Synthesis, Characterization, and Dielectric Behaviors of 4-Diethanolaminomethyl Styrene and Benzyl Methacrylate Copolymer and Its Metal Complexes

Acikses, Aslisah; Öksüz, Fethiye

doi:https://doi.org/10.1155/2019/3257569

Journal of Chemistry

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Abstract Introduction Experimental Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2019 | Article ID 3257569 | https://doi.org/10.1155/2019/3257569

Synthesis, Characterization, and Dielectric Behaviors of 4-Diethanolaminomethyl Styrene and Benzyl Methacrylate Copolymer and Its Metal Complexes

Aslisah Acikses¹and Fethiye Öksüz¹

Academic Editor: Marc Visseaux

Received07 Nov 2018

Revised04 Feb 2019

Accepted12 Mar 2019

Published03 Apr 2019

Abstract

In this paper, the copolymer of 4-diethanolaminomethyl styrene (DEAMSt) with benzyl methacrylate (BMA) was synthesized and characterized using various spectral techniques such as FT-IR, ¹H-NMR, elemental analysis, SEM, XRD, TGA, DTA, and DSC. The copolymer-metal complexes were prepared with Co(II), Ni(II), and Zn(II) metal ions, and poly(DEAMSt-co-BMA) was used as ligand. The copolymer-metal complexes were characterized using elemental analysis. FT-IR, SEM, XRD, magnetic measurements, and the thermal behaviors of the copolymer-metal complexes were studied using TGA, DTA, and DSC. The compositions of DEAMSt and BMA in the copolymer by ¹H-NMR spectra were determined as 0.49 and 0.51, respectively. Both poly(DEAMSt-co-BMA) and poly(DEAMSt-co-BMA)-Zn complexes were heated up to various temperatures. As the temperature increased, the intensities of O-H stretching bands at 3125–3429 cm⁻¹ resulting from hydrogen bond decreased and shifted to high frequency. Gel permeation chromatography was used to determine the average molecular weights and polydispersity index of the poly(DEAMSt0.49-co-BMA) ligand. Both the molecular formula and C, H, and N % were estimated using elemental analysis, and the amounts of metal by mole (%) in the complexes were estimated by SEM-EDX measurements. The XRD patterns of ligand and metal complexes showed that they were of an amorphous nature. The synthesized metal complexes were annealed at 100°C for 1 h in order to obtain crystalline metal complexes. After annealing at 100°C, the metal complexes showed the crystalline structure. The SEM and XRD analysis of the metal complexes confirmed that metal ions contributed to the structure of the ligand. According to the magnetic measurements, it was suggested that geometrical structure for all complexes was tetrahedral geometry and the ratio of ligand to metal was found to be 2 : 1. The dielectric measurements of the ligand and its metal complexes were investigated depend on frequency.

1. Introduction

In recent years, the number of studies on polymer-metal complexes has been increasing in different branches of chemistry, biology, and chemical technology [1, 2]. Furthermore, researchers are recently developing polymer materials using d-block transition metal complexes because of their novel and extraordinary properties [3–5].

The polymer-metal complexes are now being synthesized, whereupon their aromatic and aliphatic monomers with functional groups contain donor atoms such as nitrogen, sulphur, and oxygen (N, S, and O) [6, 7].

In the literature, these studies have reported on polymers/copolymers/terpolymers acting as different types of ligands with transition metal ions [8–10]. Polymer metal complexes are used in many applications, such as alkali and alkaline earth metal ion separation [11], organic synthesis and nuclear chemistry [12], thermal stability, electrical conductivity, separation, photofunctions, catalytic activity, and biomedicine, gels, and ointments for medical use [13, 14]. In addition, polymer-metal complexes are used as models for bioinorganic systems, as well as mechanochemical systems [11, 15, 16].

In the present study, the poly(DEAMSt-co-BMA) was synthesized using free-radical polymerization, and this copolymer system was used as ligand. The copolymer-metal complexes were prepared with Co(II), Ni(II), and Zn(II) metal ions. The resulting copolymer and its metal complexes were characterized using various spectroscopic techniques, including surface morphology, whereupon their dielectric and thermal behaviors were investigated for their future applications.

