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Synthesis of some new metal-containing polyurethanes
European Polymer Journal Vol. 16, pp 941 to t~44
0014-3057/80/10014)'941~120010
O Pergamon Press Lid 1980 Printed m Great Brllaln
SYNTHESIS OF SOME NEW METAL-CONTAINING POLYURETHANES* B. DURAIRAJand K. VENKATARAO Department of Physical Chemistry, University of Madras, A.C College Campus, Madras-600 025, India (Received 22 January 1980; revised 12 March 1980) Abstract--Some new metal-containing polyurethanes were synthesized from manganese and lead salts of mono(hydroxyethyl)phthalate by condensing them with hexamethylene diisocyanate and toluene diisocyanate in dimethylformamide as solvent. The polymers were characterized by viscometry, infrared spectroscopy and thermal analysis. The decomposition temperatures of these polymers were found to be significantly lower than those of metal-free polymers of similar structure. However, the rates of decomposition of metal-containing polyurethanes were lower than those of polyurethanes having no metal. Inherent viscosities in DMSO at 30 ° of these polyurethanes were low, ranging from 0.043 to 0.067.
Synthesis a n d studies on polymers containing metals in the main chain are i m p o r t a n t from the scientific and industrial view points. Recently M a t s u d a [1-7] synthesized a series of polymers using Ca, M g and Z n salts of m o n o ( h y d r o x y e t h y l ) p h t h a l a t e (HEP) and first reported the synthesis of polyurethanes containing ionic links in the polymer chain. We have reported [8] in brief the synthesis a n d characterization of M n a n d P b salts of mono(hydroxyethyl)phthalate having structure (I).
t'-IOCHzCHzOOC
~
OOMOOC
COOCH2CH20H
mixture was allowed to stand overnight to allow for completion of the reaction. This reaction mixture was treated with excess dimethylformamide, filtered through a Whatman filter paper and the filtrate was poured into stirred cold water or chloroform to precipitate the polymer. The separated product was filtered, washed several times with chloroform and dried in vacuo at 70-80 °.
Characterization of products Infrared spectra was taken in a Beckman IR-20 instrument using the KBr disc method. Thermogravimetric analysis ('I'GA/was carried out in a Perkin-Elmer TGS-2 instrument in N2 atmosphere at a heating rate of 10°C/min. Differential scanning calorimetry (DSC) was carried out in a Perkin-Elmer DSC-IB instrument in N2 atmosphere at a heating rate of 10°C/rain. Inherent viscosities of the polymers were determined at a concentration of 0.05g/10ml of DMSO at 30 ° using an Ubbelohde Viscometer.
(If where
M
RESULTS AND DISCUSSION
= M n or P b
We now describe the synthesis a n d characterization of m e t a l - c o n t a i n i n g polyurethanes, prepared by condensations of ! with 2,4-toluene diisocyanate (TDI), toluene diisocyanate (2,4 a n d 2,6 in the tool ratio 80:20) a n d hexamethylene diisocyanate (HMDI). EXPERIMENTAL
Preparation of polyurethanes A four-necked 100 ml flask was fitted with a stirrer, N 2 inlet, condenser and dropping funnel. Into this 0.0015 mol of M-(HEP)2, 15 g of dimethyl formamide and 0.25 g of anhydrous stannic chloride were placed. Then 0.0165 tool of diisocyanate dissolved in 10 g of dimethylformamide was slowly added with stirring under a stream of N 2 for 30 min at room temperature. The reaction mixture was stirred continuously at room temperature for a further period of 1 hr. Then the temperature of the reaction mixture was raised first to 80 ° and then to 100°, with continued stirring for a given time at each temperature. Finally the reaction * Presented at the International Symposium on New Frontiers in Polymer Science and Polymer Applications, Madras, India 7-11 January, 1980. 941
