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Syntheses and thermoanalytical studies of some schiff base polymers derived from 5,5′-methylene bis(2-hydroxyacetophenone)
PII:
Eur. Polym. J. Vol. 34, No. 1, pp. 133-135, 1998 0 1997 Elsevier Science Ltd. All rights reserved Printed in &eat Britain 0014-3057/97 $17.00 + 0.00 s0014-3057(97)00078-5
SHORT COMMUNICATION SYNTHESES AND THERMOANALYTICAL STUDIES OF SOME SCHIFF BASE POLYMERS DERIVED FROM 5,5’-METHYLENE BIS(2-HYDROXYACETOPHENONE) M. Y. KHUHAWAR:* bNational
A. H. CHANNAR”
and S. W. SHAHb
“Institute of Chemistry, University of Sindh, Jamshoro, Sindh, Pakistan Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Sindh, Pakistan (Received 9 September 1996; accepted in final form 7 January 1997)
Abstract-Six Schiff base polymers poly 5,5’-methylenebis(2-hydroxyacetophenone)l,2-ethylenediimine (PHAen), poly[5,5’-methylenebis(2-hydroxyacetophenone)l,2-propylenediamine] (PHAPn), poly[5,5’(PHAPR), poly[5,5’-methylenebis(2methylenebis(2-hydroxyacetophenone)l,3-propyledenediamine] hydroxyacetophenone)dl-stilbenediimine] (dl-PHAS), poly[5,5’-methylenebis(2-hydroxyacetophenone)meso-stilbenediamine] (meso-PHAS), and poly[5,5’-methylenebis(2-hydroxyacetophenone)azine] (PHAH) have been prepared by polycondensation of 5,5’-methylenebis(2-hydroxyacetophenone (MHA) with ethylenediamine, dl-stilbenediamine meso-stilbenediamine or hydrazine. Each of the polymers has been characterized by elemental microanalysis, infrared and ultraviolet spectroscopy. Their thermogravimetry (TG) and differential thermal analysis (DTA) have been recorded and evaluated. The reduced viscosity of the polymers measured in tetrahydrofuran (THF), dimethylformamide (DMF) and dimethyl sulphoxide (DMSO) was found within 0.202-0.505 dl/g. 0 1997 Elsevier Science Ltd
(0.76 cm)) was then added dropwise. Pure nitrogen gas was
INTRODUCTION
passed with continuous stirring and the mixture was heated at 95-100°C for 24 hr. The contents were poured into cold
A number of polymeric Schiff bases have been reported by polycondensation of dialdehydes or diketones such as 5,5’-methylenebis-salicylaldehyde, bis-salicylaldehyde-5,5’-sulfone, 5,5’-thiobis-sulfural, 2,6_pyridinedicarboxaldehyde terephthaldehyde, glyoxal, 4,4’-dihydroxy-3,3’-diacetylbiphenyl, and 3,3’diamino-4,4’-diformyldiphenyl-sulfone with suitably placed diamino compounds [l-13]. They are reported as useful catenation ligands, where the coordination polymeric Schiff bases have been studied extensively [5, 7, 14, 1.51 and their structures have been determined [ 161. They have thermal stability comparable to polyamides and have been used for solid phase gas chromatography [17]. Some of these are also interesting because of their semiconductor properties [ 181. The present work reports the preparation of the diketonic compound MHA and its reactions towards different diamines for the preparation of six new polymeric Schiff bases (Fig. 1). The work also examines the thermoanalytical behaviour of these compounds.
water (500cm)) and kept at room temperature (30°C) overnight. The product was filtered and recrystallized from acetone (m.p. 130°C).
