Synthesis and optical investigation of amphiphilic diblock copolymersa Faculty of Materials Technology, Ho Chi Minh City University of Technology HCMUT, Vietnam National University, 268
Trang 1Synthesis and optical investigation of amphiphilic diblock copolymers
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
Thispaperreportsonthesynthesisandpropertiesofamphiphilicdiblockcopolymerscomposedofa 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 copolymerswere synthesized via thecombination of quasi-living Grignard metathesis (GRIM) polymerization, end group modification, atom transfer radical polymerization(ATRP), and post-polymerizationmodificationof diblockcopolymerprecursorsand exhibitedanaveragemolecularweightofaround11,000g/molwithlowpolydispersitiesbelow1.5.The P3HT-b-P(DMAEMA-r-HEMA)) diblock copolymers were easily converted to amphiphilic diblock copolymersdue to esterificationofHEMA hydroxyl groupsand aminequaternizationof DMAEMA units to yield anionic orcationic amphiphilicdiblock copolymers,respectively The structureand propertiesoftheresultingdiblockcopolymerswerecharacterizedbyprotonnuclearmagneticresonance (1H NMR), gel permeation chromatography, Fourier transform infrared, UV–vis spectroscopy, and differentialscanningcalorimetry
ã2016ElsevierB.V.Allrightsreserved
1.Introduction
Theregioregularpoly(3-hexylthiophene)(P3HT)polymerhas
attractedsignificantinterestowingtoitspotentialinavarietyof
applications,includinglight-emittingdiodes(OLED’s),field-effect
transistors(OFET’s),opticalsensors,smartwindowsandpolymeric
solarcells[1–9].Thegreatimportanceofconjugatedrod-coilblock
copolymersasapowerfultooltowardssupramolecular
architec-tureswithnovelfunctionsandphysicalpropertieshasbeenwell
recognized.Inaddition,theabilityofdiblockcopolymersto
self-assemblecreatesanewroutefortuningthemolecular
organiza-tion and the resulting electronic and optoelectronic properties
value in providing controlled structures and functionality Furthermore, themicrophase separation of conjugated rod-coil blockcopolymersmayleadtonanoscalemorphologies,suchas lamellar,spherical,cylindricalandmicroporousstructures.These nanostructuresmaynotonlygiverisetointerfacialeffects,butalso openanewwayforelectronicprocesses.Also,thecombinationofa stimulus (such as light, pH or temperature)-responsive coil segmentwithtunablephoto-physicalpropertiesoftheconjugated rodsegmentcouldenablethediscoveryofnovelmultifunctional sensorymaterials[12,13].Severalclassesofp-conjugatedrod-coil blockcopolymershavebeenreportedintheliterature,including polyfluorene(PFO), polycarbazole, polyphenylene and polythio-phene as rod segments, and polymethylmethacrylate (PMMA), poly(N,N-dimethylamino-2-ethyl methacrylate) (PDMAEMA), polystyrene(PS)andpoly(2-vinylpiridine)(P2VP)ascoilsegments [14–20] Roil-coil diblock copolymers containing regioregular P3HThavealreadybeenreportedbyanumberofresearchgroups, such as the synthesis of P3HT-b-polystyrene, P3HT-b-PMMA,
* 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: nguyentranha@hcmut.edu.vn (H.T Nguyen).
http://dx.doi.org/10.1016/j.synthmet.2016.03.035
0379-6779/ã 2016 Elsevier B.V All rights reserved.
