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International Journal of Polymer Science
Volume 2015 (2015), Article ID 280325, 5 pages
http://dx.doi.org/10.1155/2015/280325
Research Article

Structure and Electrical Study of New Chemically Modified Poly(vinyl chloride)

1Laboratory of Organic Synthesis, Faculty of Sciences of Bizerte, University of Carthage, Jarzouna, 7021 Bizerte, Tunisia
2Laboratory of Materials Physics, Faculty of Sciences of Bizerte, University of Carthage, Jarzouna, 7021 Bizerte, Tunisia

Received 12 March 2015; Revised 20 May 2015; Accepted 26 May 2015

Academic Editor: Jose Ramon Leiza

Copyright © 2015 F. Ammari et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The aim of this work was to study the structural and electrical properties of a new polymer obtained by functionalization of a commercial poly(vinyl chloride) (PVC) (Mw = 48000) by grafting aminoalkyl and aminoaryl groups. Modified poly(vinyl chloride) was prepared in two steps. The structural properties of the polymer were systematically investigated by varieties of techniques as differential scanning calorimetric (DSC), thermogravimetry analysis (TG), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The electrical properties of the polymer were studied by electrochemical impedance spectroscopy (EIS).

1. Introduction

Taking into account its excellent miscibility, compatibility properties, good mechanical strength, low energy consumption, and its low cost [15], poly(vinyl chloride) (PVC) has been considered as a good candidate polymer for use in a great variety of electrochemical devices such as high energy density batteries, fuel cells, sensors, and electrochromic devices [68]. The development of PVC polymer with high ionic conductivity is one of the main objectives in polymer research. In fact, various approaches have been made to modify the structure of PVC polymer in order to improve their electrical, electrochemical, and mechanical properties. Among the modified PVC, we found those cited in many literatures [911]. In the present work, differential scanning calorimetric (DSC) studies, thermogravimetry analysis (TG), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and temperature dependent conductivity were performed on a new polymer obtained by functionalization in two steps of a commercial poly(vinyl chloride) by grafting aminoalkyl and aminoaryl groups.

2. Experimental

2.1. Chemicals

The commercial poly(vinyl chloride) Mw = 48000 (packed in Switzerland) was purchased from Fluka, diethylenetriamine and 4-methoxyaniline were purchased from Aldrich-Chemistry, 7924 Steinheim, Germany, and dioxane and THF were purchased from Prolabo (Groups Rône Poulenc).

2.2. Instrumentation

Electrochemical Impedance Spectra (EIS) were obtained using a Hewlett-Packard HP 4192 analyzer (99 Washington Street, Melrose, MA 02176-6024), IR: Thermo Scientific Nicolet IR 2000 (Verona Road, Madison, WI 53711-4495, USA), DSC: Setaram DSC 131 (7 L’Oratory Street, 69300 Caluire, France), TG: Setaram B.60 (7 L’Oratory Street, 69300 Caluire, France), and XR: X’Pert Pro. dar Panalytical min voltage 40 kV and current 30 mA (Oestliche Rheinbrückenstraße 49, 76187 Karlsruhe, Germany).

2.3. Structure of Amino-p-anisidine-PVC (P2)

Synthesis is described in our precedent work [11] as shown in Scheme 1.

Scheme 1: Structures of (a) amino-PVC (P1) and (b) amino-p-anisidine-PVC (P2).

3. Results and Discussion

3.1. DSC Analysis

The DSC diagram (Figure 1) of the commercial PVC shows a melting point at 279°C. The diagram of the material (P2) shows an exothermic peak at 177°C and an endothermic transformation at 185°C.

Figure 1: DSC diagrams of commercial PVC and polymer (P2).
3.2. TG Analysis

In order to study the thermal stability of polymer (P2), TG analysis has been done from room temperature to 800°C as shown in Figure 2. It can be seen that when (P2) is heated at 156–169°C, the weight loss is about 3 mg and 38 mg while heated at 572–577°C. It is due to two factors including the elimination of HCl and HI groups and complete decomposition of the polymer.

Figure 2: TG curves of polymer (P2).

3.3. Analysis by XRD

The X-ray diffraction pattern shows the amorphous nature of the commercial PVC and the studied polymer (P2) (Figure 3).

Figure 3: XRD of commercial PVC and polymer (P2).
3.4. IR Spectroscopy

Figure 4 shows the IR spectra of the powder form of the studied polymer. The spectrum of the commercial PVC shows a high intensity band assigned to the stretching vibration at 690 cm−1. The spectrum of P2 shows two broad peaks around 3382.97 and 3309.42 cm−1 attributed to the stretching vibration of NH primary amines, some bands of stretching vibration at 1617, 1513, and 1437 cm−1, at 1244, and bending vibration bands at 1332 and at 828 cm−1; we also note that the band at 690 cm−1 becomes very low compared to that corresponding to the PVC as a consequence to the increase of the number of chlorine atoms substituted by diethylenetriamine groups. The IR spectrum of the polymer (P2) heated at 190°C shows the appearance of a band of vibration = 1605 cm−1 and the disappearance of the band at 690 cm−1 which indicates the removal of HCl and HI groups giving rise to a conjugated system having an alternate of single and double bonds.