L
-In (1) R = (2) R = (3) R = (4 ) and
CH2-CH2 CH2-CH-CH3 CH2-CH2-CH2 (5) R = CrjHs-CH-CH-C6H5
EXPERIMENTAL Preparation of 5,5’-methylenebis(2-hydroxyacetophenone) To 2-hydroxyacetophenone (24 cm), 0.2 M) was added acetic acid (glacial) (15 cm’) and 1,3,5-trioxane (2.14 g, 0.063 M). The contents were well mixed and a mixture of sulphuric acid (98%) (0.15 cm’) and acetic acid (glacial) ‘To whom
all correspondence
should
n
(6) Fig. 1. Structural diagrams of Schiff base polymers
be addressed. 133
134
Short Communication Table I
Results of elemental
microanalyses
of Schiff base polymers
Expected (%) Found Comoound
Chemical
Decomposition temoerature ( 0
formula
Yield theoretical (% )
(%)
COlOlX
C
H
N
C,~H,~Oa
135
70
COlOWless
PHAPn
(C~,IHXNIO~),,
24s
7s
Orange
PHAPR
71.35 71.81 74.50 74.21 74.50 73.85 73.99 72.94 80.84 79 95 SO.84 80.41 72.83 72.52
5.47 5.65 6.90 6.84 6.90 6.94 6.54 6 54 6.13 6.28 6.13 5.95 5.75 5.73
8.70 8.52 8 70 8.50 Y.09 8.84 6.08 6.44 6.08 6.13 I I .42 10.95
MHA
(CwH,,NzO:),,
210
70
Orange
PHAen
(C,vHxN,O&
730
90
Brown
n,r.w-PHAS
(GHxN~OI),,
200
80
Yellow
dl-PHAS
(Ci,HzriN:O:).,
210
75
Yellow
PHAH
(CI?HXNIOZ),,
260
80
Orange
Gallenkamp viscometer bath VS 615 was used to control the temperature. The reduced viscosity (+d) was calculated by dividing the specific viscosity (urp) by the concentration (g/100 cm’).
To 5,5’-methylenebis(2-hydroxyacetophenone) (I .42 g) dissolved in ethanol (5 cm’) was added ethylenediamine (0.3 cm’), 1,2-propylenediamine (0.43 cm’), 1.3.propylenediamine (0.43 cm’), rll-stilbenediamine (I. I g), meso-stilbenediamine (1.1 g) or hydrazine hydrate (80%) (I cm’) dissolved in ethanol (5 cm’). The mixture was refluxed for 24 hr. The product as a solid mass started appearing after IO-15 hr. The precipitates were filtered and washed with water, ethanol, acetone and diethylether. PHAPn, PHAPR. (II-PHAS, mrso-PHAS and PHAH were recrystallized from tetrahydrofuran (THF) and methanol. 2_Hydroxyacetophenone, ethylenediamine, I .2-propylenediamine, 1.3-propylenediamine. hydrazine hydrate (80%) (Merck) and 1.3.5-trioxane (Fluka) were used. Meso and dl-stilbenediamines (1,2-diamino-1,2-diphenylethylene) were prepared as reported in Refs [19. 201. Mesn-stilbenediamine was prepared from hydrobenzamide to amarine. N-benzoyl-N-acetyl-mrso-stilbenediamine and n?rso-stilbenediamine [19]. dl-Stilbenediamine was prepared from hydrobenzamide to amarine. isoamarine, N-benzoyl-Nacetyl-dl[-stilbenediamine and dl-stilbenediamme [20]. The elemental microanalysis and mass spectra of MHA were recorded at the HEJ Research Instititute of Chemistry. University of Karachi. Pakistan. Infrared spectra of the compounds were recorded on a Perkin Elmer 1430 IR spectrophotometer over the range 4000-200 cm’. Spectrophotometric studies in THF, dimethylformamtde (DMF) and dimethyl sulphoxide (DMSO) were carried out on a Hitachi 220 spectrophotometer. Thermogravimetry (TG) and differential thermal analysis (DTA) were recorded on a Shimadzu DT-30B thermal analyser in the temperature range from room temperature to 800 C at a nitrogen flow rate of 50 cm’jmin. A sample of 1 I. 1 k 0.2 mg was placed in a platinum crucible and TG and DTA were recorded against r-alumina at a heating rate of IOClmin. The viscosities of mrso-PHAS in THF, d/-PHAS, PHAPR and PHAPn in DMF and PHAen and PHAH in DMSO (I g in 100 cm’ solvent) were measured at 30 ? 0.2 C using a suspended level viscometer (Technic0 ASTM 445). A
Table 2. Stxctrophotometric
RESULTS
AND DISCUSSION
