DSpace at VNU: Synthesis and characterization of diblock copolymers based on poly(3-hexylthiophene) and photo-responsive poly(methyl methacrylate-random-2-methyl methaspirooxazine)

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Synthesis and characterization of diblock copolymers based on poly(3-hexylthiophene) and

photo-responsive poly(methyl methacrylate-random-2-methyl methaspirooxazine)

Ha Tran Nguyenab, Le-Thu T Nguyena & Thang Van Leab a

Faculty of Materials Technology, Ho Chi Minh City University of Technology, Vietnam National University, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Vietnam b

Materials Technology Key Laboratory (Mtlab), Ho Chi Minh City University of Technology – Vietnam National University – Ho Chi Minh City, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Vietnam

Published online: 19 Jan 2015

To cite this article: Ha Tran Nguyen, Le-Thu T Nguyen & Thang Van Le (2015) Synthesis and characterization of

diblock copolymers based on poly(3-hexylthiophene) and photo-responsive poly(methyl methacrylate-random-2-methyl methaspirooxazine), Designed Monomers and Polymers, 18:3, 271-283, DOI: 10.1080/15685551.2014.999467

To link to this article: http://dx.doi.org/10.1080/15685551.2014.999467

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Synthesis and characterization of diblock copolymers based on poly(3-hexylthiophene) and photo-responsive poly(methyl methacrylate-random-2-methyl methaspirooxazine)

Ha Tran Nguyena,b*, Le-Thu T Nguyenaand Thang Van Lea,b

a

Faculty of Materials Technology, Ho Chi Minh City University of Technology, Vietnam National University, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Vietnam;bMaterials Technology Key Laboratory (Mtlab), Ho Chi Minh City University of Technology–

Vietnam National University– Ho Chi Minh City, 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Vietnam

(Received 24 September 2014; accepted 3 December 2014) The rod–coil diblock copolymers combining the conductive feature of a conjugated polymer and nanoscale morphologies arising from microphase separation of dissimilar blocks are attractive as potential materials for electronic applications Herein, we report on the synthesis and properties of a novel diblock copolymer containing a rod-block of regioregular poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate-random-2-methyl methaspirooxazine) (P3HT-b-P(MMA-r-MSp)) as photo-responsive coil-block Well-defined rod–coil P3HT-b-P(MMA-r-MSp) diblock copolymers with average molecular weight of around 10,000 and low molar mass dispersities (ÐM) below 1.5 were successfully synthesized via the combination of quasi-living Grignard metathesis polymerization and atom transfer radical polymerization (ATRP) Post-polymerization end-group modifications of the as-obtained P3HT were then successfully realized to give a macroini-tiator for the ATRP of MMA and MSp co-monomers, resulting in the P3HT-b-P(MMA-r-MSp) diblock copolymers 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–visible spectroscopy, and differential scanning calorimetry

Keywords: poly(3-hexylthiophene); rod–coil diblock copolymers; Grignard metathesis (GRIM) polymerization; atom transfer radical polymerization (ATRP); spirooxazine

1 Introduction

Among various types of photochromic compounds,

spi-rooxazine (SP) is well-known to have remarkable

proper-ties such as good fatigue resistance and excellent

photostability under a long period of irradiation.[1–4]

Photochromic SP compounds are molecules containing a

condensed ring-substituted 2H-[1,4]oxazine in which the

carbon atom in position 2 of the oxazine ring is involved

in a spiro linkage Under UV light irradiation, SP, in its

colorless form, isomerizes to form the blue-colored

mer-ocyanine (MC) (or the open form) by homolytic

cleav-age of the carbon–oxygen single bond of the oxazine

ring The MC form switches back to the SP form under

visible light or thermally via reformation of the carbon–

oxygen single bond of the oxazine ring Because of this

photochemical transformation behavior, spirooxazines

have successfully been used in applications such as data

recording, optical, and electrical switching.[5–9]

In recent years, light-responsive block copolymers

have gained special attention for their applications in

many new technologies such as data recording and

stor-age, optical switching, displays, and non-linear optics In

particular, light-responsive block copolymers containing

both a fluorescent group and a photochromic moiety,

such as SP, have attracted significant interest.[9–13] The

SP and ring-opened MC forms of these fluorescent-cou-pled photochromic compounds participate as ‘Switch On’ and ‘Switch Off’ functions Interestingly, the fluoro-phore moiety of block copolymers emits fluorescence which is only observed when the photochromic com-pound is in the SP form In contrast, emission is severely quenched when the photochromic compound is in the

