(2) Borchardt, H. J., Daniels, F., J . Am. Chem. Soc. 79, 41 (1957). (3) Borchardt, H. J., Thompson, B. A., Zbid., 81, 4182 (1959); 82, 355 (1960). (4) Buckle, E. R., J.Phys. Chem. 63, 1231 (1959). (5) Cohen, E., Kooy, J., Z . physik. Chem. A139, 273 (1928). (6) Fisher Scientific Co., Pittsburgh, Pa., Bull. FS231 (1959). (7) Freeman, E. S., Carroll, B., J . Phys. Chem. 62,394 (1958). (8) Gordon, S., Campbell, C., ANAL. CHEM.27, 1102 (1955).
ANAL.CHEM.17, 474 (1945). (16) Osterheld, R. K., Markowitz, M. M., J . Phys. Chem. 60, 863 (1956). (17) Simmons, J. P., Ropp, C. D. L., J. A m . Chem. SOC.50, 1650 (1928). (18) Treadwell, F. P., Hall, W T , "Analytical Chemistry," Vol. 11, Ninth English ed., pp. 383-4, Wiley, New York, 1942. (19) Van Tassel, J. H., Wendlandt, W. W., J . Am. Chem. SOC.81, 813 (1959).
(9) Ibid., 32, 271R (1960). (10) Harvey, A. E., Wassink, C. J., Rodgers, T. A:, Stern, K. H., Ann. N . Y . Acad. S a . 79, 971 (1960). (11) Hedvall, J. A,, Chem. Reus. 15, 139 (1934). (12) Lewis, G. N., 2. physik. Chem. 52, 310 (1905). (13) Markowitz, M. M., J . Phys. Chem. 62, 827 (1958). (14)7.Markowitz, M. M., Ricci, J. E., Mmternitz, P. F., J . Am. Chem. SOC.77, 3482 (1955). (15) Marvin, G. G., Woolaver, L. B.,
RECEIVED for review May 16, 1960. Accepted August, 30, 1960.
Differential Thermul Analysis of Epoxide Reactions HUGH C.
ANDERSON
Non-Metallic Materials Division, U. S. Naval Ordnance laboratory, White Oak, Silver Spring,
b Differential thermal analyses (DTA) have been carried out on six epoxides, both unreacted and reacted with various amine and anhydride polymerizing agents. Characteristic curves were obtained for the different systems. They show how the rate of heating, the concentration of the polymerizing agent, and the extent of cure can each influence the DTA curve for a particular system. They also show that the shapes and positions of the DTA peaks are dependent on the nature of the epoxide as well as on the type of polymerizing agent. The exothermic nature of the isomerization of epoxy groups to carbonyl groups i s also shown.
Md.
plate and covered with a bell jar so that the experiments could be performed in controlled atmospheres. Unless otherwise indicated, the analyses were performed in nitrogen at atmospheric pressure with the furnace temperature being increased at a nominal rate of 2.5" C. per minute up to 700' C. A typical heating curve is shown in Figure 1. The structural formulas of the six epoxides studied are shown in Figure 2. The epoxides and their suppliers were as follows: Syl-Kem 90, Dow Corning Corp.; Diepoxide AG-l3E, Rohm & Haas Co.; UC Endo isomer, Union Carbide Chemicals Co.; Epon 828, Epon 1310, and Epon X-701, Shell
This paper describes the application of DTA to the characterization of the polymerization and thermal decomposition of six epoxides reacted with various amines and anhydrides. Since the nature of the epoxide and of the reactant influences the mode of polymer formation and decomposition, the DTA curves are characteristic for the different systems. EXPERIMENTAL
The DTA apparatus used was basically similar to that described by Anderson and Freeman (f), except that the furnace was mounted on a vacuum
- TETRbYETHYLOISLOXANE
1,3-818 [ 3 ( 2 . 3 - E W X Y P R O P O X Y ) P ~ L ]
D
IFFERENTIAL
THERMAL
ANALYSIS
CH3
A
(DTA) has been used to investigate a large number of inorganic and organic reactions (3, 4, 13). However, its use in the study of polymeric systems has been scant (1, 2 , 7, 9, 10). Only one instance of its use in the study of an epoxide has been reported ( I ) .