The compound 5,5’-methylenebis(2-hydroxyacetophenone) (MHA) was prepared following a similar procedure as reported for 5,5’-methylenebis-salicylaldehyde [21]. The results of elemental microanalyses (Table I) agree reasonably with the expected values (Table 1). The mass spectrum of MHA indicates a molecular ion peak as a base peak at m/z 283.9 (100%). Main fragment peaks are observed at m/z 269 (72%) and 241 (51%) due to loss of [-CHJ and [CH,-CO] groups, respectively. A peak is observed at m/z 149 (21%) corresponding to CsH902 after loss of a 2-hydroxyacetophenone group. IR of MHA indicates a strong band at 1650 cm-’ due to hydrogen bonded C=O group. The corresponding ketonic band in the polymeric Schiff bases contributed from the group at the end of a molecule is visible only as a weak band in PHAPR, u’/-PHAS and meso-PHAS, with decreasing intensity at 1640 cm -‘. The polymeric Schiff bases indicate a prominent band within 1610-20 cm-’ due to stretching of -C=N, followed by two bands at 1580f5cmm’ and 1498+5cm-’ owing to benzoid rings. PHAH also indicates a medium intensity band at 3390cm-’ due to NH. It may be that some NH2 contribution from hydrazine is present at the end of molecules. All the polymers also indicate a band within 122@1232 cm-’ due to CO vibrations. The polymers are insoluble in ether, acetone, chloroform, but PHAPn, PHAPR, dl-PHAS, mesoPHAS and PHAH dissolve in THF, DMSO and
data of Schlff base polymers
Comoound
Solvent
Reduced viscosity at 30 C (dl,‘r)
MHA mrso-PHAS dl-PHAS PHAPn PHAPR PHAen PHAH
THF THF DMF DMF DMF DMSO DMSO
0.505 0 202 0.404 0.394 0.292 0.295
225 241 268 267 267 262 265
(46.0), 335 (22.35) (61X), 265 (511.4), 333 (207.85) (1076). 333 (490) (305), 328 (191.4) (293). 333 (197.3) (319.6). 330 (174.1) (442.5). 310 (286.5). 333 (276.2)
135
Short Communication formamide (DMF), but PHAen is sufficiently soluble in DMSO to record its spectrophotometric studies. They indicate two to three bands in the UV region due to n--7t* transitions in azomethine and benzoid rings (Table 2). MHA indicates a band at 225 nm, but in polymeric Schiff bases there is a bathochromic shift within 241267 nm with considerable enhancement in 1% absorptivity (t 1%). Thermoanalytical methods have been used extensively to characterize different polymers [22, 231. TG and DTA were carried out to evaluate the thermal stability of the polymers prepared. TG shows the loss in weight in two to three stages between 200 and 800, with a total loss of 955100%. The initial loss of 420% in the temperature range 2OWOO”C may be due to adsorbed solvent, monomeric or dimeric species. This is followed by thermal decomposition up to the recorded temperature of 800°C. Polymers dl-PHAS, PHAPR and PHAen decompose completely. PHAPn leaves 2% residue to PHAH and meso-PHAS lose 95% and 90% up to 800°C. The TG of polymers also indicates that meso-PHAS has the highest thermal stability in the series, followed by increasing order PHAPR, PHAH, PHAPn, dl-PHAS and PHAen. DTA shows a series of endotherms including an endotherm within 25&45O”C which may be due to phase transition, but a large decomposition endotherm in all the polymers is observed with a maximum within the temperature range 62&670°C. The values of reduced viscosities recorded in THF, DMF and DMSO were observed in the range of 0.202 to 0.505 dl/g at 30°C (Table 2). A similar range has been reported for related polymers [12, 131.
dimethyl
CONCLUSION
Six new Schiff base polymers have been synthesized by simple polycondensation in ethanol. The reaction is terminated by the precipitation of polymers after 10-15 hr. The polymers have a reasonably high molecular weight, as is evident from the IR spectra polymers with observation of only a weak ketonic absorption contributed from MHA and a prominent band due to azomethine. They have good thermal stability and major thermal decompositions observed above 400°C.
