The chemical and electrochemical oxidative polymerization of 2-amino-4-tert-butylphenol

Documen downloaded om: This pape mus be ci ed as: The inal publica ion is a ailable a Copy igh Addi ional In o ma ion h p://hdl.handle.ne /10251/77530 Abidi, M.; López-Be nabeu, S.; Hue a, F.; Mon illa-Jiménez, F.; Besbes-Hen a i, S.; Mo allón, E. (2016). The chemical and elec ochemical oxida i e polyme iza ion o 2-amino- 4- e -bu ylphenol. Elec ochimica Ac a. 212:958-965. doi:10.1016/j.elec ac a.2016.07.060 h p://dx.doi.o g/10.1016/j.elec ac a.2016.07.060 Else ie Accep ed Manusc ip Ti le: The chemical and elec ochemical oxida i e polyme iza ion o 2-amino-4- e -bu ylphenol Au ho : M. Abidi S. L´ opez-Be nabeu F. Hue a F. Mon illa S. Besbes-Hen a i E. Mo all´ on PII: S0013-4686(16)31565-1 DOI: h p://dx.doi.o g/doi:10.1016/j.elec ac a.2016.07.060 Re e ence: EA 27675 To appea in: Elec ochimica Ac a Recei ed da e: 20-2-2016 Re ised da e: 26-4-2016 Accep ed da e: 11-7-2016 Please ci e his a icle as: M.Abidi, S.L´ opez-Be nabeu, F.Hue a, F.Mon illa, S.Besbes-Hen a i, E.Mo all´ on, The chemical and elec ochemical oxida i e polyme iza ion o 2-amino-4- e -bu ylphenol, Elec ochimica Ac a h p://dx.doi.o g/10.1016/j.elec ac a.2016.07.060 This is a PDF ile o an unedi ed manusc ip ha has been accep ed o publica ion. As a se ice o ou cus ome s we a e p o iding his ea ly e sion o he manusc ip . The manusc ip will unde go copyedi ing, ypese ing, and e iew o he esul ing p oo be o e i is published in i s inal o m. Please no e ha du ing he p oduc ion p ocess e o s may be disco e ed which could a ec he con en , and all legal disclaime s ha apply o he jou nal pe ain. The chemical and elec ochemical oxida i e polyme iza ion o 2-amino-4- e -bu ylphenol M. Abidi1,2, S. López-Be nabeu2, F. Hue a3, F. Mon illa2, S. Besbes-Hen a i1, E. Mo allón2 1Labo a oi e de Chimie des Ma é iaux, Facul é des Sciences de Bize e. 7021, Za zouna Uni e si é de Ca hage, Tunisie. 2Dep . Química Física e Ins i u o Uni e si a io de Ma e iales, Uni e sidad de Alican e, Ap. 99, E-03080, Alican e, Spain 3Dep . Ingenie ia Tex il y Papele a, Uni e si a Poli ecnica de Valencia, Plaza Fe andiz y Ca bonell, 1. E-03801, Alcoy, Spain Abs ac Poly(2-amino-4- e -bu ylphenol), poly(2A-4TBP), was syn hesized om monome aqueous solu ion using ei he elec ochemical o chemical oxida ion p ocedu es. Se e al spec oscopic cha ac e iza ion echniques we e employed o gain in o ma ion on he chemical s uc u e and edox beha io o he ob ained ma e ials. I was ound ha he chemical polyme iza ion p oduc could be desc ibed as an oligome mix u e con aining up o 16 monome uni s. In pa allel o o he polyme s de i ed om o-aminophenol, phenoxazine ings cons i u e also he basic s uc u e o poly(2A-4TBP). In addi ion, he occu ence o N-N couplings, which a e a o ed by he p esence o he oluminous e -bu yl subs i uen , seems also ele an . No signi ican s uc u al di e ences we e ound be ween he chemically o elec ochemically syn hesized ma e ials. Keywo ds: elec ochemical polyme iza ion; in si u FTIR; polyaminophenol 2 1. In oduc ion Aminophenols cons i u e an in e es ing class o compounds o elec opolyme iza ion owing o he p esence o eac i e amino and hyd oxyl uni s. I has been epo ed ha he ela i e posi ion o hese uni s a he a oma ic ing plays a signi ican ole in he elec ochemical eac i i y o he molecule and, consequen ly, he elec ochemical beha io o he h ee posi ional aminophenol