Synthetic Metals 217 (2016) 172–184
ContentslistsavailableatScienceDirect
j o u r n a l h o m e p a g e : w w w e l s ev i er c o m / l o c a te / s y n m et
Trang 2P3HT-b-poly(isobornyl methacrylate) by atom transfer radical
polymerization(ATRP)[21–23]
Recently, amphiphilicdiblock copolymersincluding P3HTas
thehydrophobicrodsegmentandotherhydrophiliccoilsegments
have emerged as new unique materials due to their versatile
microphaseseparationbehaviorandpossibilitiesforfine-tuningof
the supramolecular architecture of the polymers [24–26] For
example,Craley etal [27] have reportedthesynthesis of poly
(3-hexylthiophene)-block-poly(acrylicacid)(P3HT-b-PAA),which
exhibitedsolvatochromicbehaviorinseveralsolventsofvarying
polarity.P3HT-b-PAAwasobtainedbyhydrolysisreactionofthe
P3HT-b-poly(tert-butylacrylate)precursor,whichwassynthesized
viaATRPoftert-butylacrylateusingabromoesterterminatedP3HT
macroinitiator An allyl-terminated P3HT was converted to a
hydroxypropyl terminated P3HT,which was subsequently
end-groupmodifiedtogivethebromoesterterminatedP3HT.However,
inthisprocedure,thehydroboration-oxidationoftheallylgroupto
formhydroxylgroupwithamaximumconversionefficiencybelow
80–85%couldresultinamixtureofbromoesterterminatedP3HT
chainsandthosehavingnofunctionalendgroupsthatleadtothe
formation of the mixture including a homopolymers and the
resulteddiblockcopolymersaftercontrolledradical
polymeriza-tionprocess.LohwasserandThelakkat[28]reportedthesynthesis
of poly(3-hexylthiophene)-block-poly(4-vinylpyridine)
(P3HT-b-P4VP) via preparing an alkoxyamine-terminated P3HT as a
macroinitiator for nitroxide-mediated radical polymerization
(NMRP) of 4VP P3HT-b-P4VP diblock copolymers with55 and
77wt%ofP4VPwereobtained,exhibitingmicrophaseseparation
andcolloidalstructuresinsolution.Mohamedetal.[29]reported
the synthesis of amphiphilic poly(3-hexylthiophene)-graft-poly
(ethylene oxide) (P3HT-g-PEO) rod–coil conjugated random
copolymersvianon-controlledoxidative polymerizationof 3HT
with FeCl3 and click chemistry These P3HT-g-PEO diblock
copolymersexhibitedmicellarmorphologiesinaqueoussolutions
with spherical particle diameters of approximately 60–75nm
Morerecently,Kumarietal.[30]hasreportedthesynthesisofpoly
(3-hexylthiophene)-block-poly(N-isopropylacrylamide)
(P3HT-b-PNIPAM)diblockcopolymersviatheazidealkyne“click”reaction
betweenanalkyne-terminatedP3HTandanazide
end-function-alizedPNIPAM.However,theuseofexcessP3HT-alkynetoreact
with PNIPAM-azide required purification of unreacted P3HT,
leadingtoarelativelylowyield(60%).Generallyinthesynthesis
of other P3HT-containing diblock copolymers via alkyne-azide
“click” reactionstrategy, greater than an equivalent amountof
eitherend-functionalized homopolymerswas normallyused to
ensurehighcouplingconversion,whichnecessitatesisolationof
excesshomopolymers[31].Ontheotherhand,inthemostcase,
especially in the synthesis of amphiphilic diblock copolymers
consisting of a permanently hydrophobic block and a strongly
hydrophilicblock,thedirectcopolymerizationmethodisdifficult
to carry out because of the solubility discrepancy between
amphiphiliccomponentsinacommonsolvent.Insuchcase,the
