:
Received 24 January 2016
Received in revised form 13 March 2016
Accepted 26 March 2016
Available online 6 April 2016
Keywords:
Poly(3-hexylthiophene)
Poly(N,N-dimethylamino-2-ethyl

methacrylate)
Poly(2-hydroxyethyl methacrylate)
Atom transfer radical polymerization
(ATRP)
Amphiphilic diblock copolymer

A B S T R A C T

This paper reports on the synthesis and properties of amphiphilic diblock copolymers composed of a
regioregular poly(3-hexylthiophene) (P3HT) block and a block of poly(N,N-dimethylamino-2-ethyl
methacrylate-random-2-hydroxyethyl methacrylate) (P(DMAEMA-r-HEMA)). Well-defined rod-coil
P3HT-b-P(DMAEMA-r-HEMA)) diblock copolymers were synthesized via the combination of quasiliving Grignard metathesis (GRIM) polymerization, end group modification, atom transfer radical
polymerization (ATRP), and post-polymerization modification of diblock copolymer precursors and
exhibited an average molecular weight of around 11,000 g/mol with low polydispersities below 1.5. The
P3HT-b-P(DMAEMA-r-HEMA)) diblock copolymers were easily converted to amphiphilic diblock
copolymers due to esterification of HEMA hydroxyl groups and amine quaternization of DMAEMA
units to yield anionic or cationic amphiphilic diblock copolymers, respectively. The structure and
properties of the resulting diblock copolymers were characterized by proton nuclear magnetic resonance
(1H NMR), gel permeation chromatography, Fourier transform infrared, UV–vis spectroscopy, and
differential scanning calorimetry.
ã 2016 Elsevier B.V. All rights reserved.

1. Introduction
The regioregular poly(3-hexylthiophene) (P3HT) polymer has
attracted significant interest owing to its potential in a variety of
applications, including light-emitting diodes (OLED’s), field-effect
transistors (OFET’s), optical sensors, smart windows and polymeric
solar cells [1–9]. The great importance of conjugated rod-coil block
copolymers as a powerful tool towards supramolecular architectures with novel functions and physical properties has been well
recognized. In addition, the ability of diblock copolymers to selfassemble creates a new route for tuning the molecular organization and the resulting electronic and optoelectronic properties

[10,11]. The p-p interaction between the conjugated rods adds

* Corresponding author at: Faculty of Materials Technology, Ho Chi Minh City
University of Technology (HCMUT), Vietnam National University, 268 Ly Thuong
Kiet, District 10, Ho Chi Minh City, Viet Nam.
E-mail address: (H.T. Nguyen).
/>0379-6779/ã 2016 Elsevier B.V. All rights reserved.

value in providing controlled structures and functionality.
Furthermore, the microphase separation of conjugated rod-coil
block copolymers may lead to nanoscale morphologies, such as
lamellar, spherical, cylindrical and microporous structures. These
nanostructures may not only give rise to interfacial effects, but also
open a new way for electronic processes. Also, the combination of a
stimulus (such as light, pH or temperature)-responsive coil
segment with tunable photo-physical properties of the conjugated
rod segment could enable the discovery of novel multifunctional
sensory materials [12,13]. Several classes of p-conjugated rod-coil
block copolymers have been reported in the literature, including
polyfluorene (PFO), polycarbazole, polyphenylene and polythiophene as rod segments, and polymethylmethacrylate (PMMA),
poly(N,N-dimethylamino-2-ethyl methacrylate) (PDMAEMA),
polystyrene (PS) and poly(2-vinylpiridine) (P2VP) as coil segments
[14–20]. Roil-coil diblock copolymers containing regioregular
P3HT have already been reported by a number of research groups,
such as the synthesis of P3HT-b-polystyrene, P3HT-b-PMMA,


T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

P3HT-b-poly(isobornyl methacrylate) by atom transfer radical

polymerization (ATRP) [21–23].
Recently, amphiphilic diblock copolymers including P3HT as
the hydrophobic rod segment and other hydrophilic coil segments
have emerged as new unique materials due to their versatile
microphase separation behavior and possibilities for fine-tuning of
the supramolecular architecture of the polymers [24–26]. For
example, Craley et al. [27] have reported the synthesis of poly
(3-hexylthiophene)-block-poly(acrylic acid) (P3HT-b-PAA), which
exhibited solvatochromic behavior in several solvents of varying
polarity. P3HT-b-PAA was obtained by hydrolysis reaction of the
P3HT-b-poly(tert-butyl acrylate) precursor, which was synthesized
via ATRP of tert-butyl acrylate using a bromoester terminated P3HT
macroinitiator. An allyl-terminated P3HT was converted to a
hydroxypropyl terminated P3HT, which was subsequently endgroup modified to give the bromoester terminated P3HT. However,
in this procedure, the hydroboration-oxidation of the allyl group to
form hydroxyl group with a maximum conversion efficiency below
80–85% could result in a mixture of bromoester terminated P3HT
chains and those having no functional end groups that lead to the
formation of the mixture including a homopolymers and the
resulted diblock copolymers after controlled radical polymerization process. Lohwasser and Thelakkat [28] reported the synthesis
of poly(3-hexylthiophene)-block-poly(4-vinylpyridine) (P3HT-bP4VP) via preparing an alkoxyamine-terminated P3HT as a
macroinitiator for nitroxide-mediated radical polymerization
(NMRP) of 4VP. P3HT-b-P4VP diblock copolymers with 55 and
77 wt% of P4VP were obtained, exhibiting microphase separation
and colloidal structures in solution. Mohamed et al. [29] reported
the synthesis of amphiphilic poly(3-hexylthiophene)-graft-poly
(ethylene oxide) (P3HT-g-PEO) rod–coil conjugated random
copolymers via non-controlled oxidative polymerization of 3HT
with FeCl3 and click chemistry. These P3HT-g-PEO diblock
copolymers exhibited micellar morphologies in aqueous solutions

