i n addition to the tests on very dilute mixtures of diborane, trimethyl boratehvdrogen of known concentration and air were passed through the monitor. The flow rate was 0.5 liter per minute, the total time of the run 10 minutes. Table I gives the boron analysis of the wash solutions from the monitor combustion tubes. The following equation is used for calculating the average volume concentration of the boron hydride in an atmosphere:
nT a =bMrt L x - 22,400 -273
(1)
where a
=
R
=
b
=
-11 =
T, = r t
= =
p.p.m. by volume of substance being detected micrograms of boron in combustion product fraction of boron in substance being detected molecular weight of substance being detected ambient temperature, OK. flow rate, cc. per minute sampling time, minutes
For example, if the sampling of a pentaborane-contaminated atmosphere is carried out over a n Rhour period at a rate of 0.5 liter per minute and the total micrograms of boron found by analysis is 10, calculation yields a n average pentaborane concentration of 0.02 p.p.m.
Table 1. Evaluation of Monitor with Trimethyl Sorate-Hydrogen-Air Mixtures
Run 1.
2 3 4
5
?B/Ml. Expected Found 2.01 3.49 2 39 2.24 2.40
2.00 3.47 2.40 2.25 2.41
%Error 0.5 0.6 0.4 0.5 0.4
Best colorimetric analytical results are obtained on solutions containing between 1 and 10 y of boron per ml. Wash water volumes should, therefore, be calculated beforehand, based on the time of sampling a n expected boron hydride concentration, t o obtain boron concentrations in the region of maximum sensitivity. In addition t o monitoring over prolonged periods, relatively quick concentration determinations of boron hydrides may be made in the range of 1 p,p.m. For example, 1 p.p.m. pentaborane sampled at a rate of 0.5 liter per minute will yield 30 y of boron as B203in onehalf hour. This quantity dissolved in 5 ml. of water t o produce a concentration c:f 6 y per ml. can be detected by visual comparison of its carmine solution I\ ith a blank standard ithout the need of a colorimeter or waiting for the development of the maximum color intensity of the carmine reagent. Such a visual comparison for toxic vapor concentra-
tion is particularly useful in contaniinated areas to determine residual vapor concentrations before permitting reentry of unprotected workers into the affected area. The results of the monitor test indicate that under the specified conditions of fl3w rate, temperature, and combustion tube design, the small quantity of boron-containing material is burned completely within the furnace and the solid product quantitatively coilccted. The apparatus described meets the need for an integrating monitor which will detect microconcentrations of toxic boron hydride' gases. It should be applicable t o all volatile boron derivatives that can react with excess air to form boric oxide. LITERATURE CITED
(1) Amehcan Conference of Governmcntal Hygienists, A . M . A . Arch. Iiid. Health 16, 261 (1957). ( 2 ) Comstock, C. C., Oberst, F. W.,
Chemical Corps hledical Laboratories,
Army Chemical Center, Rept. 206 (1953). (3) Etherington, T. L., MaCarty, I,. V., A.M.A. Arch. I d . Hyg. and Occupational Med. 5 , 447 (1952). (4) Hatcher, J. T., Wilcox, L. V., AKAL. CHEM.22, 567 (1950). (5) Hurd, D. T., "Chemistry of the Hydrides," Wiley, New York, 1052. RECEIVED for review Xovembcr 28, 1958. Accepted June 9, 1959. Work done under Contract XOrd 7386 with the Bureau of Ordnance, U. S. Savy.
Characterization of Saturated Polyesters by Differential Thermal An a Iys is DAVID A. ANDERSON and ELI S. FREEMAN Pyrofechnics Chemical Research Laboratory, Picatinny Arsenal, Dover,
p Differential ahermal analyses were carried out for an epoxy resin (ERL 2795) and 32 synthetic polymeric systems consisting of unsaturated DOIYesters copolymerized with styrene. ?he thermograms are characteristic and unique for each system. AIrhough the over-all curves differ from one another, the endothermal bands, 5etween 250' and 450' C., were used as the basis for comparison between systems. The parameters -)sed for this purpose are the areas of the endotherms, temperatures at the peaks, the number of peaks in a band, maximum rates of change in differential temperature, and the temperatures a t which these maxima occur.