I
CH,
I
CH2-CH-CH2-0-CH2 -CH2-C+-S#-O-S1-CH2
I
1
-0-w~ -CH-CHz
-%-C%
m3 C H I BIS-EPUXYOICYCLDPENTYL ETHER OF ETHYLENE ILYEPOXIOE bG-13EI
OIGLYClOn
ETHER OF BISPHENOL b
UCltLOPENTAMENE OlOXlOE IUC E N 0 0 ISOMER)
GLYCOL
0
1 O(!CH-CH2-O-
/O\
- ~ ~ ~ . 0 - C H 2 - C H - C H 2
EPON 828
CH3
TETRbGLYCIOYL ETHER OF TETRAKIS IHYDROXYPHEWL) ETHANE EFON 1310
p(xI
(ALLYL GLYCIOYL ETHER)
[EWN X-7Od
C~=C-CH2-CH-CH2-CH-CHz-~H2 I 1 I CHI CH2 CHZ W2 I 1 I I
n
01
0
40
80
120
160
200
240
280
o
0
o
I
TIME, MINUTES
Figure 1.
1592
Typical heating curve
ANALYTICAL CHEMISTRY
(SYL-KEY SO)
Figure 2.
Epoxides
25
__ 8.
-EPCU
-EFQN 828iMA
IYO/MP
...-EPCU I Y O I C L EFQN 1310
-..EPON BLBKL ---Emu 828
25 I
Y
MALEIC ANHYDRIOE.
12.5
1'
12.5
0
I20
240
1.19.
NAOIC METUVL ANUVORIOE. L.09.
360
480
TEMPERATURE OF SAMPLE
Figure 3. agents
600
I
120
(.C)
DTA curves of polymerizing 25
-L-A-pI
0
Chemical Corp. The polymerizing agents used were m-phenylenediamine, CL (General Aniline and Film Corp.); menthane diamine, M D (Shell Chemical Corp.); maleic anhydride, MA (Fisher Scientific Co.) ; nadic methyl anhydride, KMA (Allied Chemical Corp., National Aniline Division). Samples, varying from 1 to 3 grams, were intimately mixed with equal weights of aluminum oxide. The resulting mixture was packed around the thermocouple well whose bottom was located 0.5 inch from the bottom of the sample tube. The packed sample tube was weighed before and after a DTA experiment F O that the percentage weight loss could be Calculated on the basis of the original weight of the organic material. An equal height of aluminum oxide was placed in the reference tube. I n those experiments where an epoxide was to be reacted with one of the polymerizing agents, the reactants were intimately mixed and handled as above. Unless otherwise indicated, stoichiometric amounts of the polymerizing agents, based on the epoxy equivalents, were used. Each DTA experiment, unless otherwise indicated, u as started before any appreciable reaction could occur. RESULTS AND DISCUSSION
Typical D T A curves for the polymerizing agents are shown in Figure 3. The melting and boiling points of mphenylenediamine and maleic anhydride shown by the corresponding D T A peaks are in good agreement with literature values. The boiling points of menthane diamine and methyl anhydride are indicated by the corresponding DTA peaks. However, even though the samples werr heated in a nitrogen atmosphere, they probably underwent some drcompvsition at their boiling :)ointq. No literature values a t atmospheric pressure n ere nvailnble Rith which to compnre the DTA boiling pointp of these t n o materials.
I20
240 380 480 F E W E R A T U X OF SAMPLE 1.C)
Figure 4.
80-!