useofprotectinggroupchemistriesorapolymerpost-modi
fica-tionapproachisrequired
Forthatreason,inthiscontribution,wepresentthesynthesis
of a new type of diblock poly(3-hexylthiophene)-block-poly
(N,N-dimethylamino-2-ethyl
methacrylate-random-2-hydrox-yethylmethacrylate)(P3HT-b-P(DMAEMA-r-HEMA))copolymers
viathecombinationofGrignardmetathesis(GRIM)methodand
ATRPofN,N-dimethylamino-2-ethylmethacrylateand
2-hydrox-yethyl methacrylateco-monomers,that provides control of the
number average molecular weight and narrow polydispersity
indexofeach segment,resultinginwell-defineddiblock
copoly-mers.Moreover,thecoilblockofthesecopolymerscontainsboth
typesofpendantsidegroups,thehydroxylmoietiesofHEMAunits
andthedimethylaminogroupsofDMAEMAunits,whichcouldbe
easilyconvertedviaesterificationandquaternizationtogive P3HT-b-polyanion and P3HT-b-polycation copolymers, respectively (Fig.1).Thethermal andopticalpropertiesof thesecopolymers wereinvestigatedforinsightsintotheirmicrophaseseparationand crystallizationbehavior.Theseamphiphilicioniccopolymersare envisaged to be useful for forming a variety of self-assembly structures in solutions such as micelles and vesicles, or for preparingconductingpolymernanostructures[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%),sodiumborohydride(NaBH4,99%),phosphorus(V) oxychloride(POCl3,99%),copper(I)bromide(CuBr,98%),N,N,N0,N00,
N00-pentamethyldiethylenetriamine (PMDETA, 99%) were pur-chasedfromAldrich.Ni(dppp)Cl2andi-PrMgClintetrahydrofuran (THF)(2mol/L)werepurchasedfromAcrosandstoredinglovebox
at room temperature N,N-dimethylamino-2-ethyl methacrylate (99.8%)and2-hydroxyethylmethacrylate(99.8%)werepurchased from Acrosand weredistilled and stored in freezer Potassium acetate (KOAc, 99%), sodium carbonate (99%), and magnesium sulphate(98%)werepurchasedfromAcrosandusedasreceived 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%),ethylacetate(99%)and diethylether(99%)werepurchasedfromFisher/Acrosandusedas received
2.2.Characterization
1H NMR spectra were recorded in deuterated chloroform (CDCl3)withTMS asaninternal reference,ona BrukerAvance
500MHzspectrometer.FT-IRspectra,collectedastheaverageof
64scanswitharesolutionof4cm1,wererecordedfromKBrdisk
onaFT-IRBrukerTensor27.Elementalanalyseswererecordedona Carlo Elba Model 1106 analyzer MALDI TOF analysis was performedusingaVoyagerEliteapparatusinlinearmodeusing trans-2-[3-(4-tertbutylphenyl)-2-methylprop-2-enylidene]-malo-nitrile(DCTB)asmatrix.Nitrogenlaserdesorptionatawavelength equalto337nmwasapplied.Sizeexclusionchromatography(SEC) measurements were performed on a Polymer PL-GPC 50 gel permeationchromatographsystemequippedwithanRIdetector, withTHFas theeluent ata flow rate of 1.0mL/min.Molecular weightsandmolecularweightdistributionswerecalculatedwith referencetopolystyrenestandards.UV–visabsorptionspectraof polymersinsolutionandpolymerthinfilmswererecordedona ShimadzuUV-2450spectrometeroverawavelengthrangeof300–
