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Synthesis of conjugated polymer with carbynoid structure by dehydrochlorination of chlorinated polyacetylene film
ELSEVIER
SyntheticMetals
101 (1999)
59-60
Synthesis of conjugated polymer with carbynoid structure by dehydrochlorination polyacetylene film
of chlorinated
M. Kijima ‘,* S. Mukai ‘, K. Ohmura ‘, H. Shirakawa a, M. Kyotani b “Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 30.54573 , Japan b National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 3054565, Japan
Abstract Dehydrochlorinationof stereoregurallychlorinatedpolyacetylene film wascarriedout by chemicalandelectrochemicalmethods.!R spectrashowedthat the chlorinatedpolyacetylenewas almostconvertedto a carbynoidmaterialcharacterizedby IR spectra,while presenceof conjugatedpolyenemoiety in the product wasconfirmedby resonanceRamanspectra,suggesting the product beinga nconjugatedpolymer with carbyneand polyenestructures.Effect of the orientationof polymer mainchain by an uniaxial stretchingis investigatedby XRD and SEM, but alignmentofcarbynoid chainsin the productcouldnot beconfirmed. Keywords: polyacetyleneandderivatives,InfraredandRamanspectroscopy, X-ray diffraction,Amorphoussemiconducting films
1. Introduction Carbyne has been an attractive materialas a new carbon allotropeconsistingof linearspcarbons.Syntheses of somelinear carbonsand related materialshave beenattemptedto develop new carbon materials[l]. However, instability of polyyne or polycumulenetype linear-carbon-species disturbsproductionof pure carbonmaterials.Thesespeciesmight exist only in highly ordered crystalline forms, under high dilution conditions, in sterically hinderedpolymer matrices,or in stabilizedforms by intercalation.Stereoregularllychlorinatedpolyacetylene(CPA) in a form of film [2] hasdemonstrated by Akagi et al. asa candidate of precursor for synthesis of carbynoid materials [3]. Dehydrochlorinationeasily proceedsby a strong basesuch as DBU. On the other hand, we have recently reporteda mild electrocatalyticdehydrofluorinationof polyvinylidene fluoride usingt-BuOH mediator[4]. In this report,we attemptthe dehydrochlorination of oriented CPAfilm preparedfrom stretchedPA film by the electrochemical andthe chemicalmanner(Scheme1) andcharacterizethe
productsby IR andRamanspectroscopies in orderto confirmthat the orientedpolymermatrix may stabilizethe longpolyynes. 2. Experimental PA film waspreparedfrom acetyleneusingEtjAl-(,z-BuO),Ti catalystin cumeneaccordingto the generalprocedure[2], giving a cis-rich film of about 8 pm in thickness.The PA film was mechanicallystretchedto two timeslengthandimmobilizedon a Teflon windowframe.Chlorinationof the samplewascarriedout by prolongeddopingmethodin an FeCl,-saturatednitromethane solution[3]. Chemicaldehydrochlorinationof CPA was carried out in 0.1 mol dmm3 of DBU or t-BuOK in DMF at room temperature or 0 “C under Ar. Electrochemicaldehydrochlorinationwascarriedout by a cathodicappliedpotentialat 2.0 V (vs. SCE)with a Pt cathodeimmobilizedthe CPA film in the presenceof t-BuOH mediator (1 mol dme3)in DMF containing 0.1 mol dmm3of dodecyl-trimethylammonium perchlorateor LiCIO, at 0 “C underAr. Resultsand Discussion IR spectraof dehydrochlorinated productsof the stretchedCPA film by the chemicalmannerare shownin Figure 1. Both spectra exhibit a broadpeakaround2100 cm-’ due to vcGc and broad absorptions rangedfrom 1600to 1000cm-‘, that resembles the polyyne-typecarbynoidmaterialsynthesized&om non-stretched CPAwith DBU in the previouswork [3]. The absorption maximum at 2122cm” (a) is somewhat lower in wavenumber thanthat of the non-stretchedsample [3] but rather higher than those of electrosynthesized carbynoid materials[5], suggestingthat the conjugationlengthof polyynemoietyisnot solong.