with spherical particle diameters of approximately 60–75 nm.
More recently, Kumari et al. [30] has reported the synthesis of poly
(3-hexyl thiophene)-block-poly(N-isopropylacrylamide) (P3HT-bPNIPAM) diblock copolymers via the azideÀalkyne “click” reaction
between an alkyne-terminated P3HT and an azide end-functionalized PNIPAM. However, the use of excess P3HT-alkyne to react
with PNIPAM-azide required purification of unreacted P3HT,
leading to a relatively low yield (60%). Generally in the synthesis
of other P3HT-containing diblock copolymers via alkyne-azide
“click” reaction strategy, greater than an equivalent amount of
either end-functionalized homopolymers was normally used to
ensure high coupling conversion, which necessitates isolation of
excess homopolymers [31]. On the other hand, in the most case,
especially in the synthesis of amphiphilic diblock copolymers
consisting of a permanently hydrophobic block and a strongly
hydrophilic block, the direct copolymerization method is difficult
to carry out because of the solubility discrepancy between
amphiphilic components in a common solvent. In such case, the
use of protecting group chemistries or a polymer post-modification approach is required.
For that reason, in this contribution, we present the synthesis
of a new type of diblock poly(3-hexylthiophene)-block-poly
(N,N-dimethylamino-2-ethyl
methacrylate-random-2-hydroxyethyl methacrylate) (P3HT-b- P(DMAEMA-r-HEMA)) copolymers
via the combination of Grignard metathesis (GRIM) method and
ATRP of N,N-dimethylamino-2-ethyl methacrylate and 2-hydroxyethyl methacrylate co-monomers, that provides control of the
number average molecular weight and narrow polydispersity
index of each segment, resulting in well-defined diblock copolymers. Moreover, the coil block of these copolymers contains both
types of pendant side groups, the hydroxyl moieties of HEMA units
and the dimethylamino groups of DMAEMA units, which could be

173

easily converted via esterification and quaternization to give P3HTb-polyanion and P3HT-b-polycation copolymers, respectively
(Fig. 1). The thermal and optical properties of these copolymers
were investigated for insights into their microphase separation and
crystallization behavior. These amphiphilic ionic copolymers are
envisaged to be useful for forming a variety of self-assembly
structures in solutions such as micelles and vesicles, or for
preparing conducting polymer nanostructures [32–34].
2. Experiment
2.1. Materials
3-Hexylthiophene (!99%), N-bromosuccinimide (99%), iodine
(!99.8%), iodobenzene diacetate (98%), N,N-dimethylformamide
(DMF, 99.8%), sodium borohydride (NaBH4, 99%), phosphorus(V)
oxychloride (POCl3, 99%), copper(I) bromide (CuBr, 98%), N,N,N0 ,N00 ,
N00 -pentamethyldiethylenetriamine (PMDETA, 99%) were purchased from Aldrich. Ni(dppp)Cl2 and i-PrMgCl in tetrahydrofuran
(THF) (2 mol/L) were purchased from Acros and stored in glove box
at room temperature. N,N-dimethylamino-2-ethyl methacrylate
(99.8%) and 2-hydroxyethyl methacrylate (99.8%) were purchased
from Acros and were distilled and stored in freezer. Potassium
acetate (KOAc, 99%), sodium carbonate (99%), and magnesium
sulphate (98%) were purchased from Acros and used as received.
Chloroform (CHCl3, 99.5%), toluene (99.5%) and tetrahydrofuran
(THF, 99%) were purchased from Fisher/Acros and dried using
molecular sieves under N2. Dichloromethane (99.8%), n-hexane
(99%), n-heptane (99%), methanol (99.8%), ethyl acetate (99%) and
diethyl ether (99%) were purchased from Fisher/Acros and used as
received.
2.2. Characterization
1

H NMR spectra were recorded in deuterated chloroform

(CDCl3) with TMS as an internal reference, on a Bruker Avance
500 MHz spectrometer. FT-IR spectra, collected as the average of
64 scans with a resolution of 4 cmÀ1, were recorded from KBr disk
on a FT-IR Bruker Tensor 27. Elemental analyses were recorded on a
Carlo Elba Model 1106 analyzer. MALDI TOF analysis was
performed using a Voyager Elite apparatus in linear mode using
trans-2-[3-(4-tertbutylphenyl)-2-methylprop-2-enylidene]-malonitrile (DCTB) as matrix. Nitrogen laser desorption at a wavelength
equal to 337 nm was applied. Size exclusion chromatography (SEC)
measurements were performed on a Polymer PL-GPC 50 gel
permeation chromatograph system equipped with an RI detector,
with THF as the eluent at a flow rate of 1.0 mL/min. Molecular
weights and molecular weight distributions were calculated with
reference to polystyrene standards. UV–vis absorption spectra of
polymers in solution and polymer thin films were recorded on a
Shimadzu UV-2450 spectrometer over a wavelength range of 300–
700 nm. Differential scanning calorimetry (DSC) measurements
were carried on a DSC Q20 V24.4 Build 116 calorimeter under
nitrogen flow, at a heating rate of 10  C/min. Contact angle
measurements were performed on an OCA 20 contact angle system
(Dataphysics, Germany). The AFM images were obtained using an
agilent spm 5500 atomic force microscopy (AFM). The obtained
diblock copolymers were casted from chroloform solution (5%
concentration) to form thin film thickness of 15–20 mm on the
glass substrate for four-probe electrical measurement.
2.3. Synthesis of 2-bromo-3-hexylthiophene
To a solution of 3-hexylthiophene (5 g, 29.7 mmol) in anhydrous
THF (50 mL) in a 200 mL flask, a solution of N-bromosuccinimide
(5.29 g, 29.7 mmol) was added slowly at 0  C under nitrogen. The