2. Experimental

2.1. Materials

4-Diethanolaminomethyl styrene (DEAMSt) monomer was prepared through the reaction of 4-chloromethylstyrene (CMS) and diethanolamine (DEA) in accordance with the method stated in the literature [17], benzyl methacrylate (BMA) monomer, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), 1,4-dioxane, n-hexane, diethylether, ethanol (Fluka), and 2,2′-azobisisobutyronitrile (AIBN). The metal ion salts were used in the form of nickel acetate (Ni(CH₃COO)₂·4H₂O), cobalt acetate (Co(CH₃COO)₂·4H₂O), and zinc acetate (Zn(CH₃COO)₂·4H₂O).

2.2. Synthesis of Copolymer Used as the Ligand

Free-radical copolymerization of DEAMSt and BMA was carried out in a 25 mL flask equipped with a condenser. For this purpose, DEAMSt (0.272 g, 0.0012 mol) and BMA (0.855 g, 0.0048 mol) monomers were placed into a polymerization tube, whereby AIBN (0.011 g) and 1,4-dioxane (3 mL) were used as an initiator and solvent. Argon gas was passed through the mixture for 10 min, and the polymerization tube was closed. The polymerization tube was immersed in a thermostatic oil bath at 60°C, and polymerization was controlled for 22 h. The obtained copolymer was diluted with THF solvent and was precipitated with n-hexane. The product copolymer was dried at 40°C under a vacuum. Figure 1 shows the synthesis reaction of copolymer. FT-IR, ¹H-NMR, elemental analyses, SEM, and XRD were used for the characterization of the copolymer. The composition of poly(DEAMSt0.49-co-BMA) was found to be 0.49 for DEAMSt and 0.51 for BMA using ¹H-NMR.

The analytical data of FT-IR: 3429 cm⁻¹ (-OH stretching), 3090–2942 cm⁻¹ (aromatic and aliphatic C-H), 1731 cm⁻¹ (C=O in BMA), 1610 cm⁻¹ (C=C), 1370-1265-1145 cm⁻¹ (C-N), and 1066 cm⁻¹ (C-O); ¹H-NMR: 7.8–6.7 ppm (protons on aromatic ring), 3.9 ppm (phenyl CH₂-N), 3.65 ppm (CH₂-O), 4.95 ppm (CH₂-O in BMA), 2.8 ppm (N-CH₂), 1.2–2.2 ppm (aliphatic-CH₂); and elemental analysis: calculated, C: 73.65%, H: 7.36%, and N: 1.94% and found, C: 73.70%, H: 6.50%, and N: 2.06%. Figure 2 shows the FT-IR spectrum of the poly(DEAMSt0.49-co-BMA).

2.3. Synthesis of the Copolymer-Metal Complexes

The metal complexes of the ligand were investigated in relation to Co(II), Ni(II), and Zn(II). The copolymer-metal complexes were prepared in presence of ethanol as the solvent [18], whereby the synthesis of Co(II) complex of poly(DEAMSt0.49-co-BMA) was followed. For this purpose, 0.390 g (0.0008 mol) poly(DEAMSt0.49-co-BMA) used as the ligand was dissolved in 40 mL ethanol and was stirred at 65°C for 2 h, and the pH of the solution was calibrated by adding dilute 0.1 M NaOH solution in water. After one hour, a dilute solution of 0.098 g (0.0004 mol) cobalt(II)acetate was added into the mixture in drops and the reaction mixture was refluxed at 65°C for 48 h. The resulting Co(II) complex of poly(DEAMSt0.49-co-BMA) was collected using filtration, washed with distilled water up to pH = 6, and dried at 40°C under a vacuum. The Co(II) complex of poly(DEAMSt0.49-co-BMA) was black in color (yield: 70%). The same procedures were repeated for the poly(DEAMSt0.49-co-BMA)-Ni and the poly(DEAMSt0.49-co-BMA)-Zn complexes. Figure 1 shows the synthesis reaction of the copolymer-metal complexes.