REFERENCES
1. Dalelio, G. F., Crivello, J. V., Schoenig, R. K. and Huemmer, T. F., J. Macromol. Sci. Chem., 1979, Al, 1161-1249. A. D., Stein, A. A. and Simms, B. B., 2. Delman, J. Macromol. Sri. Chem., 1967, Al, 147-178. H. A. and Bailar Jr., J. C., J. Am. Chem. 3. Goodwin, Sot., 1961, 83, 2467. 4. Marvel, C. S. and Tarkey, N., J. Am. Chem. Sot., 1958, 80, 832. W., Reiderer, M. and Urban, E., Inorg. 5. Sawodny, Chem. Acta, 1978, 29, 63. 6. Patel, A. A. and Patel, S. R., Eur. Polym. J., 1983, 19, 561. I. Patel, M. N., Pate], M. M., Cassidy, P. E. and Fitch, J. W., Inorg. Chim. Acta, 1986, 118, 33. 8. Reilzle, H. and Sawondy, W., Inorg. Chim. Acta, 1985, 103, 53-55. E. T. and Tikhomirov, B. I., 9. Shelikh, A. F., Pankratova, Vestn. Leningr. (init. Ser. Fiz., 1988, 4(l), 60 (in Russian). 10. Sawondy, W. and Riedere, M., Anger. Chem., 1977,89, 897. K. and Seki, K., Jpn. Kokai Tokyo Koho 11. Kamishiro, JP 0162. 327 18962. 3271 (Cl. C08G73100). 3PP. 8 March 1989. . 1. 12. El-Sayed Mansour, M. E., Kaseem, A. A., Nour Elgin, H. and El-Torekhy, A. A., Macromol. Rep., 1991, A28, 103. M. Y. and Channar, A. H., Mncromol. 13. Khuhawar, Rep., 1995, 32, 523. P., Libertini, P. E., Reale, 14. Bottino, F. A., Fincchiaro, A. and Recta, A., Inorg. Nucl. Chem. Left., 1980, 18, 417. 15. Patel, M. N. and Patil, S. H., J. Macromol. Sci. Chem., 1982, Al& 521. A., Hulme, C. E., Mcaulisse, C. A., 16. Aurangzeb, Prilchard, R. G., Watkinson, M., Gancialdeibe, A., Bermejo, M. R. and Sousa, A., J. Chem. Sot. Commun., 1992, 1524. 1985, 17. Grunes, R. and Sawondy, W., J. Chromarogr., 322, 61. 18. Aswar, A. S. and Bhave, N. S., Colloid. Polym. Sri., 1991, 269, 547. 19. Mills, W. H. and Quibells, T. H., J. Gem. Sot., 1953. 843. 20. William, 0. F. and Bailar, J. C., J. Am. Chem. Sot., 1959, 81, 4464. 21. Marvel, C. S. and Torkoy. N., J. Am. Chem. Sot., 1957, 79, 6000. 22. Haines, P. J., Thermochim. Acta, 1989, 148, 365. J. and Schmidt, 23. Rahner, S., Knappe, K., Opfermann, M., Laborpraxis, 1994, 18, 18.