700nm Differential scanning calorimetry (DSC) measurements were carried ona DSC Q20 V24.4 Build116 calorimeter under nitrogen flow, at a heating rate of 10C/min Contact angle measurementswereperformedonanOCA20contactanglesystem (Dataphysics,Germany).TheAFMimageswereobtainedusingan agilent spm5500atomic forcemicroscopy(AFM).Theobtained diblock copolymers were castedfrom chroloform solution (5% concentration) toformthin film thicknessof 15–20mmonthe glasssubstrateforfour-probeelectricalmeasurement
2.3.Synthesisof2-bromo-3-hexylthiophene
Toasolutionof3-hexylthiophene(5g,29.7mmol)inanhydrous THF(50mL)ina200mLflask,asolutionofN-bromosuccinimide (5.29g,29.7mmol)wasaddedslowlyat0Cundernitrogen.The
T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184 173
Trang 3mixturewas stirredat0Cfor 1h Afterthat,50mLofdistilled
waterwasadded tothereactionmixture,and themixturewas
extractedwithdiethylether.Theorganiclayerwaswashedwitha
solutionofNa2S2O3(10%),asolutionofKOH(10%),anddriedover
anhydrous MgSO4 The organic layer was distilled to give a
colorlessoil(6.7g,92%).1HNMR(500MHz,CDCl3),d(ppm):7.19
(d,J=5.6Hz,1H),6.82(d,J=5.6Hz,1H),2.59(t,J=7.3Hz,2H),1.59
(s,br, 2H),1.33 (m, none,6H), 0.91 (t, J=6.2Hz, 3H).13C NMR
(75.5MHz,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.Synthesisof2-bromo-3-hexyl-5-iodothiophene Iodine(1.42g,11.18mmol)andiodobenzenediacetate(1.965g, 6.1mmol)wereaddedtoasolutionof2-bromo-3-hexylthiophene (2.5g,11.1mmol)indichloromethane(25mL)at0C.Themixture
174 T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184
Trang 4(10%)wasadded,andthemixturewasextractedwithdiethylether
anddriedoveranhydrousMgSO4.Thesolventwasevaporatedto
obtain crude product, which was purified by silica column
chromatography (eluent: n-heptane) to give pure
2-bromo-3-hexyl-5-iodothiophene as a pale yellow oil (3g,86%).1H NMR
(500MHz,CDCl3),d(ppm):6.97(s,1H),2.52(t,J=7.54Hz,2H),1.56
(quint,2H),1.32(m,6H),0.89(t,J=6.4Hz,3H).13CNMR(75.5MHz,
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.Synthesisofregioregularhead-to-tailpoly(3-hexylthiophene)
withH/Brendgroups(polymer4)
Adry,500mLthree-neckflaskwasflushedwithnitrogenand
was charged with 2-bromo-3-hexyl-5-iodothiophene (24.37g,
65mmol) Afterthree azeotropic distillations by toluene,
anhy-drousTHF(220mL)wasaddedviaasyringe,andthemixturewas
stirredat 0C for 1h i-PrMgCl(2Msolution inTHF, 30.87mL,
61.75mmol) was added via a syringe and the mixture was
continuously stirred at 0C for 1h The reaction mixture was
allowedtocooldownto0C.Themixturewastransferredtoaflask
containingasuspensionofNi(dppp)Cl2 (800mg,1.475mmol)in
THF(25mL).Thepolymerizationwascarriedoutfor24hat0C,
followedbyadditionof5MHCl.Aftertermination,thereaction
wasstirredfor15minandextractedwithCHCl3.Thepolymerwas
precipitated in cold methanol and washed several times with
n-hexane.The polymerwascharacterized by1H NMR andGPC
GPC:Mn=7100g/mol,Ð=1.18.Yield:70%
FT-IR (cm1): 721, 819,1376, 1454,1510, 2853, 2922, 2953
1
HNMR(500MHz,CDCl3),d(ppm):6.96(s,1H),2.90(t,J=7.5Hz,
2H),1.79(sex,2H),1.52(q,6H),0.94(t,J=6.4Hz,3H).Maldi-ToF
(m/z):1410,1576,1742,1908,2074,2240,2406,2572,2738,2904,
3070,3236.GPC:Mn=7000g/mol.Polydispersityindex(Ð)=1.18
UV–vis(CHCl3):lmax=450nm
2.6.Synthesisofregioregularhead-to-tailpoly(3-hexylthiophene) withCHO/Brendgroups(polymer5)