The copolymer-metal complexes prepared using metal ions from the poly(DEAMSt0.49-co-BMA) appeared as light green color for Ni(II) (yield: 72%) and white color for Zn(II) (yield: 71%). All of the copolymer-metal complexes were colored and insoluble in common organic solvents. The cause of the insoluble metal complexes in organic solvents was associated with a cross-linked structure [19, 20]. Accordingly, the characterization of copolymer-metal complexes was carried out by FT-IR, elemental analysis, magnetic susceptibility, XRD, SEM/SEM-EDX, DSC, TGA, and DTA.

The characterization with FT-IR for Co(II) complex was as follows: 3436 cm⁻¹ (-OH stretching), 3090–2936 cm⁻¹ (aromatic and aliphatic C-H stretching), 1723 cm⁻¹ (C=O in BMA), 1608 cm⁻¹ (C=C), 1374, 1242–1141 cm⁻¹ (C-N), 1073 cm⁻¹ (C-O) and elemental analysis: calculated, C: 63.95%, H: 6.39%, and N: 1.68% and found, C: 62.89%, H: 6.50%, and N: 2.06%. Figure 2 shows the FT-IR spectrum of the poly(DEAMSt0.49-co-BMA)-Co complex.

The characterization with FT-IR for the Ni(II) complex was as follows: 3440 cm⁻¹ (-OH stretching), 3087–2933 cm⁻¹ (aromatic and aliphatic C-H stretching), 1727 cm⁻¹ (C=O stretching in BMA), 1607 cm⁻¹ (C=C), 1366, 1250–1137 cm⁻¹ (C-N), 1062 cm⁻¹ (C-O) and elemental analysis: calculated, C: 63.10%, H: 6.41%, and N: 1.69% and found, C: 61.10%, H: 6.35%, and N: 2.01%. Figure 2 shows the FT-IR spectrum of the poly(DEAMSt0.49-co-BMA)-Ni complex.

The characterization with FT-IR for the Zn(II) complex was as follows: 3429 cm⁻¹ (-OH stretching), 3090–2940 cm⁻¹ (aromatic and aliphatic C-H stretching), 1723 cm⁻¹ (in BMA C=O), 1610 cm⁻¹ (C=C), 1368, 1235–1137 cm⁻¹ (C-N), 1062 cm⁻¹ (C-O) and elemental analysis: calculated, C: 63.01%, H: 6.30%, and N: 1.66% and found, C: 65.11%, H: 6.49%, and N: 1.95%. Figure 2 shows the FT-IR spectrum of the poly(DEAMSt0.49-co-BMA)-Zn complex.

2.4. Instrumentation

The infrared spectra of the ligand and metal complexes were registered on a Perkin-Elmer Spectrum One Fourier-Transform Infrared Spectroscopy (FT-IR). The spectra were collected by scanning over the range from 4000 to 450 cm⁻¹ with KBr pellets. Proton nuclear magnetic resonance (¹H-NMR) spectra were recorded on a 400 MHz Bruker AVIII 400 Spectrometer, using an interior standard (TMS) and deuterated chloroform as solvents. The GPC measurements were carried out using an Agilent 1100 system via a refractive index detector. A linear standard polystyrene was used to calibrate the GPC instrument. The tetrahydrofuran (THF) was used as a carrier solvent at a flow rate of 1 mL·min⁻¹ at room temperature. The elemental analysis was carried out on a FLASH 2000 (organic) elemental analyzer. The surface analysis of the copolymer and its metal complexes was examined under a electron microscope (SEM) (ZEISS EVO MA10), and the XRD analysis was performed using XRD (D8ADVENCE) with a CuKα tube, whereby analysis was performed at a pitch rate of 0.03 between 3 and 80° at a wavelength of 1.5406 (λ). The magnetic susceptibility values were evaluated at 300 K using a Sherwood Scientific MK1 device. The calorimetric measurements were carried out using a Shimadzu DSC-50 thermal analyzer under a N₂ flow and a heating rate of 20°C/min at 200°C. The thermal behavior of the ligand and its metal complex was observed by TGA using a Shimadzu TGA-50 and Shimadzu DTA-60 AH thermobalance under N₂ flow and a heating rate of 10°C/min at 700°C. The capacitance measurements were carried out at room temperature with a CyadTech 7600 precision LRC Mater Impedance analyzer and frequency range of 1 kHz–5 MHz. Therefore, 0.1 g polymer samples were pressed under four tons and transformed into disk. Its thickness was measured, and the disk surfaces were covered with silver paste.