isome s, o ho-, me a- and pa a-, is qui e di e en [1–3] . Despi e some ea ly con o e sy on he o ma ion, o no , o polyme ic ilms om he elec ochemical oxida ion o p-aminophenol, i seems now p o ed ha in aqueous media he monome can be elec opolyme ized o yield complex oligome ic p oduc s whose chemical s uc u e is s ongly dependen on he pH o he wo king solu ion [4]. The elec o-oxida ion o m-aminophenol has been sca cely in es iga ed because i yields an elec oinac i e polyme ha blocks he elec ode su ace and shows a c osslinked s uc u e simila o polyphenol [3,5]. On he con a y, i is well documen ed ha o-aminophenol can be elec ochemically polyme ized in acidic medium o yield an elec oac i e polyme ic ma e ial ha shows phenoxazine ladde s uc u es [3,6]. I was also sugges ed ha he p oduc s o med upon o- aminophenol elec ochemical oxida ion depend on he pH o he polyme iza ion solu ion [7] al hough i is wo h no ing ha simila s uc u e and p ope ies can be ob ained ega dless o he polyme iza ion me hod employed, ei he chemical o elec ochemical [1]. Compa isons ha e been also made in he li e a u e be ween chemical and elec ochemical polyme iza ion p oduc s ob ained om o he a oma ic anilines, wi h special a en ion paid o diamines [8]. I is usually ound ha he chemical polyme iza ion me hods esul in highe polyme yields al hough oligome ic by-p oduc s a e di icul o emo e om he eac ion mix u e. On he o he hand, elec ochemical polyme iza ion o e s he ad an age ha he ine con ol o he anodic po en ial a oids polyme o e oxida ion and, consequen ly, ma e ials wi h less de ec s can be isola ed on he elec ode su ace. The o ma ion o non- conduc ing ilms upon elec ochemical oxida ion could p e en polyme g ow h and such a possibili y should be aken in o accoun mos ly, al hough no exclusi ely, in expe imen s conduc ed in neu al and alkaline media. Chemical and elec ochemical polyme iza ion o alkyl ing-subs i u ed anilines has a ac ed in e es because o he possibili y o imp o e he poo solubili y o unmodi ied polyaniline and, besides, o in es iga e he e ec o blocking speci ic ing polyme iza ion 3 si es wi h elec on-dono subs i uen s [9–11]. Howe e , o he bes o ou knowledge, he e is s ill no epo dealing wi h he chemical o elec ochemical polyme iza ion o alkyl ing- subs i u ed aminophenols. In he p esen wo k, an a emp has been made o syn hesize a polyme om bo h ou es and o analyze he e ec o he p esence o a oluminous alkyl g oup on he well-s udied polyme iza ion p ocess o aminophenols. I is known ha he p esence o bulky g oups a ached o he a oma ic ing may a oid ππ-s acking be ween icinal chains o he esul ing polyme and his could lead o an imp o emen in solubili y and p ocessabili y o he esul ing ma e ial. To achie e hese goals, 2-amino-4- e -bu ylphenol (2A-4TBP) has been selec ed as he monome species and di e en spec oscopic echniques ha e been applied o he cha ac e iza ion o he oxida i e polyme iza ion p oduc s. 2. Expe imen al The solu ions employed o polyme iza ion we e 1.0 M HClO4, p epa ed om Me ck Sup apu concen a ed acid and 18.2 M cm wa e ob ained om an Elga Labwa e Pu elab sys em. 2-amino-4- e -bu ylphenol monome was pu chased om Me ck. Ammonium pe sul a e, om Me ck, was used as he oxidan o chemical polyme iza ion. Cyclic ol amme y expe imen s we e ca ied ou in a con en ional h ee-elec ode cell unde N2 a mosphe e. The wo king elec odes used we e ei he pla inum o ITO and a pla inum wi e was