Describes thermodynamics properties of PANI and its block PANI-PEO2000.
Polyaniline (PANI) and its block copolymer (PANI-PEO2000) has been prepared under effect of Maghnite-H+ (Algerian MMT) in different weight percentage (wt %) by cationic polymerization method. The structure of PANI and PANI-PEO2000 is predicted by the FT-IR and 1HNMR spectra. The thermal stability of homopolymer and block copolymer is confirmed by difference scanning calorimetry and analysis thermogravimetry. So after this results we can suggest that our heterogeneous catalyst called maghnite (Algerian MMT) can modified the morphology and the physical chemical properties of polyaniline (PANI) and its homolog block polyaniline-b-poly ethylene oxide (PANI-b-PEO2000) in the mild conditions under microwave irradiation.
- green catalyst
- green chemistry
- conducting polymer
- maghnite-H +
Polyaniline (PANI) and its block copolymer (PANI-PEO) are the best promising material in conducting polymers, because of environmental stability, easy processing, and economical efficiency [1, 2]. PANI has been used for electrode of light emitting diode, Li ion rechargeable battery and corrosion protection [3, 4]. Nanocomposites (PANI-MMT) and (PANI-PEO-MMT) are interesting due to the special properties as abundance, low cost of MMT and attractive features such as a large surface area and ion- exchange properties [5, 6]. The clay is supplied by a local company known as ENOF Maghnia (Algeria) [7, 8]. Microwave heating has been found to be particularly advantageous for reactions under “dry” media [9, 10]. Microwave it’s rapidly method in modern chemistry because offer a certain number of advantage, that it can be completed in a few seconds or minutes and without a solvent [2, 11]. Absence of solvent reduces the risk of explosions when reaction takes place in a microwave oven [12, 13]. The absence of solvent reduces the risk of explosions when the reaction takes place in a closed vessel in an oven [14, 15]. Aprotic dipolar solvents with high boiling points are expensive and difficult to remove from the reaction mixtures [16, 17]. The aim of this paper is to study the polymerization of aniline and its homolog block copolymer PANI-PEO catalyzed by Maghnite- H+ under microwave irradiation . This catalyst can be easily separated from the polymer product and regenerated by heating at a temperature above 100°C [19, 20]. The kinetics studies of different synthesis are discussed together with the mechanism of polymerization.
2.1 Microwave apparatus
The temperature was maintained at 160°C in all experiments. Microwave irradiation was performed in a single mode focused CEM reactor (Model Discover, CEM Co., Matthew, NC) operating at 2.45 GHz with ability to control output power.
2.2 Materials and methods
MMT clay was obtained from ENOF Maghnia (Algeria). The MMT-H+ (Mag-H+) was prepared as described by Belbachir et al. and water (pH < 7) was used to synthesize emeraldine salt clay (PANI/Mag-H+) by cationic polymerization . Polyethylene oxide (relative molecular mass of 2.103) was obtained from Sigma Aldrich. Polyaniline (PANI) homopolymer was prepared in laboratory of polymers chemistry (Oran University, Algeria) by standard chemical intercaled method .
1H nuclear magnetic resonance (NMR) measurements were carried out on a 300 MHz Bruker NMR Spectrometer equipped with a probe BB05 mm, in CDCl3. Fourier transform infrared spectroscopy (FTIR) spectra were obtained between 900 and 4000 cm −1 on an ATI Matson FTIR No 9501165. Intrinsic viscosity, [η], was measured at 30°C in benzene.GPC measurements of the samples were carried out using a WISP 712, Waters Associates chromatograph. The purification of polymers were carried out by dissolving the product in chloroform (CHCl3) and filtering to eliminate the Maghnite-H+. Then, chloroform was removed by evaporation [22, 23].
2.4 Preparation of (Maghnite-H+) as catalyst
Catalyst called (maghnite-H+) was prepared according to the process similar to that described by Belbachir et al. [24, 25]. The raw maghnite was placed in an erlenmeyer flask together with 100 ml of distilled water and a solution of sulfuric acid 0.25 M then stirred using a magnetic stirrer for 2 h at room temperature. After filtration up to pH 7, the activated maghnite-H+ is dried in the stove for 24 hours at 105°C for characterization .
