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

DSpace at VNU: Synthesis and characterization of diblock copolymers based on poly(3-hexylthiophene) and photo-responsive...

This article was downloaded by: [RMIT University] On: 13 March 2015, At: 03:29 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Designed Monomers and Polymers Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tdmp20 Synthesis and characterization of diblock copolymers based on poly(3-hexylthiophene) and photoresponsive poly(methyl methacrylate-random-2-methyl methaspirooxazine) ab a ab Ha Tran Nguyen , Le-Thu T Nguyen & Thang Van Le 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 Click for updates 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 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content This article may be used for research, teaching, and private study purposes Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions Designed Monomers and Polymers, 2015 Vol 18, No 3, 271–283, http://dx.doi.org/10.1080/15685551.2014.999467 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 Nguyena and 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 Downloaded by [RMIT University] at 03:29 13 March 2015 (Received 24 September 2014; accepted 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-rMSp)) 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 macroinitiator 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 Introduction Among various types of photochromic compounds, spirooxazine (SP) is well-known to have remarkable properties 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 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 merocyanine (MC) (or the open form) by homolytic cleavage 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 storage, optical switching, displays, and non-linear optics In particular, light-responsive block copolymers containing both a fluorescent group and a photochromic moiety, *Corresponding author Email: nguyentranha@hcmut.edu.vn © 2015 Taylor & Francis such as SP, have attracted significant interest.[9–13] The SP and ring-opened MC forms of these fluorescent-coupled photochromic compounds participate as ‘Switch On’ and ‘Switch Off’ functions Interestingly, the fluorophore moiety of block copolymers emits fluorescence which is only observed when the photochromic compound 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 the fluorophore 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 containing fluorophore and photochromic compounds have been designed and probed in molecular switching applications, such as optical sensors and optical window switches.[14–16] The regioregular poly(3-hexylthiophene) (P3HT) polymer has attracted significant interest due to its potential in a variety of applications including light-emitting diodes (OLED’s), field-effect transistors (OFET’s), optical sensors, smart windows, and solar cells.[17–21] In order to improve commercial applications, the development of more intricate electronic materials is required Downloaded by [RMIT University] at 03:29 13 March 2015 272 H.T Nguyen et al One attractive approach is to prepare block copolymers of conjugated polymers and flexible coil-like polymers The combination of conjugated and non-conjugated segments generates interesting materials, expected to phase segregate leading to the formation of nanoscale morphologies as well as improvement of mechanical properties.[22] Rod–coil diblock copolymers containing regioregular P3HT, such as P3HT-b-polystyrene, P3HTb-polymethacrylate, P3HT-b-poly(tert-butyl acrylate), and P3HT-b-poly(isobornyl methacrylate), have been synthesized 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 bearing 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 random-copolymerization of 3HT and a spiropyran-containing 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-2methyl methaspirooxazine) (P3HT-b-P(MMA-r-MSp)) as photochromic coil-block Grignard metathesis (GRIM) polymerization and ATRP were performed to sequentially polymerize the P3HT block and the P(MMA-rMSp) 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 scanning calorimetry (DSC) The conformations of the diblock copolymers were also investigated in different tetrahydrofuran/methanol solvent mixture ratios by UV– visible spectroscopy Experiment 2.1 Materials 2,7-Dihydroxynaphthalene, Na2NO2, 1,3,3-trimethyl-2methyleneindoline, triethylamine, methacryloyl chloride, 