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Synthesis and Spectroscopic Studies of DGEBA–Grafted DGEBA–Grafted Polyaniline C. H. Teh , R. Rozaidi , D. Rusli & H. A. Sahrim To cite this article: C. article: C. H. Teh , R. Rozaidi , D. Rusli & H. A. Sahrim (2008) Synthesis and Spectroscopic Studies of DGEBA–Grafted Polyaniline, Polymer-Plastics Technology Technology and Engineering, 48:1, 17-24, DOI: 10.1080/03602550802539106 10.1080/03602550802539106 To link to this article: http://dx.doi.org/10.1080/03602550802539106
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Date: 31 Date: 31 May 2016, At: 23:53
Polymer-Plastics Technology and Engineering , 48: 17–24, 2009
Copyright # Taylor & Francis Group, LLC ISSN: 0360-2559 print/1525-6111 online DOI: 10.1080/03602550802539106
Synthesis and Spectroscopic Studies of DGEBA–Grafted Polyaniline C. H. Teh1, R. Rozaidi1, D. Rusli2, and H. A. Sahrim1 1
School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia 2 School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia 6 1 0 2 y a M 1 3 3 5 : 3 2 t a ] y g o l o n h c e T & e c n e i c S f o y t i s r e v i n U n i h c o C [ y b d e d a o l n w o D
A polymer blend of PANI=epoxy resin system was N-grafted polyaniline with diglycidyl ether bisphenol A found to have various applications, such as conductive [1] [2,4] (DGEBA) was synthesized via anionic copolymerization technique. adhesive material , electrical conductive resin , and Metalation reaction was performed to cause grafting to occur electromagnetic interference (EMI) shielding materials[8]. between DGEBA with emeraldine salt polyaniline (PANI-ES) and The presence of acidic doping in PANI=epoxy resin polyleucoemeraldine base polyaniline (PANI-LEB), respectively. Fourier transform infrared (FTIR), 13 C-nuclear magnetic resonance (NMR), mer blends enhances the thermal and electrical properties [9] and 1H-NMR spectroscopies and gel permeation chromatography in the composite products. Recently, Lu and co-workers (GPC) were performed to characterize the PANI-EB-g-DGEBA reported that PANI=epoxy composites that synthesized via and PANI-ES-g-DGEBA copolymers. The gel content of the result- in situ polymerization have a high value of dielectric ant copolymers was determined by Soxhlet extraction. Results of constant and thus can be applied as embedded capacitor spectroscopic studies showed that grafting took place together with the side reaction, cross-linking, and DGEBA homopolymerization. material. In general, polymer blends are a very common technique Oxidation states of PANI were found to influence the gel content and molecular weight distribution of copolymers produced. in processing PANI=epoxy resin composites. Although polymer properties can compensate each other via this Keywords Anionic copolymerization; DGEBA; Grafting; technique, synergistic effects, such as compatibility and Polyaniline dispersion of PANI filler in the epoxy matrix, are another factor to consider as they affect final properties of the composites. Therefore, other routes to prepare the PANI with epoxy resin are desirable. INTRODUCTION Modification of PANI with epoxy resin via chemical Research involving the combination of properties of synthesis may bring some interesting findings; recently, polyaniline (PANI) with epoxy resin has been developed the addition of other functional groups in an epoxy resin for decades. There are several ways to impart the properties system shows promising results[10,11]. Better mechanical, of PANI into epoxy resin in order to achieve desired thermal, and electrical properties can be obtained from properties, such as polymer blends [1–4], emulsion polymer- the composites of designated epoxy resin with other funcization[5], electrochemical[6,7], and other reliable methods. tional groups. There are several reports showing that PANI Each method employed determines the application routes and epoxy resin can be prepared chemically using as of the PANI=epoxy resin systems. For example, PANI= emulsion polymerization[5], in-situ polymerization[9], and epoxy resin systems that are prepared via electrochemical interfacial polymerization[12]. methods can be applied as corrosion coatings materials Graft copolymerization can also be used to improve the for steel[6,7] because uniformity of film thickness can be properties of PANI in epoxy resin. It has been reported produced from this method. This behavior is important that graft copolymerization can be carried out through ring for organic coatings and electronic application. opening polymerization of epoxide via N-alkylation reaction[13–16]. Evers and co-workers [13] used sodium hydride Address correspondence to C. H. Teh, School of Applied (NaH) to produce N polyanion from the NH group of Physics, Faculty of Science and Technology, Universiti polybenzimidazole. Thus, these N polyanions caused ring Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia. E-mail: opening polymerization of the epoxide. The N-alkylation
[email protected] 17
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C. H. TEH ET AL.
