PHYSICAL SCIENCES | CHEMISTRY DOI: 10.31276/VJSTE.62(2).38-40 Synthesis of a novel polymer via the coupling reaction of cyanuric chloride and a di-amine Hung Quang Pham1, 2, Thuy Thu Truong2, Duc-Anh Song Nguyen1, 2, Le-Thu Thi Nguyen2* 1National Key Laboratory of Polymer and Composite Materials, University of Technology, Vietnam National University, Ho Chi Minh city 2Faculty of Materials Technology, University of Technology, Vietnam National University, Ho Chi Minh city Received 3 January 2020; accepted 6 March 2020 Abstract: Polymers containing hydrogen bonds are of great significance as they have the potential to strengthen the mechanical properties of a material through non-covalent crosslinking, which is the basis for paint and self-healing materials. In this work we describe a method to obtain a novel polymer via the coupling reaction of cyanuric chloride and a di-amine. We investigate the reaction conditions to optimise the polymerization yield and molecular weight polydispersity. The polymerization process was characterised by gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), and attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectrometry. Keywords: cyanuric chloride, di-amine, hydrogen bond, triazine. Classification number: 2.2 Introduction introduced into the polymer chain using a coupling reaction to cyanuric chloride. There is a growing interest in synthetic polymers with strong non-covalent crosslinking that induces ionic, π-π Cyanuric chloride is known as a multifunctional reactive stacking, and hydrogen bonding. This type of polymer is dye and can be completely controlled by temperature. applied across many fields from paint to recycled and self- The chlorine atoms of cyanuric chloride are easily healing materials. In this article, we synthesised a polymer replaced by other nucleophilic agents in the presence of a with hydrogen interaction by cyanuric chloride and amine. hydrochloride electron acceptor. The chlorine substitution The attractive interaction between a high-electron-density is temperature controlled step by step, has been observed atom and an electron-deficient hydrogen gives rise to to follow an empirical rule: mono chlorine replacement hydrogen bonding [1, 2]. A hydrogen bond forms when an occurs at a temperature of 0oC or lower, di-chlorine at electron is moved from a proton acceptor (such as N, F, O room temperature, and tri-chlorine at temperatures above atoms) to a proton donor molecule (i.e. electron-deficient 60oC [5]. hydrogen). Although hydrogen bonds are weaker than polar and covalent bonds, they are stronger than the van der This synthetic process is an easy polymerization Waals forces [3]. Thus, one can use hydrogen bonding to technique to create triazine-based polymers with hydrogen effectively enhance the mechanical properties of a material. bonding interactions. Moreover, the reaction of cyanuric chloride with a di-amine is efficient and gives a high yield. Polymerization of cyanuric chloride with a di-amine is used to introduce a triazine ring and NH group to the polymer Materials and methods backbone. Hydrogen interactions can form between the Materials proton-acceptor of the triazine ring and the proton-donor of the NH group. This hydrogen bond in the triazine ring The polypropylene oxide di-amine (PPO di-amine) is popularly used. When the coupling reaction of cyanuric was purchased from Sigma Aldrich with molecular chloride with the di-amine occurs, the obtained polymer weight of 2000 g/mol, cyanuric chloride (99%) and N,N- backbone has one nitrogen atom acceptor and two amino Diisopropylethylamine (DIPEA, 99%) were bought from hydrogen donors next to each other. This structure can form Sigma Aldrich and the solvents were received from Fisher a stronger hydrogen bond [4]. Therefore, the triazine ring is Chemicals. *Corresponding author: Email: [email protected] Vietnam Journal of Science, 38 Technology and Engineering JUNE 2020 • VOLUME 62 NUMBER 2 PHYSICAL SCIENCES | CHEMISTRY Characterisation 11090, the molecular weight (Mw) is approximated at 15160, 1 Proton nuclear magnetic resonance ( H NMR) spectra and the high PDI (Mw/Mn=1.36) is likely due to the coupling were measured at 300 MHz using a Bruker Avance 300 reaction, since the number of repetitions of the unit in the with deuterated acetone (C3D6O) and tetramethylsilane polymer cannot be controlled. internal reference. Attenuated total reflection Fourier- transform infrared (ATR FT-IR) spectra of the polymers The polymer triazine was synthesised with the