3-hexylthiophene, N-bromosuccinimide, iodine, iodobenzene 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 carbonate (99%), and magnesium sulfate (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-heptane (99%), methanol (99.8%), ethyl acetate (99%), and diethyl ether (99%) were purchased from Fisher/Acros and used as received 2.2 Measurements 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 average of 64 scans with a resolution of 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 permeation chromatograph system equipped with an RI detector, 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 HORIBA IHR 325 spectrometer Differential scanning calorimetry (DSC) measurements 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 Premier mass spectrometer equipped with a nitrogen laser, operating at 337 nm with a maximum output of 500 mW delivered to the sample in ns pulses at 20 MHz repeating 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-tertbutylphenyl)-2-methylprop-2-enylidene]-malonitrile (DCTB) as matrix prepared as a 20 mg/ml solution in CH2Cl2 The matrix solution (1 μl) was applied to a stainless steel target and air dried Polymer samples were dissolved in CH2Cl2 to obtain mg/ml solutions One microliter aliquots 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 Designed Monomers and Polymers Downloaded by [RMIT University] at 03:29 13 March 2015 Th, and all ions were transmitted into the pusher region of the time-of-flight analyzer where they were mass analyzed with 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 °C under nitrogen The mixture was stirred at °C for 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 2bromo-3-hexylthiophene (2.5 g, 11.1 mmol) in dichloromethane (25 ml) at °C The mixture was stirred at room temperature for 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: heptane) 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(3hexylthiophene) with H/Br end group A dry, 500 ml three-neck flask 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 syringe, the mixture was stirred at °C for 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 °C for h The reaction mixture was allowed to cool 273 down to °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 °C followed by a addition of M HCl After termination, the reaction was stirred for 15 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 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(3hexylthiophene) with CHO/Br end group Polymer (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 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 (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(3hexylthiophene) with CH2OH/Br end group Polymer (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 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 (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 274 H.T Nguyen et al 2.8 Synthesis of bromoester-terminated poly(3hexylthiophene) (P3HT-macroinitiator) (7) Downloaded by [RMIT University] at 03:29 13 March 2015 Polymer (500 mg, 83.3 × 10−5 mol) was dissolved in 20 ml of anhydrous THF under nitrogen To this solution, triethylamine (1 mmol) and 2-bromoisobutyryl 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 (cm−1): 724, 818, 1376, 1451, 1509, 1561, 1735, 2853, 2922, 2953 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 h at 60 °C This solution was then cooled to °C The mixture of ml of concentrated H2SO4 and 15 ml of distilled water was added dropwise to the reaction solution with the temperature remained at °C The reaction continued for h After the reaction, compound 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 (spirooxazinehydroxyl) 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 ml of anhydrous dichloromethane and added dropwise to the reaction mixture under N2 atmosphere, cooled to °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 column, 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 ml of degassed THF in the first flask The first flask was degassed by three freeze-pump-thaw cycles 10.45 μl of PMDETA and 3.6 mg of CuBr were placed in the second flask Then ml of THF was added into the flask 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 reaction 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 Designed Monomers and Polymers 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) Downloaded by [RMIT University] at 03:29 13 March 2015 Results and discussion