reaction has also been employed by Wang et al.[14] to synthesize poly(ethylene glycol) (PEG)-grafted polyaniline (PANI) copolymer, which has better solubility in common organic solvents and water. Recently, Yamaguchi and co-workers[15,16] described the synthesis and the chemical, optical, electrochemical, and thermal properties of PANI grafted with glycidyl phenyl ether (GPE) by utilizing ring opening graft copolymerization of epoxide. They reported that chemical and physical properties of N-grafted polyaniline copolymers can be controlled and tuned from the degree of grafting and length of grafted side. In this work, we apply and use the anionic copolymerization technique to carry out grafting on polyaniline via ring opening polymerization of epoxide on diglycidyl ether bisphenol A (DGEBA). Grafting of DGEBA on PANI with different oxidation states, particularly in emeraldine salt polyaniline (PANI-ES) and leucoemeraldine base polyaniline (PANI-LEB), was studied. Both PANI-LEBg-DGEBA and PANI-ES-g-DGEBA copolymers were characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies to determine the grafting section and identify the molecular structure of the copolymers. Gel permeation chromatography (GPC) was also conducted to determine the molecular weight distribution of the copolymers, and gel content of the copolymers was determined by Soxhlet extraction.
EXPERIMENTAL METHOD
was followed by drying in an oven at 80 C for 24h. The PANI-ES was later neutralized with excess amount of 1.0 M ammonium hydroxide aqueous solution and washed with excess water followed by methanol to obtain the emeraldine base polyaniline (PANI-EB). Methanol was used to remove the impurities and oligomers formed in PANI-ES polymerization. The reduced form polyaniline, leucoemeraldine base (PANI-LEB), was prepared by using hydrazine monohydrate, and 5 g of PANI-EB was added in the three neck reactor containing 50 ml of hydrazine monohydrate. The reaction was carried out under nitrogen atmosphere for 5 h. The light blue precipitate was washed thoroughly with distilled water and methanol followed by drying in an oven for 1 h at 80C. The molecular structures of general form PANI and oxidation states PANI-ES, PANI-EB, and PANI-LEB are summarized in Fig. 1.
Graft Copolymerization of PANI with DGEBA The copolymer was designed and modified via Yamaguchi and co-workers’ ring opening graft copolymerization method[16,17]. The copolymerization process was initiated by a solution of sodium methylsulfinyl carbanion in DMSO (40 ml) prepared from sodium hydride (190 mg, 7.95 mmol) in a three neck reactor. The reaction flask was kept under nitrogen atmosphere throughout the subsequent reactions by a constant flow of nitrogen gas. The mixture was stirred at 75 C for 24 h until all the sodium hydride was completely dissolved. This was followed by addition of PANI-LEB (650 mg, 6.99 mmol) and the
Materials Diglycidyl ether bisphenol A (DGEBA) with trade name EPIKOTE TM Resin 828 was supplied by the ASA Chem. This product is a medium viscosity liquid epoxy resin with epoxy values of about 0.53 mol=100 g and epoxy equivalent of 187g=equivalent. Aniline, ammonium peroxydisulphate (APS), and hydrazine monohydrate were analytical grade supplied by Alfa Aesar. Both hydrochloric acid and ammonium hydroxide were provided by Tedia Company, Inc. Sodium hydride was supplied by BDH Chemical, and DMSO was made in Lab Scan Analytical Science. Aniline was distilled at 182 C until colorless prior to use. All other reagents were used as received. Synthesis of Polyaniline in Different Oxidation States Emeraldine salt polyaniline (PANI-ES) was synthesized via chemical oxidation method similar to the report by Zeng and Ko[17] but with APS as the oxidation agent, and 10 ml of aniline and 24.5 g of APS were prepared separately in 150 ml of 1.0 M hydrochloric acid aqueous solutions. The APS solution was added dropwise to the stirred solution of aniline hydrochloride after 30 min of stirring in an ice bath. After 3.5 h, the greenish black precipitate was filtrated and washed with excess water and methanol. This
FIG. 1. Molecular structures of PANI, PANI-ES, PANI-EB, and PANI-LEB.
