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

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, H-NMR, elemental analysis, SEM, XRD, TGA, DTA, and DSC. .e copolymer-metal complexes were prepared with Co(II), Ni(II), and Zn(II) metal ions, and poly(DEAMSt-co-BMA) was used as ligand. .e 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. .e compositions of DEAMSt and BMA in the copolymer by H-NMR spectra were determined as 0.49 and 0.51, respectively. Both poly(DEAMSt-coBMA) 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 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 themolecular 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-EDXmeasurements. .e XRD patterns of ligand and metal complexes showed that they were of an amorphous nature..e 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. .e 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 tometal was found to be 2 :1. .e dielectric measurements of the ligand and its metal complexes were investigated depend on frequency.


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][4][5].
e 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][9][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.e copolymer-metal complexes were prepared with Co(II), Ni(II), and Zn(II) metal ions.e 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.

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.
e polymerization tube was immersed in a thermostatic oil bath at 60 °C, and polymerization was controlled for 22 h.e obtained copolymer was diluted with THF solvent and was precipitated with n-hexane.e product copolymer was dried at 40 °C under a vacuum.Figure 1 shows the synthesis reaction of copolymer.FT-IR, 1 H-NMR, elemental analyses, SEM, and XRD were used for the characterization of the copolymer.e composition of poly(DEAMSt0.49-co-BMA)was found to be 0.49 for DEAMSt and 0.51 for BMA using 1 H-NMR.

Synthesis of the Copolymer-Metal Complexes.
e metal complexes of the ligand were investigated in relation to Co(II), Ni(II), and Zn(II).e 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.e 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.e Co(II) complex of poly(DEAMSt0.49co-BMA)was black in color (yield: 70%).
e 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.e 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.

Instrumentation.
e infrared spectra of the ligand and metal complexes were registered on a Perkin-Elmer Spectrum One Fourier-Transform Infrared Spectroscopy (FT-IR).e spectra were collected by scanning over the range from 4000 to 450 cm −1 with KBr pellets.Proton nuclear magnetic resonance ( 1 H-NMR) spectra were recorded on a 400 MHz Bruker AVIII 400 Spectrometer, using an interior standard (TMS) and deuterated chloroform as solvents.e 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.e tetrahydrofuran (THF) was used as a carrier solvent at a flow 2 Journal of Chemistry rate of 1 mL•min −1 at room temperature.
e elemental analysis was carried out on a FLASH 2000 (organic) elemental analyzer.e 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).e magnetic susceptibility values were evaluated at 300 K using a Sherwood Scienti c MK1 device.e calorimetric measurements were carried out using a Shimadzu DSC-50 thermal analyzer under a N 2 ow and a heating rate of 20 °C/min at 200 °C.e 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 N 2 ow and a heating rate of 10 °C/min at 700 °C.e 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.erefore, 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.

FT-IR Analysis.
Figure 2 shows the FT-IR spectra of the ligand and its metal complexes.e 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

Journal of Chemistry
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.e 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.e C-N bands of the metal complexes were quite large and had a broad peak.is may be due to the coordination of metal with oxygen of the ligand.e 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].
is band at the 3429 cm −1 region was assigned to -OH stretching vibration of the intermolecular hydrogen bond. is band was also observed in the FT-IR spectra of metal complexes at 3436, 3440, and 3429 cm −1 , respectively, and was quite broad.
ose of metal complexes of Co(II), Ni(II), and Zn(II) shifted to a higher frequency.e 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.ese 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].e 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(DEAMSt0.49co-BMA)-Zncomplex 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.is 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)-Zncomplex.ese results confirmed the formation of the poly(DEAMSt0.49-co-BMA)ligand.

1 H-NMR Analysis.
e copolymer-metal complexes were insoluble in almost all organic solvents.erefore, 1 H-NMR spectra could be not recorded [19].e percent compositions of the copolymer were estimated via the 1 H-NMR spectrum.Taking into account the integral heights of the aromatic ring protons (7.8-6.7 ppm) and N-CH 2 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.

GPC Analysis.
e 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.e 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 × 10 4 , M n � 1.18 × 10 4 , and (HI) � M w /M n � 1.97, respectively.
e polydispersity index value of the ligand indicated that there was a narrow distribution of molecular weight of the copolymer.
e GPC analysis could be not measured because the complexes were insoluble.

Elemental Analysis and SEM Morphology.
e surface morphology of the ligand and its metal complexes was investigated using SEM analysis and is shown in Figures 6(a)-6(d).e SEM image of the poly(DEAMSt0.49co-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].e metal complexes showed a compact morphology [26].ese images were the result of coordination of metal ions in the polymer matrix [28].
e 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 e found results for the ligand and metal complexes confirmed the formula and structure of the molecule.

XRD Characterization. Figures 7(a)-7(d)
show the XRD patterns of the copolymer used as the ligand and its metal complexes.e 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.e synthesized metal complexes were annealed at 100 °C for 1 h in order to obtain crystalline metal complexes.e metal complexes showed sharp peaks with characteristics of the crystalline structure, and the crystalline behaviors of the metal complexes were improved [29,30].e SEM and XRD results of the metal complexes con rmed that metal ions contributed to the structure of the ligand.
e ligand and its metal complexes formed successfully.