Poly(3-hexylthiophene)-b-poly(methyl methacrylate)-random-poly(methyl methaspirooxazine) (P3HT-b-P(MMAr-MSp)) block copolymers were synthesized using a six-step procedure consisting first of a controlled ‘quasiliving’ GRIM polymerization of 2-bromo-5-iodo-3-hexylthiophene monomers in presence of Ni(dppp)Cl2 to 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 performed 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-dihydroxynaphthalene Finally, the bromoester terminated poly(3hexylthiophene) was used as macroinitiator for ATRP of MMA and MSp co-monomers as present in Scheme The telechelic P3HT (4) consisting a proton chain end and a bromo chain end was prepared by GRIM polymerization starting from 2-bromo-5-iodo-3-hexyl thiophene (3) which was treated with equiv of iPr-MgCl results in magnesium–iodine exchange reaction The polymerization was performed in THF at °C for 24 h and quickly terminated by addition of a M HCl solution to prevent any transhalogenation side-reaction As determined 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 1nitrosonaphthalene-2,7-diol (9, Scheme 1) Then, 1-nitrosonaphthalene-2,7-diol reacted with 1,3,3-trimethyl-2methyleneindoline to form spirooxazine-hydroxyl (10, Scheme 1), which subsequently reacted with methacryloyl 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- 275 ture of MSp The attribution of the 1H NMR signals of MSp is reported in Figure Finally, the MSp and MMA comonomers were polymerized 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 established 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 catalyst The diblock copolymers were recovered by precipitation in cold n-heptane, the samples were filtered and dried until constant mass The FT-IR spectra was used to characterize the diblock copolymers P3HT-b-P(MMA-r-MSp) as Figure 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 recorded 1H 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, Figure 3), respectively, with that of the methylene protons of the P3HT end-group at δ = 5.11 ppm (peak 8, Figure 3) The molecular weight of the P(MMA-r-MSp) block was determined to be 6000 g/mol and to comprise 44 and of MMA and MSp units, respectively These results correspond to weight compositions 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 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 clearly shows a shift to a smaller elution volume of the diblock copolymers compared 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 conjugated P3HT UV–vis spectroscopy can be used to probe the π overlap of conjugated polymers both in solution and in solid-state film Table presents the solution (in various solvents) and solid-state UV–vis spectra results recorded for both regioregular P3HT (Mn = 4000 g/mol, H.T Nguyen et al Downloaded by [RMIT University] at 03:29 13 March 2015 276 Scheme Synthesis of rod–coil diblock copolymers P3HT-b-P(MMA-r-MSp) Downloaded by [RMIT University] at 03:29 13 March 2015 Designed Monomers and Polymers Figure 1 Figure FTIR spectrum of P3HT-macroinitiator and diblock copolymers P3HT-b-P(MMA-r-MSp) 277 H NMR spectrum of methacrylate-spirooxazine (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 the π–π* transition around 445 nm Moreover, in more polar solvents such as ethylacetate and in solid-state film, P3HT-b-P(MMAr-MSp) also exhibited the absorption peaks that is similar to homogeneous P3HT The λmax values of the two polymers are bathochromically shifted to around 554 nm Both P3HT and P3HT-b-P(MMA-r-MSp) also revealed a H.T Nguyen et al Downloaded by [RMIT University] at 03:29 13 March 2015 278 Figure H NMR spectrum of P3HT-macroinitiator (A) and diblock copolymers P3HT-b-P(MMA-r-MSp) (B) Designed Monomers and Polymers 279 Table Macromolecular characteristics of P3HT-b-P(MMA-r-MSp) synthesized by ATRP using P3HT-Br (M nexp = 4000 g/mol, ÐM = 1.28) as the macroinitiator and CuBr/PMDETA ([CuBr]/[PMDETA] = 1/2) as the catalytic complex Diblock copolymers T (°C) Conversion (%) 60 60 MMA a 93 91 P3HT-b-P (MMA-r-MSp) MSp M nthe b M nexp c M nthe b M nexp c fd M nNMR Ðe 4500 5000 4400 4500 2000 2500 2050 2100 1 10,000 10,200 1.39 1.47 Downloaded by [RMIT University] at 03:29 13 March 2015 a Conversion as determined after precipitation in cold n-heptane: Conv = (m-mI-mCu-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 MMA and MSp theoretical number-average-molar mass as calculated by [MMA] or [MSp)]0/[P3HT-Br]0 x Conv(%) x Mw MMA(or MSp) assuming