INTRODUCTION:

The synthesized terpolymer resins, showing versatile applications and properties, attracted the attention of scientist and introduce the recent innovations in the polymer chemistry. These terpolymers can be used as high energy material [1], ion-exchanger [2], semiconductors [3], antioxidants, fire proofing agent, optical storage data, binders, molding materials etc. Literature survey reveals the chelation ion-exchange properties of 2,4-dinitrophenylhydrazone of 2-hydroxyacetophenone-formaldehyde resin [4], and oximes of 2-hydroxyacetophenone substituted benzoic acid-formaldehyde resin [5] for different metal ions. Thermogravimetric analysis of ureaformaldehyde polycondensate (UFPS) has been reported by Zeman and Tokarova [6]. Some terpolymers have been proved to have excellent ion exchange capacity for many transition metals. Terpolymer involving o-nitrophenol-thiourea-paraformaldehyde and anthranilic acid-thioureaparaformaldehyde resins were synthesized and reported for its excellent ion-exchange capacity [7].

In an earlier communication [8-11] from this department numbers of studies on such terpolymers have been reported. However no work seems to have been carried out on synthesis, characterization of the terpolymer resin from 1-Napthol-4-sulphonic acid-Hexamethylene diamine and formaldehyde. Looking the scope of high performing terpolymer resins, in the present paper, synthesis of 1-N-4-SAHDF-Resin-III; its spectral characterization by UV-Visible absorption spectra, NMR spectra have been described and morphology was studied by SEM micrographs.

MATERIALS AND METHODS:

Materials

The chemicals used in the synthesis of new terpolymer resin were procured from the market and were Sigma-Aldrich or chemically pure grade. Whenever required they were further purified by standard procedure.

Synthesis of 1-N-4-SAHDF-Resin-III terpolymer

The new terpolymer 1-N-4-SAHDF-Resin-III was synthesized by condensing 1-Naphthol-4-sulphonic acid (0.3 mol) and Hexamethylene diamine (0.1 mol) with 37% formaldehyde (0.4 mol) in a mol ratio of 3:1:4 in the presence of 2M 200 ml HCl as a catalyst at 140°C ± 20°C for 6hr in an oil bath with occasional shaking to ensure thorough mixing. The separated terpolymer was washed with hot water and methanol to remove unreacted starting materials and acid monomers. The properly washed resin was dried, powdered and then extracted with diethyl ether and then with petroleum ether to remove 1Naphthol-4-sulphonic acid formaldehyde copolymer which might be present along with 1-N-4-SAHDF-Resin-III terpolymer. The coffee brown colored powdery product was immediately removed from the flask as soon as reaction period was over and then purified. The reaction and suggested structure of 1-N-4-SAHDF-Resin-III in shown in Fig. 1.

Purification of resin

The separated terpolymer resin was washed with hot water and methanol to remove unreacted starting materials and acid monomers. The properly washed resin was dried, powdered and then extracted with diethyl ether and then with petroleum ether to remove 1-Naphthol-4-sulphonic acid -formaldehyde copolymer which might be present along with 1-N-4-SAHDF-Resin terpolymer. The product so obtained was further purified by reprecipitation technique. For this purpose the terpolymer resin was dissolved in 10% aqueous sodium hydroxide solution, filtered and reprecipitated by gradual drop wise addition of ice cold 1:1 (v/v) concentrated hydrochloric acid / distilled water with constant and rapid stirring to avoid lump formation. The process of reprecipitation was repeated twice. The terpolymer sample 1-N-4-SAHDF-Resin-III thus obtained was filtered, washed several times with hot water, dried in air, powdered and kept in vacuum desiccators over silica gel. The yield of the terpolymer resin was found to be 77%.

Figure 1: Reaction and suggested structure of representative 1-N-4-SAHDF-Resin-III terpolymer

Characterization

This terpolymer resins was subjected to microanalysis for C, H, S and N at STIC, Cochin.

The number average molecular weight (Mn) was determined by conductometric titration in DMSO using KOH in ethanol as the titrant using Equiptronics conductivity meter within built magnetic stirrer (model No EQ-664). From the graphs of specific conductance against milliequivalents of base, first and last break were noted from which degree of polymerization (DP) and the number average molecular weight (Mn) have been calculated for terpolymer resin. Electron absorption spectra of all terpolymer resins were recorded in DMSO (spectroscopic grade) on Shimadzu double beam spectrophotometer in the range of 200 to 850 nm at Sophisticated Analytical Instrumentation Facility, Punjab University, Chandigarh. Infra-red spectra of 1-N-4-SAHDF terpolymer resin was recorded on Perkin-Elmer-983 spectrophotometer in KBr pallets in the wave number region of 4000-400 cm^-1at SAIF, Punjab University, Chandigarh. Nuclear Magnetic Resonance (NMR) spectra of newly synthesized terpolymer resins have been scanned on Bruker Advanced 400 NMR spectrometer using DMSO-d⁶ at sophisticated Analytical Instrumentation Facility, Punjab University, Chandigarh. For the morphological studies of the resin, SEM was carried at STIC, Cochin.

RESULTS AND DISCUSSION:

Newly synthesized, purified 1-N-4-SAHDF-Resin-III was found to be amorphous and coffee brown in colour. The terpolymers are soluble in solvents such as DMF, DMSO , THF and aq. NaOH while insoluble in almost all other organic solvents. The resin synthesize did not show sharp melting point but undergo decomposition above 240°C .These resins were analyzed for carbon, hydrogen, nitrogen and sulphur content. The Mn of the terpolymer resin was determined by non-aqueous conductometric titration in DMSO against KOH in 50% (v/v) DMSO-Alcohol mixture using 100mg of resin sample. A plot of specific conductance against the milliequivalents of potassium hydroxide required for neutralization of 100 g of terpolymer was made. Inspection of such a plot revealed that there are many breaks in plot. From this plot the first break and the last break were noted. The calculation of (Mn) by this method is based on the following considerations. (1) The first break corresponds to neutralization of the more acidic phenolic hydroxy group of all the repeating units and (2) the break in the plot beyond which a continuous increase in conductance is observed represents the stage at which phenolic hydroxy group of all repeating units are neutralized. On the basis of the average, degree of polymerization (DP) is given by the following relation.

