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Thermally stimulated depolarization and polarization current study of C60-PU based conducting interpenetrated polymer networks (IPNs)
ELSEVIER
Synthetic Metals 84 (1997) 987-988
Thermally stimulated depolarization and polarization current study of Go-PU based conducting interpenetrated polymer networks (IPNs) David C. Lin, Lee Y. Wang, and Long Y. Chiang Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
Abstract Rubber-like conductive polyaniline-polyurethane interpenetration networks (U?Ns) were synthesized by a sequence of poly condensation and doping reactions. .The thermally stimulated depolarization and polarization current (TSDCTSPC) and the digerential scanning calorimetry @SC) techniques were used for the characterization of fullerenol-derived urethane copolymer and polyaniline/fullerenoI-PU IPNs. Dual glass transitions of fillerenol-derived polyurethane copolymers at -71 Y! and 72 ‘C have been assigned as the motion of PTMO soft segment in the glassy state and the motion of network around Mlerenol crosslinking sites respectively. A major crystal melting transition at -3 “C for all polyurethanes and an additional electric field induced crystal-crystal transformation at 17OC of the firllerenol derived polyurethane network are seen. Within polyanilinelfullerenol-PU IPN, the network of Physical aging polyaniline phase hinders the relaxation of higher Tg and the electric field induced crystal-crystal transformation. TSDC technique treatment provides an indirect method for the characterization of glass transitions of current network structure. provides a higher sensitivity in detecting structural relaxation and serves as a direct measurement of phase transitions. Keywords: thermally stimulated depolarization current, polyaniline, fullerenol, interpenetration network
1. Introduction Doped polyaniline has been extensively used as a conducting medium in many applications, including anti-static coatings, rechargeable secondary batteries, and conducting media for electronic components. Despite of its low cost, good environmental stability, and easy polymerization, the lack of mechanical features, such as elasticity and reprocessing capability, may limit their industrial uses. Various attempts have been carried out aiming to improve the desired properties by blending polyaniline with conventional polymers or by copolymerization of aniline with matrix precursor monomers. The rubber-like conducting interpenetration network (IPN) materials remain rare. Urethane copolymer&d polyether network polymers utilizing, C&derived fullererrol [l] as a hypercrosshnking agent, were synthes&ed as a supporting matrix. Rubber-like fullerenol-PU polymer and its polyaniline incorporated IPN were characterized with several thermal analytical techniques, including TSDC, TSPC and DSC. In order to explore the newly observed characteristic dual glass transitions of hypercrosslinked polyurethanes, different crosslinking agents, pentaerythriol (tetraol) and butane&o1 (diol), were also used in the preparation of the corresponding polyurethane networks for evaluation and comparision [2]. TSDC and TSPC techniques (Solamat 91000) were used to provide an ultra high sensitivity and to give reproducible results in detecting structural relaxations of polymeric materials, particularly, in dete rmining their origin of either dipolar 0379-6779i97IS17.00 8 1997 Elwier PII SO379-6779(96)04244-0
Science S.A. All rights reserved
relaxations or space charge. In the case of the former transition, a given peak observed as a positive current transition in TSDC should be corresponded by an equivalent negative peak in TSPC [3]. The effect of physical aging on properties of glassy materials has been studied thoroughly by Struik [4]. It is well known that the thermal behavior and mechanical properties of polymeric materials are highly sensitive to physical aging at temperatures ca. 20 to 50 ‘C below rg. but not lower than the transition temperature of Tp. This time and temperature dependent responses become significant as the aging temperature approaches Tg. It is also known that, below Tg, polymeric materials resemble supercooled liquids in a non-equilibrium state. Thermodynamically, these materials exhibit volume