3. Results and Discussion

3.1. FT-IR Analysis

Figure 2 shows the FT-IR spectra of the ligand and its metal complexes. The FT-IR spectra of the metal complexes had similar absorption peaks with important shifts compared to the poly(DEAMSt0.49-co-BMA) ligand. Some of the peaks in the copolymer shifted to lower frequencies in the metal complexes (Co(II), Ni(II), and Zn(II)) [21]. For example, the bands at 1370 cm⁻¹ and 1145–1265 cm⁻¹ C-N stretching vibrations were visible in the FT-IR spectrum of the poly(DEAMSt0.49-co-BMA) ligand and shifted to lower frequencies in metal complexes. The C-N stretching vibrations in the FT-IR spectrum of Co(II), Ni(II), and Zn(II) metal complexes were observed at 1374, 1242–1141 cm⁻¹, 1366, 1250–1137 cm⁻¹, and 1368, 1235–1137 cm⁻¹, respectively. The C-N bands of the metal complexes were quite large and had a broad peak. This may be due to the coordination of metal with oxygen of the ligand. The C-O bands on the metal complexes were quite broad at 1073, 1062, and 1062 cm⁻¹, respectively, which signified that they were joined in the polymer matrix of the metals [22]. When the ligand was complexed with the metal due to the electrical density on the nitrogen, those bonds shifted towards low frequencies. In addition, the M-O bands of metal complexes were seen at 500–450 cm⁻¹ [12, 22].

The FT-IR spectrum of poly(DEAMSt0.49-co-BMA) ligand indicated a characteristic absorption band at 3429 cm⁻¹ -OH stretching vibration. This band at the 3429 cm⁻¹ region was assigned to -OH stretching vibration of the intermolecular hydrogen bond. This band was also observed in the FT-IR spectra of metal complexes at 3436, 3440, and 3429 cm⁻¹, respectively, and was quite broad. Those of metal complexes of Co(II), Ni(II), and Zn(II) shifted to a higher frequency. The peak intensity depending on the formation of the complexes increased as a result of interaction between metal ions and -OH [23, 24]. While the C=O peak in the ligand was seen at 1731 cm⁻¹, these bonds in the Co(II), Ni(II), and Zn(II) metal complexes were observed at 1723, 1727, and 1723 cm⁻¹, respectively. These bands, depending on the formation of the complexes, have shifted to a lower wave number, whereby those results indicated the lower rigidity of the C=O bands in the ligand [25]. The change in the color of the complexes was caused by the orbital transition, namely, the change in the energy of the orbitals, which pointed out that metal complexes were formed.

Both poly(DEAMSt0.49-co-BMA) and poly(DEAMSt0.49-co-BMA)-Zn complex were heated up to various temperatures. As is indicated in Figure 3(a), as temperature increased, the intensities of O-H stretching bands at 3125–3429 cm⁻¹ resulting from the hydrogen bond decreased and shifted to high frequency. This behavior showed a significant weakness in O-H stretching vibration of the intermolecular hydrogen bond depending on temperature increase. As is shown in Figure 3(b), a similar behavior was also observed for free OH groups that were not attached to Zn metal in the poly(DEAMSt0.49-co-BMA)-Zn complex.