catalyst -1 were measured at 4 cm resolution using an FT-IR Tensor DIPEA as shown in Scheme 1, so that the peak at 1.4 ppm for 27 spectrometer with a diamond/ZnSe element combined the CH group in DIPEA appeared in the 1H NMR spectrum with a Pike MIRacle ATR accessory. Gel permeation 3 chromatography was recorded on a Polymer PL-GPC 50 gel of the polymer, as seen in Fig. 2. The disappearance of 1 permeation chromatograph system with a refractive index the NH2 group in the H NMR spectrum of polypropylene (RI) detector. Chloroform was used as the eluent and the oxide di-amines (2.6-3 ppm, Fig. 3) can be observed, which flow rate was 1.0 ml/min. Polystyrene standards were used indicates that all NH groups reacted with the cyanuric for the calculation of the molecular weight and molecular 2 weight distribution. chloride. The appearance of peak d (6.3-6.7 ppm, Fig. 2) corresponding to the NH groups were created. Synthesis of polymer triazine Cyanuric chloride 1.0 g (5.42 mmol) was added to Mw=15156 27.1 ml of the tetrahydrofuran solvent in a two-neck flask. Mn=11089 Polypropylene oxide di-amines 2.3 g (5.42 mmol) and N,N- PDI=1.36 diisopropylethylamine 2.1 ml (1.5 g, 11.93 mmol) was then added to the flask. The reaction was kept under constant stirring for 24 h at room temperature. Then, the solid was removed by filtration and the polymer, in liquid form, was collected. Results and discussion N Cl Cl Cl N N N N + H N NH DIPEA N N 2 O 2 O 200 250 300 350 400 450 500 550 600 650 n O N N N Cl N Cl H2N N x N Cl n H H n H Retention Time (s) Fig. 1. GPC of polymer triazine. Scheme 1. Synthesis of polymer triazine. The polymerization process H O acetone described in Scheme 1 is the 2 a reaction of the primary amine Cl Cl a g g a g N N N N with cyanuric chloride. At room f h O H2N O O h NH O b h NH N NH b c n N Cl c n d d DIPEA temperature, the first and second e reactive positions on cyanuric chloride react, while a temperature of 60oC or higher is needed to activate the third reactive site [6]. The above polymerization b,f,c process was maintained at room g temperature so that the polymer backbone was extended instead of h forming a network. The molecular d e weight of the polymer was observed by the GPC curve in Fig. 1, where the number averaged molecular 1 1 weight (Mn) is approximated at Fig.Fig. 2. 2. HH NMR NMR spectrum spectrum of polymer of polymer triazine triazine in acetone. in acetone. a, a’ Vietnam Journal of Science, JUNE 2020 • VOLUME 62 NUMBER 2 Technology and Engineering 39 c H N b b' NH 2 O 2 b,b’,c n a a' 1 Fig. 3. H NMR spectrum of polypropylene oxide di-amines in CDCl3. From the FT-IR spectra of cyanuric chloride, polypropylene oxide di-amines, and the polymer in Fig. 4, the characteristic absorption bands of cyanuric chloride at 1171 and 1265 cm-1 assigned to the triazine stretch [7] and the bands at 844 cm-1 corresponds the C-Cl stretch vibrational absorption [8] can be observed. After the coupling reaction, the band for the C-Cl H O acetone 2 a Cl Cl a g g a g N N N N f h O H2N O O h NH O b h NH N NH b c n N Cl c n d d DIPEA e b,f,c g h d e PHYSICALFig. SCIENCES 2. 1H NMR | CHEMISTRY spectrum of polymer triazine in acetone. a, a’ c H N b b' NH 2 O 2 b,b’,c n a a' 1 1 Fig. 3. H NMRFig. spectrum3. H NMR of polypropylene spectrum oxide of polypropylene di-amines in CDCl oxide3. di-amines in CDCl3. From the FT-IR spectra of cyanuric chloride, polypropylene oxide di-amines, and the From the FT-IR spectra of cyanuric chloride, ACKNOWLEDGEMENTS -1 polymer in Fig. 4, the characteristic absorption bands of cyanuric chloride at 1171 and 1265 cm polypropylene oxide di-amines, and the polymer in Fig. 4, -1 the characteristicassigned absorption to the bandstriazine of cyanuricstretch [7]chloride and atthe bandsThis researchat 844 iscm funded corresponds by Vietnam Nationalthe C- ClFoundation stretch 1171 and 1265vibrational cm-1 assigned absorption to the triazine [8] can stretch be [7]observed and the . Afterfor Science the coupling and Technology reaction, Development the band for(NAF theOSTED) C-Cl -1 -1bands at 844 cm corresponds the C-Cl stretch vibrational under grant number 104.02-2019.13. stretch at 844 cm in FT-IR spectrum of polymer disappeared. The appearance of the peak at absorption [8] can be observed. After the coupling reaction, -1 The authors declare that there is no conflict of interest 1571 cm was due theto Nband-H secondary for the C-Cl amine stretch in reaction. at 844 cm -1 in FT-IR spectrum regarding the publication of this article. -1of polymer disappeared.