Since M-(HEP)2 is insoluble in most organic solvents, the polymerizations of these salts had to be done only in those solvents which dissolve the resulting polymers. Since D M F is a good solvent for polyurethanes [9], it was selected as the solvent for the polymerizations. The details of the preparation of polyurethanes from T D I and H M D I and M-(HEP)2 are shown in Table 1. The reactions were started by the gradual addition of diisocyanates dissolved in D M F to the stirred solution of M-(HEP)2 in the same solvent at room temperature. F o r systems containing Mn-(HEP)2, the salt started dissolving as the stirring continued for approx 1 hr at r o o m temperature. The solution was completely h o m o g e n e o u s when the reaction temperature was raised to 80 ° and the stirring was continued for a given period. With Pb-(HEP)2, the system did not become h o m o g e n e o u s even after continued stirring for a long time at elevated temperatures (80--100°), so that the reaction mixture was left to stand overnight in the expectation that there would be an increase in chain length of the polymer molecule by the reaction of nearby reactive polymer endgroups. This expectation was confirmed by the observation of increase in the viscosity of the reaction mixture after 24 hr. The reaction mixture was then filtered
942
B, DURAIRAJ a n d K. VENKATA RAO
Table 1. Polyurethanes prepared from diisocyanates and M-(HEP)2 Diisocyanate
M-(HEP) 2
TDI (2,4)
Mn-(HEP)2
TDI (2,4)
Pb-(HEP) 2
TDI (2,4 and 2,6 80: 20)
Mn-(HEP)2
TDI (2,4 and 2,6 80:20)
Pb-(HEP)2
HMDI
Mn-(HEP)2
HMDI
Pb-(HEP) 2
Synthesis conditions
Yield
External appearance
Room temp./ 2 hr 70-80°/4 hr Room temp./ 1 hr 80°/2 hr 100°/3 hr Room temp./ 2 hr 70-80°/4 hr Room temp./ 1 hr 80°/2 hr 100°/2 hr Room temp./ 2 hr 70-80°/4 hr Room temp./ 1 hr 100°/5 hr
82
Dirty white powder
0.061
8.4
8.5
92
White fluffy
0.067
22.8
25.4
73
Pale brown
0.059
8.1
8.5
85
Pale yellow
0.048
22.4
25.4
Pale flesh coloured powder White
0.055
9.9
8.6
0.043
30.1
26.1
(~)
93t"
r/ inh
Metal 5/0 Found Calcd
811
* Determined at a concentration of 0.05 g/10 ml in DMSO at 30°. i" Precipitated by chloroform. to remove any unreacted Pb(HEP)2; the polymer was then precipitated. The polyurethanes prepared using TDI were precipitated by water whereas those from HMDI were precipitated by chloroform. The viscosities of the polyurethanes were low as compared to the analogues without metal. This may be due to the fact I'1] that in more polar solvents like DMSO the ionic links present in the polymer chain dissociate resulting in reduction of the molecular weight of the polymer when the concentration is low. The i.r. spectra of metal-containing polyurethanes exhibit absorption bands at 3350 cm-1 (NH stretching), 1700-1730 cm- 1 (C------O stretching), 1540-1560cm -~ (NH bending) and 1400-1410em - t and i 560-1610 cm- ~ characteristic of carboxylate
9C
_
group. The 1560-1610cm -~ and 1400--1410cm -1 bands confirm the presence of ionic links in the polyurethanes [1], T H E R M A L STABILITY O F P O L Y U R E T H A N E S
Figures 1 and 2 show the TGA curves of the M-(HEP)2 (M = Mn or Pb) salts and their polymers. The thermal stabilities of other metal-containing polyurethanes and their blank polymers are summarized in Table 2. Similar to the results of Matsuda [1] the presence of metal in the chain decreases the first decomposition temperature of the polyurethane and lowers the rate of decomposition as compared to that of blank polymer. For example, in the case of Pb-(HEP)2-HMDI polyurethane, 50% weight loss
....~.,.,. "° ""..
oc ~c
\
"... \
. -
".',
~c
2C
..=:===...........~ •
tC i
100
A
200
I
300
i
400
I
500
I
600
Temperature (°C) Fig. I. T G A curves of (A) Mn salt of HEP; (B) Polyurethane from Mn-(HEP)2 and T D I and (C)
Polyurethane from Mn-(HEP)2 and HMDI.
Synthesis of some new metal-containing polyurethanes
~
n--
6o
......
4o
\
30
~
\
943
"-,.
....