MC form, as a result of fluorescence resonance energy transfer (FRET) from the excited state of thefluorophore

to the MC form of the photochromic compound Under irradiation with visible light, the MC form recovers back

to the SP form which emits fluorescence Based on this phenomenon, diblock copolymers containingfluorophore and photochromic compounds have been designed and probed in molecular switching applications, such as opti-cal sensors and optiopti-cal window switches.[14–16]

The regioregular poly(3-hexylthiophene) (P3HT) polymer has attracted significant interest due to its poten-tial in a variety of applications including light-emitting diodes (OLED’s), field-effect transistors (OFET’s), opti-cal sensors, smart windows, and solar cells.[17–21] In order to improve commercial applications, the develop-ment of more intricate electronic materials is required

*Corresponding author Email:nguyentranha@hcmut.edu.vn

Vol 18, No 3, 271–283, http://dx.doi.org/10.1080/15685551.2014.999467

One attractive approach is to prepare block copolymers

of conjugated polymers and flexible coil-like polymers

The combination of conjugated and non-conjugated

seg-ments generates interesting materials, expected to phase

segregate leading to the formation of nanoscale

morphol-ogies as well as improvement of mechanical

proper-ties.[22] Rod–coil diblock copolymers containing

regioregular P3HT, such as b-polystyrene,

P3HT-b-polymethacrylate, P3HT-b-poly(tert-butyl acrylate), and

P3HT-b-poly(isobornyl methacrylate), have been

synthe-sized via atom transfer radical polymerization (ATRP) or

nitroxide mediated polymerization by a number of

research groups.[23–25] Recently, diblock copolymers

containing conjugated polymers and coil polymers

bear-ing the photochromic functional groups have emerged as

a new unique material due to their versatile microphase

separation, photo-responsive behavior and possibilities

for fine-tuning of the supramolecular architecture of the

polymers.[26–33] More recently, it has been reported by

Kim and coworkers that a spiropyran-polythiophene

photo-switch, where a photochromic spiropyran was

introduced as side-chain groups of polythiophene by

ran-dom-copolymerization of 3HT and a

spiropyran-contain-ing thienyl monomer, could highly selectively detect the

CN− anion Hence, the P3HT-b-P(MMA-r-MSp) diblock

copolymer may also be used as a sensor probe to detect

the toxic anion of CN−.[34]

In this work, we are addressing the synthesis and

characterization of dibock copolymers containing the

P3HT block and poly(methyl

methacrylate-random-2-methyl methaspirooxazine) (P3HT-b-P(MMA-r-MSp)) as

photochromic coil-block Grignard metathesis (GRIM)

polymerization and ATRP were performed to

sequen-tially polymerize the P3HT block and the

P(MMA-r-MSp) block, respectively, resulting in well-defined

diblock copolymers The synthesized diblock copolymers

P3HT-b-P(MMA-r-MSp) were characterized via nuclear

magnetic resonance (NMR), Fourier transform infrared

(FT-IR) spectroscopy, gel permeation chromatography

(GPC), UV–visible spectroscopy, and differential

scan-ning calorimetry (DSC) The conformations of the

di-block copolymers were also investigated in different

tetrahydrofuran/methanol solvent mixture ratios by UV–

visible spectroscopy

2 Experiment

2.1 Materials

2,7-Dihydroxynaphthalene, Na2NO2,

1,3,3-trimethyl-2-methyleneindoline, triethylamine, methacryloyl chloride,

3-hexylthiophene, N-bromosuccinimide, iodine,

iodoben-zene diacetate, N,N-dimethylformamide (DMF, 99.8%),

sodium borohydride (NaBH4, 99%), and phosphorus(V)

oxychloride (POCl3, 99%), Copper(I) bromide

(CuBr, 98%),

N,N,N′,N″,N″-pentamethyldiethylenetri-amine (PMDETA, 99%) were purchased from Aldrich Ni (dppp)Cl2, i-PrMgCl in tetrahydrofuran (THF) (2 mol/l) were also purchased from Acros and stored in glove box at room temperature Potassium acetate (KOAc), sodium car-bonate (99%), and magnesium sulfate (98%) were pur-chased 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-heptane (99%), methanol (99.8%), ethyl ace-tate (99%), and diethyl ether (99%) were purchased from Fisher/Acros and used as received

