Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 5(4), 41-44, April (2015) Res. J. Chem. Sci. International Science Congress Association 41 R - XM - Y / LigandactdeactX - Mn+1- Y / Ligandmonomer t e r m i n a t i o n Synthesis and Characterization of Mono and Di arm -halo esters as a Initiator for Atom Transfer Radical Polymerization Kabir Homayun, Chowdhury Samiul Islam and Hasan Tariqul Department of Chemistry, University of Rajshahi, Rajshahi-6205, BANGLADESHAvailable online at: www.isca.in, www.isca.me Received 31th March 2015, revised 9th April 2015, accepted 16th April 2015 AbstractAtom transfer radical polymerization (ATRP) has been a promising technique to provide polymers with well-defined composition, architecture, and functionality. In most of the ATRP processes, alkyl halides are used as an initiator. 2-Bromo-2-methyl-propionic acid 4-hydroxy-but-2-ynyl ester (BPE) and 2-Bromo-2-methyl-propionic acid but-2-ynyl diester (BPDE) were synthesized by one step reaction which involved on esterification of 2-Bromo-2-methylpropionyl bromide with 2-Butyn-1,4-diol and sufficient purity. H NMR has confirmed the structure of the both initiators. This initiator will be very useful in the polymerisation of monomers in order to produce polymers with controlled molecular weight and narrow polydispersity. Keywords: Atom transfer, ATRP, Initiator, polymerization. Introduction Free-radical polymerization is the most important industrial process for producing various vinyl polymers. However, conventional free radical polymerization techniques do not produce controlled molecular weights and molecular weight distributions due to large amount of chain transfer and termination reactions. In order to overcome these drawbacks, a polymerization technique known as Atom Transfer Radical Polymerization (ATRP) was pioneered independently1-5. Since its inception, ATRP also known as transition metal mediated living radical polymerization has proven to be robust for the design of polymers of complex architecture and precise molar mass. This type of polymerization is inert many functional groups present in monomers or solvents, tolerant to impurities present in solvents and monomers and also allows for the facile synthesis of many polymers of novel structure and topology. Mechanism of ATRP: The general mechanism for transition metal-mediatedATRP involves the generation of radicals (activespecies) through a reversible redox process catalyzedby a transition metal complex (M-Y / Ligand), where Mis a transition metal having an oxidation number n, Ymay be another ligand or a counter ion) whichundergoes a one electron oxidation with concomitantabstraction of a halogen atom (X) from an initiator(dormant species; R-X). This process occurs with arate constant of activation (kact) and deactivation(kdeact). Polymer chains grow by the addition ofintermediate radicals to monomers in a similar mannerto a conventional radical polymerization, with the rateconstant of propagation (k). Termination reaction (kmay also occur in ATRP, but it's very negligible. Thisprocess generates oxidized metal complexes (Mn+1) aspersistent radicals to reduce the concentration ofgrowing radicals thereby minimizing terminationreactions. The control of molar mass and ofpolydispersity in controlled radical polymerization isachieved by converting the chain propagating radicalsinto a “dormant form” in equilibrium with the activeform. It ensures a very low concentration of theactive species and reduces termination reaction. Scheme-1 Mechanism of metal complex-mediated ATRP Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(4), 41-44, April (2015) Res. J. Chem. Sci. International Science Congress Association 42 ATRP Initiators:Like other polymerization systems, ATRP is multicomponent system which includes monomer,initiator, catalyst, solvent and temperature. Each ofthese components plays a significant role in ATRPhence careful choice of a suitable component is veryessential for a successful ATRP.Alkyl halides (RX) or their derivatives aremostly used as ATRP initiators and their main role isto determine the number of initiated chains. Thepolymerization rates in ATRP are first order withrespect to the concentration of RX and the halidegroup (X) must rapidly and selectively migratebetween the growing chain and the transition metalcomplex. Bromine and chlorine are the halogens that afford the best molecular weight control while iodine and fluorine do not work very well in ATRP due to very low C-I and very fast C-F bond dissociation energies respectively. The choice of an ATRP initiator is a very important factor in a successful ATRP and also depends on the type of the polymer to be synthesized such as homo, block10-12, graft13,14 and multiarm star polymers15,16. Which find applications in biomedical17 tissue engineering18, materials 19and surface sciences20. Many researchers have demonstrated easier methods of preparation of ATRP initiators mostly by esterification of hydroxyl functional compounds with 2-bromo-2-methylpropionyl bromide or its derivatives21-25. Therefore, 2-Bromo-2-methyl-propionic acid 4-hydroxy-but-2-ynyl ester (BPE) and 2-Bromo-2-methyl-propionic