~.,~.~
2O IO I
2
300
40<]
500
Temperature ("C)
Fig. 2. TGA curves of (A) Pb salt of HEP; (B) Polyurethane from Pb-(HEPt2 and TDI and (C) Polyurethane from Pb-(HEP)2 and HMDI. Table 2. Thermal stability of polyurethanes
Diisocyanate
Diol
TDI (2,4) TDI (2,4) TDI (2,4 and 2,6) TDI (2,4 and 2,6) TDI HMD1 HMDI HMDI
Temp. 10~o weight loss (°C)
Mn-(HEP)2 Pb-(HEPh Mn-(HEP)2 Pb-(HEP): DEG Mn-(HEP)2 Pb-(HEP) 2 DEG
Temp. 50~o weight loss (°C)
217 197 197 204 248 198 230 295
309 306 282 282 314* 308 545 340*
* Taken from Ref. [1].
was found to occur at an abnormally high temperature (545°). The plateau observed in T G A curves above 550 ° correspond to the formation of P b O and M n 2 0 3 in the case of the respective polyurethanes. NATURE AND SOLUBILITY OF THE POLYURETHANES
The polyurethanes prepared from Pb(HEP)2-HMDI, Pb-(HEP)2-TDI and Mn-(HEP)2HMDI become sticky due to the absorption of water when they are kept in air. The are soluble in polar solvents like DMF, DMSO and DMAC and are insoluble in most other common organic solvents. Acknowledgements~ne of the authors (B.D.) thanks the University Grants Commission for the award of a Junior Research Fellowship. We thank Professor H. Kothandaraman and Dr K. Rajagopal for helpful discussions. REFERENCES
1. H. Matsuda, (1974). 2. H. Matsuda, (1974). 3. H. Matsuda, (1974). 4. H. Matsuda,
J. Polym. Sci. Polym. Chem. Ed. 12, 455 J. Polym. ScL Polym. Chem. Ed. 12, 469 J. Polym. Sci. Polym. Chem. Ed. 12, 2419 J. Macromolek. Sci-Chem. Ag, 397 (1975}.
5. H. Matsuda, J..Polym Sci. Polym. Chein. Ed. 14, 1783 (1976). 6. H. Matsuda, J. appl. Polym. Sci. 20, 995 (1976). 7. H. Matsuda, J. Macromolek. Sci-Chem. AI0, 1143 (1976). 8. B. Durairaj and K. Venkata Rao, Polym. Bull. I, 723 (1979). 9. Y. Nishijima and M. Fukushima, Kobun.shi Kayaku 30, 13 (1973). 10. E. M. Emery, Analyt. Chem. 32, 1495 (1960). I1. R. A. Friedel, J. L. Shultz and A. G. Sharke), Analyt. Chem. 28, 926 (1956). 12. D. Dollimore and K. H Tonge, 5th Int. Syrup. React. Solids, Munich. 1964, 497-508 (1965).