used as he coun e elec ode in all cases. All po en ials we e measu ed agains he e e sible hyd ogen elec ode (RHE) imme sed in he wo king solu ion h ough a Luggin capilla y. Cyclic ol ammog ams we e eco ded a a cons an sweep a e o 50 mV s-1 and a oom empe a u e. The polyc ys alline pla inum elec odes we e he mally cleaned and subsequen ly p o ec ed om he labo a o y a mosphe e by a d ople o ul apu e wa e . ITO elec odes we e cleaned wi h ace one and ul apu e wa e . Chemically p oduced polyme s we e deposi ed on he wo king elec odes by cas ing a small olume o suspension con aining 1 mg mL-1 ma e ial in THF sol en . In si u UV–Vis spec a o polyme s we e eco ded wi h a V-670 spec ome e om JASCO, which is equipped wi h a double monoch oma o sys em and a pho omul iplie ube de ec o . A Nicole 5700 spec ome e equipped wi h a ni ogen-cooled MCT de ec o was employed o he in si u FTIR expe imen s. The wo king P disc elec ode was moun ed on a 4 glass ube and i s 1.0 cm2 su ace was mi o -polished using alumina powde . The spec oelec ochemical cell was made o glass and was p o ided wi h a p isma ic CaF2 window be eled a 60°. Spec a we e collec ed a 8 cm-1 esolu ion in D2O sol en ( om Ald ich wi h 99.9% D-a om pu i y) and a e p esen ed as R/R. XPS spec a we e eco ded wi h a VG-Mic o ech Mul ilab 3000 elec on spec ome e using a non-monoch oma ized Mg-Ka (1253.6 eV) adia ion sou ce o 300 W and a hemisphe ic elec on analyze equipped wi h nine channel on elec on mul iplie s. The p essu e o he analysis chambe du ing he scans was abou 5×10-7 N m-2. A e he su ey spec a we e ob ained, highe esolu ion scans we e pe o med a pass ene gy o 50 eV. The in ensi ies o he di e en con ibu ions we e ob ained by means o he calcula ion o he in eg al one o each peak, a e ha ing elimina ed he baseline wi h S o m and adjus ing he expe imen al cu es o a combina ion o Lo en z (30%) and Gaussian (70%) lines. All he binding ene gies we e e e ed o he line o he C 1s o 284.4 eV, ob aining alues wi h a p ecision o ±0.2 eV. The high- esolu ion mass expe imen s we e pe o med in a MICROMASS Au ospec spec ome e . 3. Resul s and discussion 3.1. Elec ochemically polyme ized 2A-4TBP Fig. 1 illus a es he cyclic ol amme y cu es eco ded o a polyc ys alline pla inum elec ode imme sed in 0.1 M HClO4 + 15 mM 2A-4TBP solu ion. The oxida ion o he monome ic species s a s a 0.76 V and, as deduced om he high slope o he ol amme ic cu e, is kine ically a o ed du ing he i s ol amme ic sweep. The oxida ion peak is cen e ed a 0.87 V and, h ough he i s e e se scan, wo ca hodic peaks a e eco ded a 0.8 V and 0.7 V. The o me is clea ly associa ed wi h he e e sible educ ion o oxidized species gene a ed du ing he o wa d sweep, whe eas he 0.7 V b oad wa e seems ela ed wi h he 5 educ ion o he oligome p oduc s o med a highe po en ials. Such p oduc s canno be e- oxidized du ing successi e o wa d sweeps, as mani es ed by he absence o anodic wa es di e en om ha o monome oxida ion. The peak cu en o he main oxida ion ea u e dec eases upon cycling and i s ini ially as kine ics decays g adually. The e o e, i is clea ly deduced om he ol amme ic p o ile ha he anodic oxida ion o aminophenol monome yields elec ochemically inac i e oligome ic p oduc s ha block he elec ode hinde ing u he oxida ion. Cyclic ol ammog am in Fig. 1b e eals ha he blocking species a e s ongly adso bed on pla inum. This cu e was eco ded in a backg ound elec oly e solu ion a e 300 