O
u
-
k0
TEMPERATURE OF SAMPLE r c ]
A-
DTA curves of catalyzed and uncatalyzed epoxides
Abbreviations for epoxides deflned in Figure 2. MA, maleic onhydride; CL, m-phenylenediamine Heating rate, 2.5' C. per minute Weiaht in Groms Epon 1 3 1 O/MA, 1.5 Epon 1310/CL, 1.1 Epon 1 3 1 0 , 1.2 A G - l 3 E / M A , 1.8 AG-1 3E/CL, 1.5 A G - 1 3E, 1.6 UC Endo iromer/MA, 2.2 UC Endo isomer/CL, 1.3 UC Endo isomer, 2.1
Figure 4 shows typical DTA curves for the six epoxides (uncatalyzed and catalyzed with maleic anhydride and m-phenylenediamine). Lll of the uncatalyzed epoxides, except the UC Endo isomer, show exothermic peaks in the 300" t o 400' C. region. This particular exothermic peak is believed to be due mainly to isomerization of the epoxy groups to carbonyl groups (aldehydes for the primary epoxides and ketones for the secondary epoxides) and thermal polymerization of the epoxy groups. Peytral ( l a ) , Heckert and Mack ( 6 ) , and Parker and Issacs (11) reported that when ethylene oxide was heated to 380" C. or above, i t rearranged to acetaldehyde with evolution of about 24 kcal. per mole. Since the epoxides investigated are derivatives of ethylene oxide, it is reasonable to assume that they behave in a similar manner. The appearance of vapors in this temperature range indicated that volatilization and decomposition also occurred simultaneously with isomerization and polymerization. The Endo isomer showed an endothermic rather than an exothermic peak because the heat absorbed by volatilization and decompnsition overshadowed any heat resulting from tlie slower rate of isomerization and etherification polymerization of its epoxy groups. This comparatively slower rcactivity is probably
Epon 828/MA, 2.0 Epon 828/CL, 2.0 Epon 8 2 8 , 1.3 Syl-Kern 90/MA, 2.5 Syl-Kem 90/CL, 1.8 Syl-Kem 90, 2.0 E p m X-701 /MA, 2.9 Epon X-701 /CL, 1.9 Epon X-701, 1.2
due the attachment of the oxirane oxygen to two secondary carbon atoms rather than t o one primary and one secondary atom. This is the case for all the other epoxides except AG-13E where the attachment is similar to that of the Endo isomer, although the AG13E epmide shows an exothermic peak. For the Endo isomer, the DTA peak a t 184' C. corresponds to its melting point. The sources of the other two peaks were not determined. When each of the six epoxides was catalyzed with maleic anhydride or with m-phenylenediamine, the resulting DTA curves (Figure 4) were characteristic. Except for AG-l3E/CL and UC Endo isomer/CL, all of the systems showed two exothermic peaks. One of these peaks was in the temperature range of 100" to 150" C. and the other was in the same temperature range (300" to 400" C.) where the uncatalyzed epoxides showed exothermic peaks. The AG-l3E/CL system showed only one exothermic peak, broad and weak, in the 300" to 400" C. range. The UC Endo isomer/CL system showed no exothermic peaks and only one endothermic peak, which corresponded to the boiling points and/or decomposition points of both the epoxide and the CL (Figure 3). The lower rcactivity of a diamine with secondary eposides, as compared to that of an anhydride, VOL. 3 2 , NO. 12, NOVEMBER 1 9 6 0
1593
25
/I
I
- IODC/MIN
- MER-PHRIYLENEOUMltiE ---YNRUNE
.__ 2 swum
MAMIWE
3 1
25
I 120
I
I
1
I
TEYPERATURE ff SAMPLE LOCI
Figure 6. Effect of heating rate on isomerization and thermal polymerization of Syl-Kern 90 Heating rater: 10" C. per minute,. 1.7-gram samde; . - 2.5' C. per minute, 2.0-gram somple
I
I
0
120
I
I
240
3 0
TEYPERATURE
I
4 0
I
Bw
7
OF SAMPLE PCI
Figure 5. DTA cuwes of Epon 828 catalyzed with different polymerizing agents Heating rate, 2.5' C. per minute Epon 828/CL, 2.0 grams Epon 828/MD, 2.0 grams Epon 828/MA, 2.0 grams Epon 828/MA, 2.4 grams
at lower temperatures than for the
is clearly demonstrated in AG-13E and the Endo isomer. Comparison of the 100' to 150" C. exothermic peaks for the primary epoxy linkage contained in the other four systems indicates, however, that the diamine is more reactive than the anhydride-Le., the peaks for the diamine systems appear
anhydride systems. In addition to Figure 4, Figure 5 shows that the DTA curves are characteristic when a particular epoxide is reacted with different polymerizing agents. Maleic anhydride is more reactive than nadic methyl anhydride with Epon 828, as
I I
I
I
I
indicated by the appearance- of its DTA peaks a t lower temperatures. Another example of the effects of the relative rates of the competitive isomerization, polymerization, volatilization, and decomposition processes on the DTA thermograms is shown in Figure 6. In this case, only one epoxide (Syl-Kem 90) was used for comparison, but the nature of the DTA peak was modified by changing the heating rate. A heating rate of 10" C. per minute produced an endothermic peak while a heating rate of 2.5" C. per minute produced an exothermic one. In this instance, the faster heating rate allowed volatilization (a zero order process) to overshadow the isomerization and polymerization processes. Since the higher temperature exothermic peak always appeared. in addition to the lower temperature peak, mhcn stoichiometric amounts of either the diamine or anhydride were used, experiments were carried out with Epon 828 to see Nhat effect an increase in concentration of the curing agent would
I
- EPON 828/MA
I
CURE 24 HOURS AT IOO'C U S 4 HOURS AT 150' C PLUS 4 nouns h r 2 0 0 0 ~
I
I
I
1
I
120
240
360
4 M
600
TFYPERATURE OF SAMPLE 1%
Figure 7.
