Assessment of Maleinization Degree of Linseed Oil from Spectral Data

Transcription

1 Assessment of Maleinization Degree of Linseed Oil from Spectral Data MARIA MAGANU, NICOLETA CHIRA 2 *, CRISTINA STAVARACHE,3, CORINA ANDRONESCU 2, ANCA ANASTASIU 2 C.D. Nenitescu Center of Organic Chemistry, 202B Splaiul Independentei, , Bucharest, Romania 2 Politehnica University of Bucharest, Faculty of Applied Chemistry and Materials Science, -7 Polizu Str., 006, Bucharest, Romania 3 University of Bucharest, Faculty of Chemistry, NMR Laboratory, Soseaua Panduri, , Bucharest, Romania We report here the synthesis and spectral characterization of a functionalised linseed oil by grafting succinic anhydride (SA) moieties onto the linseed oil methyl ester (LOME) backbones via ene-reaction with maleic anhydride (MA). The maleinized linseed oil methyl esters (MLOME) were characterized through H-, 3 C- NMR and FT-IR spectroscopy. The amount of succinic anhydride grafted onto the LOME molecules (maleinization degree) was determined from FT-IR spectral data, on the basis of a calibration curve from synthetic mixtures of LOME and SA in different molar ratios. The functionalization degree was also determined from H- and 3 C-NMR (semi-quantitative experiments) spectra of MLOME by chemometric calculations. Keywords: maleinized linseed oil methyl esters, functionalized oil, grafting degree, NMR, FT-IR, calibration curve Besides their incontestable value in the food industry, vegetable oils and their derivatives are an attractive renewable resource for different applications in the energetic (biodiesel) [-4], pharmaceutical (as basis for different formulations [5], precursors of active substances [6] or as stuctured lipid vectors for a large variety of therapeutically active compounds [7]) or chemical industries (as raw materials for the synthesis of polymers coatings, or various organic synthons) [8-]. For this reason, the oil production in Romania has increased in recent years [2], not only regarding the traditional edible oils (sunflower and soybean), but also with respect to oils for technical uses (linseed and rapeseed). The use of vegetable oils for the synthesis of different materials (especially polymeric) involves in many cases a chemical functionalization of the acyl chains in order to increase their reactivity [3]. Maleic anhydride (MA) is being intensively used as functionalizing molecule for the synthesis of reactive macromolecules with linear, hyper branched or self-assembled structures to prepare high performance engineering and nano engineering materials [4]. It has been shown that the grafting of MA onto the backbone of various polyolefinic substrates leads to modified macromolecules with improved properties, acting as compatibilizers for a large number of blends, composites and nanocomposites. The precise nature of the compounds formed in the reaction of MA with non-conjugated oils has been largely studied [5, 6] and a various grafting mechanisms have been proposed, but not strictly demonstrated [3]. It is a general consensus that the grafting of MA onto acyl chains follows an ene-reaction mechanism an indirect substituting addition from a compound with an electronpoor double bond (enophil) to a compound that contains an allylic hydrogen (ene). MA plays the enophil component role, the unsaturated fatty acyl chains acting as enecomponents [7]. Through oils maleinization, MA turns into a grafted succinil anhydride motif onto the fatty acyl chains. The profile of the obtained grafted compounds is very * nicoleta.chira@chimie.upb.ro; Tel.: complex due to the fact that the substrates (oils) are complex mixtures, with different allylic or bis-allylic positions available for grafting on one hand; on the other hand, the table of compounds is getting more complicated by the change in the configuration of the C=C double-bond adjacent to the grafting position. Because of the complexity of the products obtained through oils maleinization, their spectra are complicated by overlapping signals. The grafting degree of MA onto a monomer backbone is usually determined by titration of the maleinized monomer with KOH solution of the anhydride moiety using phenolphthalein as an indicator [8]. In the case of a maleinized oil or fatty acid methyl ester, the alkaline titration method is not suitable because the saponification reaction can occur thus leading to errors. The calibration curve technique is largely used for the quantitative determinations (in oils field it was successfully used for the determination of the amount of trans double bonds being formed during the frying process [9]. The amount of grafted MA has been determined through IR spectroscopy, based on calibration curves obtained for a series of standard samples of alkenylsuccinic anhydrides (hexenylsuccinic, octenylsuccinic and decenylsuccinic anhydride) with accurately known molecular weights and the corresponding alkenyl succinic acids [20]. In another paper [2], Multiple Reflectance FT-IR was used as a simplified method for the quantitative determination of the percentage of MA grafted on the ethylene-propylene-ethylene-diene monomer (EPDM). Due to the fact that hydrolysis can occur at room temperature in variable extent, the authors have chosen to avoid simultaneous presence of MA and maleic acid by totally converting MA into maleic acid. The amount of MA grafted onto EPDM backbone was thus determined from spectral data on a basis of a calibration curve correlating the height ratios of the 707 and 460 cm - bands as a function of different maleic acid concentrations. The present paper investigates the possibility of rapidly determining the maleinization degree of linseed oil methyl esters on the basis of spectral data. The functionalization REV.CHIM.(Bucharest) 67 No.2 206

2 degree can be computed directly from H- and semiquantitative 3 C-NMR spectra, or based on a calibration curve from FT-IR spectra of a series of standard mixtures of linseed oil methyl esters (LOME) and succinic anhydride corresponding to different SA: LOME molar ratios. For a quantitative assessment, the absolute heights of the anhydride (782 cm - ) and of the reference ester (739 cm - ) bands were considered. Experimental part Materials Linseed oil was obtained from Chemont S.A. (Mouscron, Belgium). Maleic anhydride and,2-dichloroethan were purchased from Merck (Schuchardt, Germany) and Acros Organics (New Jersey, USA), respectively. Methanol and ethanol were purchased from S.C. Chimreactiv S.A. (Bucharest, Romania); sulphuric acid, acetone, diethyl ether and deuterated chloroform were purchased from Sigma-Aldrich (Steinheim, Germany). H-NMR spectra were recorded on a Bruker Fourier 300 MHz spectrometer, operating at a resonance frequency of MHz for the H nucleus, equipped with a direct detection four nuclei probe head and field gradients on z axis. Typical parameters for H- NMR spectra were: 45 o pulse, 5.37 s acquisition times, 6. khz spectral window, 6 scans, 20 K data points, s delay time. The FID was not processed prior to Fourier transformation. The average acquisition time of the H-NMR spectra was approximately 2 min. Semi-quantitative 3 C-NMR experiments The resonance frequency for the 3 C nucleus is MHz, 45 o pulse,.34 s