3.
p-doped
ctst-chlorinated
tlansp0lyacetylene
Scheme
* Corresponding
polyyne-iype
1
author. Tel: +81-298-53-5295,
polyacelylene
carbyne
Fax: +81-298-55-7440,
E-mail:
[email protected],jp
0379-6779/99/$ - seefrontmatter0 1999ElsevierScience S.A. All rightsreserved. PII: SO379-6779(98)01
124-2
60
M. Kijima
3000
4000
2000
Wavenumber
et al. J Synthetic
Metals
101 (1999)
59-60
1000
(cm -‘)
Figure1. IR spectraof dehydrochlorinated products by (a) DBUand(c) t-BuDKinDMFatroomtemperature. Next, electrochemicaldehydrochlorinationis attempted.IR spectralchangesareshownin Figure2. As the reactionproceeds, absorptionpeaksof CPA at 1270,742, and 710 cm“ dueto 6,, and a new absorptionpeak at 1676 cm” and vcmcldecreases appears. Likewisethe chemicalmethod,broadabsorptions (16001000cm-l) appearsat the endof the reactionbut the absorption due to vc -c is scarcely observed.This might be due to predominantformationof an intermediatepoly(chloroacetylene) or a cumulene-typecarbynoidmaterial.In confirmationof this, Raman spectrumof this samplewas comparedwith other productsobtainedin this study. When the samplewas excited with 7X5nm laser,apparentresonance Ramanpeaksat 1473and 1107cm-’ identicalto thoseof PA were observedalthoughthe sampleobtainedby the DBU methodscarcelyfind the peaks. From theseresult, the product obtainedin this electrochemical manneris a conjugatedpolymer with a carbynoidand polyene moieties.Thus,thenewIR peakat 1676cm-’isascribed to isolated -CH=CH- moietyby electroreduction of C-Cl bonds.
Figure3. SEMpictureof filmsurface of thecarbynoid material obtained bytheDBUmethod. Effect of the orientationof polymer main chain by the uniaxially stretchingisconiirmedby XRD andSEM observations. From the X-ray diffraction patterns,chainsof PA and CPA are apparendyalignedbut alignmentof the carbynoidchainsin the productscan not be cotirmed for their non-crystallineforms without intensediffraction peaks.PA and CPA preparedin this study has no characteristicsurfacemorphology,but carbynoid materialspreparedfrom the stretchedPA exhibit an interesting SEM view, that is, a micro-mesh morphology(Figure3). In this study,it remindusthat the dehydrochlorination of CPA must be carriedout usingan effective reagentso as not to be reduced the C-Cl linkage. Molecular regularity and artificial alignmentof raw materialsdo not seemto be effective for the molecularorderingandorientationof linearcarbonspecies, sofar. Further investigationsusing highly oriented PA with fiblilar morphologyasthe startingmaterialareunderway, This work was supportedby the Ministry of Education, Science,SportsandCulture,Grant-in-Aidfor Scientific Research on Priority Areas(CarbonAlloys), 10137205,1998andpartiBlly supportedby IketaniScienceandTechnologyFoundation.
I,
3000
2000 Wavenumber
;; ,,
I
1000 (cm-‘)
Figure2. IR spectraof (a) CPA anddehydrochlorinated products obtained by theelectrochemical method for (b) 16 h, (c)22h, and(c)66h.
4. References [I] Y. P. Kudryavtsev,R. B. Heimann,S. E. Evsyukov, J. Mater. Sci., 31 (1996)5557. l2] K. Akagi, T. Kadokura,H. Shirakawa,Polymer, 33 (1992) 405x. [3] K. Akagi, M. Nishiguchi,H. Shirakawa,Synth. Met., 17 (1987)557. [4] M. Kijima, T. Toyabe,H. Shirakawa,Chem.Lett., (1995)553. [5] M. Kijima, Y. Sakai,H. Shirakawa,Chem.Lett., (1994)2011; M. Kijima, Y. Sakai,H. Shirakawa,Synth. Met., 71 (1995) 1837;M. Kijima, T. Toyabe,H. Shirakawa,.I. Chem.Sot., Chem. Commun.,(1996) 2273; M. Kijima, T. Toyabe, H. Shirakawa,S.Kawata,H, Kyotani, M. Kyotani, Y. Nakamura, T. Endo,Synth.Met,, 86(1997)2279.