1594
72
I
25
120
Effect of concentration on epoxy polymerization
SA, stoichiometric amount; heoting rate, 2.5' C. per minute Epon 828/CL(SA), 1.6 grams Epon 828/CL(1.5 SA), 3.0 grams Epon 828/MA(SA), 1.4 grams Epon 828/MA(1.5 SA), 1.4 grams
ANALYTiCAL CHEMISTRY
I
290
180
4 BO
600
TrYPERATJRE OF SAMPLE ('CI
Figure 8.
DTA curves of polymerized E ~ O I I828 Heating rate, 2.5' C. per minute Epon 826/MA, 1.4 grams Epon R28/81. !.4 gtamo
720
have on these peaks. Figure 7 shows that the system using 1.5 times the stoichiometric amounts of CL gives a ratio of the 120' C. peak to the 350" C. about twice that of the system employing a stoichiometric amount of CL. This peak ratio was not noticeably affected by a change in concentration when MA was used. This indicates that when larger than stoichiometric amounts of the two polymerizing agents were used, CL effected the cleavage of more epoxy rings than did MA. Figure 8 gives typical DTA curves for Epon S28/MA and Epon 828/CL for samples which were extensively cured and finely pulverized before subjecting to DTA. The low temperature exothermic peak has disappeared, but the usual high temperature one is still present for each of the systems. This indicates that it is very difficult for a stoichionietric amount of either M A or CL to wart with all of the epoxy groups. This is cvidently due to the decreasing mobility of the molecules as well as to the decreasing concentration of the reactive groups. I n Table I, comparison of the uItimate weight losses involved in the UC Ilntlo isomcr,'CL and UC Endo isomer/ MA q.atcms serves to corroborate the indication of the corresponding DTd curves (Figure 4) that X d n-as more reactive than CL. The n-eight loss of thc former system was almost the same :is that of thcx uncatalyzed IIJ..,Polymer Sei. 28,447 (1958). (10) Ibid., p. 453. ' 1 1 ) Parker, R. E., Issacs, N. S.,Chem. Revs. 59, 737 (1959). (12) Peytral, E., Bull. SOC. chim. 39, 306 (1926). (13) Smothers, Is'. J., Chiang, T.,"Ilif-
ferential Thermal .Inalysis," Chemical Pub. Co., K e a York, 1958. RECEIVED for review February 15, 1960. Accepted June 21, 1960. Presented i n part, Division of Paint, Plastics, and Printing Ink Chemistry, 136th Mreting, ACS, Atlantic City, N. J., September 1959.
Trace Analysis Summer Symposium of the Analytical Division, Houston, Tex., 1960 Summary prepared by WARREN W. BRANDT, Department of Chemistry, Purdue University, Lafayette, Ind.
T
1960 Summer Symposium sponsored 11). ASALYTICAL CHEJIISTRY and the Division of Analytical Chemistry was devoted to n e x approaches to an old analytical prob1c.m: trace analysis. Each of five half-day sessions was devoted to a separate instrumental approach t o the determination of trace constituents. The coverage included a survey of past usage of the technique to determine trace amounts, followed by a look at the new developments and sonie specific applications. The number HE
of sessions-five-is grossly inadequate to cover all of the techniques which are anicnable to application in trace analysis. Each represented an area in which recent advances appear to be improving its utility for determining small percentages of material-inorganic and organic. X-RAY EMISSION SPECTROGRAPHY
H. A. Liebhafsky, General Electric Co. and chairman of the Division of
Analytical Chemistry, opcwd tlic program with an introduction to trace analysis by x-ray emission spectrograph!.. He pointed out that x-ray emission spcrtrography has become a powerful mrthod for trace determinations, mainly for tn o reasons. X-ray spectra are simple arid methods of x-ray detection have improved to the point where intensit!, measurements can be made easily and reliably by counting the quanta emitted by elements present in microgram or even smaller amounts. VOL. 32, NO. 12, NOVEMBER 1960
1595