(a)

(b)

3.2. ¹H-NMR Analysis

Figure 4 shows the ¹H-NMR spectrum of the poly(DEAMSt0.49-co-BMA) ligand. The ¹H-NMR spectrum of the ligand showed the characteristic signals at 7.8–6.7 ppm (aromatic ring protons), at 3.90 ppm (phenyl CH₂-N protons), at 3.65 ppm (CH₂-O), at 4.95 ppm (in BMA (CH₂-O)), at 2.80 ppm (N-CH₂), and at 1.2–2.2 ppm (signals of aliphatic CH₂ and CH₃ protons on main chain). These results confirmed the formation of the poly(DEAMSt0.49-co-BMA) ligand. The copolymer-metal complexes were insoluble in almost all organic solvents. Therefore, ¹H-NMR spectra could be not recorded [19]. The percent compositions of the copolymer were estimated via the ¹H-NMR spectrum. Taking into account the integral heights of the aromatic ring protons (7.8–6.7 ppm) and N–CH₂ protons at 2.80 ppm, the calculated composition of % DEAMSt and % BMA for the copolymer was found to be 49% in DEAMSt and 51% in BMA by mole.

3.3. GPC Analysis

The average molecular weight (M_w and M_n) and polydispersity index of the poly(DEAMSt0.49-co-BMA) ligand were estimated using gel permeation chromatography (GPC) and tetrahydrofuran (THF) as a solvent. Figure 5 shows the GPC curve. The average molecular weight, number average molecular weight, and polydispersity index of the poly(DEAMSt0.49-co-BMA) ligand were estimated as M_w = 2.33 × 10⁴, M_n = 1.18 × 10⁴, and (HI) = M_w/M_n = 1.97, respectively. The polydispersity index value of the ligand indicated that there was a narrow distribution of molecular weight of the copolymer. The GPC analysis could be not measured because the complexes were insoluble.

3.4. Elemental Analysis and SEM Morphology

The surface morphology of the ligand and its metal complexes was investigated using SEM analysis and is shown in Figures 6(a)–6(d). The SEM image of the poly(DEAMSt0.49-co-BMA) ligand was quite smooth, and there was no image indicating any damage. In addition, the ligand showed a uniform morphology with amorphous layer-like structure [26]. When compared to the metal complexes, the pore numbers on the surface of the Co(II), Ni(II), and Zn(II) metal complexes increased considerably and rough and damaged images were formed [27]. The metal complexes showed a compact morphology [26]. These images were the result of coordination of metal ions in the polymer matrix [28].

(a)

(b)

(c)

(d)

The molecular formula and C, H, and N percentages were estimated via elemental analysis, and the amounts of metal by mole (%) in the complexes were found through SEM-EDX measurements. In the poly(DEAMSt0.49-co-BMA)-Co(II), Ni(II), and Zn(II) complexes, calculated/found values were found as follows: for Co(II) = 10.33/13.63, for Ni(II) = 15.26/13.44, and for Zn(II) = 15.28/14.90, respectively.

The molecular formula according to elemental analysis results of the ligand and metal complexes was found to be C₂₄H₃₁O₄N for ligand and (C₂₄H₂₉O₄N)₂-Co, (C₂₄H₂₉O₄N)₂-Ni, and (C₂₄H₂₉O₄N)₂-Zn for the complexes. The found results for the ligand and metal complexes confirmed the formula and structure of the molecule.

3.5. XRD Characterization

Figures 7(a)–7(d) show the XRD patterns of the copolymer used as the ligand and its metal complexes. The XRD patterns of ligand and metal complexes showed a broad peak at 2θ value of 20°, which showed that they were of an amorphous nature. The synthesized metal complexes were annealed at 100°C for 1 h in order to obtain crystalline metal complexes. The metal complexes showed sharp peaks with characteristics of the crystalline structure, and the crystalline behaviors of the metal complexes were improved [29, 30].

(a)

(b)

(c)

(d)

The SEM and XRD results of the metal complexes confirmed that metal ions contributed to the structure of the ligand. The ligand and its metal complexes formed successfully.

3.6. Magnetic Susceptibility

The magnetic susceptibility results of the copolymer-complexes showed that the Co(II) and Ni(II) were paramagnetic and Zn(II) was diamagnetic [13]. The measured μ_eff values of Co(II) and Ni(II) were 3.79 B.M. (d⁷, three unpaired electrons) and 2.90 B.M. (d⁸, two unpaired electrons), respectively. Consequently, these values indicated that the Co(II), Ni(II), and Zn(II) complexes had a tetrahedral geometrical structure (sp³ hybrid) [31]. According to the magnetic measurements, the ratio of ligand to metal was found to be 2 : 1.