Polymer4(1g)wasdissolvedin260mLofanhydroustoluene under nitrogen DMF (5.12mL, 66.3mmol) and phosphorus(V) oxychloride (POCl3)(5.30mL,58mmol)werethenadded tothe solution.Thereactionwasperformedat75Cfor24h.Thesolution wascooleddowntoroomtemperature,followedbytheadditionof
asaturatedaqueoussolutionofsodiumacetate.Thesolutionwas stirredfor4h.Then,thepolymerwasextractedwithCHCl3.The polymerwasprecipitatedincoldmethanolandwashedwithcold n-hexane After drying under vacuum, 96mg of polymer was obtained Theyieldwas93%.FT-IR(cm1):721,819,1376,1453,
1509,1649,2854,2923,2953.1HNMR(500MHz,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.Synthesisofregioregularhead-to-tailpoly(3-hexylthiophene) withCH2OH/Brendgroup(polymer6)
Polymer5(500mg)wasdissolvedin30mLofanhydrousTHF undernitrogen.NaBH4(41.8mg)wasthenadded.Themixturewas keptstirringatroomtemperaturefor2h.Then,thesolventwas evaporatedundervacuum.Thepolymerwasprecipitatedincold methanol.Afterdryingundervacuum,480mgofthepolymerwas obtained Theyieldwas96%.FT-IR(cm1):724,817,1376,1453,
1509,1561,2853,2922,2953.1HNMR(500MHz,CDCl3),d(ppm):
T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184 175
Trang 5(t,3H).Maldi-ToF(m/z):1440,1606,1772,1938,2104,2270,2436,
2602,2768,2934,3100
2.8.Synthesisofbromoester-terminatedpoly(3-hexylthiophene)
(P3HT-macroinitiator)
Polymer6(500mg)wasdissolvedin20mLofanhydrousTHF
undernitrogen.Tothis solution,triethylamine(1mmol) and
2-bromoisobutyryl bromide (0.83mmol) were added Then the
reactionwas carried out at 50C overnight The polymer was
extracted by CHCl3 The solution was washed two times with
distilledwater.The polymerwasprecipitated incoldmethanol
Afterdryingundervacuum,475mgofthepolymerwasobtained
Theyieldwas95%.FT-IR(cm1):724,818,1376,1451,1509,1561,
1735,2853,2922,2953.1HNMR(500MHz,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=7200g/mol, Ð=1.28.Mn
estimatedby1HNMR=7000g/mol
2.9.Synthesisof
poly(3-hexylthiophene)-block-poly(N,N-dimethylamino-2-ethylmethacrylate-random-2-hydroxyethyl
methacrylate)(P3HT-b-P(DMAEMA-r-HEMA))
P3HT-b-P(DMAEMA-r-HEMA) wassynthesizedbyATRPusing
the P3HT-macroinitiator 0.1g of P3HT-macroinitiator (MnNMR=
7000)wasplacedina25mLflask,towhich2mLofdegassedTHF
was added by syringe The P3HT-macroinitiator solution was
stirreduntilitbecamehomogeneous.Asolutioncontaining
N,N-dimethylamino-2-ethyl methacrylate (DMAEMA) (0.28mmol,
44.0mg), 2-hydroxyethyl methacrylate (HEMA) (0.168mmol,
21.9mg), PMDETA (0.028mmol, 4.9mg) and CuBr (2.0mg,
0.014mmol)waspreparedseparately,andwasdegassedbythree
freeze-pump-thawcycles.Themonomersolutionwasstirreduntil
itbecamehomogeneous,andthenplacedina60Coilbath.When the macroinitiator solution was added by cannula into the monomer solution, themixture solutionbecame homogeneous withadarkorangecolor.Afterthesolutionwasallowedtoreactfor
16hat 60C, the resultant polymer solutionwas diluted with
20mLofTHF.Thesolutionwasthenpassedthroughacolumnof
Al2O3toremovecopper.Thepolymersolutionwasconcentrated and thenprecipitated inton-heptane.Theprecipitated polymer wascollectedbyvacuumfiltrationandsubsequentlywashedwith n-heptane,followedbydryingundervacuumtogive165mgofthe desiredproductcorrespondingtoaconversionof83%
Fig 2 FT-IR spectra of P3HT-macroinitiator and P3HT-b-P(DMAEMA-r-HEMA).