DGEBA–GRAFTED POLYANILINE
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reaction was allowed to continue for 24 h at 40C. The metalation reaction was expected to occur between PANI-LEB with the sodium methylsulfinyl carbanion solution[18]. The dark blue solution was cooled to 30 C before adding DGEBA (8.37 g, 44.81 mmol) into it. The reaction was allowed to continue for another 24 h. The distilled water was poured into the reaction flask, under vigorous stirring to precipitate the copolymer. The gel formed black precipitation and was recovered by using vacuum filtration and washed excessively with distilled water and methanol. The black precipitate was later dried in an oven at 80C for 48 h. The product obtained was labeled as PANI-LEB-g-DGEBA copolymer. The same procedure was employed to prepare the PANI-ES-gDGEBA copolymer by replacing the PANI-LEB with PANI-ES (1 g, 10.75 mmol).
Characterization All samples used for characterization were in powder form. The FTIR spectra were recorded on a GX model Perkin-Elmer Infrared Spectrometer using KBr discs. The spectra were recorded in the range of 4,000 cm1 to 370cm1. The 1H and 13C NMR spectra were obtained through the ECP 400 model Jeol FT-NMR spectrometer using deuterated chloroform (CDCl 3) as solvent. The molecular weight distribution of copolymer was determined by Waters 2410 gel permeation chromatography with polystyrene as standard and toluene as eluent. Approximately 0.3 g of each sample were weighed exactly and placed in a thimble, which later underwent Soxhlet extraction for 24 h using THF as solvent. After the extraction, the thimble was dried in an oven at 90C until constant weight was achieved. The gel content was calculated as follows: Gel content ð%Þ ¼
Weight after extraction 100 Initial weight
ð1Þ
RESULTS AND DISCUSSION Copolymerization of Polyaniline (PANI) with DGEBA Samples of PANI with two different oxidation states were used to study the grafting and cross-linking behavior with DGEBA. The metalation reaction on PANI was carried out in the sodium methylsulfinyl carbanion solution, which was prepared using sodium hydride in DMSO. The metalation reaction was as illustrated (Scheme 1a). This mechanism was used by Evers et al.[13] and Yamaguchi et al.[15,16] to produce N polyanion from the NH groups. Yamaguchi and co-workers[16] described that sodium methylsulfinyl carbanion solution in DMSO caused deprotonation of NH groups and produced an anion N on PANI backbones chains. This anion later promotes b-scission of DGEBA followed by epoxide ring
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SCHEME 1. (a) Metalation reaction of PANI with sodium methylsulfinyl carbanion solution followed by (b) epoxide ring opening of DGEBA grafting on polyaniline backbones.
opening polymerization (Scheme 1b). Through this method, both PANI-LEB-g-DGEBA and PANI-ES-gDGEBA copolymers can be obtained. In this work, we found that samples of PANI with different oxidation states used to prepare copolymers with DGEBA showed different levels of cross-linking besides desired grafting and side reaction, DGEBA homopolymerization. This shows that anionic grafting techniques used in this work are unavoidable with the side reaction of cross-linking and homopolymer contamination as also reported by Noshay and McGrath[19]. The PANI-LEB-g-DGEBA was found solidified in the reactor before the reaction was quenched while PANIES-g-DGEBA was still in gel form after 24 h of copolymerization. This may explain why PANI-LEB, which has additional benzenoid rings, was expected to change back to typical PANI-EB due to oxidation and formed more cross-linked sections as the PANI intermolecular Michael reaction occurred[20] during metalation reaction. The PANI-ES-g-DGEBA copolymer was expected to have few partially cross-linked sections.