3.7. DSC Analysis

The Tg (glass transition temperature) of the ligand and metal complexes was determined by a Shimadzu DSC-50 thermal analyzer. The Tg value of the ligand was 67°C, and Tg values of metal complexes (Co(II), Ni(II), and Zn(II)) were 77, 79, and 70°C, respectively. These values were determined under conditions similar to those used for the ligand. Figure 8 shows the DSC curves of the ligand and metal complexes. All of the ligand and its metal complexes showed a single transition. Metal complexes had Tg values higher compared to the ligand due to the decrease in free volume as a result of the coordination of metal and ligand in the metal complexes. Therefore, Tg values of the metal complexes increased [32, 33].

3.8. Thermal Behaviors

Thermal behaviors of the ligand and its metal complexes were measured using TGA and DTA. Figures 9(a)–9(d) show the thermograms of the ligand and metal complexes, and Figure 10 shows the comparative TGA thermograms of ligand-metal complexes.

(a)

(b)

(c)

(d)

3.8.1. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA) Ligand

As is indicated in Figure 9(a), the TGA thermogram of the ligand showed that there was a decomposition with two stages (240–373 and 421–496°C). Before the initial decomposition stage, there was a very negligible mass loss below 240°C. In the first stage of decomposition, maximum weight loss was 74.50% between 240 and 373°C. The second stage of decomposition showed a maximum weight loss of 22.60% between 421 and 496°C. The ligand lost was 97.10% of its original weight and 2.76% of the residue left at 600°C.

In the DTA thermogram of the poly(DEAMSt0.49-co-BMA) ligand in Figure 9(a), the maximum exothermic region for ligand was between 483 and 578°C [34].

3.8.2. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA)-Co Complex

The TGA thermogram of the Co(II) complex in Figure 9(b) indicated that there were two stages of decomposition (210–337 and 380–414°C). Before the initial decomposition stage, there was very negligible weight loss below 210°C. It was revealed that the Co(II) complex was stable up to 210°C. The first stage of decomposition indicated a maximum weight loss of 46.50% between 210 and 337°C. The second stage of decomposition showed a maximum weight loss of 10.60% between 380 and 414°C. The Co(II) complex lost 57.10% of its original weight and 42.70% of the residue left at 600°C.

In the DTA thermogram of the poly(DEAMSt0.49-co-BMA)-Co complex in Figure 9(b), the maximum exothermic region for the Co(II) complex was between 326 and 332°C and the second maximum exothermic region was between 360 and 380°C [34].

3.8.3. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA)-Ni Complex

In the TGA thermogram of the Ni(II) complex in Figure 9(c), it was observed that there was a two-stage decomposition (220–365 and 404–450°C). Before the initial decomposition stage, there was a very negligible weight loss below 220°C, showing that the Ni(II) complex was stable up to 220°C. The first stage of decomposition indicated a weight loss of 66.3% between 220 and 365°C. The second stage of decomposition observed a maximum weight loss of 17.20% between 404 and 450°C. The Ni(II) complex lost 83.50% of its original weight and 16.40% of the residue left at 600°C.

As seen in Figure 9(c), in the DTA thermogram of the poly(DEAMSt0.49-co-BMA)-Ni complex, the maximum exothermic region for the Ni(II) complex was observed between 378 and 451°C [34].

3.8.4. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA)-Zn Complex

In the TGA thermogram of the Zn(II) complex in Figure 9(d), it was observed that there was a two-stage decomposition (230–380 and 421–505°C). Before the initial decomposition stage, there was a very negligible weight loss below 230°C, showing that the Zn(II) complex was stable up to 230°C. The initial stage of decomposition observed a maximum weight loss of 60.60% between 230 and 380°C. The second stage of decomposition showed a maximum weight loss of 30.90% between 421 and 505°C. The Zn(II) complex lost 91.50% of its original weight and 8.30% of the residue left at 600°C.

In the DTA thermogram of poly(DEAMSt0.49-co-BMA)-Zn complex in Figure 9(d), the maximum endothermic region for Zn(II)-complex was between 281 and 374°C and the second maximum exothermic region was between 473 and 581°C [34].