2.2 Measurements 1

H NMR spectra were recorded in deuterated chloroform (CDCl3) with TMS as an internal reference, on a Bruker Avance 300 MHz FT-IR spectra, collected as the aver-age of 64 scans with a resolution of 4 cm−1, were recorded from KBr disk on the FT-IR Bruker Tensor 27 Elemental analyses were recorded on a Carlo Elba Model

1106 analyzer

Size exclusion chromatography (SEC) measurements were performed on a Polymer PL-GPC 50 gel perme-ation chromatograph system equipped with an RI detec-tor, with THF as the eluent at a flow rate of 1.0 ml/min Molecular weight and molecular weight distribution 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 Fluorescence spectra were measured on a HOR-IBA IHR 325 spectrometer

Differential scanning calorimetry (DSC) measure-ments were carried out with a DSC 204 F1-NETZSCH instruments under nitrogen flow (heating rate 10 °C/ min) The AFM images were obtained using a Veeco Dimension 3100 atomic force microscopy (AFM) Matrix-assisted laser desorption/ionization (MALDI) mass spectra were recorded using a Waters QToF Pre-mier mass spectrometer equipped with a nitrogen laser, operating at 337 nm with a maximum output of 500 mW delivered to the sample in 4 ns pulses at 20 MHz repeat-ing rate Time-of-flight mass analyses were performed in the reflectron mode at a resolution of about 10,000 All samples were analyzed using trans-2-[3-(4-tertbutylphe-nyl)-2-methylprop-2-enylidene]-malonitrile (DCTB) as matrix prepared as a 20 mg/ml solution in CH2Cl2 The matrix solution (1μl) was applied to a stainless steel tar-get and air dried Polymer samples were dissolved in

CH2Cl2 to obtain 1 mg/ml solutions One microliter ali-quots of those solutions were applied onto the target area already bearing the matrix crystals, and air dried For the recording of the single-stage MS spectra, the quadrupole (rf-only mode) was set to pass ions from 100 to 3000

Th, and all ions were transmitted into the pusher region

of the time-of-flight analyzer where they were mass

ana-lyzed with 1 s integration time Data were acquired in

continuum mode until acceptable averaged data were

obtained

2.3 Synthesis of 2-bromo-3-hexylthiophene (2)

To a solution of 3-hexylthiophene (5 g, 29.7 mmol),

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 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 (300 MHz, CDCl3), δ (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),

δ (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

dichloro-methane (25 ml) at 0 °C The mixture 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 Then the solvent

was evaporated to obtain crude products, which were

purified by silica column chromatography (eluent:

hep-tane) to give pure 2-bromo-3-hexyl-5-iodothiophene as a

pale yellow oil (3 g, 86%) 1H NMR (300 MHz, CDCl3),

δ (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),δ (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 group

A dry, 500 ml three-neckflask was flushed with nitrogen

and was charged with 2-bromo-3-hexyl-5-iodothiophene

(15 g, 40 mmol) After three azeotropic distillations by

toluene, anhydrous THF (220 ml) was added via a

syr-inge, the mixture was stirred at 0 °C for 1 h i-PrMgCl

(2 M solution in THF, 19.14 ml, 38.28 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 a addition of

5 M HCl After termination, the reaction was stirred for

15 min and extracted with CHCl3 The polymer was pre-cipitated in cold methanol and washed several times with n-hexane The polymer was characterized by 1H NMR and GPC Yield: 70%

FT-IR (cm−1): 721, 819, 1376, 1454, 1510, 2853,

2922, 2953.1H NMR (300 MHz, CDCl3),δ (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 (m/z): 1410,

1576, 1742, 1908, 2074, 2240, 2406, 2572, 2738, 2904,

3070, 3236 GPC: Mn= 4000 g/mol Polydispersity index (Đ), 1.18 UV–vis (CHCl3): λmax= 450 nm PL (CHCl3):