acquisition times, 24 khz spectral window, 2048 scans, 64 K data points, relaxation delay 0 s. The average acquisition time of the semi-quantitative 3 C NMR spectra was approximately 6 h. Samples were analysed in 5 mm NMR tubes (Norell 507). The chemical shifts are reported in ppm, using the TMS as internal standard. FT-IR spectra were recorded on a Bruker Vertex 70 spectrometer, with horizontal device for attenuated reflectance and diamond crystal, on a spectral window ranging from 4000 to 400 cm -, at a spectral resolution of 2 cm -. Spectra were recorded without any sample preparation and were processed with OPUS 5.5 software (Bruker). A series of standard mixtures (used for the calibration curve) were prepared by weighing accurately to the nearest g appropriate amounts of linseed oil methyl esters and succinic anhydride corresponding to SA: LOME molar ratios of 0.2, 0.4, 0.6, 0.8, 0.9,.2 and.4. Due to the fact that SA does not dissolve into LOME, the standard mixtures were diluted (: w/w) with acetone. Acetone exhibits an intense characteristic C=O band in the spectral region of interest for the calibration curve ( cm - ), therefore the FTIR spectra of the solutions were recorded after complete solvent evaporation on the crystal. Note: The following symbols were adopted for FT-IR band assignment:ν =stretching vibration, δ=bending vibration, ρ=rocking vibration. Preparation of LOFA 200 g (0.23 mole, assuming an average molecular weight 867) linseed oil (LO) was refluxed with 300 ml KOH solution 0.5 M in ethanol for h. After the saponification is achieved (the mixture becomes homogeneous), the mixture is neutralized with the appropriate amount of aqueous H 2 SO 4 solution 6N in order to convert the soap into its corresponding linseed oil fatty acids (LOFA). The organic phase is extracted twice with Et 2 O then washed several times with NaCl 0% solution to neutral ph and dried over anhydrous MgSO 4. After Et 2 O removal, crude LOFA were obtained in 95% yield as a dark yellow oil and were immediately used in the esterification reaction. Preparation of LOME 65 g (0.60 mole, assuming an average molecular weight 276) LOFA were dissolved in 300 ml,2- dichloroethan and continuously refluxed with 80 ml MeOH and 4 ml H 2 SO 4 98% for 24 h with efficient stirring to obtain the corresponding linseed oil methyl esters (LOME). Water is then added to separate the two phases; the,2- dichloroethane phase which contains LOME is washed several times with NaCl 0% solution until neutral ph and dried on anhydrous MgSO 4. After solvent removal, LOME were obtained in 88% yield as a light yellow oil. H-NMR (CDCl 3, 300 MHz), δ (ppm) : 0.85 (m, 3H, - ) ; 0.94 (t, 3H, -CH=CH- ); (m, - -) ; (cv, -H 2 C- -CO-) ; (m, - -CH=CH-) ; 2.27 (t, - -CO-); (m, - CH=CH- -CH=CH-); 3.63 (s, 3H, CH 3 OCO-); (m, -CH=CH-). 3 C-NMR (CDCl 3, MHz), ρ (ppm): 4 (- ); (- -); 5 (CH 3 OCO-); (-CH=CH-); 74 (- CO-). FT-IR (ATR, ν, cm - ): 30 w (ν =C-H ); 2925 vs, 2855 s (ν C-H asym, sym ); 74 vs (ν C=O ); 459 m (δ CH from CH2 ); 722 m (ρ CH2 ). Preparation of MLOME 20 g (0.4 mole, assuming an average molecular weight 290 and an average number of C=C groups 2.2) LOME were placed in a flask fitted with a condenser with water at 60 o C, magnetic stirrer, N 2 inlet and thermometer. Maleic anhydride (77 g,.80 mole, to ensure a ratio of 2 molecules MA per CH=CH- group) was added and the mixture was heated with efficient stirring to 95 o C and maintained for 2 h. The colour of the solution changed from yellow to reddish brown and the reaction mixture became viscous. After 2 h the unreacted MA was removed by evaporation under reduced pressure (0 mm Hg, at 50 o C). MLOME was obtained in 85% yield as a dark brown viscous mass. H-NMR (CDCl 3, 300 MHz), δ (ppm) : 0.85 (m, 3H, - ) ; (t, 3H, -CH=CH- ); (m, - -) ; (m, -H 2 C- -CO-) ; (m, - -CH=CH-) ; 2.27 (t, - -CO-); (m, 3H, -CO- -CH-CO- from grafted succinic anhydride); 3.63 (s, 3H, CH 3 OCO-); (m, -CH=CH-); (conjugated double bonds). 