Magnetic Susceptibility.
e magnetic susceptibility results of the copolymer-complexes showed that the Co(II) and Ni(II) were paramagnetic and Zn(II) was diamagnetic [13].
e measured μ e values of Co(II) and Ni(II) were 3.79 B.M. (d 7 , three unpaired electrons) and 2.90 B.M. (d 8 , two unpaired electrons), respectively.Consequently, these values indicated that the Co(II), Ni(II), and Zn(II) complexes had a tetrahedral geometrical structure (sp 3 hybrid) [31].According to the magnetic measurements, the ratio of ligand to metal was found to be 2 : 1.

DSC Analysis.
e Tg (glass transition temperature) of the ligand and metal complexes was determined by a Shimadzu DSC-50 thermal analyzer.e 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.ese 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.

ermal Behaviors.
ermal behaviors of the ligand and its metal complexes were measured using TGA and DTA.Figures 9(a

TGA-DTA ermograms 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 rst stage of decomposition, maximum weight loss was 74.50% between 240 and 373 °C.e second stage of decomposition showed a maximum weight loss of 22.60% between 421 and 496 °C.e ligand lost was 97.10% of its original weight and 2.76% of the residue left at 600 °C.6 Journal of Chemistry 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].

TGA-DTA ermograms of the Poly(DEAMSt0.49-co-BMA)-Co Complex.
e 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.e rst stage of decomposition indicated a maximum weight loss of 46.50% between 210 and 337 °C.
e second stage of decomposition showed a maximum weight loss of 10.60% between 380 and 414 °C.e 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)-Cocomplex 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].

TGA-DTA ermograms 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 twostage 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.e rst stage of decomposition indicated a weight loss of 66.3% between 220 and 365 °C.e second stage of decomposition observed a maximum weight loss of 17.20% between 404 and 450 °C.e Ni(II) complex lost 83.50% of its original weight and 16.40% of the residue left at 600 °C.

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

TGA-DTA ermograms 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 twostage 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.e initial stage of decomposition observed a maximum weight loss of 60.60% between 230 and 380 °C.e second stage of decomposition showed a maximum weight loss of 30.90% between 421 and 505 °C.e 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)-Zncomplex 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].ermal 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]. is 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].e order of thermal stability of the metal complexes was found as Zn(II) > Ni(II) > Co(II) complexes.
e reason for the lower thermal stability of the metal complexes can be due to forming of coordination and cross-linking structure with bulk e ect 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.e DTA curves showed a maximum peak between 400 and 600 °C for the ligand and copolymer-metal complexes, which were stable [37].

Dielectric Properties.
e change of dielectric constant (ε′) and dielectric loss factor (ε″) of the poly(DEAMSt049co-BMA) ligand and its metal complexes at room temperature depending on the frequency is demonstrated in Figures 11 and 12. e electric behaviors of the ligand and metal complexes showed a di erence according to the metal ions.
e 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.erefore, 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.erefore, 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][43][44].
is situation can be attributed to the increase in the number of dipoles, which caused an increased polarization [45,46].e dielectric constant (ε′) occurred more greatly at lower frequencies and at higher temperatures.

Conductivity Measurements.
e 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.e conductivity of the poly(DEAMSt0.49-co-BMA)ligand and its metal complexes increased proportionally with frequency.
e electrical conductivity of the polymer was based on the presence of free ions connected chemically with macromolecule [47].e ionic conductivity proportionally increased with the number of load carriers and their motion.e conductivity values of the ligand and its metal complexes were found at room temperature and at 1 kHz.e 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.us, 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).e 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.e conductivity increased according to the sequence of binding metals Ni(II) > Zn(II) > Co(II).
ese 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].e conductivity value is an event related to the conduction mechanism occurring within materials during the application of an electromagnetic eld.
e ligand and metal complexes were successfully con rmed by FT-IR, XRD, SEM, and elemental analysis, as well.e compositions of DEAMSt and BMA in the copolymer by 1 H-NMR spectra were determined.
e 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 × 10 4 , M n 1.18 × 10 4 , and (HI) M w / M n 1.98 respectively.e 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 (sp 3 hybrid).According to XRD patterns of the ligand, the complexes showed an amorphous structure.e synthesized metal complexes were annealed at 100 °C for 1 h in order to obtain crystalline metal complexes.
e 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 re ect 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.e presence of -OH and C O groups in the ligand structure caused the polarity to be very high.
Data Availability e data used to support the results of this study are available upon request from the corresponding author.
)-9(d) show the thermograms of the ligand and metal complexes, and Figure10shows the comparative TGA thermograms of ligand-metal complexes.
/ 13.63, for Ni(II) � 15.26/13.44,and for Zn(II) � 15.28/ 14.90, respectively.e molecular formula according to elemental analysis results of the ligand and metal complexes was found to be C 24 H 31 O 4 N for ligand and (C 24 H 29 O 4 N) 2 -Co, (C 24 H 29 O 4 N) 2 -Ni, and (C 24 H 29 O 4 N) 2 -Zn for the complexes.