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T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

mixture was stirred at 0  C for 1 h. After that, 50 mL of distilled
water was added to the reaction mixture, and the mixture was
extracted with diethyl ether. The organic layer was washed with a
solution of Na2S2O3 (10%), a solution of KOH (10%), and dried over
anhydrous MgSO4. The organic layer was distilled to give a
colorless oil (6.7 g, 92%). 1H NMR (500 MHz, CDCl3), d (ppm): 7.19
(d, J = 5.6 Hz, 1H), 6.82 (d, J = 5.6 Hz, 1H), 2.59 (t, J = 7.3 Hz, 2H), 1.59
(s, br, 2H), 1.33 (m, none, 6H), 0.91 (t, J = 6.2 Hz, 3H). 13C NMR

(75.5 MHz, CDCl3), d (ppm): 141.0, 128.2, 125.1, 108.8, 31.6, 29.7,
29.4, 28.0, 22.6, 14.1.
2.4. Synthesis of 2-bromo-3-hexyl-5-iodothiophene
Iodine (1.42 g, 11.18 mmol) and iodobenzene diacetate (1.965 g,
6.1 mmol) were added to a solution of 2-bromo-3-hexylthiophene
(2.5 g, 11.1 mmol) in dichloromethane (25 mL) at 0  C. The mixture

Scheme 1. Synthetic routes for the synthesis of ionic sulfonated P3HT-b-P(DMAEMA-r-HEMA) and quaternized P3HT-b-P(DMAEMA-r-HEMA) diblock copolymers.


T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

was stirred at room temperature for 4 h. Then, aqueous Na2S2O3
(10%) was added, and the mixture was extracted with diethyl ether
and dried over anhydrous MgSO4. The solvent was evaporated to
obtain crude product, which was purified by silica column
chromatography (eluent: n-heptane) to give pure 2-bromo-3hexyl-5-iodothiophene as a pale yellow oil (3 g, 86%). 1H NMR

(500 MHz, CDCl3), d (ppm): 6.97 (s, 1H), 2.52 (t, J = 7.54 Hz, 2H), 1.56
(quint, 2H), 1.32 (m, 6H), 0.89 (t, J = 6.4 Hz, 3H). 13C NMR (75.5 MHz,
CDCl3), d (ppm): 144.3, 137.0, 111.7, 71.0, 31.5, 29.6, 29.2, 28.8, 22.5,
14.1.
2.5. Synthesis of regioregular head-to-tail poly(3-hexylthiophene)
with H/Br end groups (polymer 4)
A dry, 500 mL three-neck flask was flushed with nitrogen and
was charged with 2-bromo-3-hexyl-5-iodothiophene (24.37 g,
65 mmol). After three azeotropic distillations by toluene, anhydrous THF (220 mL) was added via a syringe, and the mixture was
stirred at 0  C for 1 h. i-PrMgCl (2 M solution in THF, 30.87 mL,
61.75 mmol) was added via a syringe and the mixture was
continuously stirred at 0  C for 1 h. The reaction mixture was
allowed to cool down to 0  C. The mixture was transferred to a flask
containing a suspension of Ni(dppp)Cl2 (800 mg, 1.475 mmol) in
THF (25 mL). The polymerization was carried out for 24 h at 0  C,
followed by addition of 5 M HCl. After termination, the reaction
was stirred for 15 min and extracted with CHCl3. The polymer was
precipitated in cold methanol and washed several times with
n-hexane. The polymer was characterized by 1H NMR and GPC.
GPC: Mn = 7100 g/mol, Ð = 1.18. Yield: 70%.
FT-IR (cmÀ1): 721, 819, 1376, 1454, 1510, 2853, 2922, 2953.
1
H NMR (500 MHz, CDCl3), d (ppm): 6.96 (s, 1H), 2.90 (t, J = 7.5 Hz,
2H), 1.79 (sex, 2H), 1.52 (q, 6H), 0.94 (t, J = 6.4 Hz, 3H). Maldi-ToF

175

(m/z): 1410, 1576, 1742, 1908, 2074, 2240, 2406, 2572, 2738, 2904,
3070, 3236. GPC: Mn = 7000 g/mol. Polydispersity index (Ð) = 1.18.
UV–vis (CHCl3): lmax = 450 nm.