a living process c MMA (or MSp) experimental number-average molar mass as determined by 1H NMR spectroscopy (see Figure 3): M nexp = DPexp × Mw MMA (or MSp) where DPexp 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 efficiency as calculated from M ntheofPðMMẦrÀMSpÞ /M nexpofPðMMẦrÀMSpÞ : e Dispersity index as determined by GPC in THF at 35 °C Figure GPC traces of P3HT-macroinitiator (dash line) and diblock copolymers P3HT-b-P(MMA-r-MSp) (solid line) Table 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 solidstate films Solvents P3HT (λ = nm) P3HT-b-P (MMA-r-MSp) THF CHCl3 Toluene Carbontetrachloride (CCl4) Ethyl acetate Heptane Solid-state film 445 450 450 440 Insoluble Insoluble 527, 558, 602 445 451 450 438 510, 560, 605 Insoluble 524, 558, 608 Figure The UV–visible absorption spectra of P3HT-b-P (MMA-r-MSp) in THF (CM = 0.1 mM) after irradiation for (a) and P3HT-b-P(MMA-r-MSp) in solid-state film after irradiation for (b) shoulder at around 606 nm related to vibronic absorption, indicating a high degree of ordering in the polymer films even when amorphous P(MMA-r-MSp) is covalently linked to P3HT Downloaded by [RMIT University] at 03:29 13 March 2015 280 H.T Nguyen et al In order to explore the optical properties of diblock copolymers related to fluorescence switching, a THF (0.1 mM) solution of P3HT-b-P(MMA-r-MSp) was irradiated with 365 nm light (1 mW cm−1) The UV–visible absorption spectra monitored before and after UV-irradiation shows that UV-irradiation for results in the formation of a new absorption band at 590 nm, corresponding to the MC form of the SP (Figure 5(a)) In the other hand, the absorption of P3HT-b-P(MMA-r-MSp) in solid-state film after UV-irradiation for did not change when compared with absoption of P3HT-b-P (MMA-r-MSp) before UV-irradiation (Figure 5(b)) To investigate the ability of fluorescence switching, a solution of P3HT-b-P(MMA-r-MSp) diblock copolymers was prepared in THF (CM = 0.1 M) A solution of P3HT-b-P(MMA-r-MSp) was irradiated with 365 nm light (1 mW cm−2) UV-irradiation resulted in a decrease in fluorescence intensity, dropping of 7% of the initial value This phenomenon is referred to fluorescence quenching, which is caused by effective energy transfer from poly(3-hexylthiophene) moieties to the MC form of the SP Following this, we aimed to demonstrate the possibility of the spirooxazine–poly(3-hexylthiophene) conjugate as a FRET-based chemosensor Based on the report of Kim and his coworkers,[34] we considered that the spirooxazine–poly(3-hexylthiophene) conjugate could interact with cyanide anion after being transformed to the MC form by UV-irradiation In order to test this proposal, a solution of P3HT-b-P(MMA-r-MSp) diblock copolymer (Table 1, entry 1) in THF (CM = 0.1 mM) containing 10 mM of CN− anion was irradiated in Interestingly, the PL spectra showed that the degree of the fluorescence quenching of the irradiated solution containing cyanide anion is much smaller than that of the cyanide anion non-containing solution (Figure 6) The fluorescence intensity of the cyanide anion-containing copolymer solution decreases by about 57% upon irradiation This phenomenon can be attributed to the formation of an adfuct between the MC form of SP and the CN− anion (Figure – insert structure image) which prevents the FRET process The micro- and nanoscopic morphologies of thin deposits of the diblock copolymer P3HT-b-P(MMA-rMSp) were investigated by AFM in intermittent-contact mode These films have been prepared by drop-casting onto mica substrates from a good solvent (CHCl3) for both P3HT and P(MMA-r-MSp) segments, followed by annealing at 150 °C for 24 h Thin films of the studied P3HT-b-P(MMA-r-MSp) show a fibrillar (nanowire-like) morphology (Figure 7) The continuous nanofibril structure with 10–15 nm widths was observed clearly for a 40/60 (w/w) composition of P3HT and P(MMA-r-MSp) domains, respectively This observation is attributed to the microphase separation between flexible P(MMA-rMSp) segments and P3HT rod-segments Indeed, this fibrillar morphology is typical from the crystalline assembly of P3HT into π-stacked structures, as observed and described for highly regioregular poly(thiophene)s Figure Emission spectra of the P3HT-b-P(MMA-r-MSp) diblock copolymer (Table – entry 1, 0.1 mM in THF) monitored after 365 nm UV-irradiation for (dot line) and in the presence of 10 mM of CN− anions (dash line) Designed Monomers and Polymers AFM images of