DP = Total meq. of base required for complete neutralization

Meq. of base required for smallest interval

(Mn) = (DP) X Repeat unit weight

On the basis of degree of polymerization (DP), the average number molecular weight (Mn) is calculated by multiplying the (DP) by the formula weight of repeating unit.

The details of Elemental analysis, molecular weight determination are incorporated in Table 1.

Table 1:

Empirical formula of repeat unit

Carbon%

Hydrogen%

Nitrogen%

Sulphur%

Empirical

weight of

repeat unit, g

Average degree

of polymerization

(DP)

Average

molecular

weight (Mn)

C₄₀H₄₀O₁₂S₃N₂

57.41(Cal)

4.54(Cal)

3.34(Cal)

11.48(Cal)

836

18.00

15048

57.64 (F)

4.33(F)

2.99(F)

10.98(F)

The UV-Visible spectra of 1-N-4-SAHDF-Resin-III is incorporated in Fig.2. It is recorded in pure DMSO in the region 200-850 nm at a scanning rate of 100 nm min-1 and a chart speed of 5 cm min-1. 1-N-4-SAHDF-Resin-III gave two characteristics bands at 330 nm and 480 nm. These observed positions for the absorption bands have different intensities. The more intense band is due to p®p*transition and the less intense is due to n ®p* transition. p®p* transition indicates the presence of aromatic nuclei and n ® p *transition indicates the presence of –NH and –OH group. The hyperchromic effect is due to the presence of –OH and –NH groups, which act as auxochrome[12]. It is found that, as numbers of aromatic ring and auxochrome phenolic -OH and -NH groups in the repeated unit increases, there will be increase in ε max values. The observation is in good agreement with proposed structures of above terpolymer resins.

Figure 2: Uv-visible spectrum of 1-N-4-SAHDF-Resin-III

The IR spectra of 1-N-4-SAHDF-Resin-III is incorporated in Fig.3 and the studies revealed that terpolymers give rise to nearly similar pattern of IR spectra. A broad absorption band appeared in the region 3500-3510 cm-¹ may be assigned tothe stretching vibrations of phenolic hydroxyl (-OH) groups exhibiting intramolecular hydrogen bonding [13-14]. A sharp strong peak at 1500-1650 cm^-1 may be ascribed to aromatic skeletal ring. The bands obtained at 1150-1250 cm^-1 suggest the presence of methylene (-CH2) bridge. The 1, 2, 3, 5 substitution of aromatic benzene ring recognized by the sharp, medium / weak absorption bands appeared at 960-980, 1120-1055, 1210-1182 and 1320-1280 cm^-1 respectively. The presence of sharp and strong band at 3390-3410 cm^-1 indicates the presence of -NH bridge. This band seems to be merged with very broad band of phenolic hydroxyl group.

The NMR spectra of 1-N-4-SAHDF-Resin-III, incorporated in Fig.4, was scanned in DMSO-d6 solvent. The chemical shift (δ) ppm observed is assigned on the basis of data available in literature. The singlet obtained in the region 5.12-4.92 (δ) ppm may be due to the methylene proton of Ar-CH2-N moiety. The signals in the region 7.30-7.39(δ) ppm are attributed to protons of –NH bridge. The weak multiplate signals (unsymmetrical pattern) in the region of 8.21-8.18(δ) ppm may be attributed to aromatic proton (Ar-H). The signals in the range at 9.08 to 9.02(δ) ppm may be due to phenolic hydroxyl protons. The much downfield chemical shift for phenolic -OH indicates clearly the intramolecular hydrogen bonding of -OH group [15]. The signals in the range of 10.02-10.08(δ) ppm are attributed to proton of -SO₃H groups.

Scanning Electron Microscopy (SEM)

SEM enables imaging to surface feature of 10-105 times magnification and resolution of features down to 3-100 nm depending upon the sample. Surface analysis has been found to be of great use in understanding the surface features of the materials. The morphology of the synthesized and purified terpolymer resins under investigation has been reported by scanning electron microscopy which is shown in Fig. 5. The white bar at the bottom of the SEM microscopy represents the scale. The morphology of the terpolymer resin shows fringed, scattered, miscellaneous model of the crystalline amorphous structure. The fringe and scattered structure represent transition material between the crystalline and amorphous phases. This tends to draw attention away from the details of the fine structure and gives little insight into the structure of large entities such as spherulites. The SEM photographs exhibits such spherulties which are the aggregate of crystalline present along with the some amorphous regions. The amorphous region shows secondary structural feature such as corrugations and having shallow pits.

Fig. 5: SEM micrographs of 1-N-4-SAHDF-Resin-III

CONCLUSION:

The new 1-N-4-SAHDF-Resin-III based on the condensation polymerization of 1-Naphthol-4-sulphonic acid and Hexamethylene diamine with formaldehyde in the presence of acid catalyst has been prepared. The newly synthesized terpolymer resin is soluble in DMF, DMSO, THF and aq. NaOH and insoluble in common organic solvents. From the elemental analysis, UV-visible, FT-IR and ¹H NMR spectral studies the proposed structure of the 1-N-4-SAHDF-Resin-III has been determined.

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Received on 14.08.2014 Modified on 15.10.2014

Asian J. Research Chem. 7(11): November, 2014; Page 1007-1010