APPENDIX
Characterization of divalent metal salts of HEP(I) Pb-(HEP)2 and Mn-(HEP)2 were prepared as described previously [8]. The purities of these salts were confirmed by elemental and spectral analyses. TGA and DSC (Fig. 3) of these salts gave interesting results about structure and stability. The thermograms showed that the Pb-(HEP)2 salt was stable only up to 147 whereas the Mn-(HEP)2 salt was stable up to 251 in N2. Above these temperatures, the modes of decomposition of these two salts were different. Emery [10] studied the mass spectrum of diethylphthal-
944
B. DURAIRAJand K. VENKATARAO
E o hl
4 50
500
550
600
650
70O
750
Temperature ( ° K )
Fig. 3. DSC curves of (A) Mn salt of HEP and (B) Pb salt of HEP. ate at 250 ° and reported that there was initial elimination of ethoxyradical followed by the loss of ethylene. The mass spectrum of ethylene glycol [11] however showed the elimination of---CH2OH group in the first stage of decomposition. In the case of Mn-(HEP)2, the first phase of decomposition started at 251 ° and extended up to 279 ° with a weight loss of 23%. These results indicate the possibility that this weight loss of 23% for Mn-(HEP)2 is due to the simultaneous decomposition of ---CH2CH2OH and --OCH2CH2OH groups (calc 22.4%). The sharp endotherm (255°) followed by an exotherm (265 °) in the DSC curve may correspond to this decomposition. The second (28% weight loss; 279-328 °) and third (32% weight loss; 328-498 °) phases of decomposition correspond to the loss of II (calc 27.8%) and llI (calc. 32%) groups respectively. The decomposition of II is not reflected in DSC curve, but the endotherms (398 and 437 °) followed by an exotherm (454 °) may be associated with the decomposition of ill group. The manganese oxide which is formed by the decomposition of oxy salt and carbonate of manganese is
"k
I
o
I
usually Mn203 above 550 ° [12]. Hence the residue of the decomposed product will correspond to Mn203 only. In the case of Pb-(HEP)2, the thermogram showed that the first phase of decomposition occurs in two different steps (193-230 ° and 230-290 ° corresponding to 6.5 and 7.0% weight loss respectively). The sharp endotherm (205 °) followed by an exotherm (217°) and the break in the DSC curve (260°) may represent the gradual loss of two ---CH2CH2OH (14.4%) groups. The second phase of decomposition (26.5% weight loss; 290-378 °) may be due to the breakage of IV (26.2% calc.) group, as indicated by a break in the DSC curve at ~ 292 ° and a sharp endotherm at 368 °. The third phase of decomposition took place in two stages (i.e. 5.5% weight loss; 378-384 ° and 16.5% weight loss; 384-498 ~) which can be attributed to the stepwise loss of CO2 and CO in the first stage (5.7% calc. and a mixture of Ph-CO and Ph-COO in the second stage (17.9% calc). These decompositions correspond to the sharp ¢ndotherm at 379 ° followed by the exotherm at 385 °. The final residue was confirmed to be PbO.
/
I
ol
I o
o
,
111
""
Fragmentation pattern of Mn - ( HEP )2
0
o -
/ I
0
I t
I
"It 0
- i - o - Pb
0
o -
I
I
i
I
-
o +
c.
t \\ IV
Fragmentation
t
Pattern of P b - ( H E P ) z
c.2o.
0014-3057/80/10014)'941~120010
O Pergamon Press Lid 1980 Printed m Great Brllaln
SYNTHESIS OF SOME NEW METAL-CONTAINING POLYURETHANES* B. DURAIRAJand K. VENKATARAO Department of Physical Chemistry, University of Madras, A.C College Campus, Madras-600 025, India (Received 22 January 1980; revised 12 March 1980) Abstract--Some new metal-containing polyurethanes were synthesized from manganese and lead salts of mono(hydroxyethyl)phthalate by condensing them with hexamethylene diisocyanate and toluene diisocyanate in dimethylformamide as solvent. The polymers were characterized by viscometry, infrared spectroscopy and thermal analysis. The decomposition temperatures of these polymers were found to be significantly lower than those of metal-free polymers of similar structure. However, the rates of decomposition of metal-containing polyurethanes were lower than those of polyurethanes having no metal. Inherent viscosities in DMSO at 30 ° of these polyurethanes were low, ranging from 0.043 to 0.067.
Synthesis a n d studies on polymers containing metals in the main chain are i m p o r t a n t from the scientific and industrial view points. Recently M a t s u d a [1-7] synthesized a series of polymers using Ca, M g and Z n salts of m o n o ( h y d r o x y e t h y l ) p h t h a l a t e (HEP) and first reported the synthesis of polyurethanes containing ionic links in the polymer chain. We have reported [8] in brief the synthesis a n d characterization of M n a n d P b salts of mono(hydroxyethyl)phthalate having structure (I).
t'-IOCHzCHzOOC
~
OOMOOC
COOCH2CH20H
mixture was allowed to stand overnight to allow for completion of the reaction. This reaction mixture was treated with excess dimethylformamide, filtered through a Whatman filter paper and the filtrate was poured into stirred cold water or chloroform to precipitate the polymer. The separated product was filtered, washed several times with chloroform and dried in vacuo at 70-80 °.