λmax= 570 nm

2.6 Synthesis of regioregular head-to-tail poly(3-hexylthiophene) with CHO/Br end group

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 per-formed at 75 °C for 24 h The solution was cooled down

to room temperature, followed by the addition of a satu-rated 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 vac-uum, 96 mg of polymer was obtained The yield was 93% FT-IR (cm−1): 721, 819, 1376, 1453, 1509, 1649,

2854, 2923, 2953 1H NMR (300 MHz, CDCl3), δ (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 5 (500 mg) was dissolved in 30 ml of anhy-drous THF under nitrogen NaBH4 (41.8 mg) was then added The mixture was kept stirring at room tempera-ture for 2 h Then, the solvent was evaporated under vac-uum The polymer was precipitated in cold methanol After drying under vacuum, 480 mg of the polymer was obtained The yield was 96% FT-IR (cm−1): 724, 817,

1376, 1453, 1509, 1561, 2853, 2922, 2953 1H NMR (300 MHz, CDCl3), δ (ppm): 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) (7)

Polymer 6 (500 mg, 83.3 × 10−5mol) was dissolved in

20 ml of anhydrous THF under nitrogen To this

solu-tion, triethylamine (1 mmol) and 2-bromoisobutyryl

bro-mide (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

dis-tilled water The polymer was precipitated in cold

metha-nol After drying under vacuum, 475 mg of the polymer

was obtained The yield was 95% FT-IR (cm−1): 724,

818, 1376, 1451, 1509, 1561, 1735, 2853, 2922, 2953

1

H NMR (300 MHz, CDCl3), δ (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= 4000 g/mol, PDI: 1.28

2.9 Synthesis of 1-nitrosonaphthalene-2,7-diol

After dissolving NaOH (2.5 g, 62.4 mmol) in 100 ml of

H2O, 2,7-dihydroxynaphthalene (1) (10 g, 62.4 mmol)

and Na2NO2 (4.46 g, 64.6 mmol) were added to the

solution and stirred for 1 h at 60 °C This solution was

then cooled to 0 °C The mixture of 8 ml of concentrated

H2SO4and 15 ml of distilled water was added dropwise

to the reaction solution with the temperature remained at

0 °C The reaction continued for 1 h After the reaction,

compound 2 as a brown powder was obtained Yield:

93% 1H NMR, (300 MHz, methanol-d4), δ (ppm): 7.42

(d, 1H), 7.59 (d, 1H), 7.56 (d, 1H), 6.8 (d, 1H), 6.18 (s,

2H) FT-IR (cm−1): 3143 (O–H), 1301 (N=O) M.p.:

243 °C; MS m/z (M+) 189 Anal Calcd for C10H7NO3:

C, 63.49; H, 3.73; N, 7.40 Found: C, 63.68; H, 3.79; N,

7.65

2.10 Synthesis of 1,3,3-trimethylspiro[indoline-2,3

′-naphtho[2,1-b][1,4]oxazin]-9′-ol

(spirooxazine-hydroxyl)

To a suspension of 2,7-dihydroxy-1-nitrosonaphthaline

(compound 2) (1.88 g, 10 mmol) in absolute ethanol

(50 ml) was added dropwise, under refluxing a solution

of 1,3,3-trimethyl-2-methyleneindoline (10 mmol) in

absolute ethanol (5 ml) After continuous refluxing under

a N2-stream, the obtained brown solution was purified

over silica column with ethyl acetate/hexane (2:1) to

obtain the crude product Then, solvents were evaporated

under vacuum to give a black powder The black powder

was washed with distilled water and extracted with

CHCl3 Finally, the product was crystallized in methanol

to obtain the pure white powder of SP Yield: 53% 1H

NMR, (300 MHz, CDCl3), δ (ppm): 1.35 (s, 6H), 2.77

(s, 3H), 6.58 (t, J = 7.40 Hz, 1H), 6.84 (d, J = 8.84 Hz,

1H), 6.9 (d, J = 7.46 Hz, 1H), 7.02 (d, J = 8.68 Hz, 1H),

7.09 (d, 1H), 7.23 (t, J = 7.74 Hz, 1H), 7.58 (d,

J = 8.60 Hz, 1H), 7.65 (d, J = 8.56 Hz, 1H), 7.71 (s, 1H), 7.88 (s, 1H) FT-IR (cm−1): 3313 (O–H), 3065 (=C–H), 1627 (C=N) Anal Calcd for C22H20N2O2: C, 76.72; H, 5.85; N, 8.13 Found: C, 75.63; H, 5.67; N, 8.01