2.6. Synthesis of regioregular head-to-tail poly(3-hexylthiophene)
with CHO/Br end groups (polymer 5)
Polymer 4 (1 g) was dissolved in 260 mL of anhydrous toluene
under nitrogen. DMF (5.12 mL, 66.3 mmol) and phosphorus(V)
oxychloride (POCl3) (5.30 mL, 58 mmol) were then added to the
solution. The reaction was performed at 75  C for 24 h. The solution
was cooled down to room temperature, followed by the addition of
a saturated aqueous solution of sodium acetate. The solution was
stirred for 4 h. Then, the polymer was extracted with CHCl3. The
polymer was precipitated in cold methanol and washed with cold
n-hexane. After drying under vacuum, 96 mg of polymer was
obtained. The yield was 93%. FT-IR (cmÀ1): 721, 819, 1376, 1453,
1509, 1649, 2854, 2923, 2953. 1H NMR (500 MHz, CDCl3), d (ppm):
9.99 (s, 1H), 6.96 (s, 1H), 2.78 (t, 2H), 1.69 (sex, 2H), 1.49 (q, 6H), 0.89
(t, 3H). Maldi-ToF (m/z): 1602, 1768, 1934, 2100, 2266, 2432, 2598,
2764, 2930, 3096, 3262.
2.7. Synthesis of regioregular head-to-tail poly(3-hexylthiophene)
with CH2OH/Br end group (polymer 6)
Polymer 5 (500 mg) was dissolved in 30 mL of anhydrous THF
under nitrogen. NaBH4 (41.8 mg) was then added. The mixture was
kept stirring at room temperature for 2 h. Then, the solvent was
evaporated under vacuum. The polymer was precipitated in cold
methanol. After drying under vacuum, 480 mg of the polymer was
obtained. The yield was 96%. FT-IR (cmÀ1): 724, 817, 1376, 1453,
1509, 1561, 2853, 2922, 2953. 1H NMR (500 MHz, CDCl3), d (ppm):

Fig. 1. Schematic illustration of P3HT-b-polycation and P3HT-b-polyanion diblock copolymers generated from P3HT-b-P(DMAEMA-r-HEMA).


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T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

Fig. 2. FT-IR spectra of P3HT-macroinitiator and P3HT-b-P(DMAEMA-r-HEMA).

6.96 (s, 1H), 2.78 (t, 2H), 3.7 (t, 2H), 1.69 (sex, 2H), 1.49 (q, 6H), 0.89
(t, 3H). Maldi-ToF (m/z): 1440, 1606, 1772, 1938, 2104, 2270, 2436,
2602, 2768, 2934, 3100.
2.8. Synthesis of bromoester-terminated poly(3-hexylthiophene)
(P3HT-macroinitiator)
Polymer 6 (500 mg) was dissolved in 20 mL of anhydrous THF
under nitrogen. To this solution, triethylamine (1 mmol) and 2bromoisobutyryl bromide (0.83 mmol) were added. Then the
reaction was carried out at 50  C overnight. The polymer was
extracted by CHCl3. The solution was washed two times with
distilled water. The polymer was precipitated in cold methanol.
After drying under vacuum, 475 mg of the polymer was obtained.
The yield was 95%. FT-IR (cmÀ1): 724, 818, 1376, 1451, 1509, 1561,
1735, 2853, 2922, 2953. 1H NMR (500 MHz, CDCl3), d (ppm): 6.96 (s,
1H), 5.29 (t, 2H), 2.78 (t, 2H), 1.93 (t, 6H), 1.69 (sex, 2H), 1.49 (q, 6H),
0.89 (t, 3H). Maldi-ToF (m/z): 1420, 1586, 1752, 1918, 2084, 2250,
2416, 2582, 2748, 2914, 3080. GPC: Mn = 7200 g/mol, Ð = 1.28. Mn
estimated by 1H NMR = 7000 g/mol.

it became homogeneous, and then placed in a 60  C oil bath. When
the macroinitiator solution was added by cannula into the
monomer solution, the mixture solution became homogeneous
with a dark orange color. After the solution was allowed to react for
16 h at 60  C, the resultant polymer solution was diluted with
20 mL of THF. The solution was then passed through a column of
Al2O3 to remove copper. The polymer solution was concentrated

and then precipitated into n-heptane. The precipitated polymer
was collected by vacuum filtration and subsequently washed with
n-heptane, followed by drying under vacuum to give 165 mg of the
desired product corresponding to a conversion of 83%.

2.9. Synthesis of poly(3-hexylthiophene)-block-poly(N,Ndimethylamino-2-ethyl methacrylate-random-2-hydroxyethyl
methacrylate) (P3HT-b-P(DMAEMA-r-HEMA))
P3HT-b-P(DMAEMA-r-HEMA) was synthesized by ATRP using
the P3HT-macroinitiator. 0.1 g of P3HT-macroinitiator (MnNMR =
7000) was placed in a 25 mL flask, to which 2 mL of degassed THF
was added by syringe. The P3HT-macroinitiator solution was
stirred until it became homogeneous. A solution containing N,Ndimethylamino-2-ethyl methacrylate (DMAEMA) (0.28 mmol,
44.0 mg), 2-hydroxyethyl methacrylate (HEMA) (0.168 mmol,
21.9 mg), PMDETA (0.028 mmol, 4.9 mg) and CuBr (2.0 mg,
0.014 mmol) was prepared separately, and was degassed by three
freeze-pump-thaw cycles. The monomer solution was stirred until

Fig. 3. 1H NMR spectrum of P3HT-b-P(DMAEMA-r-HEMA).