Thermal stability was determined according to the initial decomposition temperatures in TGA curves. According to revealed results, all of the metal complexes have less thermal stability than the poly(DEAMSt0.49-co-BMA) ligand due to the coordination of the metal ions in the ligand [32, 35]. This is a result of interaction between the molecules due to the –OH in the molecular structure of the ligand. Compared to the metal complexes, the Zn(II) complexes were more thermally stable than the other Co(II) and Ni(II) metal complexes [12, 30]. The order of thermal stability of the metal complexes was found as Zn(II) > Ni(II) > Co(II) complexes. The reason for the lower thermal stability of the metal complexes can be due to forming of coordination and cross-linking structure with bulk effect of the metal complexes [36]. Also, the metal complex with Co(II) of the ligand demonstrated the most residue (42.70%), and metal complexes became stable at 600°C. The DTA curves showed a maximum peak between 400 and 600°C for the ligand and copolymer-metal complexes, which were stable [37].

3.9. Dielectric Properties

The change of dielectric constant (ε′) and dielectric loss factor (ε″) of the poly(DEAMSt049-co-BMA) ligand and its metal complexes at room temperature depending on the frequency is demonstrated in Figures 11 and 12. The electric behaviors of the ligand and metal complexes showed a difference according to the metal ions. The electric constants (ε′) of the poly(DEAMSt0.49-co-BMA) ligand and Co(II), Ni(II), and Zn(II)-complexes at 1 kHz were found to be 5.03, 2.69, 3.59, and 2.83, respectively. The dielectric loss factor (ε″) of the poly(DEAMSt0.49-co-BMA) and Co(II), Ni(II), and Zn(II) complexes at 1 kHz was found to be 0.310, 0.011, 0.140, and 0.075, respectively. According to the results, the dielectric constant of the poly(DEAMSt0.49-co-BMA) ligand was found to be higher than that of the metal complexes. It was observed that the dielectric constant of the poly(DEAMSt0.49-co-BMA) ligand increased as the number of –OH and C=O groups increased. Therefore, the presence of polar groups such as –OH and C=O groups showed that was poly(DEAMSt0.49-co-BMA) ligand with a polar structure is one cause for the increase in dielectric constant [38, 39]. When these results were compared with the results of the metal complex, the dielectric constant of Ni(II) complex was found to be higher than the dielectric constant of the Co(II) and Zn(II) complexes. Therefore, the participation of the metal ions within the copolymer matrix decreased the polarity of the -OH groups, which thus increased their tendency to compose a complex. Similar results were found in the dielectric loss factor. A similar type of dielectric behavior is reported in the literature [40, 41].

According to Figures 11 and 12, the dielectric constant and dielectric loss factor with increasing frequency decreased and remained stable at high frequencies [42–44]. This situation can be attributed to the increase in the number of dipoles, which caused an increased polarization [45, 46]. The dielectric constant (ε′) occurred more greatly at lower frequencies and at higher temperatures.

3.10. Conductivity Measurements

The conductivity (σ) measurements of the poly(DEAMSt0.49-co-BMA) ligand and its metal complexes at room temperature were determined to be a function of frequency and are shown in Figure 13. The conductivity of the poly(DEAMSt0.49-co-BMA) ligand and its metal complexes increased proportionally with frequency. The electrical conductivity of the polymer was based on the presence of free ions connected chemically with macromolecule [47]. The ionic conductivity proportionally increased with the number of load carriers and their motion. The conductivity values of the ligand and its metal complexes were found at room temperature and at 1 kHz.