1
176 T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184
Trang 62953,3550.1HNMR(500MHz,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=12500g/mol
Ð=1.42
2.10.SulfonationofP3HT-b-P(DMAEMA-r-HEMA)
Sulfonation reactions were carried out in THF at room
temperature For a typical reaction, 60mg of P3HT-b-P
(DMAEMA-r-HEMA) was dissolved in 20mLof THFand purged
byN2.Oncethediblockcopolymerwasdissolvedinthesolvent,
triethylamine(2equivalentstoHEMA)wasadded.Thesolutionof
2-sulfobenzoic acid cyclic anhydride (SBA) (2 equivalents to
HEMA)in about 10mL of THFwas then slowlyadded into the
reaction.Thesolutionturnedturbidimmediately,andthereaction
was stopped after 24h The resulting reaction mixture was
precipitated in n-heptane to obtain the sulfonated P3HT-b-P
(DMAEMA-r-HEMA)diblockcopolymer.Theyieldwas95%
FT-IR(cm1):724,818,10901376,1451,1509,1561,1735,2853,
2922,2953.1HNMR(500MHz,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.QuaternizationofP3HT-b-P(DMAEMA-r-HEMA)
QuaternizationreactionswerecarriedoutinTHFat60C for
18h.Foratypicalreaction,100gofP3HT-b-P(DMAEMA-r-HEMA) wasdissolvedin20mLofTHFandpurgedbyN2.Tothissolution
CH3I(1.19mg)wasadded Thesolutionturnedturbidgradually, and the reactionwas stopped after24h The obtainedcationic diblockcopolymerwasisolatedbyconcentrationofthereaction solution under reduced pressure and precipitation in cold n-heptane The obtained cationic diblock copolymer was dried
toconstantweightundervacuum.Thedegreeofquaternizationof P3HT-b-P(DMAEMA-r-HEMA)wasestimatedby1HNMR spectros-copy
FT-IR(cm1):724,818,10901376,1451,1509,1561,1735,2853,
2922,2953.1HNMR(500MHz,CDCl3);d(ppm):6.97(s,1H),4.08
Fig 4 GPC traces of P3HT-macroinitiator (dash line) and P3HT-b-P(DMAEMA-r-HEMA) (solid line).
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 Temperature (C) Conversion a
(%) DMAEMA HEMA P3HT-b- P(DMAEMA-r-HEMA)
M ntheb M nexpc M ntheb M nexpc f d
M nMMR Ð e
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
DMAEMA and HEMA theoretical number-average-molar mass as calculated by [DMAEMA] or [HEMA] 0 /[P3HT-Br] 0 Conv(%) M wDMAEMA(orHEMA) assuming a living process.
c DMAEMA (or HEMA) experimental number-average molar mass as determined by 1 H NMR spectroscopy (see Fig 3 ): M nexp = DP exp M wMMA(orMSp) where DP exp is the experimental degree of polymerization, as calculated from the relative intensities ofa-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 M ntheofP(DMAEMA-r-HEMA) /M nexpofP(DMAEMA-r-HEMA)
T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184 177
Trang 7(s,6H),1.98(m,6H),1.69(sex,2H),1.48(q,6H),0.89(t,3H)
3.Resultsanddiscussion
The well-defined poly(3-hexylthiophene)-block-poly
(N,N-dimethylamino-2-ethyl
methacrylate-random-2-hydrox-yethyl methacrylate) (P3HT-b-P(DMAEMA-r-HEMA)) diblock
copolymerswerepreparedvia thecombinationof ‘quasi-living’
GRIM polymerization of the P3HT block and subsequent atom
transferradicalpolymerization(ATRP)ofDMAEMAandHEMA
co-monomersaccordingtoScheme1
Inthefirststate,theP3HT-macroinitiatorwassynthesizedvia
6steps,includingacontrolled‘quasi-living’GRIMpolymerizationof
the 2-bromo-3-hexyl-5-iodothiophene monomer The obtained
P3HTwithH/BrendgroupshadaGPCrecordednumberaverage
molecularweight(Mn)valueof7100g/mol,whichisclosetothe
theoreticalone,andmoderatepolydispersityindexof1.18.Then,a quantitativeconversionofBr-P3HT-Hintoa-bromo-v -bromoiso-butyrate poly(3-hexylthiophene) (7) was achieved by a 3-step procedure.Basedontheintegralratiobetweenthemethine(ring) protonsofP3HTat6.96ppmandmethylprotonsofthev -bromoi-sobutyrateendgroupat1.95ppm,anMnvalueof7000g/molwas estimated.Finally,thebromoesterterminatedP3HTwasusedasthe macroinitiator fortheATRP ofDMAEMAandHEMA co-monomers,in presenceofCuBrandPMDETAascatalyticsystem.Thefeedratioof DMAEMA/HEMA co-monomers of about 1.7 was established for obtainingagoodcontrolovertheATRP ([DMAEMA]/[HEMA]/[P3HT-Macroinitiator]/[CuBr]/[PDMAEMA]=20/12/1/1/2) The unreacted monomerswereeliminatedandtheresulting P3HT-b-P(DMAEMA-r-HEMA)diblockcopolymerswerecollectedviaprecipitationin coldn-heptane
Fig.2 comparesthe FT-IR spectra of the obtainedP3HT-b-P (DMAEMA-r-HEMA) and the P3HT macroinitiator A strong
Fig 5 1
H NMR spectrum of sulfonated P3HT-b-P(DMAEMA-r-HEMA).