polyme iza ion cycles, when he su ace appea ed co e ed wi h a pu ple ilm. The elec ode was emo ed om he polyme iza ion solu ion, washed wi h ul apu e wa e and ans e ed o he 0.1M HClO4 es solu ion wi h no monome added. The ol amme ic cu e shows he cha ac e is ic p o ile o a pla inum elec ode co e ed wi h a hin, almos elec oinac i e oligome ic ilm. The ea u eless oxida ion p ocess unde gone by poly(2A-4TBP) in Fig. 1b was moni o ed by in si u UV- is spec oscopy in o de o disce n whe he o no pola onic species a e o med upon anodic pola iza ion o his ma e ial. The polyme was deposi ed on an ITO coa ed glass elec ode in a pa allel expe imen o ha shown in Fig. 1a and hen ans e ed o he spec oelec ochemical cell, whe e i was imme sed a 0.05 V. In si u UV–Vis spec a we e hen eco ded a inc easing po en ials and hose ob ained in he ange om 0.05 o 0.65 V ha e been depic ed in Fig.2. The i s UV–Vis spec um collec ed a 0.05 V shows one main abso p ion ea u e a 558 nm. The in ensi y o his peak emains almos cons an a po en ials below 0.45 V bu ises sha ply abo e ha alue. Such a beha io sugges s a edox ans o ma ion o he oligome ic ma e ial, wi h he abso p ion p obably associa ed wi h a benzenoid- o-quinoid ansi ion ela ed o pola onic moie ies o med upon elec ochemical doping [12]. Such a band is sligh ly blue-shi ed wi h espec o polyaniline and close o he pola onic ansi ions obse ed o o he ing-subs i u ed polyanilines, indica ing he p esence o pola onic domains wi h sho conjuga ed segmen s. Howe e , he o ma ion o quinone-like moie ies upon oligome oxida ion could also con ibu e signi ican ly o his band [13]. The occu ence o a 6 edox pola onic ans o ma ion in poly(2A-4TPB) is also suppo ed by o he spec al ea u es in Fig 2. Speci ically, he spec um acqui ed a 0.65V shows he appea ance o h ee addi ional bands cen e ed a 397, 416 and 447 nm. The o me one can be assigned o a pola on-π* ansi ion, whe e pola ons a e isola ed one om ano he e lec ing low elec ical conduc i i y o he oligome ic ma e ial [14]. Rega ding he o he wo ea u es i is wo h men ioning ha , acco ding o li e a u e da a on polyaminophenols, elec onic abso p ions in he 410-450 nm ange can be a ibu ed o he p og essi e o ma ion o adical ca ions in phenoxazine ings o , al e na i ely, o he occu ence o N-N coupling o o m azobenzene de i a i es [15–18]. In he p esen case, bo h s uc u es a e p obably p omo ed by he p esence o he oluminous e bu yl g oup in me a posi ion ela i e o he ni ogen a om, which ends o hinde he C-N pa a-coupling and hyd azine- ype dime s could be o med due o such s e ic hind ance [19]. Finally, he band a 742 nm, whose in ensi y emains almos cons an a inc easing po en ials, is o unce ain na u e bu i has been assigned ei he o he bipola onic ansi ion in pa a-coupled polyaniline de i a i es o o he pola on ansi ion in poly(o-aminophenols) [15,16]. Acco ding o hese esul s, poly(2A-4TBP) seems an oligome ic p oduc o igina ed om a a ie y o C-N, C-O and N-N monome couplings. In si u FTIR spec oscopy has been used o con i m he exis ence o a edox ansi ion in he elec ochemically deposi ed poly(2A-4TBP). The ilmed P elec ode was ans e ed o he IR spec oelec ochemical cell, which con ained a ee o monome es solu ion p epa ed wi h D2O o acili a e assignmen s in he 1500-1700 cm-1 spec al ange. A e some po en ial cycles, he P su ace was ca e ully p essed agains he p isma ic CaF2 window, a e e ence spec um was hen collec ed a 0.1 