T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

177

Fig. 4. GPC traces of P3HT-macroinitiator (dash line) and P3HT-b-P(DMAEMA-r-HEMA) (solid line).

FT-IR (cmÀ1): 724, 818, 1376, 1451, 1509, 1561, 1735, 2853, 2922,
2953, 3550. 1H NMR (500 MHz, CDCl3); d (ppm): 6.97 (s, 1H), 4.08
(s, 4H), 3.95 (s, 2H), 2.77 (s, 2H), 2.58 (s, 2H), 2.43 (s, 6H), 1.98 (m,
6H), 1.69 (sex, 2H), 1.48 (q, 6H), 0.89 (t, 3H). GPC: Mn = 12500 g/mol.

Ð = 1.42.

FT-IR (cmÀ1): 724, 818, 1090 1376, 1451, 1509, 1561, 1735, 2853,
2922, 2953. 1H NMR (500 MHz, CDCl3); d (ppm): 7.5–8.5 (m, 3H),
6.97 (s, 1H), 4.08 (s, 4H), 3.95 (s, 2H), 2.77 (s, 2H), 2.58 (s, 2H), 2.43
(s, 6H), 1.98 (m, 6H), 1.69 (sex, 2H), 1.48 (q, 6H), 0.89 (t, 3H).
2.11. Quaternization of P3HT-b-P(DMAEMA-r-HEMA)

2.10. Sulfonation of P3HT-b-P(DMAEMA-r-HEMA)
Sulfonation reactions were carried out in THF at room
temperature. For a typical reaction, 60 mg of P3HT-b-P
(DMAEMA-r-HEMA) was dissolved in 20 mL of THF and purged
by N2. Once the diblock copolymer was dissolved in the solvent,
triethylamine (2 equivalents to HEMA) was added. The solution of
2-sulfobenzoic acid cyclic anhydride (SBA) (2 equivalents to
HEMA) in about 10 mL of THF was then slowly added into the
reaction. The solution turned turbid immediately, and the reaction
was stopped after 24 h. The resulting reaction mixture was
precipitated in n-heptane to obtain the sulfonated P3HT-b-P
(DMAEMA-r-HEMA) diblock copolymer. The yield was 95%.

Quaternization reactions were carried out in THF at 60  C for
18 h. For a typical reaction, 100 g of P3HT-b-P(DMAEMA-r-HEMA)
was dissolved in 20 mL of THF and purged by N2. To this solution
CH3I (1.19 mg) was added. The solution turned turbid gradually,
and the reaction was stopped after 24 h. The obtained cationic
diblock copolymer was isolated by concentration of the reaction
solution under reduced pressure and precipitation in cold
n-heptane. The obtained cationic diblock copolymer was dried
to constant weight under vacuum. The degree of quaternization of

P3HT-b-P(DMAEMA-r-HEMA) was estimated by 1H NMR spectroscopy.
FT-IR (cmÀ1): 724, 818, 1090 1376, 1451, 1509, 1561, 1735, 2853,
2922, 2953. 1H NMR (500 MHz, CDCl3); d (ppm): 6.97 (s, 1H), 4.08

Table 1
Macromolecular characteristics of P3HT-b-P(DMAEMA-r-HEMA) synthesized by ATRP using P3HT-Br (nexp = 7000 g/mol) as the macroinitiator and CuBr/PMDETA ([CuBr]/
[PMDETA] = 1/2) as the catalytic complex.
Entry

1
2

Temperature ( C)

60
60

Conversiona (%)

83
79

DMAEMA

HEMA

P3HT-b- P(DMAEMA-r-HEMA)
d

Mntheb

Mnexpc

Mntheb

Mnexpc

f

2610
2484

2490
2260

1296
1260

1640
1500

1
1

MnMMR

Ðe

11130
10760

1.42
1.44

a
Conversion as determined after precipitation in cold n-heptane: Conv. = (m À mI À mCu À mL)/mM where m denotes the weight of product, and mI, mCu, mL, mM the weights
of the initiator, copper catalyst, ligand (PMDETA) and monomers, respectively.
b
DMAEMA and HEMA theoretical number-average-molar mass as calculated by [DMAEMA] or [HEMA]0/[P3HT-Br]0 Â Conv(%) Â MwDMAEMA(orHEMA) assuming a living
process.
c
DMAEMA (or HEMA) experimental number-average molar mass as determined by 1H NMR spectroscopy (see Fig. 3): Mnexp = DPexp  MwMMA(orMSp) where DPexp is the
experimental degree of polymerization, as calculated from the relative intensities of a-amino methylene protons of DMAEMA (d = 2.32 ppm), a-methylene proton of HEMA
(d = 4.00 ppm) and the methine (ring) protons of P3HT (d = 6.98 ppm).
d
Initiation efficiency as calculated from MntheofP(DMAEMA-r-HEMA)/MnexpofP(DMAEMA-r-HEMA).
e
Dispersity index as determined by GPC in THF at 35  C.


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T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

Fig. 5. 1H NMR spectrum of sulfonated P3HT-b-P(DMAEMA-r-HEMA).