2.11 Synthesis of methacrylate spirooxazine monomer (MSp)

Spirooxazine-hydroxyl (1.25 g, 3.81 mmol) was added to

25 ml of anhydrous dichloromethane in a 50 ml round bottomed flask Triethylamine (0.6 g, 5.5 mmol) was added and the reaction was stirred for an hour Then, methacryloyl chloride (0.5 g, 4.4 mmol) was dissolved in

5 ml of anhydrous dichloromethane and added dropwise

to the reaction mixture under N2 atmosphere, cooled to

0 °C The reaction was continuously stirred for 24 h at room temperature Then, the mixture was washed by

50 ml of 0.5 M HCl solution, 50 ml of distilled water, and 50 ml of brine The mixture was dried by MgSO4 The final solution was rotary evaporated to produce the crude product This crude product was purified over col-umn, and the received product was recrystallized in methanol Yield: 75% 1H NMR, (300 MHz, CDCl3), δ (ppm): 1.35 (s, 6H), 2.1 (s, 3H), 2.77 (s, 3H), 5.6 (s, 1H), 6.3 (s, 1H), 6.58 (s, 1H), 6.84 (s, 1H), 6.9 (s, 1H), 7.02 (d, 1H), 7.09 (d, 1H), 7.23 (d, 1H), 7.58 (d, 1H), 7.71 (s, 1H), 7.65 (d, 1H), 7.88 (s, 1H) Anal Calcd for

C26H24N2O3: C, 75.70; H, 5.82; N, 6.79 Found: C, 75.53; H, 5.77; N, 6.73

2.12 Synthesis of diblock copolymers poly(3-hexyl thiophene)-b-poly(methyl methacrylate)-r-poly(methyl methaspirooxazine) (P3HT-b-P(MMA-r-MSp)) Hundred milligram of P3HT macroinitiator (Mn= 4000 g/mol, 0.025 mmol), 113 mg (1.13 mmol) of MMA, and 50 mg (0.12 mmol) of MSp were dissolved

in 2 ml of degassed THF in the first flask The first flask was degassed by three freeze-pump-thaw cycles 10.45μl of PMDETA and 3.6 mg of CuBr were placed

in the second flask Then 2 ml of THF was added into theflask via syringe The mixture was stirred for 30 min, and the mixture was degassed by three freeze-pump-thaw cycles Afterward, the mixture solution in the first flask was transferred to the second flask via cannula The reaction was performed at 60 °C for 24 h Then, the reac-tion was cooled down by liquid nitrogen Five milliliter

of THF was added to the solution, and the mixture was passed via an aluminum column to remove CuBr The block copolymer was precipitated in cold n-heptane from the obtained solution The block copolymer was filtrated and dried at 50 °C overnight to obtain 245 mg of the dried copolymer Conversion (by gravimetry) = 93% 1H

NMR, (300 MHz, CDCl3), δ (ppm): 0.5–2.1 (m, 32H),

2.7 (m, 5H), 3.55 (m, 3H), 5.11 (s, 2H), 6.5–7.65 (m,

10H), 8.18 (s, 1H)

3 Results and discussion

Poly(3-hexylthiophene)-b-poly(methyl

methacrylate)-ran-dom-poly(methyl methaspirooxazine)