2.5 Synthesis of polyaniline (PANI)
Into a flask with 100 mL and stirred to allow proper mixing was put a mixture of Maghnite-H+ (5%) and solution of (H2SO4 0.25 M), adequate amount of aniline (0.05 mol) was added to a solution. The reaction mixture was then submitted to microwave irradiation at 160°C for 4 minutes. Finally, the mixture was cooled at room temperature, filtered and washed extensively with distilled water and methanol to remove catalyst and any unreacted aniline [27, 28].
2.6 Synthesis of block copolymer PANI-PEO
Copolymer PANI-PEO was synthesized via a cationic polymerization. To a (0.05 mol) of monomer aniline was added a solution of PEO (0.05 g in 25 mL of distilled water) and (5 wt %) of maghnite-H+ as an initiator. The mixture was stirred for 15 min. Then it is treated in a microwave oven at the power of 950 W, the temperature and viscosity of the reactive mixture increase fast and gelation point is reached after 4 min at 160°C. The mixture was cooled at room temperature, filtered and washed extensively with distilled water and methanol to remove impurity [16, 29].
3. Results and discussion
3.1 Spectroscopy characterization
Synthesized polyaniline was confirmed by noticing the predominant peaks at the wave numbers of 1501 cm−1corresponding to C═C stretching of quinine ring, 1557 cm−1for C═C stretching of benzenoid ring, 1293 cm−1for C▬N stretching, 755 and 838 cm−1for C▬H vibration of Para coupling benzenoid and benzene rings. Finally, C▬H bending at 694–593 cm−1 corresponds to aromatic ring and 507 cm−1is stretching at out of the plane [30, 31].
As shown in (Figure 2), there are significant changes in both the intensities and the frequencies in the product (PANI-PEO2000). There are more pronounced between 690 and 1574 cm−1, significant interaction between the oxygen of the ether group of PEO and the nitrogen in the PANI . As shown in (Figure 1), polyethylene oxide (PEO2000) show a band of methylene group (CH2) stretching between 2950 and 2840 cm−1 and a large broad band appears centered at 3442 cm−1which confirms that PEO2000 is highly hydrophilic .
Polyaniline was successfully synthesized as show in (Figure 3) and the different hydrogen peaks are present. The strongest sharp peaks centered at 7 and 7.8 ppm due to protons from phenylene and disubstituted phenylene units and the weak peak at 4.81 ppm due to (-NH) group but the peak at 6.22 ppm due to (–NH2) as end group [33, 34].
1H NMR spectroscopy at 300 MHz (Solvent CDCl3) and according to the work published by Yahiaoui et al., (Figure 4) for pure PEO showed different peaks: (a) the methylene groups (CH2−) at 2.6 ppm, and (b) the methylene (CH2O−) at 3.7 ppm [35, 36].
The block copolymer (PANI-PEO2000) was confirmed by 1HNMR spectrum as show in (Figure 5). The wide signal in the region of 6.8 to 8 ppm was assigned to benzenoid hydrogen of polyaniline. Signals at 3.25–3.75 ppm indicate peak of CH2O− and CH2CH2O− hydrogen of polyethylene oxide reported . Peak at 1.5–2 ppm is due to CH2 hydrogen respectively [37, 38].
3.2 Optical properties
Conductive polymers synthesized PANI and PANI-PEO2000 has a conjugated system of double bonds in a backbone polymer. The UV-visible spectral peak in the 250–300 nm region is due to the aniline groups and π → π* is a conjugated couple system of the benzoic states in the 350 to 400 nm regions (Figure 6) [39, 40].
3.3 Thermal properties
As shown in (Figures 7 and 8), the thermogram analysis of catalyst (maghnite-H+) shown two stages of weight loss. The weight loss in below 100°C is a result of free water and the weight loss around 600°C is associated with the dehydroxylation of silicate structure [37, 41].
For the thermogram analysis (TGA) of polyaniline (PANI), it can be found that the weight loss amounted 61, 17% at the temperature range of 187–600°C, which be true because polyaniline it is known a hygroscopic polymer as show in (Figure 9) [42, 43]. in the DSC thermogram of the PANI as show in (Figure 10), there were two endothermic peaks at 55.99 and 103.46°C.Therefore, these endothermic peaks were due to the evaporation of water, this is in agreement with the literature [44, 45]. The glass transition (Tg) appears at 74.06°C .