and enthalpy relaxations when they approach an equilibrium state, a process commonly known as a physical aging. In response of physical aging, a polymer sample becomes stiff and brittle that slows down the relaxation rate. The loss of enthalpy and volume due to the aging at temperatures below Tg can be recovered by heating the material to temperature above Tg. This recovery process results in an endothermic “relaxation” showing a peak near the glass transition temperature in the DSC profile. Physical aging, on the other hand, refers to a change in the physical structure and conformation of macromolecules below Tg which can be reversed by heating above Tg. This reversible endothermic relaxation phenomenon reveals the intrinsic glassy structure of the material indirectly [5]
D.C. Lin et al. /Sy~theticMetals
987-988
2. Resultsand Discussion
0.0 DSC Scans of Fullerenol Aged al 6OC for Varloun
81(1997)
Baaed PU Copolymer Time, la. [mrnj
Thermal history pre-erased samples of fullerenol crosslinkedPU copolymerandits polyanilin&E’Nswere studied with DSC measurement.Fig. 1 showeda seriesof DSC profles of fillerenol-derivedpolyurethanecopolymerat a scanrate of 10 “C/min. Sampleswereagedat 50 OCfor a periodof 0, 120,600, or 1000 min. Two characteristicglasstransitions,rg and a crystal meltingtransition, Tm,at -3.4 OC!were observedin the first DSC profile of samplewithout aging. As expected,the -100 0 100 200 melting transition is most likely due to the melting of crystal Temperature[ ‘C!] structureof flexible segmentof PTMO. A lower Tgl at -71 OCis Fig 1 DSCprofilesof fhllerenol-based PLJcopolymeragedat attributedto the relaxationof soft PTMO segments.The second 50 ‘C for variousperiodof timesasindicated. glasstransition,rgz, at a higher temperatureof 72 ‘%I!as amuch weaker transition.than Tgl. Presumably, the secondglass transitionarisesfrom the relaxationof poly(uret@e-ether) arms near the fullerenol crosslikingsites. All other aged samples -9 B showedan endothermicrelaxation peak at ca. 75 OC!,which -s -0.4 superimpose with rgz, i.e. a normalbaselineshit%.Magnitudeof 3I.+ this endothermincreaseswith the increaseof agingperiod. In Fig. 2, the DSC profile of the conducting polyaniline 4 -0.8 interpenetratedelastomershowsno significantdifferencein ral i -I I I 6 and ZII as comparedwith thoseof the parentmatrix. However, I I I -100 0 100 a00 no clear raz transition is evident in the profile. In fig. 3, Temperature[ ‘C ] fillerenol derived polyurethanecopolymerswere studiedwith Fig 2 DSCprofile of conductivepolyaniline&llerenol-PU elastomer TSDC andTSPCtechniquesundera polingelectricfield strength of 10 V/mm. Surprisingly,the TSDC spectrumshoweddual m-13 crystal melting transition peaksat -9 OCand 17 OC!and dual glasstransitionsat -71 “C and72 ‘C, corresponding to the phase transition of PTMO soft segment and the relaxation of fullerenol 46-13 crosslinkingnetworks,respectively. Ihe TSPCprofile showeda quite symmetricalmirror imageof peaksin a negativecurrent direction as comparedwith the TSDC profile. Interestingly, in g oeto Fig. 4 the TSDC profile of the conductingpolyaniline/fullerenolTfi PU showed no electric field induced crystal-crystal J transformationand no glasstransition Tgz. Apparently, the -41-13 thermal characteristicsof the polyurethanematrix has been alteredduringthe processof polyanilineinterpenetration.
- O*O*
-81-13
I
I
,
I
-100
100
Tempera&e [ “C 1 Fig 3 TSDC and TSPC profiles of fullerenol derived PU, with a polingfield strengthof 10 V/mm.
awli
TSC Scan of Polysnlline/Cle.PU Field Strength = 200 V/mm
IPN
Pollnp L
o!wo I -100
Temp I I 100
1
Temperahe [ “C ] Fig 4 TSDCprofile of conductivepolyaniline.%llerenol-PLJ..
Acknowledgement This work wassupportedby the National ScienceCouncil of Republicof ChinaunderGrantNo. NSC 85-2113-M002-025. References [l] L.Y. Chiang,L. Y. Wang, andC. S. Kuo, Macromolecules, 28 (1995)7574. [2] L.Y. Wang,J. S. Wy S. M. Tseng,C. S. Kuo, K. H. Hsieh, W. B. Liay andL. Y. Chiang,J. Polym. Res. 3 (1996)1. [3] J. P. Tbar,“Fundamenlals of Thermal Stimulared Current and Relaxation Map Analysis”, SLP Press,(1993). [4] L.C.E.Struik, Physical Aging in Amorphous Polymer and other Materials, Elsvier, HollandInc. N.Y. (1978). [5] D. C. Lin andP.H. Geil, .7 Thermoplastic Comp. Matl., 4 (1991)377.
