untitled European Journal of Chemistry 7 (4) (2016) 405‐409 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2016 Atlanta Publishing House LLC ‐ All rights reserved ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.7.4.405-409.1480 European Journal of Chemistry Journal webpage: www.eurjchem.com Synthesis, characterization and thermal properties of the nano four arms poly(pentaerythritollactide‐b‐N,N‐dimethylaminoethyl methacrylate) derivatives Baqer Al‐Mayyahi, Hadi Al‐Lami * and Athir Haddad Department of Chemistry, College of Science, University of Basrah, Basrah, 61001, Iraq * Corresponding author at: Department of Chemistry, College of Science, University of Basrah, Basrah, 61001, Iraq. Tel.: +964.790.1681631. Fax: +964.770.7377488. E‐mail address: hadisalman54@yahoo.com (H. Al‐Lami). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.7.4.405-409.1480 Received: 27 July 2016 Received in revised form: 05 September 2016 Accepted: 10 September 2016 Published online: 31 December 2016 Printed: 31 December 2016   The nano four arms poly(lactide‐b‐N,N‐dimethylaminoethylmethacrylate) were prepared by pentaerythritol‐lactide atom transfer radical polymerization initiators having different repeating units (10, 25, 50 and 100) of L‐lactide with the same amount of N,N‐ dimethylaminoethyl methacrylate by atom transfer radical polymerization reaction. The copolymers were characterized FT‐IR, 1H NMR, 13C NMR and Gel permeation chromatography. These characterization methods confirmed the structures of prepared copolymers. Scanning electron microscopy, on the other hand, revealed that the presence of a nanostructure in the prepared copolymers attributed to the lactide fibers. Then, the thermal study was carried out on the copolymers the results have proven to increase the thermal stability of the copolymers with the increasing chain length of the lactide. KEYWORDS ATRP L‐Lactide Lactide fibers Nanostructure Nano four arms N,N‐Dimethylaminoethyl methacrylate Cite this: Eur. J. Chem. 2016, 7(4), 405‐409 1. Introduction The first report in atom transfer radical polymerization (ATRP), by Kato et al. employed RuCl2(PPh3) as a catalyst system in the polymerization of methyl methacrylate (MMA) initiated by CCl4 [1]. The second system reported by Matyjaszewski et al. is the polymerization of styrene using CuCl/2,2’‐bipyridyl (bpy) as catalyst and 1‐phenylethyl chloride as an initiator [2]. Since then, ATRP of styrene, acrylates, methacrylates, and acrylonitrile was carried out using various transition metal complexes, such as nickel, iron, palladium, and rhodium. Compared to other controlled radical polymerization methods, ATRP is very versatile [3‐6]. Vivek and Dhamodharan [7] synthesized polystyrene‐ graft‐poly(N,N‐dimethyl‐2‐aminoethyl methacrylate) via ambient temperature ATRP from polystyrene macro‐initiator with pendant bromo initiating groups. A cationic star polymer, poly(2‐dimethylamino)ethyl methacrylate (PDMAEMA), was prepared via ATRP by Zheng et al. [8], they are used brominated calix[4]resorcinarene as an initiator. Hydrophobic moieties, methyl methacrylate (MMA) and butyl acrylate (BA), were further incorporated via one‐pot method. Well‐defined eight‐armed star block copolymers bearing hydrophilic blocks inside and hydrophobic blocks outside were synthesized. ATRP can be carried out in a wide range of polymerization temperatures with controlled molecular weight and narrow (Molecular Weight Distribution, MWD), and it is not very sensitive to the presence of oxygen and other inhibitors [9]. In this work, we reported to the synthesis of nano four arm poly(pentaerythritollactide‐b‐N,N‐dimethylaminoethylmetha‐ crylate) via ATRP and evaluating some of their thermal properties. 