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Preparation and structural characterization of copolymer of Melamine-Silicic Acid--N, N'Dimethylthiourea by elemental and spectroscopic analysis (IR, UV and NMR).


In the new era of polymer synthesis, the research emphasized on finding a new binder having highly replaceable with more active bonding sites for condensation polymerization in comparison to traditationally used formaldehyde binder. In the present work, Silicic acid is used as a binder because it has more active replaceable hydroxyl groups, with wide range applications. Therefore it is used to prepare a copolymer of Melamine- N, N'Dimethylthiourea.

Recently, great attention has been paid to synthesize high performance polymeric materials with enhanced thermal stability, heat resistance and good mechanical properties, the ingredient of modern technological applications [1, 2]. The preparation of the polymer materials [3] with several useful molecule is fascinating for the nanotechnological applications [4], especially weakly conducting synthetic biopolymers due to their tremendous applications in biochips and, biophysics. However the polymer composites have been an asset for multipurpose uses [5, 6] but most of them are not eco- friendly and their physico-chemical properties have not been extensively studied. Thus, preparations of the copolymers with various applications have been urgent need of the hour. In present work, the copolymer of Melamine- N, N' Dimethylthiourea bonded with Silicic acid is prepared and characterized. The copolymer is supposed to be metal and radial scavenging [7-9] due to thiourea in its basal structural framework and it also act as conducting material due to the presence of silicon. A concept of developing silicon based conducting polymer has never been reported yet. A synthesis of copolymer from acetylated melamine, N, N' Dimethylthiourea and adjoining them with binder (Silicic acid) is fundamentally a new concept based on condensation reactions. Such compounds are of current industrial interests, for fibre optics (they can be used in filters) and nanotechnology (as a biosensor) [10-11]. The structural elucidation of this copolymer has become an informatory approach for assessing the feasibility of their structure and applications. Such work might boost up the semiconductor and defence science for coded messages, optics [12], etc and facilitate the other allied sciences [13-15] emerging for specific applications in conducting materials. Currently Singh and Chauhan [17] have reported glycine and PVP based Silicon polymers with enormous industrial uses.


Melamine [E. Merck (A.R grade,], silicic acid 99.9% [Sigma Aldrich] and N, N' Dimethyl thiourea 99% [E. Merck,] were used as received. The copolymer was prepared at 70[degrees]C temperature by condensation reaction. It was prepared in two step. Firstly, the melamine was acetylated with acetic anhydride and glacial acetic acid [16]. This was done in order to protect the two active sites of the melamine because melamine has three active N[H.sub.2] sites which would react with Silicic Acid and left no vacant sites for N,N' Dimethylthiourea to react. So to carry out the process of acetylation acetic anhydride is added to melamine in 1:2 ratio (melamine: acetic anhydride) in a 100 ml RB flask then add 4ml of glacial acetic acid. The above mixture was refluxed by heating the contents at 60[degrees]C for about 1 h. The reaction was quenched by pouring the reaction mixture in ice cold water. The precipitates of acetylated melamine (AcMe) settled down which were filtered. Precaution were taken to avoid the direct contact of reaction mixture with skin during filtration. Then these were filtered and washed cold water.

In the second step stochiometric ratio of AcMe, Silicic Acid and N, N' Dimethylthiourea (3:3:1) in ethanol, and subjected to condensation for about 9.30 h at 70[degrees]C resulting a clear mixture indicates the complete mixing. Further, refluxing is carried for 18 h at 70[degrees]C. The condensation reaction (Fig. I) forms a white copolymer of acetylated melamine-silicic acid--N, N' Dimethylthiourea (MSDMTU).The product was separated by Whatman filter paper No. 41 under vacuum. Washings were done with 30% aqueous ethanol. The product was vacuum dried r for 24 h and stored in vacuum desiccator containing dried [P.sub.2][O.sub.5]. The yield of the polymer was found 80.6%.

Result and Discussion

This MSDMTU has been characterized with elemental (Table I) and spectral analysis (IR, UV and [sup.1]H NMR).