Characterization of products Infrared spectra was taken in a Beckman IR-20 instrument using the KBr disc method. Thermogravimetric analysis ('I'GA/was carried out in a Perkin-Elmer TGS-2 instrument in N2 atmosphere at a heating rate of 10°C/min. Differential scanning calorimetry (DSC) was carried out in a Perkin-Elmer DSC-IB instrument in N2 atmosphere at a heating rate of 10°C/rain. Inherent viscosities of the polymers were determined at a concentration of 0.05g/10ml of DMSO at 30 ° using an Ubbelohde Viscometer.
(If where
M
RESULTS AND DISCUSSION
= M n or P b
We now describe the synthesis a n d characterization of m e t a l - c o n t a i n i n g polyurethanes, prepared by condensations of ! with 2,4-toluene diisocyanate (TDI), toluene diisocyanate (2,4 a n d 2,6 in the tool ratio 80:20) a n d hexamethylene diisocyanate (HMDI). EXPERIMENTAL
Preparation of polyurethanes A four-necked 100 ml flask was fitted with a stirrer, N 2 inlet, condenser and dropping funnel. Into this 0.0015 mol of M-(HEP)2, 15 g of dimethyl formamide and 0.25 g of anhydrous stannic chloride were placed. Then 0.0165 tool of diisocyanate dissolved in 10 g of dimethylformamide was slowly added with stirring under a stream of N 2 for 30 min at room temperature. The reaction mixture was stirred continuously at room temperature for a further period of 1 hr. Then the temperature of the reaction mixture was raised first to 80 ° and then to 100°, with continued stirring for a given time at each temperature. Finally the reaction * Presented at the International Symposium on New Frontiers in Polymer Science and Polymer Applications, Madras, India 7-11 January, 1980. 941
Since M-(HEP)2 is insoluble in most organic solvents, the polymerizations of these salts had to be done only in those solvents which dissolve the resulting polymers. Since D M F is a good solvent for polyurethanes [9], it was selected as the solvent for the polymerizations. The details of the preparation of polyurethanes from T D I and H M D I and M-(HEP)2 are shown in Table 1. The reactions were started by the gradual addition of diisocyanates dissolved in D M F to the stirred solution of M-(HEP)2 in the same solvent at room temperature. F o r systems containing Mn-(HEP)2, the salt started dissolving as the stirring continued for approx 1 hr at r o o m temperature. The solution was completely h o m o g e n e o u s when the reaction temperature was raised to 80 ° and the stirring was continued for a given period. With Pb-(HEP)2, the system did not become h o m o g e n e o u s even after continued stirring for a long time at elevated temperatures (80--100°), so that the reaction mixture was left to stand overnight in the expectation that there would be an increase in chain length of the polymer molecule by the reaction of nearby reactive polymer endgroups. This expectation was confirmed by the observation of increase in the viscosity of the reaction mixture after 24 hr. The reaction mixture was then filtered
942
B, DURAIRAJ a n d K. VENKATA RAO
Table 1. Polyurethanes prepared from diisocyanates and M-(HEP)2 Diisocyanate
M-(HEP) 2
TDI (2,4)
Mn-(HEP)2
TDI (2,4)
Pb-(HEP) 2
TDI (2,4 and 2,6 80: 20)
Mn-(HEP)2
TDI (2,4 and 2,6 80:20)
Pb-(HEP)2
HMDI
Mn-(HEP)2
HMDI
Pb-(HEP) 2
Synthesis conditions
Yield
External appearance
Room temp./ 2 hr 70-80°/4 hr Room temp./ 1 hr 80°/2 hr 100°/3 hr Room temp./ 2 hr 70-80°/4 hr Room temp./ 1 hr 80°/2 hr 100°/2 hr Room temp./ 2 hr 70-80°/4 hr Room temp./ 1 hr 100°/5 hr
82
Dirty white powder
0.061
8.4
8.5
92
White fluffy
0.067