(s, 4H), 3.95 (s, 2H), 3.62 (s, 3H), 2.77 (s, 2H), 2.58 (s, 2H), 2.43
(s, 6H), 1.98 (m, 6H), 1.69 (sex, 2H), 1.48 (q, 6H), 0.89 (t, 3H).
3. Results and discussion
well-defined

poly(3-hexylthiophene)-block-poly
The
(N,N-dimethylamino-2-ethyl
methacrylate-random-2-hydroxyethyl methacrylate) (P3HT-b-P(DMAEMA-r-HEMA)) diblock
copolymers were prepared via the combination of ‘quasi-living’
GRIM polymerization of the P3HT block and subsequent atom
transfer radical polymerization (ATRP) of DMAEMA and HEMA comonomers according to Scheme 1.
In the first state, the P3HT-macroinitiator was synthesized via
6 steps, including a controlled ‘quasi-living’ GRIM polymerization of
the 2-bromo-3-hexyl-5-iodothiophene monomer. The obtained
P3HT with H/Br end groups had a GPC recorded number average
molecular weight (Mn) value of 7100 g/mol, which is close to the

theoretical one, and moderate polydispersity index of 1.18. Then, a
quantitative conversion of Br-P3HT-H into a-bromo-v-bromoisobutyrate poly(3-hexylthiophene) (7) was achieved by a 3-step
procedure. Based on the integral ratio between the methine (ring)
protons of P3HT at 6.96 ppm and methyl protons of the v-bromoisobutyrate end group at 1.95 ppm, an Mn value of 7000 g/mol was
estimated. Finally, the bromoester terminated P3HT was used as the
macroinitiator for the ATRP of DMAEMA and HEMA co-monomers, in
presence of CuBr and PMDETA as catalytic system. The feed ratio of
DMAEMA/HEMA co-monomers of about 1.7 was established for
obtaining a good control over the ATRP ([DMAEMA]/[HEMA]/[P3HTMacroinitiator]/[CuBr]/[PDMAEMA] = 20/12/1/1/2). The unreacted
monomers were eliminated and the resulting P3HT-b-P(DMAEMAr-HEMA) diblock copolymers were collected via precipitation in
cold n-heptane.
Fig. 2 compares the FT-IR spectra of the obtained P3HT-b-P
(DMAEMA-r-HEMA) and the P3HT macroinitiator. A strong

Fig. 6. 1H NMR spectrum of quaternized P3HT-b-P(DMAEMA-r-HEMA).

T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

179

Fig. 7. UV–vis spectra of sulfonated P3HT-b-P(DMAEMA-r-HEMA) in different solvents and in a solid state film.

absorption signal at 1725 cmÀ1 appears in the spectrum of the
diblock copolymer and is attributed the stretching vibration of the
carbonyl groups of the P(DMAEMA-r-HEMA) block.
The polymerization degree of the P(DMAEMA-r-HEMA)
block was calculated from the the 1H NMR spectrum (Fig. 3)
by comparing the relative signal intensities of the dimethylamino group (peak p) of DMAEMA moieties and methylene
hydroxyl group of HEMA moieties (peak k) with the methine
(ring) protons of P3HT at d = 6.96 ppm. As a result, the NMR

recorded molecular weight of the P(DMAEMA-r-HEMA) block
was around 4000 g/mol, and the molar fraction of HEMA in this
block was about 0.45. Accordingly, the numbers of DMAEMA and
HEMA units were calculated via 1H NMR to be 16 and 13,
respectively.
The GPC curves of the P3HT-b-P(DMAEMA-r-HEMA) diblock
copolymer and P3HT-macroinitiator are shown in Fig. 4, revealing
single peaks and relatively narrow molecular weight distributions,
indicating well-controlled chain growth during the ATRP process.

Fig. 8. UV–vis spectra of quaternized P3HT-b-P(DMAEMA-r-HEMA) in different solvents and in a solid state film.


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Table 2
Solution UV–vis spectral peaks for regioregular P3HT, sulfonated P3HT-b-P(DMAEMA-r-HEMA) and quaternized P3HT-b-P(DMAEMA-r-HEMA).
Solvent

sulfonated P3HT-b-P(DMAEMA-r-HEMA)
(l = nm)

quaternized P3HT-b-P(DMAEMA-r-HEMA)
(l = nm)

P3HT
(l = nm)

Chloroform
Tetrahydrofuran
Toluene
Dichloromethane
Ethyl acetate
Water (pH < 7 and pH > 10)
Solid-state film

445
452
452
449
520, 550, 610
513, 555, 605
515, 550, 600

450
452
452
451
505, 559, 610
520, 555, 610
520, 550, 607

452
447
451
455
Insoluble
Insoluble
527, 558, 610

The GPC recorded Mn and Ð of P3HT-b-P(DMAEMA-r-HEMA) were
around 12500 g/mol and 1.42, respectively.
The molecular weight characteristics of P3HT-b-P(DMAEMA-rHEMA) are summarized in Table 1. Similar results of comparable
experiments with the same conditions are shown, indicating the
repeatability of the experimental method. As seen in Table 1, the P
(DMAEMA-r-HEMA) block was obtained with a relatively good
approximation between theoretical and experimental molar
masses, attesting for an initiation efficiency close to 1.
The coil block of P3HT-b-P(DMAEMA-r-HEMA) was sulfonated via esterification reaction between the hydroxyl group of
HEMA units and 2-sulfobenzoic acid cyclic anhydride (SBA),
following the method previously described [35]. In this reaction,
triethylamine was used as the catalyst and a 2–1 molar ratio of

SBA to ÀÀOH groups was employed to ensure complete
sulfonation. It was noted that upon the addition of SBA, the
reaction solution turned turbid immediately, indicating a change
in the solubility of the diblock copolymer as a result of the
formation of anionic moieties. The 1H NMR spectrum of the
sulfonated P3HT-b-P(DMAEMA-r-HEMA) showed the appearance
of aromatic proton peaks (peaks q) at 7.4–8.1 ppm assigned to
the phenyl group of sulfobenzoic moieties, suggesting that
2-sulfobenzoic acid cyclic anhydride was covalently linked to the
OH groups (Fig. 5). The resulting relative intensity of the phenyl
peak regions (peaks q), with respect to either the signal of the
methylene group in the side chain of HEMA units (peak k) or the
signal of thiophene moieties (peak a or b), indicated that all the
hydroxyl side groups were sulfonated.