P3HT-b-P(MMA-r-MSp) (Table 1, entry 1) Figure DSC thermograms of homo P3HT (solid line) and P3HT-b-P(MMA-r-MSp) (dash line) (Table 1, entry 1) Downloaded by [RMIT University] at 03:29 13 March 2015 Figure 281 and other conjugated polymers It is also noted in the AFM phase image that adjacent fibrils (in bright) are close to each other, and appear to be separated by narrow dark bands, indicating that the amorphous copolymer segments are very likely in a compact conformation in between the P3HT assemblies Therefore, the selfassembly of the P3HT-b-P(MMA-r-MSp) diblock copolymer is driven by the ordering of the P3HT backbone (intralamellar π-stacking of conjugated backbones and interlamellar interdigitation between alkyl groups) rather than by the assembly of the P(MMA-r-MSp) block, which are very likely in a coiled configuration in between the P3HT fibrils Last but not least, the thermal properties of both P3HT (Mn = 4000 g/mol, Đ = 1.28) and a representative P3HT-b-P(MMA-r-MSp) were characterized by DSC The DSC of homo P3HT and P3HT-b-P(MMA-r-MSp) are presented in Figure For such studied molecular weights, the glass transition temperature (Tg) value of P (MMA-r-MSp) is around 106 °C Otherwise, the melting point (Tm) of P3HT is observed at ca 199 °C The P3HT-b-P(MMA-r-MSp) diblock copolymers exhibited both a Tg at 106 °C and Tm at 199 °C that corresponding to the P(MMA-r-MSp) and P3HT segments, respectively This results suggest that the phase segregation appearing in the P3HT-b-P(MMA-r-MSp) diblock copolymers 282 H.T Nguyen et al Downloaded by [RMIT University] at 03:29 13 March 2015 Conclusion We have successfully prepared new rod–coil diblock copolymers P3HT-b-P(MMA-r-MSp) using the GRIM method, end group modification, ATRP of methyl methacrylate, and 2-methyl methaspirooxazine comonomers These P3HT-b-P(MMA-r-MSp) diblock copolymers were characterized via 1H NMR, GPC, FTIR, DSC, AFM, fluorescence, and UV–vis spectrocospy UV–vis spectra exhibited the presence of a vibronic structure in polar solvents, indicating the ordering of P3HT caused by the self-assembly of P3HT-b-P(MMA-r-MSp) The DSC results evidenced clearly the phase-segregation of each domain of the diblock copolymer It is interesting that the UV–vis spectrum of P3HT-b-P(MMA-r-MSp) in solution showed an absorption band at 590 nm after irradiation which revealed the MC form of the spirooxazine units as photo-responsive moieties with potential applications toward optical switches, photovoltaic or photo-controlled materials [11] [12] [13] [14] [15] [16] [17] Funding This research was supported by The Department of Science and Technology (DOST) – Ho Chi Minh City [grant number VL_2014_02] [18] [19] References [1] Ryu CK, Wang R, Schmehl RH, Ferrere S, Ludwikow M, Merkert JW, Headford CEL, Elliott CM Photoinduced electron transfer in linked ruthenium(II) diimine–diquat complexes: linkage dependence J Am Chem Soc 1992;114:430–438 [2] Nakazumi H, Maeda K, Yagi S, Kitao T Novel merocyanine dyes are converted into the spiropyran form by irradiation with visible light J Chem Soc., Chem Commun 1992;1188–1189 [3] Zelichenok A, Buchholtz F, Yitzchaik S, Ratner J, Safro M, Krongauz V Steric effects in photochromic polysiloxanes with spirooxazine side groups Macromolecules 1992;25:3179–3183 [4] Biteau J, Chaput F, Boilot JP Photochromism of spirooxazine-doped gels J Phys Chem 1996;100:9024–9031 [5] Paquette MM, Patrick BO, Frank NL Determining the magnitude and direction of photoinduced ligand field switching in photochromic metal-organic complexes: molybdenum-tetracarbonyl spirooxazine complexes J Am Chem Soc 2011;133:10081–10093 [6] Berkovic G, Krongauz V, Weiss V Spiropyrans and spirooxazines for memories and switches Chem Rev 2000;100:1741–1754 [7] Levy D Photochromic sol–gel materials Chem Mat 1997;9:2666–2670 [8] Beyer C, Wagenknecht H-A Synthesis of spiropyrans as building blocks for molecular switches and dyads J Org Chem 2010;75:2752–2755 [9] Minkin VI Photo-, thermo-, solvato-, and electrochromic spiroheterocyclic compounds Chem Rev 2004;104:2751–2776 [10] di Nunzio MR, Gentili PL, Romani A, Favaro G Photochromism and thermochromism of some spirooxazines [20] [21] [22] [23] [24] [25] [26] [27] [28] and naphthopyrans in the solid state and in polymeric film J Phys Chem C 2010;114:6123–6131 Yassar A, Moustrou C, Youssoufi HK, Samat A, Guglielmetti R, Garnier F Synthesis and characterization of poly(thiophenes) functionalized by photochromic