2. Experimental 2.1. Materials N,N‐Dimethylaminoethyl methacrylate, copper(I) bromide, N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine, magnesium sul‐ fate, CDCl3 and dimethyl sulfoxide‐d6 were supplied by Sigma‐ Aldrich, dichloromethane (DCM) (≥ 99.5%), dimethyl formamide (DMF) (≥ 99.8%) and triethyl amine (≥ 99.5 %) were supplied by MACRON Company, Michigan, USA. 2.2. Instrumentation Nicolet IR‐42, Mid‐IR spectrometer was used to record FT‐ IR spectra. Agilent DDR2 500 MHz NMR spectrometer was used 406 Al‐Mayyahi et al. / European Journal of Chemistry 7 (4) (2016) 405‐409 Table 1. Amount of reactants used in the preparation of PL25Br‐Dm, PL50Br‐Dmand PL100Br‐Dm copolymers. Copolymer Code Amount of PLnBr Weight of DMAEMA Weight of CuBr (g) Volume of PMDETA (µL) Yield (%) Physical state Weight (g) No. of moles Weight (g) No. of moles PL25BrDm 0.4 0.00005 0.8 0.005 0.05 20 67 Solid PL50BrDm 0.4 0.00003 0.8 0.005 0.05 20 71 Solid PL100BrDm 0.4 0.00001 0.8 0.005 0.05 20 69 Solid + DMF / PMDETA CuBr / 60 oC / 15 h O N O H3C CH3 CH3 n = 10, 25, 50 and 100 C O O O O C C C C CH HC CH H C O O O O CH3 CH3 CH3 H3C O O O O O O O O H3C CH3 Br CH3 H3C Br H3C CH3 Br CH3 H3C Br n n n n C O O O O C C C C CH H C CH CH OO O O CH3 H3C H3C CH3 O O O O O O O O H3C CH3 CH3 H3C H3C H3C CH3 CH3 O N O H3C CH3 H3C Br O N O CH3 H3C CH3 Br O N O CH3 H3C CH3 Br O N O CH3 CH3 H3C Br m = 10, 25, 50 and 100 n n n n m m m m Figure 1. Synthesis of prepared the copolymers PL10BrDm, PL25BrDm, PL50BrDm and PL100BrDm (m ≈ 10, 25, 50 and 100). to record 1H NMR and 13C NMR spectra. Copolymers molecular weights and molecular weight distributions (Mw/Mn) were determined using a Waters 1515 Gel Permeation Chromato‐ graphy (GPC) equipped with a refractive‐index detector (Waters 2412), DMF was used as the eluent at a flow rate of 1.0 mL/min and calibrated with poly(methyl methacrylate) standard. The prepared copolymers were examined under Scanning electron microscope type JEOL 7500F supplied by JEOL Company, USA. Computer controlled thermal analysis Instrumentals, TGA‐Q500 V20.10 was used to study the thermal stability of the prepared polymers. 2.3. Preparation of pentaerythritol‐lactide tetrakis (2‐bromoisobutyrate) (Tetrafunctional initiator) (PLnBr) Pentaerythritol‐lactideisobutyryl bromide ATRP initiators having different repeating units (10, 25, 50 and 100) of L‐ Lactide have been prepared according to previous works [10] and characterized by FT‐IR and NMR spectroscopy. Copolymer PL10Br: Color: White. Yield: 70%. FT‐IR (KBr, , cm‐1): 2991 (C‐H), 1741 (C=O), 1195 (C‐O), 649 (C‐Br). 1H NMR (500 MHz, CDCl3, δ, ppm): 5.3 (O‐CH2), 5.2 (O‐CH groups of repeating unit of L‐lactide), 1.6 (CH3 groups of repeating unit of L‐lactide), 1.95 (CH3‐C‐Br). 13C NMR (500 MHz, CDCl3, δ, ppm): 170 (C=O of repeating unit of L‐lactide), 166 (C=O of isobutyryl bromide), 69 (CH3 group in repeating unit of L‐ lactide segments), 67 (carbon atom in methine group of pentaerythritol), 55 (C‐Br), 41 (center carbon atom of penta erythritol), 30 (CH3 of end chains), 17 (O‐CH‐CH3 group in repeating unit of L‐lactide segments). Copolymer PL25Br: Color: White. Yield: 73%. FT‐IR (KBr, , cm‐1): 2996 (C‐H), 1746 (C=O), 1197 (C‐O), 647 (C‐Br). 1H NMR (500 MHz, CDCl3, δ, ppm): 5.3 (O‐CH2), 5.15 (O‐CH groups of repeating unit of L‐lactide), 1.97 (CH3‐C‐Br), 1.55 (CH3 groups of repeating unit of L‐lactide). Copolymer PL50Br: Color: White. Yield: 76%. FT‐IR (KBr, , cm‐1): 2998 (C‐H), 1751 (C=O), 1198 (C‐O), 641 (C‐Br). 