Gel Content and GPC Analysis Both PANI-ES-g-DGEBA and PANI-LEB-g-DGEBA were successfully produced from the anionic copolymerization method. Without using this method, both polymers possibly become a polymer blend with no grafting section. However, cross-linking will take place in this polymer blend because PANI, which has amine functional groups, will partially cure the DGEBA[2,4]. We found that the PANI-ES-g-DGEBA copolymer has higher total monomer conversion of DGEBA, which consisted of grafted sections and DGEBA homopolymer and cross-linked section compared with PANI-LEB-g-DGEBA copolymer. As well, THF was used in Soxhlet extraction because it will mostly
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dissolve the oligoether side of the copolymer together with the grafting section, leaving behind the cross-linked residues. This can be determined from the IR spectra. In this work, PANI-ES-g-DGEBA yielded 72.7% of total monomer conversion of DGEBA compared with only 42.8% for PANI-LEB-g-DGEBA. Upon extraction using th Soxhlet method, PANI-ES-g-DGEBA did not have much cross-linked section found. The PANI-ES-g-DGEBA yielded nearly 12% of gel content compared with PANILEB-g-DGEBA, which yielded 62.7% of gel content. The gel content of PANI-LEB-g-DGEBA was found to be 5 times more than PANI-ES-g-DGEBA. This explained that more cross-linked section was formed in the PANI-LEB-gDGEBA compared to PANI-ES-g-DGEBA. Sodium methylsulfinyl carbanion solution was used to increase the neucleophilicity of nitrogen by deprotonation the NH groups. Thus, PANI-LEB, which has more benzenoid units compared with the PANI-ES, will form more N polyanion, which later caused epoxide ring opening on DGEBA. Unfortunately, there were also cross-linked sections formed in the PANI-LEB-g-DGEBA. Mikhael and his coworkers[20] explained that the emeraldine anion from PANI-ES or PANI-EB that has a halide anion was unstable when left at room temperature. Therefore, it formed cross-linked sections via the intermolecular Michael reaction wherein the N anion was added to the C¼C of other quinoid rings. This side reaction can be avoided by carrying out the reaction on the reduced form of PANI as reported by Levon [21]. In this work, it was expected that the PANI-LEB was oxidized to typical PANI-EB during the metalation reaction, followed by intermolecular Michael reaction on quinoid rings before copolymerization conducted. This probably reduced the grafting reaction between PANI-LEB and DGEBA. From the GPC results, PANI-LEB-g-DGEBA had a number average molecular weight (M n) of 0.38 104 and weight average molecular weight (Mw) of 0.50 104. The index of polydispersity (PDI) of 1.55 explained that PANI-LEB-g-DGEBA underwent additional polymerization and it terminated via a coupling reaction [22]. As for PANI-ES-g-DGEBA copolymer, GPC did not show any results. This possibly was due to the insolubility of PANI-ES-g-DGEBA in toluene.
IR Analysis The IR spectra of PANI-LEB-g-DGEBA and PANIES-g-DGEBA copolymer showed all characteristic bands of PANI, respectively, at 1606 and 1607 cm1 (assigned as C¼C stretching of the quinoid rings), 1508 and 1509 cm1 (C¼C stretching of benzenoid rings), 1292 and 1297 cm1 (C-N stretching mode), 1182 and 1184 cm1 (C-H bending of aromatic rings), and 828 and 830 cm1 (C-H out of plane bending of p -disubstituted benzene ring). These absorption peaks indicated the presence of the PANI
main chain structure[17,23] in both copolymers. Upon reduction to PANI-LEB from PANI-ES, the wave numbers of related absorption peaks and intensity shifted to higher values. Figure 2 shows the comparison of IR spectra of epoxy resin (DGEBA) with both PANI-LEB-g-DGEBA and PANI-ES-g-DGEBA copolymers. The DGEBA consists of bisphenol A and diglycidyl ether moieties. The secondary alcohol functional group in epoxy resin was represented by the absorption peaks at 3492cm1 (OH stretching vibration); 1430 cm1 (in plane OH deformation vibration coupled with CH wagging vibration); 1298 cm1 (OH deformation vibration); 1132, 1108, and 1085 cm1 (CO stretching); and 737 cm1 (OH out of plane deformation vibration). The CO stretching mode has multiple bands due to the coupling with the nearby carbon [23]. Bisphenol A moiety, which has a C(CH 3)2 group, exhibited absorption peaks at 2967 and 2872cm1 due to the CH3 asymmetrical and symmetrical stretching vibration, respectively. The methylene ether, OCH2, which linked the bisphenol A moiety with the epoxide group, showed 2 absorption peaks at 2928cm1 (asymmetric CH2 stretching) and 2872 cm1 (symmetric CH2 stretching). These two peaks were reported to have the same intensity, but due to overlapping with the methyl groups, the peak at 2872 cm1 was found to have lower intensity compared with the asymmetric CH2. The deformation vibration modes of methyl group were represented by the absorption peaks at 1456 cm1 (asymmetric CH3), 1385 cm1 (symmetric CH3), and 1346 cm1 (symmetric CH3). The peak at 1362 cm1 should be due to the wagging vibration of the methylene group. The skeletal vibration modes of aromatic ring can be determined by the absorption peaks at 1607, 1582, 1511, and 1456 cm1. The step-type band at 1456 cm1 showed
FIG. 2. IR spectra of (a) DGEBA, (b) PANI-LEB-g-DGEBA copolymer and, (c) PANI-ES-g-DGEBA copolymer.