V and, inally, he po en ial was s epped o highe alues o collec sample spec a. By e e ing each sample o he unique e e ence, we can ob ain in o ma ion on he edox ans o ma ions unde gone by he oligome ic ma e ial as a unc ion o he applied po en ial. The compu ed in si u FTIR spec a a e displayed in Fig. 3 wi hin he equency ange 1100-2200 cm-1. The e, he p esence o se e al nega i e (downwa d) and posi i e (upwa d) bands e eals he ac i a ion o ib a ional modes a inc easing po en ials, which is a cha ac e is ic beha io o e e sible oxida ion p ocesses. In ac , since no spec al ea u es appea in he spec a ob ained a 0.3 V and 0.4 V, i can be in e ed ha poly(2A-4TBP) canno be oxidized a so mode a e po en ials. This obse a ion is consis en wi h he esul s ob ained om he in si u UV- is expe imen s in Fig. 2. On he con a y, se e al IR abso p ion bands appea in he spec a collec ed om 0.5 V. 7 The onse o oligome oxida ion a a ound his po en ial is es i ied by he occu ence o a clea nega i e band a 1613 cm-1, a g oup o less in ense nega i e abso p ions in he 1330- 1400 cm-1 equency ange and, inally, wo posi i e bands peaking a 1518 and 1445 cm-1. I can be obse ed ha he in eg a ed in ensi y o all hese ea u es, and he e o e he oligome oxida ion le el, inc eases a inc easing po en ials and, besides, new abso p ions showing ei he nega i e o posi i e cha ac e a e de eloping. Assignmen s p oposed o he main bands a e summa ized in Table 1. Be ween he wo main bands clea ly ela ed wi h he educed o m o poly(2A-4TBP), he ea u e appea ing a 1518 cm-1 can be unambiguously assigned o he p og essi e anishing o he a oma ic C-C s e ching due o oligome oxida ion, whe eas he peak a 1312 cm-1 is ela ed wi h he pa allel ans o ma ion o seconda y a oma ic amines. The high in ensi y eached by he o me ea u e is p obably due o he p esence o he elec on-dono alkyl g oup in he a oma ic ing [20]. The band a 1445 cm-1 has been some imes a ibu ed o he skele al C-C s e ching ib a ion o he a oma ic ing, al hough he in e p e a ion o his band is no unanimous. Apa om he C-C s e ching, i has been also asc ibed ei he o he exis ence o N-N coupling o o he o ma ion o phenazine s uc u es in polyaniline de i a i es [21,22]. In ou case, owing o he p esence o adjacen alcohol and amino g oups, i is e y likely he o ma ion o phenoxazine ings and/o N-N coupling. This hypo hesis seems suppo ed by he in si u UV- is esul s p esen ed in Fig. 2. Wi h ega d o he oxidized s a e, i is wo h no ing ha he abso p ion bands appea ing, oughly, below 1600 cm-1 suppo he exis ence o a e e sible edox ans o ma ion o poly(2A-4TBP). On he con a y, mos ea u es appea ing abo e ha equency s ongly sugges an i e e sible deg ada ion p ocess o he oligome ic ma e ial a high po en ials. Indeed, he e e sible o ma ion o quinoid ings and in e media e-o de C≈N bonds, which is common o mos polyaniline de i a i es, is con i med espec i ely by he 1578 cm-1 ea u e and he g oup o o e lapped bands in he su oundings o 1350 cm-1. Quinone imine cen e s a e esponsible o he ea u e a 1617 cm-1, while he couple o nega i e-going bands a 1750 cm-1 and 1292 cm-1 suppo s he o ma ion o ca boxylic acid e mina ions and con i ms he occu ence o an o e oxida ion p ocess a po en ials beyond 0.9V. Fu he mo e, he nega i e band peaking a 1650 cm-1 e eals he o ma ion o deg aded quinone s uc u es a 0.9V [3]. 