3 C-NMR (CDCl 3, MHz), δ (ppm): 4 (- ); (- -); (-CO- -CH-CO- from grafted succinic anhydride); 5 (CH 3 OCO-); (-CH=CH-); (-CO-). FT-IR (ATR, ν, cm - ): 300 w (ν =C-H ); 2925 vs, 2855 s (ν C- H asym, sym ); 739 vs (ν C=O ); 862 (ν C=O sym ); 782 (ν C=O asym ); 46 m (δ CH from CH2 ); 437 m (δ CH3 asym ); 362 m (δ CH3 sym ); 97 m (ν C-O ); 7 m (ν C-O-C asym ); 065 w (ν C-O ); 97 w (δ C-O-C ); 723 m (ρ CH2 ). Results and discussions Linseed oil was chemically functionalized by grafting reactive succinyl anhydride moieties onto the LOME backbones, through an ene-reaction mechanism, using maleic anhydride. The maleinization of LOME was carried out at 95 o C with an excess of MA in such extent to ensure REV.CHIM.(Bucharest) 67 No

3 Scheme. Preparation of maleinized linseed oil methyl esters from LO (R 2, R 3 =different acyl chains occurring in LO) a ratio of 2 molecules MA per CH=CH group (scheme ). Prior to maleinization, the starting material (LO) was converted into its corresponding methyl esters in two steps: a saponification followed by neutralization leading to the corresponding fatty acids (LOFA), which were further esterified with MeOH to obtain LOME. FT-IR spectra The FT-IR spectrum (fig. c) of the maleinized linseed oil methyl esters (MLOME) displays specific bands due to the grafted anhydride moiety (fig.a) at 862 and 782 cm - assigned to C=O stretching (symmetric and asymmetric, respectively) or 97 cm - corresponding to the C-O-C stretching (typical for five-membered cyclic anhydrides), and from the LOME backbone (fig. b) such as 309 cm - (unsaturated C-H stretching), 2925 cm - ( stretching), 2855 cm - (C-H stretching), 739 cm - (C=O stretching of ester), 46 cm - (asymmetric CH 3 bending,), 437 cm - ( -C=C bending), 245 cm - (C-O stretching), 7 cm - (C-O-C asymmetric stretching of ester) and 723 cm -, due to multiple split from ( ) n [22, 23]. The grafted anhydride moieties are intact (no ring opening through hydrolysis occurred) since no large band in the cm - spectral region corresponding to the O-H stretch (free or H-bonded) is present in the FT-IR spectrum of MLOME. The absence of the band at 699 cm -, corresponding to the stretching vibration of the H-C=C-H in MA, indicates that unreacted MA was practically completely removed, which means that only the grafted succinyl moiety contributes to the specific anhydride bands from 862 and 782 cm -. The amount of succinyl anhydride grafted on LOME can thus be determined on the basis of a calibration curve, taking into consideration the asymmetric stretching C=O band (782 cm - ), being more intense and sharp than the corresponding symmetric stretch C=O band (862 cm - ). The intense sharp band at 739 cm - (ester C=O stretching vibration) will be used as internal reference band since it is independent of the amount of anhydride (fig. 2). The orthogonal representation of I 782 cm- / I ref ratio on x axis and the corresponding SA: LOME molar ratios of the synthetic calibration mixtures on y axis where I 782 cm- and I ref are the absolute heights of the anhydride (782 cm - ) and of the reference (739 cm - ) bands, respectively (fig. 2) leads to a calibration curve in 8 points, with the linear regression equation y = x (R 2 = 0.988). Through interpolation we have found for