Synthetic Metals 84 (1997) 987-988
Thermally stimulated depolarization and polarization current study of Go-PU based conducting interpenetrated polymer networks (IPNs) David C. Lin, Lee Y. Wang, and Long Y. Chiang Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
Abstract Rubber-like conductive polyaniline-polyurethane interpenetration networks (U?Ns) were synthesized by a sequence of poly condensation and doping reactions. .The thermally stimulated depolarization and polarization current (TSDCTSPC) and the digerential scanning calorimetry @SC) techniques were used for the characterization of fullerenol-derived urethane copolymer and polyaniline/fullerenoI-PU IPNs. Dual glass transitions of fillerenol-derived polyurethane copolymers at -71 Y! and 72 ‘C have been assigned as the motion of PTMO soft segment in the glassy state and the motion of network around Mlerenol crosslinking sites respectively. A major crystal melting transition at -3 “C for all polyurethanes and an additional electric field induced crystal-crystal transformation at 17OC of the firllerenol derived polyurethane network are seen. Within polyanilinelfullerenol-PU IPN, the network of Physical aging polyaniline phase hinders the relaxation of higher Tg and the electric field induced crystal-crystal transformation. TSDC technique treatment provides an indirect method for the characterization of glass transitions of current network structure. provides a higher sensitivity in detecting structural relaxation and serves as a direct measurement of phase transitions. Keywords: thermally stimulated depolarization current, polyaniline, fullerenol, interpenetration network
1. Introduction Doped polyaniline has been extensively used as a conducting medium in many applications, including anti-static coatings, rechargeable secondary batteries, and conducting media for electronic components. Despite of its low cost, good environmental stability, and easy polymerization, the lack of mechanical features, such as elasticity and reprocessing capability, may limit their industrial uses. Various attempts have been carried out aiming to improve the desired properties by blending polyaniline with conventional polymers or by copolymerization of aniline with matrix precursor monomers. The rubber-like conducting interpenetration network (IPN) materials remain rare. Urethane copolymer&d polyether network polymers utilizing, C&derived fullererrol [l] as a hypercrosshnking agent, were synthes&ed as a supporting matrix. Rubber-like fullerenol-PU polymer and its polyaniline incorporated IPN were characterized with several thermal analytical techniques, including TSDC, TSPC and DSC. In order to explore the newly observed characteristic dual glass transitions of hypercrosslinked polyurethanes, different crosslinking agents, pentaerythriol (tetraol) and butane&o1 (diol), were also used in the preparation of the corresponding polyurethane networks for evaluation and comparision [2]. TSDC and TSPC techniques (Solamat 91000) were used to provide an ultra high sensitivity and to give reproducible results in detecting structural relaxations of polymeric materials, particularly, in dete rmining their origin of either dipolar 0379-6779i97IS17.00 8 1997 Elwier PII SO379-6779(96)04244-0
Science S.A. All rights reserved
relaxations or space charge. In the case of the former transition, a given peak observed as a positive current transition in TSDC should be corresponded by an equivalent negative peak in TSPC [3]. The effect of physical aging on properties of glassy materials has been studied thoroughly by Struik [4]. It is well known that the thermal behavior and mechanical properties of polymeric materials are highly sensitive to physical aging at temperatures ca. 20 to 50 ‘C below rg. but not lower than the transition temperature of Tp. This time and temperature dependent responses become significant as the aging temperature approaches Tg. It is also known that, below Tg, polymeric materials resemble supercooled liquids in a non-equilibrium state. Thermodynamically, these materials exhibit volume and enthalpy relaxations when they approach an equilibrium state, a process commonly known as a