14 o poly(o-aminophenol). In addi ion o he e e sible edox ansi ion, he o ma ion o o e oxidized s uc u es con aining quinone-like s uc u es has been also de ec ed by FTIR, while UV- is sugges s ha hese s uc u es a e mo e abundan in he elec ochemically ob ained ma e ial han in he chemical p oduc . The conduc i i y o poly(2A-4TBP) is lowe han ha o poly(o-aminophenol) and h ee o de s o magni ude in e io o poly(o- oluidine). Acco ding o his esul , he key ac o go e ning he poo poly(2A-4TBP) conduc i i y seems he o ma ion o azo g oups (which can b eak he ex ended conjuga ion) and, p obably, no he e en ual o sion angle be ween adjacen ings ha elie es he s e ic s ains p omo ed by he e -bu yl g oup. UV- is ansien species ela ed wi h he polyme main oxida ion peak seem absen in poly(2A- 4TBP), ye hey play a signi ican ole in he elec ical conduc i i y o he pa en poly(o- aminophenol) polyme . Acknowledgmen s Financial suppo om he Spanish Minis e io de Economía y Compe i i idad and FEDER unds (MAT2013-42007-P) and om he Gene ali a Valenciana (PROMETEO2013/038) is g a e ully acknowledged. M. Abidi hanks he Minis y o Highe Educa ion and Scien i ic Resea ch o Tunisia o unding he s ay a he Uni e si y o Alican e. Re e ences [1] C. Ba be o, J.J. Silbe , L. 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Tes solu ion: 0.1M HClO4. = 50 mV s-1 18 400 480 560 640 720 800 880 0.00 0.04 0.08 0.12 0.16 Abso bance Wa eleng h / nm 397 416 558 742 447 Fig. 2. In si u UV– is spec a eco ded o a poly (2A-4TBP) ilm a di e en applied elec ode po en ials ( om bo om o op: 0.05V, 0.25V, 0.45V, 0.55V, 0.65V). The poly(2A- 4TBP) ilm was p epa ed on ITO coa ed glass om a solu ion con aining 15mM monome in aqueous 0.1 M HClO4. 19 Fig. 3. Se o in si u FTIR spec a collec ed du ing he oxida ion o an elec ochemically ob ained poly(2A-4TBP) ilm in 0.1M HClO4/D2O es solu ion. Re e ence po en ial 0.1 V. Sample po en ial labelled o each spec um. 100 in e e og ams a each po en ial. 20 282 285 288 291 0.0 2.0x104 4.0x104 6.0x104 In ensi y /a.u. Binding ene gy / eV C 1s 396 399 402 405 408 0.0 2.0x103 4.0x103 In ensi y /a.u. Binding ene gy / eV N 1s 528 531 534 537 540 0.0 5.0x103 1.0x104 1.5x104 2.0x104 In ensi y /a.u. Binding ene gy / eV O 1s Fig.4. High esolu ion XPS signals o C 1s, N 1s and O 1s ob ained om a poly(2A-4TBP) ilm elec odeposi ed on a pla inum subs a e. 21 0.0 0.2 0.4 0.6 0.8 -100 -50 0 50 I / A E / V s RHE Fig.5. Cyclic ol ammog am eco ded in 0.1M HClO4 elec oly e o poly(2A-4TBP) syn hesized chemically and cas ed on a polyc ys alline pla inum elec ode. = 50 mV s-1. 400 480 560 640 720 800 0.00 0.04 0.08 0.12 0.16 Abso bance Wa eleng h / nm 385 445 562 739 Fig. 6. In si u UV- is spec a eco ded a di e en elec ode po en ials ( om bo om o op: 0.05V, 0.25V, 0.45V, 0.55V, 0.65V) o a chemically syn hesized poly (2A-4TBP) deposi ed on ITO. Tes solu ion 0.1M HClO4. 22 Fig. 7. In si u FTIR spec a collec ed du ing he oxida ion o a chemically syn hesized poly(2A-4TBP) in 0.1M HClO4/D2O es solu ion. Re e ence po en ial 0.1 V. Sample po en ial labelled o each spec um. 100 in e e og ams a each po en ial. 23 282 285 288 291 294 0 1x104 2x104 3x104 4x104 5x104 In ensi y /a.u. Binding ene gy / eV C 1s 393 396 399 402 405 408 0 1x103 2x103 3x103 In ensi y /a.u. Binding ene gy / eV N 1s 528 531 534 537 540 543 0.0 5.0x103 1.0x104 1.5x104 In ensi y /a.u. Binding ene gy / eV O 1s Fig. 8. High- esolu ion XPS spec a o chemically syn hesized poly (2A-4TBP) showing he cu e- i ed signals o C 1s, N 1s and O 1s.