The conductivity values of the poly(DEAMSt0.49-co-BMA) and Co(II), Ni(II), and Zn(II) complexes at 1 kHz were found to be 2.81 × 10⁻⁹, 1.50 × 10⁻⁹, 1.99 × 10⁻⁹, and 1.58 × 10⁻⁹ S/cm, respectively. According to the results, the conductivity of the poly(DEAMSt0.49-co-BMA) ligand was higher than the metal complexes. Thus, the higher polarity of the -OH and C=O groups in the structure of ligand caused the increase in electrical conductivity (2.81 × 10⁻⁹ S/cm at 1 kHz). The higher conductivity values of the ligand showed more polarization. When these results were compared with those found for the metal complexes, the conductivity values decreased by binding the metals and Ni(II) complexes and were found to be higher than the conductivity value of the Co(II) and Zn(II) complexes. The conductivity increased according to the sequence of binding metals Ni(II) > Zn(II) > Co(II). These may be associated with the higher ionic character between the functional groups of the polymer and the metal ion. In general, the direct current conductivity and electrode polarization and dielectric relaxation phenomenon can be distinguished at both low- and high-frequency intermediates, respectively [48, 49]. The conductivity value is an event related to the conduction mechanism occurring within materials during the application of an electromagnetic field.

4. Conclusions

We synthesized and characterized a new poly(DEAMSt0.49-co-BMA) used as ligand and three copolymer-metal complexes, poly(DEAMSt0.49-co-BMA)-Co, poly(DEAMSt0.49-co-BMA)-Ni, and poly(DEAMSt0.49-co-BMA)-Zn. The ligand and metal complexes were successfully confirmed by FT-IR, XRD, SEM, and elemental analysis, as well. The compositions of DEAMSt and BMA in the copolymer by ¹H-NMR spectra were determined. The average molecular weight, number average molecular weight, and polydispersity index of the poly(DEAMSt0.49-co-BMA) ligand were estimated as M_w = 2.33 × 10⁴, M_n = 1.18 × 10⁴, and (HI) = M_w/M_n = 1.98 respectively. The magnetic susceptibility results of the copolymer complexes showed that the Co(II) and Ni(II) were paramagnetic and Zn(II) was diamagnetic and that the Co(II), Ni(II), and Ni(II) complexes showed a tetrahedral geometrical structure (sp³ hybrid). According to XRD patterns of the ligand, the complexes showed an amorphous structure. The synthesized metal complexes were annealed at 100°C for 1 h in order to obtain crystalline metal complexes. The Tg value of the ligand was estimated as 67°C, and the Tg values of the metal complexes (Co(II), Ni(II), and Zn(II)) were measured as 77, 79, and 70°C, respectively. Considering the initial decomposition temperatures in all thermogravimetric analyses to reflect thermal stability, all of the metal complexes were thermally less stable than the poly(DEAMSt0.49-co-BMA) ligand. As the frequency increased, the dielectric constant and the dielectric loss factor decreased, whereas as the frequency increased, the conductivity increased. As a result, the dielectric constant, the dielectric loss factor, and the conductivity value of the poly(DEAMSt0.49-co-BMA) ligand had the highest value at 1 kHz. The presence of –OH and C=O groups in the ligand structure caused the polarity to be very high.

Data Availability

The data used to support the results of this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgments

The authors would like to thank FUBAP (FF-17-27) for financially supporting this project.

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Copyright © 2019 Aslisah Acikses and Fethiye Öksüz. 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.

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Journal of Chemistry

Synthesis, Characterization, and Dielectric Behaviors of 4-Diethanolaminomethyl Styrene and Benzyl Methacrylate Copolymer and Its Metal Complexes

Abstract

1. Introduction

2. Experimental

2.1. Materials

2.2. Synthesis of Copolymer Used as the Ligand

2.3. Synthesis of the Copolymer-Metal Complexes

2.4. Instrumentation

3. Results and Discussion

3.1. FT-IR Analysis

3.2. 1H-NMR Analysis

3.3. GPC Analysis

3.4. Elemental Analysis and SEM Morphology

3.5. XRD Characterization

3.6. Magnetic Susceptibility

3.7. DSC Analysis

3.8. Thermal Behaviors

3.8.1. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA) Ligand

3.8.2. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA)-Co Complex

3.8.3. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA)-Ni Complex

3.8.4. TGA-DTA Thermograms of the Poly(DEAMSt0.49-co-BMA)-Zn Complex

3.9. Dielectric Properties

3.10. Conductivity Measurements

4. Conclusions

Data Availability

Conflicts of Interest

Acknowledgments

References

Copyright

3.2. ¹H-NMR Analysis