MLOME a grafting degree of. mole succinic anhydride per one mole fatty acid methyl ester. To determine the grafting degree for a maleinized triglyceride oil (e.g. linseed, sun-flower, rapeseed), the calibration curve should be obtained from standard binary mixtures of the corresponding unmodified oil and SA in different molar ratios, following a similar procedure. H-NMR spectra The structure of the functionalized oil derivative (MLOME) was investigated through NMR spectroscopy. Figure 3 shows the H-NMR spectra of LOME (a) and MLOME (b). Grafting of anhydride groups onto LOME backbone produces evident differences in the H-NMR spectrum of MLOME with respect to the spectrum of LOME. The grafted succinic anhydride is proven by the multiplet signals in the ppm spectral region, generated by the three diastereotopic protons (Ha, Hb, Hc) of the anhydride [24]. Other changes due to the grafted anhydride Fig.. FT-IR spectra of SA (a), LOME (b) and MLOME (c) REV.CHIM.(Bucharest) 67 No.2 206

4 Fig. 2. Calibration curve for the determination pf the grafting degree of SA moiety onto fatty acid methyl ester chains Fig. 3. H-NMR spectra of LOME (a) and MLOME (b) moiety concern the C=C region: the deshielded signals in MLOME ( ppm) are assigned to different C=C conjugated systems formed during maleinization, in accordance with the ene-reaction mechanism of the maleinization process. The unreacted MA was practically removed since the singlet from 7.05 ppm, attributed to the unreacted MA has a small integral value corresponding to an amount of approx. 2-3%, which could not be removed from the viscous MLOME mass. The maleinization reaction occurs mainly on the linolenic chains, an evidence being the change in the shapes and ratios of the marginal methyl signals from linolenic ( ppm) and the rest of the fatty acyl chains ( ppm) in MLOME (fig. 4b) as compared to LOME (fig. 4a). The rest of the signals in the H-NMR spectrum of MLOME are similar with those from LOME: the singlet at 3.63 ppm corresponding to the protons in the methyl ester group, the methylene protons adjacent to the C=O group at 2.27 ppm (t, - -CO-), the protons of the methylene groups situated in â position with respect to the C=O group at ppm, the allylic protons in the ppm region and the rest of the methylene groups at ppm. The grafting degree of succinic anhydride moiety in MLOME is difficult to compute from H-NMR data since the signals of Fig. 4:. Detail from H-NMR spectra of LOME (a) and MLOME (b) of the terminal signals the three diastereotopic protons from grafted SA ( ppm) overlap the possibly remanent signal of the bis-allylic protons ( ppm). In the present work we consider that the signal of the bis-allylic protons in MLOME H-NMR spectrum is practically negligible since we have performed the maleinization reaction with considerable excess of MA (2 molecules MA per CH=CH group) and the integrals ratio Ha:Hb:Hc=.33:.56:.39. The cumulative integral REV.CHIM.(Bucharest) 67 No

5 Fig.5: 3 C-NMR spectra of LOME (a) and MLOME (b) of the ppm region (I = =4.28) practically accounts for the three diastereotopic atoms from the grafted SA, which means that the mean integral per one H in the grafted anhydride moiety is.42. On the other hand, the mean integral per one H in the acyl chain can be computed on the basis of the cumulative integral value of the chain ending region ( ppm). This cumulative integral value I =.92+.8=3.73 accounts for three protons (methyl group), which means that the integral value corresponding to one proton in the fatty acyl chain is.24. The grafting degree in MLOME is then.42/.24=. mole of grafted SA per one mole fatty acid methyl ester. 