SPECTROSCOPIC STUDIES ON DEGRADATION OF POLY N,N'-METHYLENE BISACRYLAMIDE

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________________________________________

*_{Author for correspondence; drsri14@yahoo.com}

SPECTROSCOPIC STUDIES ON DEGRADATION OF POLY

N,N'-METHYLENE BISACRYLAMIDE

V. SRIDHAR

*

, S. KALAHASTI

a

,

B. SANJEEVA RAO

b

, S. INDIRA,

K. GOPALA KISHAN RAO

c

and T. V. APPA RAO

d

Department of Chemistry, Kakatiya University, WARANGAL – 506 009 (A.P.) INDIA

a_{Department of Physics, Kakatiya University, WARANGAL – 506 009 (A.P.) INDIA} b_{Department of Physics, Kakatiya Govt. College, HANAMKONDA – 506 001 (A.P.) INDIA} c_{Central Instrumentation Centre, Kakatiya University, WARANGAL – 506 009 (A.P.) INDIA}

d_{Department of Physics, NIT, WARANGAL – 506 002 (A.P.) INDIA}

ABSTRACT

Degradation of poly N,N'-methylene bisacrylamide (PNNMBA) has been probed by electron spin resonance (ESR) and Fourier transform infrared (FTIR) techniques. ESR spectra of PNNMBA irradiated to different radiation doses have been recorded at room temperature (RT) and at liquid nitrogen temperature (LNT). The ESR spectra at RT and LNT are singlets. ESR intensities have been measured by double integration methods. It is observed that intensity of the spectrum increased with increase in dose of irradiation. FTIR spectra of unirradiated and irradiated PNNMBA have been recorded to identify chemical changes, which occurred on irradiation of the copolymer. These studies suggest the cleavage of CONH groups on irradiation of this polymer.

Key words: N,N'-methylene bisacrylamide, Spectroscopic, Degradation.

INTRODUCTION

Various authors have reported degradation of acrylamide polymer previously1-4_.

These studies suggest that cross-linking occurs in polyacrylamide and polymethacrylamide on gamma irradiation. However, such studies were not attempted previously for PNNMBA polymer. Therefore, the authors have undertaken this work on degradation studies of PNNMBA polymer. Since the ESR and FTIR techniques are very useful to ascertain changes induced by gamma irradiation, the authors have used them for this purpose.

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EXPERIMENTAL

Poly N,N'-methylene bisacrylamide has been synthesized by Suresh Babu et al.5

previously. The polymer is in powder form and it is characterized by various experimental techniques. The same sample is used in the present studies and chemical formula of polymer is as shown in Fig. 1. CH2 CH CH CH2 CO CO NH NH CH₂ a a n

Fig. 1: Chemical formula of Poly N, N'-methylene bisacrylamide

Gamma irradiation of polymer is done by a cobalt 60-gamma source with a dose rate of 0.15 M rad/hour. ESR spectra were recorded on Varian E-line spectrometer operating at X-band frequencies and 100 KHz modulation. FTIR spectra have been recorded on Perkin spectrometer.

RESULTS AND DISCUSSION

The ESR spectra of irradiated PNNMBA at RT are shown in Fig. 2. Curves 1, 2, 3

4 3 2 1 20G H 3250G

Fig. 2: ESR spectra of N,N'-methylene bisacrylamide irradiated to various doses at RT

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and 4 indicate the spectra recorded for the polymer irradiated to 3.5, 7.0, 10.5 and 14 M rad doses of irradiation, respectively. The spectra are almost singlets. The ESR spectra of irradiated PNNMBA at liquid nitrogen temperature (LNT) are also singlets (Fig. 3). Curves 1, 2, 3 and 4 represent the ESR spectra observed for 3.5, 7.0, 10.5 and 14 M rad, respectively.