physical aging. In response of physical aging, a polymer sample becomes stiff and brittle that slows down the relaxation rate. The loss of enthalpy and volume due to the aging at temperatures below Tg can be recovered by heating the material to temperature above Tg. This recovery process results in an endothermic “relaxation” showing a peak near the glass transition temperature in the DSC profile. Physical aging, on the other hand, refers to a change in the physical structure and conformation of macromolecules below Tg which can be reversed by heating above Tg. This reversible endothermic relaxation phenomenon reveals the intrinsic glassy structure of the material indirectly [5]
D.C. Lin et al. /Sy~theticMetals
987-988
2. Resultsand Discussion
0.0 DSC Scans of Fullerenol Aged al 6OC for Varloun
81(1997)
Baaed PU Copolymer Time, la. [mrnj
Thermal history pre-erased samples of fullerenol crosslinkedPU copolymerandits polyanilin&E’Nswere studied with DSC measurement.Fig. 1 showeda seriesof DSC profles of fillerenol-derivedpolyurethanecopolymerat a scanrate of 10 “C/min. Sampleswereagedat 50 OCfor a periodof 0, 120,600, or 1000 min. Two characteristicglasstransitions,rg and a crystal meltingtransition, Tm,at -3.4 OC!were observedin the first DSC profile of samplewithout aging. As expected,the -100 0 100 200 melting transition is most likely due to the melting of crystal Temperature[ ‘C!] structureof flexible segmentof PTMO. A lower Tgl at -71 OCis Fig 1 DSCprofilesof fhllerenol-based PLJcopolymeragedat attributedto the relaxationof soft PTMO segments.The second 50 ‘C for variousperiodof timesasindicated. glasstransition,rgz, at a higher temperatureof 72 ‘%I!as amuch weaker transition.than Tgl. Presumably, the secondglass transitionarisesfrom the relaxationof poly(uret@e-ether) arms near the fullerenol crosslikingsites. All other aged samples -9 B showedan endothermicrelaxation peak at ca. 75 OC!,which -s -0.4 superimpose with rgz, i.e. a normalbaselineshit%.Magnitudeof 3I.+ this endothermincreaseswith the increaseof agingperiod. In Fig. 2, the DSC profile of the conducting polyaniline 4 -0.8 interpenetratedelastomershowsno significantdifferencein ral i -I I I 6 and ZII as comparedwith thoseof the parentmatrix. However, I I I -100 0 100 a00 no clear raz transition is evident in the profile. In fig. 3, Temperature[ ‘C ] fillerenol derived polyurethanecopolymerswere studiedwith Fig 2 DSCprofile of conductivepolyaniline&llerenol-PU elastomer TSDC andTSPCtechniquesundera polingelectricfield strength of 10 V/mm. Surprisingly,the TSDC spectrumshoweddual m-13 crystal melting transition peaksat -9 OCand 17 OC!and dual glasstransitionsat -71 “C and72 ‘C, corresponding to the phase transition of PTMO soft segment and the relaxation of fullerenol 46-13 crosslinkingnetworks,respectively. Ihe TSPCprofile showeda quite symmetricalmirror imageof peaksin a negativecurrent direction as comparedwith the TSDC profile. Interestingly, in g oeto Fig. 4 the TSDC profile of the conductingpolyaniline/fullerenolTfi PU showed no electric field induced crystal-crystal J transformationand no glasstransition Tgz. Apparently, the -41-13 thermal characteristicsof the polyurethanematrix has been alteredduringthe processof polyanilineinterpenetration.
- O*O*
-81-13
I
I
,
I
-100
100
Tempera&e [ “C 1 Fig 3 TSDC and TSPC profiles of fullerenol derived PU, with a polingfield strengthof 10 V/mm.
awli
TSC Scan of Polysnlline/Cle.PU Field Strength = 200 V/mm
IPN
Pollnp L
o!wo I -100
Temp I I 100
1
Temperahe [ “C ] Fig 4 TSDCprofile of conductivepolyaniline.%llerenol-PLJ..
Acknowledgement This work wassupportedby the National ScienceCouncil of Republicof ChinaunderGrantNo. NSC 85-2113-M002-025. References [l] L.Y. Chiang,L. Y. Wang, andC. S. Kuo, Macromolecules, 28 (1995)7574. [2] L.Y. Wang,J. S. Wy S. M. Tseng,C. S. Kuo, K. H. Hsieh, W. B. Liay andL. Y. Chiang,J. Polym. Res. 3 (1996)1. [3] J. P. Tbar,“Fundamenlals of Thermal Stimulared Current and Relaxation Map Analysis”, SLP Press,(1993). [4] L.C.E.Struik, Physical Aging in Amorphous Polymer and other Materials, Elsvier, HollandInc. N.Y. (1978). [5] D. C. Lin andP.H. Geil, .7 Thermoplastic Comp. Matl., 4 (1991)377.