Fig. 9. Absorption spectra of sulfonated P3HT-b-P(DMAEMA-r-HEMA) in THF/methanol mixtures with varied volume ratios (A), and an image showing (from left to right)
color changes of the copolymer solutions with increasing methanol content (B).


T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

181

Fig. 10. Absorption spectra of quaternized P3HT-b-P(DMAEMA-r-HEMA) in THF/methanol mixtures with varied volume ratios (A), and an image showing (from left to right)
color changes of the copolymer solutions with increasing methanol content (B).

On the other hand, the dimethylamino pedant groups of
P3HT-b-P(DMAEMA-r-HEMA) were quaternized using iodomethane (CH3I), with an equimolar ratio of dimethylamino groups to
CH3I. A change in the solubility of the diblock copolymer in THF
was realized as the solution became turbid after 2 h, with the

turbidity increasing gradually, indicating the formation of quaternized P3HT-b-P(DMAEMA-r-HEMA). Fig. 6 shows the 1H NMR

spectrum of the obtained quaternized diblock copolymer. The
occurrence of quaternization reaction was confirmed by the
appearance of the methyl peak (peaks q) at 3.60 ppm. By
integration of corresponding 1H NMR signals, a degree of
quaternization was estimated to be approximately 80%.
The optical behavior of sulfonated and quaternized P3HT-b-P
(DMAEMA-r-HEMA) diblock copolymers in solvents of different

Fig. 11. Water contact angles on quaternized P3HT-b-P(DMAEMA-r-HEMA) (A) and sulfonated P3HT-b-P(DMAEMA-r-HEMA) (B) films. The inset photographs show profiles of
water droplets on the copolymer surfaces taken at t = 0 s and t = 35 s after deposition of the droplets.


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T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

Fig. 12. DSC thermograms of P3HT-b-P(DMAEMA-r-HEMA) (a) and corresponding
sulfonated and quaternized copolymers (b and c, respectively).

polarities was studied, using UV–vis to monitor changes in the
p-p* transition of P3HT chains. It should be noted that the
solubility of P3HT chains depends on the polarity of the solvent
used. Fig. 7 and Fig. 8 show the UV–vis absorbance spectra of
sulfonated and quaternized P3HT-b-P(DMAEMA-r-HEMA)s in
different solvents, respectively, and the position of absorption
peaks are summarized in Table 2. In less polar aprotic solvents,
such as THF, chloroform, dichloromethane and toluene, the
absorption maxima of both sulfonated and quaternized P3HT-bP(DMAEMA-r-HEMA)s were around 445–450 nm, indicating that

the P3HT block adopted a coil conformation in these solvents.
In polar solvents such as ethyl acetate and water (basic water for
the sulfonated copolymer and acidic water for the quaternized
copolymer), the UV–vis spectra of both ionic P3HT-b-P(DMAEMAr-HEMA) copolymers showed a main absorption peak at around
513–520 nm and and two vibronic peaks at 550–559 nm and
605–610 nm, similar to the spectra of these copolymers and of
P3HT in the solid state (Table 2). This indicates aggregation of the
P3HT block. As such, polar solvents caused long-range order in
solution of P3HT segments, while the other block remained as
random coil.
Since THF is a good solvent for the regioregular P3HT block and
a bad solvent for the ionic sulfonated/quaternized P(DMAEMA-rHEMA) block and vice versa for methanol, in these homogeneous
solvents these diblock copolymers coexist in two conformations.
Thus, to study this phenomenon, their optical absorption behavior
in mixtures of THF/methanol with varied volume ratios from
0/100 to 100/0 (%/%) was investigated. As shown in Figs. 9 A and 10
A for both ionic diblock copolymers, in pure THF, the p-p*
absorption band of the regioregular P3HT chains was located at
452 nm indicative of the coil conformation. The ionic diblock
copolymers adopted predominantly coil-like conformations at low
methanol contents (below or equal to 20% and 50% for sulfonated
and quaternized P3HT-b-P(DMAEMA-r-HEMA)s, respectively).
Further increasing the methanol content led to bathochromic
shifts of this band, accompanied by gradual appearance of
two vibronic peaks at higher wavelengths. This phenomenon
corresponds to conformational changes toward the formation of
aggregates of P3HT chains due to their poor solubility in methanol.
In pure methanol, the aggregation of P3HT chains was evidenced
by the presence of a main peak at 515 nm and two vibronic peaks