1H NMR (500 MHz, CDCl3, δ, ppm): 5.3 (O‐CH2), 5.17 (O‐CH groups of repeating unit of L‐lactide), 1.96 (CH3‐C‐Br), 1.57 (CH3 groups of repeating unit of L‐lactide). Copolymer PL100Br: Color: White. Yield: 78%. FT‐IR (KBr, , cm‐1): 3011 (C‐H), 1745 (C=O), 1191 (C‐O), 635 (C‐Br). 1H NMR (500 MHz, CDCl3, δ, ppm): 5.3 (O‐CH2), 5.16 (O‐CH groups of repeating unit of L‐lactide), 1.96 (CH3‐C‐Br), 1.58 (CH3 groups of repeating unit of L‐lactide). 2.4. Synthesis of four arms poly(pentaerythrirol‐lactide‐b‐ N,N‐dimethylaminoethylmethacrylate) (PL10BrDm) Pentaerythritol‐lactideisobutyryl bromide (PL10Br) (0.4 g, 0.11 mmol), N,N‐dimethylaminoethyl methacrylate (DMA EMA) (0.8 g, 5.0 mmol), copper(I) bromide (0.05 g, 0.4 mmol) and N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) (20 μL) were dissolved in 15 mL dimethyl formamide (DMF) at 60 °C. After stirring for 1 h under nitrogen atmosphere, the reaction was stirred for a further 14 h at 60 °C. Afterwards, the product was added slowly to 500 mL cold diethyl ether to precipitate the copolymer which was then filtered on a Buchner funnel and washed with diethyl ether and then the filtrate was dissolved in DMF (15 mL). The copolymer was recovered through the column chromatography filled with silica gel. The solvent DMF was removed by rotary evaporator and the copolymer was dried in vacuum oven at 25 °C for 24 hours, (Solid, yield: 65%). The same procedure was repeated to prepare the copolymers PL25BrDm, PL50BrDm and PL100BrDm. Table 1 shows the quantities of reactants used in the preparation of these copolymers and Figure 1 exhibits the chemical equations of the preparation method. Copolymer PL10BrDm: Color: Light green. Yield: 65%. FT‐IR (KBr, , cm‐1): 1741 (C=O), 1133 (N‐C). 1H NMR (500 MHz, DMSO‐d6, δ, ppm): 5.19 (O‐CH groups in branched part of DMAEMA), 4.2 (O‐CH2), 4.1 (O‐CH2), 3.4 (N‐CH2 groups in branched part of DMAEMA), 2.9 (N‐CH3 groups in branched part of DMAEMA), 2.7 (CH2 groups of repeating unit of DMAEMA), 2.3 (CH3 groups of repeating unit of DMAEMA), 1.45 (O‐CH‐CH3), 1.4 (CH3). Al‐Mayyahi et al. / European Journal of Chemistry 7 (4) (2016) 405‐409 407 Table 2. GPC results for prepared copolymers. No Copolymer Value of m Mn (Daltons) Mw (Daltons) Polydispersity index (PDI) 1 PL10BrDm 13 11725 12651 1.08 2 PL25BrDm 28 25475 27339 1.07 3 PL50BrDm 57 50947 58105 1.14 4 PL100BrDm 115 101795 110018 1.08 Table 3. TGA data for prepared copolymers PL10BrDm, PL25BrDm, PL50BrDm and PL100BrDm. Copolymer First decomposition step Ti (°C) Tf (°C) Rate of decomposition Activation energy Weight loss (%) PL10BrDm 145.82 216.80 0.38 0.015 27.77 PL25BrDm 158.33 241.70 0.37 0.020 24.95 PL50BrDm 173.92 246.26 0.32 0.023 32.71 PL100BrDm 190.03 253.74 0.31 0.044 20.97 Copolymer Second decomposition step Ti (°C) Tf (°C) Rate of decomposition Activation energy Residue (%) T50 (°C) PL10BrDm 289.74 356.11 0.67 0.016 18.39 294.05 PL25BrDm 295.37 375.75 0.65 0.018 17.21 296.43 PL50BrDm 291.71 388.38 0.63 0.021 19.09 292.32 PL100BrDm 306.03 384.04 0.51 0.033 14.86 315.48 13C NMR (500 MHz, DMSO‐d6, δ, ppm): 178 (C=O), 174 (C=O), 170 (C=O), 69 (CH‐O), 63 (CH2‐O), 59 (CH2‐O), 56 (C‐ quat.), 50 (CH2), 47 (CH3‐N), 44 (C‐quat.), 32 (CH3), 20 (CH3), 17 (CH3). Copolymer PL25BrDm: Color: Light green. Yield: 67%. FT‐IR (KBr, , cm‐1): 1746 (C=O), 1134 (N‐C). 1H NMR (500 MHz, DMSO‐d6, δ, ppm): 5.2 (O‐CH groups in branched part of DMAEMA), 4.2 (O‐CH2), 4 (O‐CH2), 3.35 (N‐CH2 groups in branched part of DMAEMA), 2.88 (N‐CH3 groups in branched part of DMAEMA), 2.71 (CH2 groups of repeating unit of DMAEMA), 2.25 (CH3 groups of repeating unit of DMAEMA), 1.45 (O‐CH‐CH3), 1.41 (CH3). 