(P3HT-b-P(MMA-r-MSp)) block copolymers were synthesized using a

six-step procedure consisting first of a controlled

‘quasi-living’ GRIM polymerization of

2-bromo-5-iodo-3-hexyl-thiophene monomers in presence of Ni(dppp)Cl2to form

α-bromo, poly(3-hexylthiophene) (Br-P3HT-H) Then,

the quantitative conversion of Br-P3HT-H into α-bromo,

ω-bromoisobutyrate poly(3-hexylthiophene) (7) was

per-formed by a 3-step procedure In the other hand, methyl

methaspirooxazine (MSp) was synthesized via a 3-step

procedure from commercial chemical of

2,7-dihydroxy-naphthalene Finally, the bromoester terminated

poly(3-hexylthiophene) was used as macroinitiator for ATRP of

MMA and MSp co-monomers as present in Scheme 1

The telechelic P3HT (4) consisting a proton chain end

and a bromo chain end was prepared by GRIM

polymer-ization starting from 2-bromo-5-iodo-3-hexyl thiophene

(3) which was treated with 1 equiv of iPr-MgCl results

in magnesium–iodine exchange reaction The

polymeri-zation was performed in THF at 0 °C for 24 h and

quickly terminated by addition of a 5 M HCl solution to

prevent any transhalogenation side-reaction As

deter-mined by gravimetry, a conversion of 70% was recorded

(Mnth= 4500 g/mol) A good correlation between the

theoretical molecular weight (Mnth) and the value

determined by GPC (Mnexp= 4000 g/mol) was obtained

attesting for the control over the GRIM polymerization,

which was further confirmed by the symmetrical and

narrow molecular weight distribution (PDI = 1.18)

A high regioregularity content (>99%) was determined

by 1H NMR while the presence of the expected

end-groups (H/Br) was fully evidenced by MALDI-ToF

analysis

First, 2,7-dihydroxynaphthalene (8) was nitrosated by

NaNO2 in presence of NaOH and H2SO4 to obtain

1-nitrosonaphthalene-2,7-diol (9, Scheme 1) Then,

1-nitr-osonaphthalene-2,7-diol reacted with

1,3,3-trimethyl-2-methyleneindoline to form spirooxazine-hydroxyl (10,

Scheme 1), which subsequently reacted with

methacry-loyl chloride to give methacrylate-spirooxazine (MSp)

(11, Scheme 1) The 1H NMR spectrum of MSp

(Figure 1) showed the proton resonance of methylene

linkage of methacrylate at 5.7 and 6.3 ppm The 1H

NMR spectrum of MSp also showed the imine linkage

in SP ring at 8.4 ppm All other proton resonances

appear in the exact intensities and are correlated to SP

structure, thus confirming the expected molecular

struc-ture of MSp The attribution of the 1H NMR signals of MSp is reported in Figure1

Finally, the MSp and MMA comonomers were poly-merized via ATRP using P3HT-macroinitiator (Mn= 4000 g/mol, ÐM= 1.28) in presence of CuBr and PMDETA as catalyst and ligand, respectively The feed ratio of MMA/MSp comonomers of about 9/1 was estab-lished for achieving a good control over ATRP ([MMA]/ [MSp]/[P3HT-Br]/CuBr]/[PMDETA] = 45/5/1/1/2) The polymerization was performed in THF at 60 °C for 24 h under nitrogen atmosphere The polymerization was stopped by cooling the reaction mixture followed by dilution with an extra volume of THF, then the mixture was purified over aluminum column to remove CuBr cat-alyst The diblock copolymers were recovered by precip-itation in cold n-heptane, the samples were filtered and dried until constant mass

The FT-IR spectra was used to characterize the di-block copolymers P3HT-b-P(MMA-r-MSp) as Figure 2 The appearance of the high intensity signal observed at

1728 cm−1 that attributed to carbonyl vibrational (υ C=O) of P(MMA-r-MSp) block In addition, the N=C linkage of MSp in P3HT-b-P(MMA-r-MSp) was also exhibited at 1651 cm−1

The polymerization degree of the P(MMA-r-MSp) block was calculated from the recorded1H NMR spectrum

by comparing the relative signal intensities of the imine proton of the MSp and methylene protons of the MMA residue at δ = 8.18 ppm (peak d′, Figure 3) and

δ = 3.55 ppm (peak c, Figure3), respectively, with that of the methylene protons of the P3HT end-group at

δ = 5.11 ppm (peak 8, Figure3) The molecular weight of the P(MMA-r-MSp) block was determined to be

6000 g/mol and to comprise 44 and 4 of MMA and MSp units, respectively These results correspond to weight com-positions of 44 and 16% of MMA and MSp, respectively,

in the P3HT-b-P(MMA-r-MSp) diblock copolymers

As seen from Table 1, the P(MMA-r-MSp) block was obtained with a relatively good approximation between theoretical and experimental molar masses, attesting for an initiation efficiency close to 1 A quite narrow molecular weight distribution of the diblock copolymer P3HT-b-P(MMA-r-MSp) was recorded by SEC, with ÐM= 1.39 Figure 4clearly shows a shift to a smaller elution volume of the diblock copolymers com-pared to the trace initially recorded for the P3HT-Br macroinitiator