3 C-NMR spectra Signal acquisition of 3 C-NMR spectra consists of a modified pulse sequence acquiring 64 scans in order to ensure a semi-quantitative feature of the spectra. A bigger number of scans, although leading to the improvement of the quantitative feature of the 3 C-NMR data, is not justified as it considerably increases the acquisition time. Figure 5 presents the 3 C-NMR spectra of LOME (a) and MLOME (b). Signals in both spectra are grouped on different spectral regions assigned to specific sites of the molecules. The most deshielded signals at ppm are due to the -COO- groups (both from the methyl ester group and from the grafted SA). The C=O carbons from the unreacted MA give a distinct signal at 65 ppm. The C=C signals appear at ppm; in MLOME this region is more complicated than in LOME because of the complex changes occurring during maleinization (concerning both trans isomerization and migration. Evidence of migration of the double bonds in MLOME leading to conjugated C=C double bond systems are the C=C signals which are more deshielded as compared to the corresponding C=C region in LOME. The methyl ester signals appear at 5 ppm in both LOME and MLOME. The marginal methyl groups (CH 3 - -) from the alkyl chains appear in the 0-5 ppm region, the shape being more complicated in MLOME as a consequence of the grafting of anhydride moieties. The methylene groups in both LOME and MLOME generate signals in the ppm region. The grafted SA generates signals in two spectral regions: the carbon atoms involved in C=O double bonds appear as a part of the most deshielded group of signals at ppm (in the same spectral region as the ester groups), while the C sp 3 atoms from the grafted SA moieties give signals in the ppm region. The overall spectrum of MLOME is more complicated than the corresponding LOME spectrum because of the random feature of the maleinization reaction (the grafting process statistically occur on different sites of the molecule, in both allylic and bis-allylic positions), leading to a complex mixture of compounds. The amount of grafted SA can be computed on the basis of the -COO- region at ppm, since the corresponding carbonyl carbons from the unreacted MA give a distinct, well separated signal at 65 ppm, thus allowing the convenient integration of the -COO- region. From the cumulative integral of the ppm region accounting signals from both the methyl ester group (one atom per molecule) and the grafted SA (two atoms per molecule) - the contribution of the carbon atoms from the grafted SA can be deduced by subtracting the integral value of the 5 ppm signal (the amount of COO- ester carbons being equal to the amount of CH 3 -COO- atoms), as described by the following system of chemometric equations: I COO ester + 2 I COO anh =.00 () I COO ester = I COO-CH3 = 0.34 (2) where: I COO ester and I COO anh are the integrals per proton corresponding to the ester -COO- and anhydride -COOgroups, respectively, while I COO-CH3 is the integral value of the signal at 50 ppm, corresponding to the methyl ester group. The calculations lead to I COO anh = 0.33, I COO ester being The grafting degree of SA in MLOME can thus be computed as the I COO anh / I COO ester ratio. Thus, 3 C-NMR data lead to a grafting degree of one mole SA on one mole acyl chain. Conclusions Linseed oil methyl esters have been functionalized by grafting succinic anhydride structural motifs through enereaction with maleic anhydride. The functionalization degree has been determined directly from H- and semiquantitative 3 C-NMR spectra, or based on a calibration curve from FT-IR spectra of a series of standard mixtures of linseed oil methyl esters (LOME) and succinic anhydride corresponding to different SA: LOME molar ratios, considering the absolute heights of the anhydride (782 cm - ) and of the reference ester (739 cm - ) bands. The results obtained from FT-IR data (grafting degree of. REV.CHIM.(Bucharest) 67 No.2 206