22.8
25.4
73
Pale brown
0.059
8.1
8.5
85
Pale yellow
0.048
22.4
25.4
Pale flesh coloured powder White
0.055
9.9
8.6
0.043
30.1
26.1
(~)
93t"
r/ inh
Metal 5/0 Found Calcd
811
* Determined at a concentration of 0.05 g/10 ml in DMSO at 30°. i" Precipitated by chloroform. to remove any unreacted Pb(HEP)2; the polymer was then precipitated. The polyurethanes prepared using TDI were precipitated by water whereas those from HMDI were precipitated by chloroform. The viscosities of the polyurethanes were low as compared to the analogues without metal. This may be due to the fact I'1] that in more polar solvents like DMSO the ionic links present in the polymer chain dissociate resulting in reduction of the molecular weight of the polymer when the concentration is low. The i.r. spectra of metal-containing polyurethanes exhibit absorption bands at 3350 cm-1 (NH stretching), 1700-1730 cm- 1 (C------O stretching), 1540-1560cm -~ (NH bending) and 1400-1410em - t and i 560-1610 cm- ~ characteristic of carboxylate
9C
_
group. The 1560-1610cm -~ and 1400--1410cm -1 bands confirm the presence of ionic links in the polyurethanes [1], T H E R M A L STABILITY O F P O L Y U R E T H A N E S
Figures 1 and 2 show the TGA curves of the M-(HEP)2 (M = Mn or Pb) salts and their polymers. The thermal stabilities of other metal-containing polyurethanes and their blank polymers are summarized in Table 2. Similar to the results of Matsuda [1] the presence of metal in the chain decreases the first decomposition temperature of the polyurethane and lowers the rate of decomposition as compared to that of blank polymer. For example, in the case of Pb-(HEP)2-HMDI polyurethane, 50% weight loss
....~.,.,. "° ""..
oc ~c
\
"... \
. -
".',
~c
2C
..=:===...........~ •
tC i
100
A
200
I
300
i
400
I
500
I
600
Temperature (°C) Fig. I. T G A curves of (A) Mn salt of HEP; (B) Polyurethane from Mn-(HEP)2 and T D I and (C)
Polyurethane from Mn-(HEP)2 and HMDI.
Synthesis of some new metal-containing polyurethanes
~
n--
6o
......
4o
\
30
~
\
943
"-,.
....
~.,~.~
2O IO I
2
300
40<]
500
Temperature ("C)
Fig. 2. TGA curves of (A) Pb salt of HEP; (B) Polyurethane from Pb-(HEPt2 and TDI and (C) Polyurethane from Pb-(HEP)2 and HMDI. Table 2. Thermal stability of polyurethanes
Diisocyanate
Diol
TDI (2,4) TDI (2,4) TDI (2,4 and 2,6) TDI (2,4 and 2,6) TDI HMD1 HMDI HMDI
Temp. 10~o weight loss (°C)
Mn-(HEP)2 Pb-(HEPh Mn-(HEP)2 Pb-(HEP): DEG Mn-(HEP)2 Pb-(HEP) 2 DEG
Temp. 50~o weight loss (°C)
217 197 197 204 248 198 230 295
309 306 282 282 314* 308 545 340*
* Taken from Ref. [1].
was found to occur at an abnormally high temperature (545°). The plateau observed in T G A curves above 550 ° correspond to the formation of P b O and M n 2 0 3 in the case of the respective polyurethanes. NATURE AND SOLUBILITY OF THE POLYURETHANES
The polyurethanes prepared from Pb(HEP)2-HMDI, Pb-(HEP)2-TDI and Mn-(HEP)2HMDI become sticky due to the absorption of water when they are kept in air. The are soluble in polar solvents like DMF, DMSO and DMAC and are insoluble in most other common organic solvents. Acknowledgements~ne of the authors (B.D.) thanks the University Grants Commission for the award of a Junior Research Fellowship. We thank Professor H. Kothandaraman and Dr K. Rajagopal for helpful discussions. REFERENCES
1. H. Matsuda, (1974). 2. H. Matsuda, (1974). 3. H. Matsuda, (1974). 4. H. Matsuda,
J. Polym. Sci. Polym. Chem. Ed. 12, 455 J. Polym. ScL Polym. Chem. Ed. 12, 469 J. Polym. Sci. Polym. Chem. Ed. 12, 2419 J. Macromolek. Sci-Chem. Ag, 397 (1975}.