The diblock copolymers are expected to be soluble

in a wider range of solvents than in case of the conju-gated P3HT UV–vis spectroscopy can be used to probe the π overlap of conjugated polymers both in solution and in solid-state film Table 2 presents the solution (in various solvents) and solid-state UV–vis spectra results recorded for both regioregular P3HT (M = 4000 g/mol,

Scheme 1 Synthesis of rod–coil diblock copolymers P3HT-b-P(MMA-r-MSp).

PDI = 1.20) and a representative (Table 1, entry 1) In

non-polar solvents such as THF, CHCl3, toluene, both

P3HT and P3HT-b-P(MMA-r-MSp) show very similar

single maximum absorption (λmax) for theπ–π* transition

around 445 nm Moreover, in more polar solvents such

as ethylacetate and in solid-state film, P3HT-b-P(MMA-r-MSp) also exhibited the absorption peaks that is similar

to homogeneous P3HT Theλmaxvalues of the two poly-mers are bathochromically shifted to around 554 nm Both P3HT and P3HT-b-P(MMA-r-MSp) also revealed a

Figure 1 1H NMR spectrum of methacrylate-spirooxazine (MSp)

Figure 2 FTIR spectrum of P3HT-macroinitiator and diblock copolymers P3HT-b-P(MMA-r-MSp)

Figure 3 1H NMR spectrum of P3HT-macroinitiator (A) and diblock copolymers P3HT-b-P(MMA-r-MSp) (B).

shoulder at around 606 nm related to vibronic absorp-tion, indicating a high degree of ordering in the polymer films even when amorphous P(MMA-r-MSp) is cova-lently linked to P3HT

Table 1 Macromolecular characteristics of P3HT-b-P(MMA-r-MSp) synthesized by ATRP using P3HT-Br (Mnexp= 4000 g/mol,

ÐM= 1.28) as the macroinitiator and CuBr/PMDETA ([CuBr]/[PMDETA] = 1/2) as the catalytic complex

P3HT-b-P (MMA-r-MSp)

a

Conversion as determined after precipitation in cold n-heptane: Conv = (m-m I -m Cu -m L )/m M where m denotes the weight of product, and m I , m Cu , m L ,

m M the weights of the initiator, copper catalyst, ligand (PMDETA), and monomers, respectively.

b MMA and MSp theoretical number-average-molar mass as calculated by [MMA] or [MSp)] 0 /[P3HT-Br] 0 x Conv(%) x M w MMA(or MSp) assuming a living process.

c MMA (or MSp) experimental number-average molar mass as determined by 1 H NMR spectroscopy (see Figure 3 ): Mnexp= DP exp × M w MMA (or MSp)

where DP exp is the experimental degree of polymerization, as calculated from the relative intensities of methylene protons of MMA ( δ = 3.55 ppm), imine proton of MSp ( δ = 8.18 ppm), and methylene protons of the P3HT end-group (δ = 5.11 ppm).

d

Initiation ef ficiency as calculated from M ntheofPðMMArMSpÞ /MnexpofPðMMArMSpÞ:

e Dispersity index as determined by GPC in THF at 35 °C.

Figure 4 GPC traces of P3HT-macroinitiator (dash line) and

diblock copolymers P3HT-b-P(MMA-r-MSp) (solid line)

Table 2 UV–vis absorption peaks for regioregular P3HT

(Mn= 4000 g/mol, Đ = 1.28) and P3HT-b-P(MMA-r-MSp)

(Mn= 10,000 g/mol,Đ = 1.39) recorded in solution or on

solid-statefilms

Solvents

P3HT (λ = nm) P3HT-b-P(MMA-r-MSp)

Figure 5 The UV–visible absorption spectra of P3HT-b-P (MMA-r-MSp) in THF (CM= 0.1 mM) after irradiation for

5 min (a) and P3HT-b-P(MMA-r-MSp) in solid-state film after irradiation for 5 min (b)