1
178 T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184
Trang 8absorptionsignal at1725cm1 appearsin the spectrum of the
diblockcopolymerandisattributedthestretchingvibrationofthe
carbonylgroupsoftheP(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
dimethyla-mino group (peak p) of DMAEMA moieties and methylene
hydroxyl group of HEMA moieties (peak k) with the methine
(ring) protons of P3HT at d=6.96ppm As a result, the NMR
recorded molecular weight of the P(DMAEMA-r-HEMA) block wasaround4000g/mol,andthemolarfractionofHEMAinthis blockwasabout0.45.Accordingly,thenumbersofDMAEMAand 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 copolymerandP3HT-macroinitiatorareshowninFig.4,revealing singlepeaksandrelativelynarrowmolecularweightdistributions, indicatingwell-controlledchaingrowthduringtheATRPprocess
Fig 7 UV–vis spectra of sulfonated P3HT-b-P(DMAEMA-r-HEMA) in different solvents and in a solid state film.
T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184 179
Trang 9around12500g/moland1.42,respectively
Themolecularweightcharacteristicsof
P3HT-b-P(DMAEMA-r-HEMA)aresummarizedinTable1.Similarresultsofcomparable
experimentswiththesameconditionsareshown,indicatingthe
repeatabilityoftheexperimentalmethod.AsseeninTable1,theP
(DMAEMA-r-HEMA) block was obtainedwith a relativelygood
approximation between theoretical and experimental molar
masses,attestingforaninitiationefficiencycloseto1
The coilblockofP3HT-b-P(DMAEMA-r-HEMA)was
sulfonat-ed via esterification reaction between the hydroxyl group of
HEMA units and 2-sulfobenzoic acid cyclic anhydride (SBA),
followingthemethodpreviouslydescribed[35].Inthisreaction,
triethylaminewas usedasthecatalystanda2–1 molarratioof
SBA to OH groups was employed to ensure complete sulfonation It was noted that upon the addition of SBA, the reactionsolutionturnedturbidimmediately,indicatingachange
in the solubility of the diblock copolymer as a result of the formation of anionic moieties The 1H NMR spectrum of the sulfonatedP3HT-b-P(DMAEMA-r-HEMA)showedtheappearance
of aromatic protonpeaks (peaksq) at 7.4–8.1ppm assigned to the phenyl group of sulfobenzoic moieties, suggesting that 2-sulfobenzoicacidcyclicanhydridewascovalentlylinkedtothe
OHgroups(Fig.5).Theresultingrelativeintensityofthephenyl peak regions(peaksq),withrespecttoeitherthesignalof the methylenegroupinthesidechainofHEMAunits(peakk)orthe signalofthiophenemoieties(peakaorb),indicatedthatallthe hydroxyl side groups weresulfonated
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)
Ethyl acetate 520, 550, 610 505, 559, 610 Insoluble Water (pH < 7 and pH > 10) 513, 555, 605 520, 555, 610 Insoluble Solid-state film 515, 550, 600 520, 550, 607 527, 558, 610
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)
180 T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184
Trang 10On the other hand, the dimethylamino pedant groups of
P3HT-b-P(DMAEMA-r-HEMA) were quaternized using
iodome-thane(CH3I),withanequimolarratioofdimethylaminogroupsto
CH3I.AchangeinthesolubilityofthediblockcopolymerinTHF
was realized as thesolution became turbid after2h, with the
turbidityincreasinggradually,indicatingtheformationof
quater-nized 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 3.60ppm By integration of corresponding 1H NMR signals, a degree of quaternizationwasestimatedtobeapproximately80%
Theopticalbehaviorofsulfonated andquaternizedP3HT-b-P (DMAEMA-r-HEMA) diblock copolymersin solventsof different
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).
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
T.A Nguyen et al / Synthetic Metals 217 (2016) 172–184 181