6 mole succinic anhydride per one mole fatty acid methyl ester) are in agreement with those obtained from H- and semi-quantitative 3 C-NMR spectra (grafting degrees of. and.0 mole SA on one mole acyl chain, respectively). Acknowledgments: The work has been funded by the Sectoral Operational Programme Human Resources Development of the Ministry of European Funds through the Financial Agreement POSDRU/59/.5/S/ Authors kindly thank Chemont S.A (Mouscron, Belgium) for providing the starting material (linseed oil). References.DRAGOMIR, R.E.; BOGATU, L.; ROSCA, P.; OPRESCU, E.E.; JUGÍNARU, T., Rev. Chim. (Bucharest), 66, no. 4, 205, p TULUC, A.; IANCU, P.; PLESU, V.; BONET-RUIZ, J.; BOZGA, G.; BUMBAC, G., Rev. Chim. (Bucharest), 66, no. 4, 205, p DRAGOMIR, R.E.; ROSCA, P.; JUGANARU, T.; OPRESCU, E.E., Rev. Chim. (Bucharest), 66, no. 2, 205, p ANDREI, M., Rev. Chim. (Bucharest), 65, no., 204, p. 7 5.CITU, I.M., TOMA, C., TRANDAFIRESCU, C., ANTAL, D., ZAMBORI, C., OPREAN, C.; BOJIN, F., BORCAN, F., PAUNESCU, V., LAZUREANU, V., Rev. Chim. (Bucharest), 66, no. 3, 205, p TANASE, C.; CIOATES-NEGUT, C.; UDEANU, D.I.; UNGUREANU, E.M.; HRUBARU, M.; MUNTEANU, C.V.A.; PETRACHE VOICU, S.; COCU, F.; IONITA, A.C., Rev. Chim. (Bucharest), 65, no. 7, 204, p. 768; 7.BORS, A.; NICULAE, G.; STAN, R.; MEGHEA, A., Rev. Chim. (Bucharest), 65, no. 6, 204, p. 67; 8.BALANUCA, B.; LUNGU, A.; HANGANU, A.; STAN, L.R.; VASILE, E.; IOVU H., Eur. J. Lipid Sci. Technol., 6, no. 4, 204, p. 458; 9.CHIRA, N.; STAN, R.; TODASCA, C.; MAGANU, M.; CONSTANTINESCU, T.; GAREA, S.; ROSCA, S., Rev. Chim. (Bucharest), 66, no. 7, 205, p BALANUCA, B.; LUNGU, A.; CONICOV, I.; STAN, R.; VASILE, E.; VULUGA, D.M.; IOVU, H., Polym. Adv. Technol., 26, no., 205, p. 9;.BALANUCA, B.; STAN, R.; HANGANU, A.; IOVU, H., UPB Sci. Bull. Series B, 76, no. 3, 204, p. 29; 2.MIHALACHE, M.; BRATU, A.; HANGANU, A.; CHIRA, N.A. ; TODASCA, M.C.; ROSCA, S., Rev. Chim. (Bucharest), 63, no. 9, 202, p. 877; 3.LOUTELIER-BOURHIS, C.; ZOVI, O.; LECAMP, L.; BUNEL, C.; HUBERT-ROUX, M.; LANGE, C.M., Rapid Commun. Mass Spectrom., 26, 202, p. 265; 4.RZAYEV, Z.M.O., Int. Rev. Chem. Eng., 3, no. 2, 20, p. 53; 5.METZGER, V.J.O.; BIERMANN, U., Fat. Sci. Technol., 96, no. 9, 994, p. 32; METZGER, V.J.O.; LEISINGER, K.F., Fat. Sci. Technol., 90, no., 988, p. ; 6.RHEINECK, A.E.; KHOE, T.H., Fette, Seifen, Anstrichmittel, 7, no. 8, 969, p. 644; 7.QUESADA, J.; MORARD, M.; VACA-GARCIA, C.; BORREDON, E., JAOCS, 80, no.3, 2003, p. 28; 8.MA, P.; JIANG, L.; Ye, T.; DONG, W.; CHEN, M.; Polymers, 6, 204, p.528; 9.MIHALACHE, M.; BRATU, A.; HANGANU, A.; CHIRA, N.A.; TODASCA, M.-C.; ROSCA, S., Rev. Chim. (Bucharest); 63, no.0, 202, p. 984; 20.PLIEV, T.N.; KARPOV, O.N.; GLAVATI, O.L.; POPOVICH, T.D., Zhurnal Prikladnoi Spektroskopii, 8, no., 973, p. 94; 2.BARRA, G.M.O.; CRESPO, J.S.; BERTOLINO, J.R.; SOLDI, V.; NUNES PIRES, A.T., J. Bras. Chem. Soc., 0, no., 999, p. 3; 22.GUNDUZ, G.; KHALID, A.H.; MECIDOGLU, I.A.; ARAS, L., Prog. Polym. Sci., 49, 2004, p. 259; 23.PRETSCH, E.; BUHLMANN, P.; AFFOLTER, C., Structure Determination of Organic Compounds. Tables of Spectral Data, Springer-Verlag, Berlin, 2000; 24.EREN, T.; KUSEFOGLU, S.H.; WOOL, R., J. Appl. Polym. Sci. 90, 2003, p. 97. Manuscript received: REV.CHIM.(Bucharest) 67 No