SyntheticMetals
101 (1999)
59-60
Synthesis of conjugated polymer with carbynoid structure by dehydrochlorination polyacetylene film
of chlorinated
M. Kijima ‘,* S. Mukai ‘, K. Ohmura ‘, H. Shirakawa a, M. Kyotani b “Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 30.54573 , Japan b National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 3054565, Japan
Abstract Dehydrochlorinationof stereoregurallychlorinatedpolyacetylene film wascarriedout by chemicalandelectrochemicalmethods.!R spectrashowedthat the chlorinatedpolyacetylenewas almostconvertedto a carbynoidmaterialcharacterizedby IR spectra,while presenceof conjugatedpolyenemoiety in the product wasconfirmedby resonanceRamanspectra,suggesting the product beinga nconjugatedpolymer with carbyneand polyenestructures.Effect of the orientationof polymer mainchain by an uniaxial stretchingis investigatedby XRD and SEM, but alignmentofcarbynoid chainsin the productcouldnot beconfirmed. Keywords: polyacetyleneandderivatives,InfraredandRamanspectroscopy, X-ray diffraction,Amorphoussemiconducting films
1. Introduction Carbyne has been an attractive materialas a new carbon allotropeconsistingof linearspcarbons.Syntheses of somelinear carbonsand related materialshave beenattemptedto develop new carbon materials[l]. However, instability of polyyne or polycumulenetype linear-carbon-species disturbsproductionof pure carbonmaterials.Thesespeciesmight exist only in highly ordered crystalline forms, under high dilution conditions, in sterically hinderedpolymer matrices,or in stabilizedforms by intercalation.Stereoregularllychlorinatedpolyacetylene(CPA) in a form of film [2] hasdemonstrated by Akagi et al. asa candidate of precursor for synthesis of carbynoid materials [3]. Dehydrochlorinationeasily proceedsby a strong basesuch as DBU. On the other hand, we have recently reporteda mild electrocatalyticdehydrofluorinationof polyvinylidene fluoride usingt-BuOH mediator[4]. In this report,we attemptthe dehydrochlorination of oriented CPAfilm preparedfrom stretchedPA film by the electrochemical andthe chemicalmanner(Scheme1) andcharacterizethe
productsby IR andRamanspectroscopies in orderto confirmthat the orientedpolymermatrix may stabilizethe longpolyynes. 2. Experimental PA film waspreparedfrom acetyleneusingEtjAl-(,z-BuO),Ti catalystin cumeneaccordingto the generalprocedure[2], giving a cis-rich film of about 8 pm in thickness.The PA film was mechanicallystretchedto two timeslengthandimmobilizedon a Teflon windowframe.Chlorinationof the samplewascarriedout by prolongeddopingmethodin an FeCl,-saturatednitromethane solution[3]. Chemicaldehydrochlorinationof CPA was carried out in 0.1 mol dmm3 of DBU or t-BuOK in DMF at room temperature or 0 “C under Ar. Electrochemicaldehydrochlorinationwascarriedout by a cathodicappliedpotentialat 2.0 V (vs. SCE)with a Pt cathodeimmobilizedthe CPA film in the presenceof t-BuOH mediator (1 mol dme3)in DMF containing 0.1 mol dmm3of dodecyl-trimethylammonium perchlorateor LiCIO, at 0 “C underAr. Resultsand Discussion IR spectraof dehydrochlorinated productsof the stretchedCPA film by the chemicalmannerare shownin Figure 1. Both spectra exhibit a broadpeakaround2100 cm-’ due to vcGc and broad absorptions rangedfrom 1600to 1000cm-‘, that resembles the polyyne-typecarbynoidmaterialsynthesized&om non-stretched CPAwith DBU in the previouswork [3]. The absorption maximum at 2122cm” (a) is somewhat lower in wavenumber thanthat of the non-stretchedsample [3] but rather higher than those of electrosynthesized carbynoid materials[5], suggestingthat the conjugationlengthof polyynemoietyisnot solong.