IR Spectroscopy

The FTIR spectrum of MSDMTU (fig 2) was recorded in the form of a thin film within a KBr disc using a Nicolet Protege-460 Spectrometer and vibration frequencies were noted. The absence of band in the region 3400 [cm.sup.-1] to 3600 [cm.sup.-1] indicates absence of -OH in MSDMTU [17]. It shows replacement of all hydroxyl groups of the silicic acid. The appearance of broad weak intensity band at 3309.8 [cm.sup.-1] indicates the N-H stretching bonding vibrations of 2[degrees] amide group. It infers the protection of two -N[H.sup.2] of melamine by C[H.sub.3]CO- group. The shoulders at 2980 [cm.sup.-1] and 2820 [cm.sup.-1] represented asymmetric and symmetric C-H stretching vibrations respectively of the--C[H.sub.3] (methyl group). The appearance of shoulders instead of a sharp peaks for methyl groups is due to different electronic arrangement of -C[H.sub.3] in the molecule. It is due to steric hindrance exerted by two -C[H.sub.3] groups in N, N' Dimethylthiourea. A shoulder at 2345 [cm.sup.-1] indicates the presence of 3[degrees] amino groups which infer that molecule formed is stable and optimized because it does not involve in any bonding. The appearance of band at 2068 [cm.sup.-1] indicates bending vibrations of N-Si-N. The appearance of bands at 1280 [cm.sup.-1] and 1044.28 [cm.sup.-1] indicates asymmetric and symmetric stretching for Si-N bond of N, N'Dimethylthiourea.These bands indicate dominance of nitride of N-C[H.sub.3] of N, N' dimethylthiourea to the nitride of melamine. The appearance of the strong and sharp band at 472 [cm.sup.-1] infer Si=N bond in MSDMTU. These results are in agreement with the work reported by Leonardo T. Ueno and Fernando R. Ornellas [18]. The strong bands at 1683.96 [cm.sup.-1]is due to the C=O stretching vibrations for amide I band. It infers the protection of two -N[H.sub.2] groups of melamine by acetyl group. The absorptions at 1572.02 [cm.sup.-1] (amide II band) and shoulder at 1320 [cm.sup.-1](amide III band) exhibit N-H in plane bending and C-N stretching vibrations respectively of 2[degrees] amide group. The shoulder at 752.06 [cm.sup.-1] and weak peak at 604.08 [cm.sup.-1] are due to N-H out of plane bending (amide V band) vibrations [19].

Because of mixed vibrations of -N-C=S moiety, the C=S band of N,N' Dimethylthiourea is observed at 1420 [cm.sup.-1]. It corroborates the basic concept given by Rao and Venkataraghavan [20], which correlates data of IR spectra of thiocarbonyl derivatives. It was concluded that strong vibrational coupling was operative in case of nitrogen containing thiocarbonyl derivatives.

In various oligomers a combinations of vibrations frequencies for =C-N and -N[H.sub.2] of melamine ring appear at about 1560 [+ or -] 4 [cm.sup.-1] but it is shifted to higher value 1572 [cm.sup.-1] due to extension of conjugation. The bands at 804.89 [cm.sup.-1] and 652.50 [cm.sup.-1] belongs to the triazine ring stretching [21].


NMR Spectral Characteristics

High resolution spectra of polymer were measured in DMSO-[d.sub.6] solvent on DPX-dix 300 MHZ Bruker Avance spectrometer using TMS as an internal reference. (Fig 3)

At 3.5[delta] a chemical shifts of a residual protons in solvent DMSO-[d.sub.6] [19] is observed. A peak at 2.1 [delta] observed for methyl protons equivalent to 3H (Hd) sandwiched between silicon and silicic acid, shows deshielding of the methyl proton by two electron withdrawing groups and favours the geometry shown in Fig. I. A signal appeared at 2.5 [delta], equivalent to 3H (Ha) indicates the methyl protons of--NHCOC[H.sub.3] and it confirms the formation of acetylated melamine and is in agreement with IR and UV spectroscopy. A broad weak signal appeared at 2.8 [delta] equivalent to 3H (Hc) of free -C[H.sub.3] group of N, N'Dimethylthiourea. A weak signal of singlet appeared at 10 [delta] due to the -NH proton [23] suggests the protection of two -N[H.sub.2] of melamine rings by C[H.sub.3]CO- group and infer the molecular structure depicted in Fig.1. It is NMR active molecule due to -NH functional groups of N, N'Dimethylthiourea which is further connected to Si of silicic acid that contribute much to NMR spectra.


Ultraviolet Spectroscopy

The UV spectra of polymer were measured in a Perkin Elmer UV-VIS spectrophotometer model 554 was used for recording electronic spectra.

The UV spectroscopy of the copolymer (Fig 4) infers the results obtained by IR and NMR spectroscopic method. In the UV region, the complexes showed an intense band at ~263 nm arising due to the [PI]-[[PI].sup.*] transitions of the N = Si chromophores [23]. It also shows that there is an extension of conjugation in the molecules which confirms the presence of double bond between Si and N of the amino group attached to the triazine ring of the melamine. Another band was appeared to occur at ~365nm and was associated with the unequivalence of C[??]S bonds by the two attached -N-C[H.sub.3] groups. Absorption at ~446nm was seen due to the presence of Si metal [22-23]. The absorption in these regions refers to an orientation and stability of the molecules, and supports the given structure (fig 1).