4 3 2 1 20G H 3250G

Fig. 3: ESR spectra of N,N'-methylene bisacrylamide irradiated to various doses at LNT

Double integration methods have been used to find out area under the ESR spectrum. Since total area under each spectrum is directly proportional to the free radicals generated on irradiation, the free radical concentration in each case has been evaluated by the integration method. The values obtained by these methods are as listed in Tables 1 and 2.

The chemical formula of N, N′ – methylene bisacrylamide is shown in Fig 1. Considering the chemical formula, it is likely that radiation attack may takes place at the bulky side group other than the main chain. The cleavage may occur as shown in this diagram. CH₂ CH CH CH₂ CO CO NH NH CH₂ a n (I) (II)I . . COCH ~ + NHCH₂ ~

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The ESR spectrum of irradiated PNNMBA possesses no hyperfine structure, indicating that there are neither alpha nor beta proton in the nearest vicinity of unpaired

electron. Therefore, degradation may occur forming C

.

OCH ~ (I) and N

.

HCH2 ~ (II) free

radicals. Radical (I) can give component singlet in the event of absence of beta protonic interaction and radical (II) also gives a component singlet. The remaining cleavages are not viable in the absence of hyperfine interaction. This type of cleavage indicates that degradation can occur through the cleavage of bulky side groups, instead of main chain scission.

The values of intensities are obtained by double integration method. The values are listed in Tables 1 and 2. It can be observed from the tables that the ESR intensity gradually increases with radiation dose at RT and LNT. Histograms are plotted to observe the behaviors. Figs. 4 and 5 are the histograms as a plot of radiation doses against ESR intensity. The histogram indicates that the increase in intensity with radiation dose increases as more number of free radicals are generated. This is in consequence with the radiation behaviour of

most of the polymers6_.

Table 1: ESR intensities of PNNMBA irradiated to various radiations doses at room temperature (RT) Dose (Mrad) Intensity (Arbitrary units) 3.5 7.0 10.5 14.0 478 606 982 1358

Table 2: ESR intensities of PNNMBA irradiated to various radiations doses at liquid nitrogen temperature Dose (Mrad) Intensity (Arbitrary units) 3.5 7.0 10.5 14.0 636 1375 1487 1886

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0 200 400 600 800 1000 1200 1400 1600 3.5 7 10.5 14

Radiation dose (Mrad)

In

te

n

sit

y

Fig. 4: Variation in ESR intensity against radiation dose

0 200 400 600 800 1000 1200 1400 1600 1800 2000 3.5 7 10.5 14

Radiation dose (Mrad)

In

te

n

sit

y

Fig. 5: Variation in ESR intensity against radiation dose

FTIR studies of PNNMBA have also confirmed these results. The FTIR spectra of unirradiated polymer (Fig. 6) possess absorption bands at 3400, 2930, 1650, 1550, 1450,

1390 and 1250 cm-1_{positions. With the increase the radiative dose, a reduction in CO and}

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4000 3000 2000 1000 Wave number (cm )-1 T ra n sm it ta n ce

Fig. 6: FTIR spectra of pure and irradiated N,N'-methylene bisacrylamide Curve 1: FTIR spectrum of pure sample ( ___ )

Curve 2: FTIR spectrum of irradiated sample (- - -)

CONCLUSION

It is concluded that irradiation of PNNMBA results in the formation of radicals (I) and (II) as the radiation attack may take place at the bulky side groups other than the main chain.

REFERENCES

1. H. Ueda and Z. Kuri, J. Polym. Sci., 8, 333 (1962).

2. U. Ramelow and B. Baysal, J. Appl. Polym. Sci. Symposium Series, 35, 329 (1979).

3. N. Subbarami Reddy, Y. Sudarshana Reddy and B. Sanjeeva Rao, Rad. Eff. Def.

Solids, 129, 273 (1994).

4. J. A. Harris, O. Hinojosa and J. C. Arthur, J. Polym. Sci., A, 11, 3215 (1973).

5. B. Suresh Babu, Ph. D. Dissertation, Osmania University, Hyderabad (1988).

6. M. Dole and C. D. Koining, J. Am. Chem. Soc., 75, 6082 (1952).