3.
p-doped
ctst-chlorinated
tlansp0lyacetylene
Scheme
* Corresponding
polyyne-iype
1
author. Tel: +81-298-53-5295,
polyacelylene
carbyne
Fax: +81-298-55-7440,
E-mail:
[email protected],jp
0379-6779/99/$ - seefrontmatter0 1999ElsevierScience S.A. All rightsreserved. PII: SO379-6779(98)01
124-2
60
M. Kijima
3000
4000
2000
Wavenumber
et al. J Synthetic
Metals
101 (1999)
59-60
1000
(cm -‘)
Figure1. IR spectraof dehydrochlorinated products by (a) DBUand(c) t-BuDKinDMFatroomtemperature. Next, electrochemicaldehydrochlorinationis attempted.IR spectralchangesareshownin Figure2. As the reactionproceeds, absorptionpeaksof CPA at 1270,742, and 710 cm“ dueto 6,, and a new absorptionpeak at 1676 cm” and vcmcldecreases appears. Likewisethe chemicalmethod,broadabsorptions (16001000cm-l) appearsat the endof the reactionbut the absorption due to vc -c is scarcely observed.This might be due to predominantformationof an intermediatepoly(chloroacetylene) or a cumulene-typecarbynoidmaterial.In confirmationof this, Raman spectrumof this samplewas comparedwith other productsobtainedin this study. When the samplewas excited with 7X5nm laser,apparentresonance Ramanpeaksat 1473and 1107cm-’ identicalto thoseof PA were observedalthoughthe sampleobtainedby the DBU methodscarcelyfind the peaks. From theseresult, the product obtainedin this electrochemical manneris a conjugatedpolymer with a carbynoidand polyene moieties.Thus,thenewIR peakat 1676cm-’isascribed to isolated -CH=CH- moietyby electroreduction of C-Cl bonds.
Figure3. SEMpictureof filmsurface of thecarbynoid material obtained bytheDBUmethod. Effect of the orientationof polymer main chain by the uniaxially stretchingisconiirmedby XRD andSEM observations. From the X-ray diffraction patterns,chainsof PA and CPA are apparendyalignedbut alignmentof the carbynoidchainsin the productscan not be cotirmed for their non-crystallineforms without intensediffraction peaks.PA and CPA preparedin this study has no characteristicsurfacemorphology,but carbynoid materialspreparedfrom the stretchedPA exhibit an interesting SEM view, that is, a micro-mesh morphology(Figure3). In this study,it remindusthat the dehydrochlorination of CPA must be carriedout usingan effective reagentso as not to be reduced the C-Cl linkage. Molecular regularity and artificial alignmentof raw materialsdo not seemto be effective for the molecularorderingandorientationof linearcarbonspecies, sofar. Further investigationsusing highly oriented PA with fiblilar morphologyasthe startingmaterialareunderway, This work was supportedby the Ministry of Education, Science,SportsandCulture,Grant-in-Aidfor Scientific Research on Priority Areas(CarbonAlloys), 10137205,1998andpartiBlly supportedby IketaniScienceandTechnologyFoundation.
I,
3000
2000 Wavenumber
;; ,,
I
1000 (cm-‘)
Figure2. IR spectraof (a) CPA anddehydrochlorinated products obtained by theelectrochemical method for (b) 16 h, (c)22h, and(c)66h.
4. References [I] Y. P. Kudryavtsev,R. B. Heimann,S. E. Evsyukov, J. Mater. Sci., 31 (1996)5557. l2] K. Akagi, T. Kadokura,H. Shirakawa,Polymer, 33 (1992) 405x. [3] K. Akagi, M. Nishiguchi,H. Shirakawa,Synth. Met., 17 (1987)557. [4] M. Kijima, T. Toyabe,H. Shirakawa,Chem.Lett., (1995)553. [5] M. Kijima, Y. Sakai,H. Shirakawa,Chem.Lett., (1994)2011; M. Kijima, Y. Sakai,H. Shirakawa,Synth. Met., 71 (1995) 1837;M. Kijima, T. Toyabe,H. Shirakawa,.I. Chem.Sot., Chem. Commun.,(1996) 2273; M. Kijima, T. Toyabe, H. Shirakawa,S.Kawata,H, Kyotani, M. Kyotani, Y. Nakamura, T. Endo,Synth.Met,, 86(1997)2279.