13C NMR (500 MHz, DMSO‐d6, δ, ppm): 177 (C=O), 174 (C=O), 170 (C=O), 70 (CH‐O), 62 (CH2‐ O), 60 (CH2‐O), 58 (C‐quat.), 50 (CH2), 48(CH3‐N), 44 (C‐quat.), 30 (CH3), 22 (CH3), 17 (CH3). Copolymer PL50BrDm: Color: Light green. Yield: 71%. FT‐IR (KBr, , cm‐1): 1751 (C=O), 1136 (N‐C). 1H NMR (500 MHz, DMSO‐d6, δ, ppm): 5.2 (O‐CH groups in branched part of DMAEMA), 4.19 (O‐CH2), 4.0 (O‐CH2), 3.36 (N‐CH2 groups in branched part of DMAEMA), 2.86 (N‐CH3 groups in branched part of DMAEMA), 2.71 (CH2 groups of repeating unit of DMAEMA), 2.24 (CH3 groups of repeating unit of DMAEMA), 1.44 (O‐CH‐CH3), 1.41 (CH3). 13C NMR (500 MHz, DMSO‐d6, δ, ppm): 176 (C=O), 174 (C=O), 170 (C=O), 69 (CH‐O), 64 (CH2‐ O), 62 (CH2‐O), 58 (C‐quat.), 54 (CH2), 50 (CH3‐N), 44 (C‐quat.), 32 (CH3), 20 (CH3), 16 (CH3). Copolymer PL100BrDm: Color: Light green. Yield: 69%. FT‐IR (KBr, , cm‐1): 1745 (C=O), 1133 (N‐C). 1H NMR (500 MHz, DMSO‐d6, δ, ppm): 5.19 (O‐CH groups in branched part of DMAEMA), 4.19 (O‐CH2), 4.1 (O‐CH2), 3.34 (N‐CH2 groups in branched part of DMAEMA), 2.86 (N‐CH3 groups in branched part of DMAEMA), 2.72 (CH2 groups of repeating unit of DMAEMA), 2.26 (CH3 groups of repeating unit of DMAEMA), 1.45 (O‐CH‐CH3), 1.41 (CH3). 13C NMR (500 MHz, DMSO‐d6, δ, ppm): 175 (C=O), 174 (C=O), 169 (C=O), 69 (CH‐O), 64 (CH2‐ O), 62 (CH2‐O), 59 (C‐quat.), 51 (CH2), 48 (CH3‐N), 44 (C‐quat.), 31 (CH3), 20 (CH3), 17 (CH3). 3. Results and discussion 3.1. Characterization of new copolymers by FT‐IR The prepared solid copolymers were characterized as KBr discs. The FT‐IR spectra of copolymers PL10BrDm, PL25BrDm, PL50BrDm and PL100BrDm showed characteristic intense absorption bands due to the ν(N‐C) groups at 1133, 1134, 1136 and 1133 cm‐1, respectively, and the ν(C=O) groups at 1741, 1746, 1751 and 1745 cm‐1, respectively. 3.2. Characterization of new copolymer by NMR 1H NMR and 13C NMR of PL10BrDm, PL25BrDm, PL50BrDm and PL100BrDm copolymers was recorded by using dimethyl sulfoxide‐d6 as solvent. The signals belong to the O‐CH‐CO, O‐ CH2, O‐CH‐CH3 and CH3 groups in repeating unit of L‐lactide segments of the synthesized all copolymers were observed approximately at δ 5.2, 4.0 1.5 and 1.4 ppm in the 1H NMR spectra, respectively. Also, the signals belong to the CH2 and CH3 groups in repeating unit of DMAEMA and O‐CH2, N‐CH2 N‐ CH3 groups in branched part of DMAEMA were showed around at δ 2.7, 2.3, 4.1, 3.4 and 2.9 ppm, respectively. In the 13C NMR spectra, the signals belong to the C=O group of DMAEMA segments of the synthesized all copolymers were observed approximately at δ 175 ppm. Also, the signals belong to the CH2 and CH3 groups in repeating unit of DMAEMA and O‐CH2, N‐CH2 N‐CH3 groups in branched part of DMAEMA were showed around at δ 50, 59, 62, 62 and 46 ppm, respectively. 3.3. Copolymers molecular weight and polydispersity index The molecular weight and the polydispersity index (Mw/Mn) were determined by GPC for all prepared copolymers and Table 2 shows the results. The results of GPC showed that the prepared copolymers had a polydispersity index (PDI) close to unity. This implies that the correctness of the suggested structure for the prepared copolymers. 