spironaphthoxazine groups Macromolecules 1995;28:4548–4553 Lone S, Ahn JI, Kim MR, Lee HM, Kim SH, Lodge TP, Cheong IW Photoresponsive phase separation of a poly (NIPAAm-co-SPO-co-fluorophore) random copolymer in w/o droplet Langmuir 2014;30:9577–9583 Such GK, Evans RA, Davis TP The use of block copolymers to systematically modify photochromic behavior Macromolecules 2006;39:9562–9570 Zhu L, Zhu M-Q, Hurst JK, Li ADQ Light-controlled molecular switches modulate nanocrystal fluorescence J Am Chem Soc 2005;127:8968–8970 Guo X, Zhang D, Zhou Y, Zhu D Synthesis and spectral investigations of a new dyad with spiropyran and fluorescein units: toward information processing at the single molecular level J Org Chem 2003;68:5681–5687 Lee CW, Song YH, Lee Y, Ryu KS, Chi K-W Reversible photochromic switch ensemble and its photoimaging using H+ transfer between spiropyran and fluorescein in a polymer matrix Chem Commun 2009;6282–6284 McCullough RD The chemistry of conducting polythiophenes Adv Mater 1998;10:93–116 Kim JY, Lee K, Coates NE, Moses D, Nguyen T-Q, Dante M, Heeger AJ Efficient tandem polymer solar cells fabricated by all-solution processing Science 2007; 317:222–225 Thompson BC, Fréchet JMJ Polymer-fullerene composite solar cells Angew Chem Int Ed 2008;47:58–77 Wei Q, Nishizawa T, Tajima K, Hashimoto KS Selforganized buffer layers in organic solar cells Adv Mater 2008;20:2211–2216 Wang G, Swensen J, Moses D, Heeger AJ Increased mobility from regioregular poly(3-hexylthiophene) fieldeffect transistors J Appl Phys 2003;93:6137–6141 Bates FS Polymer-polymer phase behavior Science 1991;251:898–905 Iovu MC, Craley CR, Jeffries-EL M, Krankowski AB, Zhang R, Kowalewski T, McCullough RD Conducting regioregular polythiophene block copolymer nanofibrils synthesized by reversible addition fragmentation chain transfer polymerization (RAFT) and nitroxide mediated polymerization (NMP) Macromolecules 2007;40:4733–4735 Iovu MC, Jeffries-EL M, Sheina EE, Cooper JR, McCullough RD Regioregular poly(3-alkylthiophene) conducting block copolymers Polymer 2005;46:8582–8586 Iovu MC, Zhang R, Cooper JR, Smilgies DM, Javier AE, Sheina EE, Kowalewski T, McCullough RD Conducting block copolymers of regioregular poly(3-hexylthiophene) and poly(methacrylates): electronic materials with variable conductivities and degrees of interfibrillar order Macromol Rapid Commun 2007;28:1816–1824 Scherf U, Gutacker A, Koenen N All-conjugated block copolymers Acc Chem Res 2008;41:1086–1097 Kong X, Jenekhe SA Block copolymers containing conjugated polymer and polypeptide sequences: synthesis and self-assembly of electroactive and photoactive nanostructures Macromolecules 2004;37:8180–8183 Park S-J, Kang S-G, Fryd M, Saven JG, Park S-J Highly tunable photoluminescent properties of amphiphilic conjugated block copolymers J Am Chem Soc 2010;132:9931–9933 Designed Monomers and Polymers Downloaded by [RMIT University] at 03:29 13 March 2015 [29] Lu S, Fan Q-L, Chua S-J, Huang W Synthesis of conjugated−ionic block copolymers by controlled radical polymerization Macromolecules 2002;36:304–310 [30] Dai C-A, Yen W-C, Lee Y-H, Ho C-C, Su W-FJ Facile synthesis of well-defined block copolymers containing regioregular poly(3-hexyl thiophene) via anionic macroinitiation method and their self-assembly behavior J Am Chem Soc 2007;129:11036–11038 [31] Lu S, Liu T, Ke L, Ma D-G, Chua S-J, Huang W Polyfluorene-based light-emitting rod−coil block copolymers Macromolecules 2005;38:8494–8502 283 [32] Lee E, Hammer B, Kim J-K, Page Z, Emrick T, Hayward RC Hierarchical helical assembly of conjugated poly(3hexylthiophene)- block -poly(3-triethylene glycol thiophene) diblock copolymers J Am Chem Soc 2011;133:10390–10393 [33] Segalman RA, McCulloch B, Kirmayer S, Urban JJ Block copolymers for organic optoelectronics Macromolecules 2009;42:9205–9216 [34] Park IS, Jung YS, Lee KJ, Kim JM Photoswitching and sensor applications of a spiropyran–polythiophene conjugate Chem Commun 2010;46:2859–2861  ... One attractive approach is to prepare block copolymers of conjugated polymers and flexible coil-like polymers The combination of conjugated and non-conjugated segments generates interesting materials,... 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...Designed Monomers and Polymers, 2015 Vol 18, No 3, 271–283, http://dx.doi.org/10.1080/15685551.2014.999467 Synthesis and characterization of diblock copolymers based on poly(3-hexylthiophene) and photo-responsive