Eur. Polym. J. Vol. 34, No. 1, pp. 133-135, 1998 0 1997 Elsevier Science Ltd. All rights reserved Printed in &eat Britain 0014-3057/97 $17.00 + 0.00 s0014-3057(97)00078-5
SHORT COMMUNICATION SYNTHESES AND THERMOANALYTICAL STUDIES OF SOME SCHIFF BASE POLYMERS DERIVED FROM 5,5’-METHYLENE BIS(2-HYDROXYACETOPHENONE) M. Y. KHUHAWAR:* bNational
A. H. CHANNAR”
and S. W. SHAHb
“Institute of Chemistry, University of Sindh, Jamshoro, Sindh, Pakistan Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Sindh, Pakistan (Received 9 September 1996; accepted in final form 7 January 1997)
Abstract-Six Schiff base polymers poly 5,5’-methylenebis(2-hydroxyacetophenone)l,2-ethylenediimine (PHAen), poly[5,5’-methylenebis(2-hydroxyacetophenone)l,2-propylenediamine] (PHAPn), poly[5,5’(PHAPR), poly[5,5’-methylenebis(2methylenebis(2-hydroxyacetophenone)l,3-propyledenediamine] hydroxyacetophenone)dl-stilbenediimine] (dl-PHAS), poly[5,5’-methylenebis(2-hydroxyacetophenone)meso-stilbenediamine] (meso-PHAS), and poly[5,5’-methylenebis(2-hydroxyacetophenone)azine] (PHAH) have been prepared by polycondensation of 5,5’-methylenebis(2-hydroxyacetophenone (MHA) with ethylenediamine, dl-stilbenediamine meso-stilbenediamine or hydrazine. Each of the polymers has been characterized by elemental microanalysis, infrared and ultraviolet spectroscopy. Their thermogravimetry (TG) and differential thermal analysis (DTA) have been recorded and evaluated. The reduced viscosity of the polymers measured in tetrahydrofuran (THF), dimethylformamide (DMF) and dimethyl sulphoxide (DMSO) was found within 0.202-0.505 dl/g. 0 1997 Elsevier Science Ltd
(0.76 cm)) was then added dropwise. Pure nitrogen gas was
INTRODUCTION
passed with continuous stirring and the mixture was heated at 95-100°C for 24 hr. The contents were poured into cold
A number of polymeric Schiff bases have been reported by polycondensation of dialdehydes or diketones such as 5,5’-methylenebis-salicylaldehyde, bis-salicylaldehyde-5,5’-sulfone, 5,5’-thiobis-sulfural, 2,6_pyridinedicarboxaldehyde terephthaldehyde, glyoxal, 4,4’-dihydroxy-3,3’-diacetylbiphenyl, and 3,3’diamino-4,4’-diformyldiphenyl-sulfone with suitably placed diamino compounds [l-13]. They are reported as useful catenation ligands, where the coordination polymeric Schiff bases have been studied extensively [5, 7, 14, 1.51 and their structures have been determined [ 161. They have thermal stability comparable to polyamides and have been used for solid phase gas chromatography [17]. Some of these are also interesting because of their semiconductor properties [ 181. The present work reports the preparation of the diketonic compound MHA and its reactions towards different diamines for the preparation of six new polymeric Schiff bases (Fig. 1). The work also examines the thermoanalytical behaviour of these compounds.
water (500cm)) and kept at room temperature (30°C) overnight. The product was filtered and recrystallized from acetone (m.p. 130°C).