The curves of weight loss versus temperature showing the behavior of PANI-PEO2000 sample was presented in (Figure 11). The first significant weight loss occurs already at temperature between 50 and 100°C, that PANI-PEO2000 is hygroscopic and during the heating to 100°C the residual water evaporates . Then the main mass loss, which corresponds to polymer degradation starts at about 200 and 500°C .
In polyaniline (PANI) monomer and block copolymer (PANI-PEO2000) as show in (Figure 12). Firstly, we notice the presence of two endothermic peak at (68, 39 and 190, 09°C) it is associated respectively to the evaporation of water absorbed by the copolymer and melting POE2000 block [48, 49]. The glass transition temperature of block copolymer (Tg = 16, 79°C) which is in agreement with the literature .
3.4 Gel permeation chromatography
Tables 2 and 3 describes the molecular weight distribution averages for the polymer and it’s copolymer in the other hand (Figures 13 and 14) indicate a bimodal distribution. The macromolecular weight distribution of the obtained polymer and copolymer are narrow, this confirming the formation of the polymer PANI and the block copolymer PANI-PEO [51, 52].
|Sample name||RT||Area||% Area||Mn||Mw||Polydispersity|
|Sample name||RT||Area||% Area||Mn||Mw||Polydispersity|
3.5 Electrical properties
|Sample||e (cm)||R(Ω)||ρ (Ω. cm)||σ (S/cm)|
3.6 Solubility of product
The polyaniline powder was added to 50 ml of different solvent (DMF, Acetonitrile, toluene, dichloromethane, THF, and chloroform). The dry weight of the filter paper was used to calculate the solubility of the composites. The best solvents for PANI and its block are determined to be DMF and Toluene as show in (Table 5) and (Figure 15). Finally, we can calculate the band of energy by equation (3) .
The solubility parameter (δ) is usually calculate by equation (4) and expressed in (cal/cm3)1/2 or preferably (j/cm3)1/2 units for many compound is defined from Hildebrand-Scotchard Solution theory is:
3.7 Viscosimertic parameters of PANI and PANI-PEO
|Visct. Intr (ml/g−1)||25.80||25.78||25.77|
4. Kinetics studies
4.1 Effect of the amount of mag-H + on the yield of copolymerization
Figure 9 describe the effect of the amount of catalyst on the yield of this copolymerization (PANI-PEO). As can be seen in (Figure 16 and 19), the copolymerization rate increased with the amount of Mag-H + and reaches a maximum at 160°C with (5% wt) of catalyst, above this temperature and percentage of catalyst, the yield decreases.
The increase in yield with temperature and molecular weight of catalyst is mainly due to the number of active sites in the catalyst responsible for initiating the reaction. Similar results are obtained by many research [55, 56].
4.2 Effect of the amount of Mag-H + on the molecular weight of copolymer
We have used (2%,5% and 10%) by weight as the amount maghnite and varying time after keeping the other parameters (the amount of monomers and the temperature). It is observed that the average molecular weight increases with time and reaches a maximum at 4 minutes of reaction and decrease after this time as show in (Figure 17) .
4.3 Effect of molar ratio aniline/PEO on the yield of copolymerization
We notice a significant change in the yield with increasing the amount ratio, in particular with increasing the amount of PEO used in this reaction processing. The (Figure 18.) below summarizes the influence of the molar ratio on Aniline/PEO upon the reaction yield. This phenomenon can explain by the high reactivity and solubility of the POE in water compared to the aniline in particular at high temperature .
5. Proposed mechanism of polymerization and copolymerization
Based on Maghnite-H+ (Algerian ecologic catalyst MMT) and under microwave irradiation our polymer (PANI) and block copolymer (PANI-b-PEO) were successfully synthesized and investigate. This product was prepared in order to combine the mechanical and physical properties of PEO2000 with conducting properties of PANI. A possible mechanism of this cationic polymerization is discussed based on the results of the 1H NMR Spectroscopic analysis of these compounds. Thus all the two types of composites (PANI and PEO) provide opportunities and rewards creating new world wide interest in these new materials in electronics devises.
All work was supported by the DGRSDT of Algeria republic and was performed using the equipment of the center of research scientific and technics in analysis chemical and physical (CRAPC)-Tipaza-Algeria.