Figure 4: IR spectra of (a) PVC and (P2) and (b) (P2) and (P2) heated at 190°C.
3.5. Electrical Study
3.5.1. Electrical Measurements

The powders were ground in an agate mortar and then pressed at 4 tons into cylindrical pellets with 11.8 mm in diameter and 2.7 mm in thickness. Electrochemical Impedance Spectra (EIS) were obtained using a Hewlett-Packard HP 4192 analyzer. The impedance measurements were taken in an open circuit using two electrode configurations with signal amplitude of 50 mV and a frequency band ranging from 5 Hz to 13 MHz. Both pellet surfaces were coated with silver pastes electrodes while the platinum wires attached to the electrodes were used as current collectors. All these measurements were performed at equilibrium potential at a temperature ranging between 160°C and 220°C.

3.5.2. Electrochemical Characterization

Figure 5 shows the Nyquist diagram obtained from pellet of amino-p-anisidine-PVC (P2) between 160°C and 220°C which appears as a semicircle and the amplitude of this arc is thermally dependent. The impedance spectra plotted in Figure 5 were analyzed by fitting the data with the equivalent circuit shown in Figure 6. In this figure, corresponds to an inductance which is usually associated with the platinum current-voltage probes; is the ohmic resistance of the amino-p-anisidine-PVC (P2); is resistance and CPE is a constant phase element representing time-dependent capacitive elements.

Figure 5: Complex plane impedance plots of polymer (P2) at different temperatures.
Figure 6: Equivalent circuit used for fitting the impedance data.

(1) dc Conductivity Study. For a pellet with thickness and section area , the dc conductivity was calculated using the following relation:

Activation energies () were obtained by fitting the conductivity data to the Arrhenius relation for thermally activated conduction which is calculated using the following equation:where , , , , and are, respectively, the conductivity, preexponential factor, activation energy, Boltzmann constant, and absolute temperature.

Figure 7 shows the Arrhenius plot of the dc electrical conductivity for the sample named amino-p-anisidine-PVC (P2) in the temperature range 160–220°C. As can be seen in Figure 7, the Arrhenius plot shows a significant curve which may be interpreted as a transition behavior of the polymer. This curvature is observed at around 190–200°C and arises from the differences in the conduction mechanism due to the changes in the behaviors of the polymer at 160–190°C and 200–220°C temperatures. On the other hand, most likely the transport of ions must occur via indirect motion along a convoluted path restricted to the plasticizer-phase, which is responsible for low conductivity at PVC polymer [4].

Figure 7: Arrhenius plots of the conductivity of polymer (P2) solid solutions.

The increase in conductivity may be explained by the formation of a conjugate system with the elimination of HCl and HI groups as shown in the TG analysis described previously.

The observed conductivity of this polymer was equal to 2.16 10−7 S/cm at 190°C, which was higher than 10−8 S/cm found for the polyacene quinone radical (PAQR) [12] and also higher than that reported in literature [13] for the polymer poly-2-[(4-mercaptophenyl) imino methyl] phenol (P-4-MPIMP) and polymer-metal complex compounds which is between 10−11 and 10−10 S/cm.

(2) Frequency Dependence of ac Conductivity. The dependence of with frequency at different temperature is shown in Figure 8. Its value is related to frequency by the following relation [14]:where is a temperature dependent constant and is the power exponent. The evolution of with temperature is tributary to the conduction mechanism.

Figure 8: versus for amino-p-anisidine-PVC (P2).

The estimated power exponent values are shown in Table 1 in terms of temperature. This power exponent fluctuates with temperature between 0.84 and 0.95 in 170°C–220°C domain.

Table 1: Power exponent of the polymer (P2) for different temperatures.

Variations of the power exponent with the temperature do not meet any of the known models, such as the quantum mechanical tunneling (QMT) model [1517], the overlapping-large-polaron tunneling (OLPT) model [1618], and correlated barrier hopping (CBH) model, developed by Elliott [19, 20].

4. Conclusion

This work allowed for studying the new material amino-p-anisidine-PVC (P2) obtained by functionalization of a PVC (Mw = 48000). XRD result shows amorphous nature of P2. The endothermic transformations were confirmed by electrical properties. These results show that the polymer (P2) may be useful in a great variety of electrochemical devices such as rechargeable batteries, super-capacitors, and gas sensors.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors wish to thank the officials of Organic Synthesis Laboratory and Materials Physics Laboratory.

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