L
-In (1) R = (2) R = (3) R = (4 ) and
CH2-CH2 CH2-CH-CH3 CH2-CH2-CH2 (5) R = CrjHs-CH-CH-C6H5
EXPERIMENTAL Preparation of 5,5’-methylenebis(2-hydroxyacetophenone) To 2-hydroxyacetophenone (24 cm), 0.2 M) was added acetic acid (glacial) (15 cm’) and 1,3,5-trioxane (2.14 g, 0.063 M). The contents were well mixed and a mixture of sulphuric acid (98%) (0.15 cm’) and acetic acid (glacial) ‘To whom
all correspondence
should
n
(6) Fig. 1. Structural diagrams of Schiff base polymers
be addressed. 133
134
Short Communication Table I
Results of elemental
microanalyses
of Schiff base polymers
Expected (%) Found Comoound
Chemical
Decomposition temoerature ( 0
formula
Yield theoretical (% )
(%)
COlOlX
C
H
N
C,~H,~Oa
135
70
COlOWless
PHAPn
(C~,IHXNIO~),,
24s
7s
Orange
PHAPR
71.35 71.81 74.50 74.21 74.50 73.85 73.99 72.94 80.84 79 95 SO.84 80.41 72.83 72.52
5.47 5.65 6.90 6.84 6.90 6.94 6.54 6 54 6.13 6.28 6.13 5.95 5.75 5.73
8.70 8.52 8 70 8.50 Y.09 8.84 6.08 6.44 6.08 6.13 I I .42 10.95
MHA
(CwH,,NzO:),,
210
70
Orange
PHAen
(C,vHxN,O&
730
90
Brown
n,r.w-PHAS
(GHxN~OI),,
200
80
Yellow
dl-PHAS
(Ci,HzriN:O:).,
210
75
Yellow
PHAH
(CI?HXNIOZ),,
260
80
Orange
Gallenkamp viscometer bath VS 615 was used to control the temperature. The reduced viscosity (+d) was calculated by dividing the specific viscosity (urp) by the concentration (g/100 cm’).
To 5,5’-methylenebis(2-hydroxyacetophenone) (I .42 g) dissolved in ethanol (5 cm’) was added ethylenediamine (0.3 cm’), 1,2-propylenediamine (0.43 cm’), 1.3.propylenediamine (0.43 cm’), rll-stilbenediamine (I. I g), meso-stilbenediamine (1.1 g) or hydrazine hydrate (80%) (I cm’) dissolved in ethanol (5 cm’). The mixture was refluxed for 24 hr. The product as a solid mass started appearing after IO-15 hr. The precipitates were filtered and washed with water, ethanol, acetone and diethylether. PHAPn, PHAPR. (II-PHAS, mrso-PHAS and PHAH were recrystallized from tetrahydrofuran (THF) and methanol. 2_Hydroxyacetophenone, ethylenediamine, I .2-propylenediamine, 1.3-propylenediamine. hydrazine hydrate (80%) (Merck) and 1.3.5-trioxane (Fluka) were used. Meso and dl-stilbenediamines (1,2-diamino-1,2-diphenylethylene) were prepared as reported in Refs [19. 201. Mesn-stilbenediamine was prepared from hydrobenzamide to amarine. N-benzoyl-N-acetyl-mrso-stilbenediamine and n?rso-stilbenediamine [19]. dl-Stilbenediamine was prepared from hydrobenzamide to amarine. isoamarine, N-benzoyl-Nacetyl-dl[-stilbenediamine and dl-stilbenediamme [20]. The elemental microanalysis and mass spectra of MHA were recorded at the HEJ Research Instititute of Chemistry. University of Karachi. Pakistan. Infrared spectra of the compounds were recorded on a Perkin Elmer 1430 IR spectrophotometer over the range 4000-200 cm’. Spectrophotometric studies in THF, dimethylformamtde (DMF) and dimethyl sulphoxide (DMSO) were carried out on a Hitachi 220 spectrophotometer. Thermogravimetry (TG) and differential thermal analysis (DTA) were recorded on a Shimadzu DT-30B thermal analyser in the temperature range from room temperature to 800 C at a nitrogen flow rate of 50 cm’jmin. A sample of 1 I. 1 k 0.2 mg was placed in a platinum crucible and TG and DTA were recorded against r-alumina at a heating rate of IOClmin. The viscosities of mrso-PHAS in THF, d/-PHAS, PHAPR and PHAPn in DMF and PHAen and PHAH in DMSO (I g in 100 cm’ solvent) were measured at 30 ? 0.2 C using a suspended level viscometer (Technic0 ASTM 445). A
Table 2. Stxctrophotometric
RESULTS
AND DISCUSSION