acid but-2-ynyl diester (BPDE) initiators were synthesized. Material and Methods Materials: 2-Bromo-2-methyl-propionylbromide was purchased from Sigma Aldrich and used without further purification. Pyridine was purified by distillation followed by stirring with CaH for 24 hrs. 2-Butyn-1, 4-diol was purchased from Fluka. The solvents were used as received. Analytical Methods: H NMR spectra of polymers were recorded at room temperature on a JEOL GX 500 spectrometer operated at 400 MHz in pulse Fourier transform mode with chloroform- as solvent. The peak of chloroform in chloroform- (7.26 ppm for H) was used as internal reference. Synthesis of Alkyne End- and Mid- functional Bromoesters: 2-Butyn-1,4-diol (6.36 gm, 73.84 mmol) was dissolved in CHCl (15 mL). Dried pyridine (8.10 gm, 102.33 mmol) was added to the solution of 2-Butyn-1,4-diol. The mixture was then cooled to 0C. To the mixture 2-Bromo-2-methyl propionyl bromide (16.98 gm, 73.84 mmol) was added by using syringe. The reaction mixture was stirred for 48 hrs at room temperature using magnetic stirrer. The aqueous layer was extracted with CHCl2 (3×50 mL), then washed with water (50 mL), dried with MgSO, filtered and concentrated in vacuum. The residue was separated by (silica gel) column chromatography (EtOAc/ Petroleum ether = 1:50) and two products were isolated as yellowish liquid. The purity of the separated products was investigated by TLC using same solvent mixture. The expected products 2-Bromo-2-methyl-propionic acid but-2-ynyl diester (BPDE) (4.23 gm) and 2-Bromo-2-methyl-propionic acid 4-hydroxy-but-2-ynyl ester (BPE) (2.72 gm) were obtained as yellowish liquid followed by evaporation of solvent from each eluent under vacuum. Finally, the structure of the products, BPDE and BPE were confirmed by H NMR analysis. H NMR of BPE (CDCl): 1.85 ppm (S, 6H, -C(Br)(C, at 3.84 ppm (broad , 1H, -O)), 4.28 ppm (S , 2H, -C-OH), 4.77 ppm (S, 2H, -CO-(C=O)-). H NMR of BPDE (CDCl): 1.84 ppm (S, 12H, -C(Br)(C), 4.72 ppm (S, 4H, -CO-(C=O)-).Results and Discussion The expected initiators BPE and BPDE,were synthesized from the reaction between 2-Butyn-1,4-diol and 2-Bromo-2-methyl propionyl bromide in the presence of pyridine and methylene chloride as following scheme 2. The structure of the initiator BPE and BPDE obtained were characterized by H NMR analysis. In the H NMR spectrum of the initiators, several signals including the signals of 2-bromo-2-methyl propionyl bromide were observed. All signals correspond to the different protons of BPE and BPDE was assigned clearly and labeled in figure-1 and figure-2. Scheme-2 Preparation of functional initiators BPE and BPDE Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(4), 41-44, April (2015) Res. J. Chem. Sci. International Science Congress Association 43 The H NMR spectrum of 2-Bromo-2-methyl-propionic acid 4hydroxy-but-2-ynyl ester (BPE), was displayed in figure-1. In the H NMR spectrum, three singlets appeared at 1.85 ppm , 4.72 ppm, 4.28 ppm for -C(Br)(CH, -CHO-(C=O)- 2H, -CH-OH protons denoted by d, c, b and a broad peak appeared at 3.84 ppm for –OH protons denoted by a respectively. The presence of two additional weak peaks with main peak suggested the presence of the conformers of this product. All these different types of protons and their corresponding H NMR signals are indicated in the following figure-1. The H NMR spectrum of 2-Bromo-2-methyl-propionic acid but-2-ynyl diester (BPDE) was displayed in figure-2. In the H NMR spectrum, two singlets appeared at 1.843 ppm and 4.72 ppm for -C(Br)(CH and -CHO-(C=O)- protons, respectively. In both signals, the presence of two additional weak peaks suggested the presence of the conformers of this product. All these different types of protons and their corresponding signals are indicated in the following figure-2. Conclusion The initiators of BPE and BPDE were synthesized in a good yield. Initiators were synthesized by one step reaction which involved on esterification of 2-Bromo-2-methylpropionyl bromide with 2-Butyn-1,4-diol. The structure of initiators was characterized by H NMR analysis. -halo esters are good initiator for ATRP because of their fast initiation property. In view of the current need of conducting polymerisation is non-toxic, relatively cheaper and environmentally friendly, this initiator will be very useful in the polymerisation of various monomers in order to produce polymers with well-defined molecular weight and narrow polydispersity. References 1.Wang J.S. and Matyjaszewski K., Controlled "living" radical polymerization. atom transfer radical polymerization in the presence of transition-metal complexes, J. Am. Chem. Soc., 117, 5614-5615 (1995) 2.Wang J.S. and Matyjaszewski K., Controlled/"Living" Radical Polymerization. Halogen Atom Transfer Radical Polymerization Promoted by a Cu(I)/Cu( 11) Redox Process, Macromolecules,28, 7901 (1995) Figure-1 H NMR spectrum of initiator BPE Figure-2 H NMR spectrum of BPDE Research Journal of Chemical Sciences ___________________________________________________________ ISSN 2231-606XVol. 5(4), 41-44, April (2015) Res. J. Chem. Sci. 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