DGEBA–GRAFTED POLYANILINE
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that there are peaks of other functional groups on the same band. The CH stretching vibration of aromatic rings was represented by the peak at 3056 cm1. The paradisubstituted benzene was determined by the absorption peak at 831 cm1. The peak at 1180 cm1 corresponds to the CH in plane deformation vibration of aromatic ring. Methyl aromatic ether was found to have two strong bands at 1247 and 1036 cm1 due to asymmetric and symmetric COC stretching vibration, respectively. The absorption peaks at 1414 cm1 (CH deformation vibration), 1158 cm1 (CH2 twisting deformation vibration), 915 cm1 (ring deformation vibration), and 772 cm1 (ring vibration) were assigned to the epoxide ring. Figure 2 shows the comparison of IR spectra of both copolymers with the DGEBA. The IR spectra of copolymers were found to possess most of the absorption peaks from the PANI and DGEBA counterpart. Due to only 15% of PANI used to prepare the copolymer, the IR spectra of the resultant copolymers was mainly influenced by the DGEBA functional groups. As shown in Fig. 3c, the CN stretching of secondary aromatic amine functional group of PANI-LEB appeared at 1376cm1. The grafting between PANI with DGEBA was expected to raise a new absorption peak in the region of 1380–1265 cm1, which was attributed to the CN stretching of the tertiary aromatic amine group. There were reports showing that the reaction between secondary amine with epoxide will produce a tertiary aromatic amine group[24,25]. This new functional group was confirmed as the formation of a grafted section between PANI and
FIG. 3. IR spectra of (a) PANI-LEB-g-DGEBA, (b) PANI-ESg-DGEBA, (c) PANI-LEB, and (d) DGEBA in the region of 1500–500cm 1.
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FIG. 4. IR spectra of PANI-ES-g-DGEBA copolymer (a) before and (b) after Soxhlet extraction.
DGEBA. Unfortunately, the absorption peaks of this functional group were overlapped by the absorption peaks of other functional groups, such as OH, C(CH3)2, and OCH2 from bisphenol A and diglycidyl ether moiety (Refer Fig. 3), so it was hard to determine. Although the grafting between PANI with DGEBA was unable to be determined from the IR spectra, there was a reaction between these two polymers. Figures 3a and 3b show that the copolymers exhibit two new absorption peaks at about 574 and 426cm1, and these peaks cannot be found in the IR spectra of DGEBA. It was believed that these peaks belonged to the 1,2,4-trisubstituted benzene groups, and it was stated as a cross-linked section due to the intermolecular Michael reactions on the quinoid rings of PANI [20]. The IR spectra of PANI-ES-g-DGEBA before and after Soxhlet extraction are shown in Fig. 4. As can be seen, the peaks that correspond to the grafted section (1380– 1265 cm1) and epoxide rings (915cm1) disappeared in the spectrum of PANI-ES-g-DGEBA after Soxhlet extraction. This meant that Soxhlet extraction extracted most of the grafted section and epoxide rings homopolymer. The gel content obtained after extraction was actually a cross-linked section, which cannot be removed by THF solvent. Therefore, the gel content gave us information about the percentage of cross-linked section formed in the copolymers.
NMR Studies Figure 5 shows the comparison of 13C-NMR spectra of DGEBA, PANI-LEB-g-DGEBA, and PANI-ES-gDGEBA copolymers. There were three peaks with high intensity that appeared in the range of dc 77.5–76.9 ppm, which referred to the resonance peak of residual carbon of deuterated chloroform (CDC1 3)[26,27].