The compound 5,5’-methylenebis(2-hydroxyacetophenone) (MHA) was prepared following a similar procedure as reported for 5,5’-methylenebis-salicylaldehyde [21]. The results of elemental microanalyses (Table I) agree reasonably with the expected values (Table 1). The mass spectrum of MHA indicates a molecular ion peak as a base peak at m/z 283.9 (100%). Main fragment peaks are observed at m/z 269 (72%) and 241 (51%) due to loss of [-CHJ and [CH,-CO] groups, respectively. A peak is observed at m/z 149 (21%) corresponding to CsH902 after loss of a 2-hydroxyacetophenone group. IR of MHA indicates a strong band at 1650 cm-’ due to hydrogen bonded C=O group. The corresponding ketonic band in the polymeric Schiff bases contributed from the group at the end of a molecule is visible only as a weak band in PHAPR, u’/-PHAS and meso-PHAS, with decreasing intensity at 1640 cm -‘. The polymeric Schiff bases indicate a prominent band within 1610-20 cm-’ due to stretching of -C=N, followed by two bands at 1580f5cmm’ and 1498+5cm-’ owing to benzoid rings. PHAH also indicates a medium intensity band at 3390cm-’ due to NH. It may be that some NH2 contribution from hydrazine is present at the end of molecules. All the polymers also indicate a band within 122@1232 cm-’ due to CO vibrations. The polymers are insoluble in ether, acetone, chloroform, but PHAPn, PHAPR, dl-PHAS, mesoPHAS and PHAH dissolve in THF, DMSO and
data of Schlff base polymers
Comoound
Solvent
Reduced viscosity at 30 C (dl,‘r)
MHA mrso-PHAS dl-PHAS PHAPn PHAPR PHAen PHAH
THF THF DMF DMF DMF DMSO DMSO
0.505 0 202 0.404 0.394 0.292 0.295
225 241 268 267 267 262 265
(46.0), 335 (22.35) (61X), 265 (511.4), 333 (207.85) (1076). 333 (490) (305), 328 (191.4) (293). 333 (197.3) (319.6). 330 (174.1) (442.5). 310 (286.5). 333 (276.2)
135
Short Communication formamide (DMF), but PHAen is sufficiently soluble in DMSO to record its spectrophotometric studies. They indicate two to three bands in the UV region due to n--7t* transitions in azomethine and benzoid rings (Table 2). MHA indicates a band at 225 nm, but in polymeric Schiff bases there is a bathochromic shift within 241267 nm with considerable enhancement in 1% absorptivity (t 1%). Thermoanalytical methods have been used extensively to characterize different polymers [22, 231. TG and DTA were carried out to evaluate the thermal stability of the polymers prepared. TG shows the loss in weight in two to three stages between 200 and 800, with a total loss of 955100%. The initial loss of 420% in the temperature range 2OWOO”C may be due to adsorbed solvent, monomeric or dimeric species. This is followed by thermal decomposition up to the recorded temperature of 800°C. Polymers dl-PHAS, PHAPR and PHAen decompose completely. PHAPn leaves 2% residue to PHAH and meso-PHAS lose 95% and 90% up to 800°C. The TG of polymers also indicates that meso-PHAS has the highest thermal stability in the series, followed by increasing order PHAPR, PHAH, PHAPn, dl-PHAS and PHAen. DTA shows a series of endotherms including an endotherm within 25&45O”C which may be due to phase transition, but a large decomposition endotherm in all the polymers is observed with a maximum within the temperature range 62&670°C. The values of reduced viscosities recorded in THF, DMF and DMSO were observed in the range of 0.202 to 0.505 dl/g at 30°C (Table 2). A similar range has been reported for related polymers [12, 131.
dimethyl
CONCLUSION
Six new Schiff base polymers have been synthesized by simple polycondensation in ethanol. The reaction is terminated by the precipitation of polymers after 10-15 hr. The polymers have a reasonably high molecular weight, as is evident from the IR spectra polymers with observation of only a weak ketonic absorption contributed from MHA and a prominent band due to azomethine. They have good thermal stability and major thermal decompositions observed above 400°C.
REFERENCES
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