5. H. Matsuda, J..Polym Sci. Polym. Chein. Ed. 14, 1783 (1976). 6. H. Matsuda, J. appl. Polym. Sci. 20, 995 (1976). 7. H. Matsuda, J. Macromolek. Sci-Chem. AI0, 1143 (1976). 8. B. Durairaj and K. Venkata Rao, Polym. Bull. I, 723 (1979). 9. Y. Nishijima and M. Fukushima, Kobun.shi Kayaku 30, 13 (1973). 10. E. M. Emery, Analyt. Chem. 32, 1495 (1960). I1. R. A. Friedel, J. L. Shultz and A. G. Sharke), Analyt. Chem. 28, 926 (1956). 12. D. Dollimore and K. H Tonge, 5th Int. Syrup. React. Solids, Munich. 1964, 497-508 (1965).
APPENDIX
Characterization of divalent metal salts of HEP(I) Pb-(HEP)2 and Mn-(HEP)2 were prepared as described previously [8]. The purities of these salts were confirmed by elemental and spectral analyses. TGA and DSC (Fig. 3) of these salts gave interesting results about structure and stability. The thermograms showed that the Pb-(HEP)2 salt was stable only up to 147 whereas the Mn-(HEP)2 salt was stable up to 251 in N2. Above these temperatures, the modes of decomposition of these two salts were different. Emery [10] studied the mass spectrum of diethylphthal-
944
B. DURAIRAJand K. VENKATARAO
E o hl
4 50
500
550
600
650
70O
750
Temperature ( ° K )
Fig. 3. DSC curves of (A) Mn salt of HEP and (B) Pb salt of HEP. ate at 250 ° and reported that there was initial elimination of ethoxyradical followed by the loss of ethylene. The mass spectrum of ethylene glycol [11] however showed the elimination of---CH2OH group in the first stage of decomposition. In the case of Mn-(HEP)2, the first phase of decomposition started at 251 ° and extended up to 279 ° with a weight loss of 23%. These results indicate the possibility that this weight loss of 23% for Mn-(HEP)2 is due to the simultaneous decomposition of ---CH2CH2OH and --OCH2CH2OH groups (calc 22.4%). The sharp endotherm (255°) followed by an exotherm (265 °) in the DSC curve may correspond to this decomposition. The second (28% weight loss; 279-328 °) and third (32% weight loss; 328-498 °) phases of decomposition correspond to the loss of II (calc 27.8%) and llI (calc. 32%) groups respectively. The decomposition of II is not reflected in DSC curve, but the endotherms (398 and 437 °) followed by an exotherm (454 °) may be associated with the decomposition of ill group. The manganese oxide which is formed by the decomposition of oxy salt and carbonate of manganese is
"k
I
o
I
usually Mn203 above 550 ° [12]. Hence the residue of the decomposed product will correspond to Mn203 only. In the case of Pb-(HEP)2, the thermogram showed that the first phase of decomposition occurs in two different steps (193-230 ° and 230-290 ° corresponding to 6.5 and 7.0% weight loss respectively). The sharp endotherm (205 °) followed by an exotherm (217°) and the break in the DSC curve (260°) may represent the gradual loss of two ---CH2CH2OH (14.4%) groups. The second phase of decomposition (26.5% weight loss; 290-378 °) may be due to the breakage of IV (26.2% calc.) group, as indicated by a break in the DSC curve at ~ 292 ° and a sharp endotherm at 368 °. The third phase of decomposition took place in two stages (i.e. 5.5% weight loss; 378-384 ° and 16.5% weight loss; 384-498 ~) which can be attributed to the stepwise loss of CO2 and CO in the first stage (5.7% calc. and a mixture of Ph-CO and Ph-COO in the second stage (17.9% calc). These decompositions correspond to the sharp ¢ndotherm at 379 ° followed by the exotherm at 385 °. The final residue was confirmed to be PbO.
/
I
ol
I o
o
,
111
""
Fragmentation pattern of Mn - ( HEP )2
0
o -
/ I
0
I t
I
"It 0
- i - o - Pb
0
o -
I
I
i
I
-
o +
c.
t \\ IV
Fragmentation
t
Pattern of P b - ( H E P ) z
c.2o.