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the quaternary carbon of bisphenol A moiety has an intense peak at 41.9 ppm (C10). Both PANI-ES-g-DGEBA and PANI-LEB-g-DGEBA copolymers displayed similar 13C-NMR spectra. The grafting was expected to occur on the center and chain end of the PANI structure. The epoxide ring opening on the center of the PANI structure was represented by dc 63.9 (C12), 69.3 (C13), and 70.5ppm (C14). Meanwhile, the grafting on the chain end of the PANI structure can be determined by the chemical shift at dc 41.1 ppm (C15). The assignment of the 13C chemical shift on the copolymer molecular structure is illustrated in Fig. 6. As for the cross-linked section, the carbon resonance peaks for 1,2,4-trisubstituted benzene could not be identified because the percentage of cross-linked formation were expected to be much less. In addition, the resonance peaks were possibly overlapped by the para-disubstituted benzene from bisphenol A moiety and benzenoid rings of PANI in the range of d c 100–150 ppm. Figure 6 also shows the assignment of 1H chemical shift on the DGEBA-grafted PANI copolymer. According to the reports[28,30,31], resonance peaks (f) and (g) at dH 7.1 FIG. 5. Comparison of 13C NMR spectra of DGEBA, PANI-LEBand 6.8 ppm, respectively, were due to the aromatic g-DGEBA, and PANI-ES-g-DGEBA copolymers. protons of bisphenol A moiety. The resonance peak (h) at dH 1.6 ppm referred to the methyl proton. The protons 13 The assignments of C-NMR spectra of copolymers of the glycidyl terminal group were characterized by the were characterized based on the works reported by other resonance peaks at dH 4.2ppm (d), 3.9ppm (e), 3.3ppm research[13,16,26–29]. The resonance peaks at dc 44.9 (C1), (c), 2.9 ppm (b), and 2.7 ppm (a). The aliphatic proton of 50.4 (C2), and 68.9ppm (C3) represented the carbon of oligomers, which synthesized in low molecular weight the glycidyl terminal groups. The aromatic carbon in copo- epoxy resin, was found to have a resonance peak at dH lymer was assigned by the resonance peaks at 156.5 (C 4), 4.0 ppm[30], and it was assigned as resonance peak (i). 143.8 (C7), 127.9 (C6, C8), and 114.1ppm (C 5, C9). The Grafting between PANI with DGEBA was represented high intense peaks at d c 127.9 and 114.1 ppm indicated that by resonance peaks (k)–(m). It was expected that the anion these aromatic carbons were bonded to the hydrogen atom, N on PANI backbones initiated the epoxide ring opening. and it can be found in the para-disubstituted benzene rings The grafting was found to occur at the center and chain in the copolymer. Meanwhile, low intensity peaks centered end of PANI backbones, and these were configured from at d c 156.48 and 143.8 ppm indicated that the aromatic car- the 13C and 1H-NMR spectra. The terminal hydroxyl bon was bonded to another atom that has higher electrone- hydrogen was observed at dH 1.8 ppm (k), and the peak gativity than the hydrogen atom. The resonance peak at for ring opening was expected to appear at dH 3.4 ppm, 31.2 ppm (C11) represented the methyl carbon, whereas which was represented by resonance peak (l). Grafting on
FIG. 6. Assignment of 13C and 1H chemical shift of the DGEBA grafted PANI copolymer.
DGEBA–GRAFTED POLYANILINE
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the center of PANI backbones can be determined from the resonance peak (m) at dH 3.0 ppm. Meanwhile, the resonance peak (n) at dH 2.6 ppm represented the chain end grafting on PANI backbones. The resonance peak of methylene proton, which grafted, displayed a sharp singlet pattern. This was due to the electrical quadrupole moment of the nitrogen nucleus[27]. The 1H-NMR spectra for PANI-ES-g-DGEBA copolymer was assigned as follows: H aromatic, 7.1–6.8 (m); H diglycidyl ether, 2.7 (dd), 2.9 (t), 3.3 (m), 3.9 (dd), and 4.2 (dd); C(CH3)2, 1.6 (s); N-CH 2, 2.6–3.0 (m); CH(OH), 1.7 (s); and O-CH 2, 4.1 (t). The 1H resonance peaks for cross-linked sections were also found overlapped by the resonance peaks from para-disubstituted benzene in the range of d H 6.5–8.0 ppm. This can be explained by the 1H found located in the same chemical environment in the cross-linked section and under the same influence of magnetic field as 1H of para-disubstituted benzene.
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center and chain end of PANI backbones. The epoxide ring opening on the center of the PANI backbones was represented by dc 63.9 (CHOH), 69.3 (CH2-N), and 70.5 ppm (CH2-O). Meanwhile, the chain end grafting of PANI backbones can be determined at dc 41.1 ppm (CH2-N). This was also supported by the 1H-NMR spectra, where (CH2-N) has 1H resonance peak at d H 3.0 ppm for the center grafting and dH 2.6 ppm for the chain end grafting. Both PANI-ES-g-DGEBA and PANI-LEB-g-DGEBA have similar resonance peaks for the grafted section. The grafted section on this copolymer was important because it was believed that the conductive properties of PANI could be imparted into the epoxy resin system in order to produce a conductive resin material.
ACKNOWLEDGEMENT The authors would like to acknowledge the financial support provided by the Ministry of Science, Technology, and Innovation, Malaysia (MOSTI) under the IRPA 03-02-01-0124 PR 001 grant.
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