3.4. Scaning electron microcsopy (SEM) All the spectroscopic examinations of the prepared copolymers, FT‐IR, 1H NMR and 13C NMR proved the suggested structure for the prepared copolymers and promoted this matter with greater accuracy results of GPC as they are shown a significant matching to the molecular weight calculated theoretically and result the awesome polydispersity index (PDI) is close to one. The examination of the morphology and the nanoparticles geometry of the prepared copolymers was performed by using SEM at different amplifications (10 µm and 100 nm). Figures 2 and 3 are show the SEM micrographs of examined PL25BrDm and PL100BrDm copolymers. The images obtained from Scanning electronic microscopy revealed the existence of nano‐structures in the prepared copolymers due to the presence of the lactide array to give nanofiber within the final compositions. 3.5. Thermogravimetric analysis (TGA) Thermal stability of the prepared copolymers was studied and Figure 4 shows the resulted thermograms. Table 3 shows some thermal functions resulted from the thermal analysis, namely initiation and final decomposition temperatures Ti and Tf, rate of decomposition, the activation energy of the decomposition, temperature of 50% weight loss (T50), and char content for first and second decomposition step. 408 Al‐Mayyahi et al. / European Journal of Chemistry 7 (4) (2016) 405‐409 Figure 2. SEM image of PL25BrDm. Figure 3. SEM image of PL100BrDm. Figure 4. Thermogram of PL10BrDm, PL25BrDm, PL50BrDm and PL100BrDm copolymers. Thermal gravimetric results indicates that the initial decomposition temperature (Ti) ranging between 145 and 190 °C for first decomposition and between 289‐306 °C for second decomposition. Table 3 indicates that the initial decomposition temperature for prepared polymers were increased with increasing of repeating units of lactide and the rate of decomposition were decreased with increasing of repeating units, this is an expected result because with increasing molecular weight of the copolymers will increase the thermal stability. 4. Conclusions A series of block copolymers are obtained by reaction of pentaerythritol‐lactide and dimethylamino ethyl methacrylate by atom transfer radical polymerization. Spectroscopic examination of the preparedness copolymers by FT‐IR, 1H NMR and 13C NMR proved the suggested structure for the prepared copolymers, also GPC results revealed that all the preparations copolymers are of nearly monodispers polymer with very narrow distributions accompanied by nano Al‐Mayyahi et al. / European Journal of Chemistry 7 (4) (2016) 405‐409 409 structures were obtained as shown by SEM micrographs due to the presence of lactide polymer chains. The thermal gravimetric results showed that the initial and final decomposition temperatures for preparing polymers were increased with the increasing of repeating units of lactide whereas the rate of decompositions decreased with the increasing of repeating units. Acknowledgement The authors would like to thank Prof. Babak Borhan and Dr. Kumar Ashtekar from Chemistry Department, Michigan State University, USA, for their help in spectroscopic and GPC measurements and their kindness to Dr. Baqer Al‐Mayyahi during his staying time at the Michigan State University, USA. References [1]. Kato, M.; Kamigaito, M.; Sawamoto, M.; Higashimura, T. Macromolecules 1995, 28(5), 1721‐1723. [2]. Wang, J. S.; Matyjaszewski, K. Amer. Chem. Soc. 1995, 117(20), 5614‐ 5615. [3]. Matyjaszewski, K. Controlled‐Living Radical Polymerization: Progress in ATRP, American Chemical Society (Publisher); Washington, D.C., 2009, ISBN: 978‐0‐8412‐6995‐8. [4]. Bharathwaj, R.; Natarajan, U.; Dhamodharan, R. Appl. Clay Sci. 2010, 48(3), 300‐306. [5]. He, W.; Zhang, L.; Zhu, G.; Zhang, Z.; Zhou, N.; Cheng, Z.; Zhu, X. J. Control. Release 2011, 152, 192‐269. [6]. Fu, Y.; Li, G.; Yu, H.; Liu, Y. Appl. Surf. Sci. 2012, 258(7), 2529‐2533. [7]. Vivek, A. V.; Dhamodharan, R. React. Funct. 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