The presence of -N-Si-N- and -Si=N- frequencies confirms the binding of the electronic site in copolymer. The absence of the frequencies for the -OH group confirms the replacement of -OH group. A signal appeared at 2.5 [delta], equivalent to 3H (Ha) indicates the methyl protons of -NHCOC[H.sub.3] and it confirms the formation of acetylated melamine and is in agreement with IR and UV spectroscopy. Also the absorption at ~446nm confirms presence of silicon metal in molecule. The elemental and spectral analysis confirms the molecular structure of copolymer MSDMTU (Fig. 1).


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[2] Critchley J.P., Knight G.J., Wright W.W., 1983, "Heat Resistant Polymers: Technological useful materials", Plenum, Newyork, 463 pp.

[3] Man Singh, 2004, "Preparation and structural characterization of melamine-methylurea-formaldehyde resin and its blends separately with ethyl cellulose, starch, teakwood, and almond shell powders by [sup.13]C NMR, IR, TGA, and SEM techniques" J. Appl. Poly. Sci., 92, pp 3437-3446.

[4] Nicholas A. Peppas and Yanbin Huang, 2004, "Nanoscale technology of mucoadhesive interactions" Advanced Drug delivery rev., 56, pp 1675-1687.

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[14] M. Naito, K. Nakahira, Y. Fukuda, H. Mori and J. Tsubaki., 1997, "Process conditions on the preparation of supported microporous Si[O.sub.2] membranes by sol-gel modification techniques" J. Memb. Sci., 129 (2), pp 263-269.

[15] Katsuki Kusakabe, Fumio Shibao, Guibing Zhao, Ken-Ichiro Sotowa, Kensuke atanabe and Tomonari Saito, 2003, "Surface modification of silica membranes in a tubular-type module" J. Memb. Sci,. 215 (1-2), pp 321- 326.

[16] J.M. Sehgal, Basic organic experimental book, Narosa Publications, 1974

[17] Man Singh and Sushila Chauhan, "Synthesis and molecular weight and structural determinations of (polyvinylpyrrolidone)-oximate-silico-benzoyl glycine copolymer with IR and NMR spectroscopy". Journal of Applied polymer Science. 2006, 104, pp. 3261-3268

[18] Leonardo T. Ueno and Fernando R. Ornellas, "Structures and Energetics of Si3N2 Clusters", 2000, Journal of Brazilian Chemistry, ISSN 0103-5053

[19] Jagmohan, Organic spectroscopy Principles and applications, Narosa Publications, 2004

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[21] Yu-Lin Wang, Alexander M. Mebel, Chung-Jen Wu, a Yit-Tsong Chen, Ching-Erh Lina and Jyh-Chiang Jianga, 1997, "IR spectroscopy and theoretical vibrational calculation of the melamine molecule", J.Chem.Soc., Farday Trans., 93(19), 3445-3451.

[22] Man Singh and Sushila Chauhan, 2007, "Molecular Weight and Structural Determinations of (polyvinylpyrrolidone)-oximate silico-benzoyl glycine [POSBG] copolymer with IR and NMR Spectroscopy", Journal of Applied polymer Science, 104 pp3261-3268.

[23] Sangari. H.S, Sodhi, G.S., and Kaur J, 1993, "N Alkylcyclohexyldithiocarbamato complexes of Fe(III),Co(III) and Ni(II)", Indian J.Chem., 32A, 730.

Vandana (1), Pratibha Chaudhary (2) and Man Singh (3)

(1) Delhi Institute of Technology and Management, Gannaur.

(2) Deenbandhu Chhotu Ram University of Science and Technology, Murthal.

(3) Chemistry Research Lab., Deshbandhu College, Kalkaajee, New Delhi.

E-mail: (1), (2)
Table I: Analytical data for acetylated melamine-silicic
acid--N,N' Dimethylthiourea (MSDMTU).

                            Found (Calcd.) (%)
Compound   Colour   (%)       Si        C

MSDMTU     WHITE    80.6     7.63     34.68
                            (6.36)   (35.45)

           Found (Calcd.) (%)

Compound     H        N       S

MSDMTU      4.32    31.87    9.72
           (4.54)   (31.81) (14.54)
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Author:Vandana; Chaudhary, Pratibha; Singh, Man
Publication:International Journal of Applied Chemistry
Article Type:Report
Date:Jan 1, 2009
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