at 560 nm and 610 nm. The conformational changes of the ionic
diblock copolymers were additionally indicated by characteristic
color changes from yellow to purple, as shown in Figs. 9 B and 10 B.
It should be noted that the presence of an ionic block, such as
the sulfonated and quaternized P(DMAEMA-r-HEMA) blocks, can
impact the hydrophilicity of P3HT-based materials. Thus, the
surface wettability of the regioregular P3HT and the ionic diblock
copolymer films was determined by carrying out contact angle
measurements. Fig. 11 shows the water contact angle as a function
of time after deposition of a water droplet on surfaces of the
homopolymeric P3HT and ionic copolymers. As a reference, the
homopolymeric P3HT surface was expectedly hydrophobic and the
water contact angle remained constant at 92 (Æ1 ) throughout the
duration of the experiment. The water contact angles on
copolymer surfaces were high, at first. But after a couple of
seconds, the water droplets collapsed and the surfaces suddenly
changed from hydrophobic to hydrophilic as evidenced by the
abrupt drop of contact angle from 92 to 59  (Æ1 ) for quaternized
P3HT-b-P(DMAEMA-r-HEMA) (Fig. 11A) and to 18 (Æ1 ) for
sulfonated P3HT-b-P(DMAEMA-r-HEMA) (Fig. 11B), and remained
unchanged afterwards.
The thermal properties of the diblock copolymers were studied
via DSC. Fig. 12 shows that the thermal profile of the non-ionized
P3HT-b-P(DMAEMA-r-HEMA) copolymer exhibits a glass transition of the P(DMAEMA-r-HEMA) block at 32.8  C and a melting
transition of the P3HT block at 204.7  C (DH = 11.27 J/g). Note that
the melting peak temperature (Tm) and and melting enthalpy of a
previously reported linear P3HT homopolymer (Mn = 4500 g/mol)
were 239  C and 17.14 J/g, respectively [36]. This illustrates that the
coil P(DMAEMA-r-HEMA) block can hinder the crystallization of
P3HT. Upon either sulfonation or quaternization of the P

(DMAEMA-r-HEMA) block, the glass transition temperature (Tg)
slightly increased to 45.1 and 43.5  C, respectively, as a result of
intermolecular ionic associations of ionic block chains [37,38].
Accordingly, these ionic copolymers featured melting transitions
of crystallized P3HT block chains at around 190–200  C but
composed of overlapping multiple endotherms. The multiple
melting behavior has previously been reported for P3HT and is
attributed to a “meltingÀrecrystallizationÀmelting” process
[39,40]. Thus, the final melting enthalpy did not reflect the degree
of crystallinity of the copolymer samples.
At room temperature, the DC conductivity of P3HT-b-P
(DMAEMA-r-HEMA) diblock copolymers film was measured about
8 Â 10À11 S/cm. On the contrary, the DC conductivity of sulfonated
P3HT-b-P(DMAEMA-r-HEMA)
and
quaternized
P3HT-b-P
(DMAEMA-r-HEMA) diblock copolymers were measured about
4 Â 10À10 S/cm and 6 Â 10À10 S/cm, respectively which are higher
than the DC conductivity of precursor P3HT-b-P(DMAEMA-rHEMA). This phenomenon can be explained that the ionic
sulfonated/quaternized P3HT-b-P(DMAEMA-r-HEMA) diblock
copolymers could be self-doped by ionic pendant groups such
as SO3À or IÀ. The micro- and nanoscopic morphologies of thin
deposits of the diblock copolymer P3HT-b-P(DMAEMA-r-HEMA),
quaternized P3HT-b-P(DMAEMA-r-HEMA) and sulfonated P3HT-bP(DMAEMA-r-HEMA) were investigated by AFM in intermittentcontact mode. These films have been prepared by drop-casting
onto glass substrates from a good solvent (CHCl3) for both P3HT
and P(DMAEMA-r-HEMA) segments followed by annealing at
150  C for 24 h. Thin films of the studied copolymers show a
fibrillar (nanowire-like) morphology (Fig. 13). This observation is
attributed to the microphase separation between flexible P

(DMAEMA-r-HEMA) segments and P3HT rod-segments. Indeed,
this fibrillar morphology is typical from the crystalline assembly of
P3HT into p-stacked structures, as observed and described for
highly regioregular poly(thiophene)s and other conjugated
polymers.


T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

183

Fig. 13. AFM images of P3HT-b-P(DMAEMA-r-HEMA) (A) and corresponding sulfonated and quaternized copolymers (B and C, respectively).

4. Conclusion
We have successfully prepared new rod-coil P3HT-b-P
(DMAEMA-r-HEMA) diblock copolymers via the combination
of the GRIM method, end group modifications and ATRP of
N,N-dimethylamino-2-ethyl methacrylate-and 2-hydroxyethyl
methacrylate co-monomers. These diblock copolymers were
characterized by 1H NMR, GPC and FT-IR methods. P3HT-b-P

(DMAEMA-r-HEMA) could be facilely converted to either cationic
or anionic diblock copolymers upon quaternization of DMAEMA
units or sulfonation of HEMA moieties, respectively. The resulting
ionic diblock copolymers exhibited the typical behavior of
amphiphilic diblock copolymers and were found to be readily
soluble in a variety of organic solvents as well as in acidic/basic
water. It is worth pointing out that the introduction of either
quaternized or sulfonated side groups in the coil block allowed for

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T.A. Nguyen et al. / Synthetic Metals 217 (2016) 172–184

significant improvement of the surface wettability of P3HT
containing diblock copolymer films, which is the focus of much
interest in the fabrication of printed electronic devices.

[21]

Acknowledgement
[22]

This research was supported by The Department of Science and
Technology (DOST)—Ho Chi Minh City [grant number VL_2014_02].

[23]

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