D
IFFEREYTIAL
N.1.
TH>:RIMAL
ANALYSIS
(DTA) has bern applied to the
investigation of the chemistry ( 8 ) and kinetics (2) of a variety of inorganic and organic compounds, and for vharacterization and identification ( 3 , 5 ) . Little has been reported on its IISC for the characterization of polymeric systems (6,7 ) . T h k paper describes the application of differential thermal analysis to the characterization of a scries of saturated polyesters. As the nature of the chemical bonding, the degree of cross linking, and the constituents of a polymer determine its mode of degradation, the differential thermograms should be distinctive and provide a rapid means for comparing poiymeric
systems. For this purpow, .I 111 oc~~lu:c is used nhich involves conipwisons tu parameters related to thc thrrnwchemistry and kinetics of rwctioni.e., area encompassed by the c w x thermal and evothcrmal lunds, tcw.peratures a t peaks, maximum ratcs of change in differential tempcraturc, :inti the number of praks i n the 1)antis. The treatment is concwncd 111th the endothermal region ovrr i\hich thrrinnl degradation occurs, which for t h i v polymers is gcnerally Sctn w n 250' and 450' C. EXPERIMENTAL
'The differential thermal analysis apparatus used has been drscrthed by VOL. 31, NO. 10, OCTOBER 1959
1697
-
Hogan, Gordon, and Campbell (.4). The sample t u b were r u t down so that the top extended no more than 0.28 inch above the furnace block. This prevented refluxing of products and reaction between condensate and rvactant. The thermocoupie \yell was fused to the upper part of the test tube and centered 0.5 cm. from the bottom to prevent temperature flurtuat'ions caused by thermocouple movement resulting from agitation during nirlting. boiling, and decomposition. B R- S S o . 28 Chromel-Alumel therniocouplrs n-ere used. This small-dianicter wire permitted relatively small thermocouple heads which are advantagcsous nhcn response time is considered important. Aluminum oxide powder was used :IS the reference material. The heating ratc was controlled by a Gardsnian proportioning, indicating pyrometric controller (West Instrument Co., Chic*sgo, Ill.). Differential tetnpcrature was recorded on a Moseley, 3Iodel 3. h t o g r a p h X-Y recorder, as a funct.ion a i sample temperature. 1Iany of the unsaturateti saniplrr; obtained had been prepared by a condensation reaction of a diol with two dicarboxylic acids, one of which was msaturated. Saturation, through a cross-linking reaction, was subsequent1~effected by copolymerization of the unsaturated polyester with styrene monomer. The reaction was initiated. a t room temperature, by the addition of benzoyl peroxide and cobalt naphthenate. After curing, the samples \wre crushed to a n average particle size of approximately 1 mni. Two-gram samples were heated in air a t atniosphcric pressure, the furnare temperature twing increased a t a nominnl rntc of 13" C. per minute. The samples and supplirrs are tabuIn tcd below :
.-
Sample (Saturated Polyesters) Laminac 4116, 4134 !C 312, i30, 1191, 937, 401! 1154 Glidpol l00lA Aropol7110, 7120, T300 Pleogen 1006, 1150 Polylite 8007, 8001; El) 199 Stypol 4051, 405 MR 28C; M X 314 Selectron 5025 DLL 4262; ERL 2795 (cross-linked epoxy resin) Betron 92 Parapiex 444, 49, 12,17, 1 3 Vibrin 117, lOSSl3
The following procedure \I as used to ixcasurp the areas of the endotheriiial %nds found over the temperature range ,I 2.50" to 450' I-. A straight line is ( l r n ~ ntrrm the beginning to the end of I( endotherm tangentially meeting the cittcr mrt of the curve. T i t h the 1 , w k of the endotherm as an apex, the niain:rig sides of the triangle of best n e t f wmpleted and the triangle area * as cle.iermined. Where multipie peaks I r e ,n\olved, the peak having the l m z e s t .impiitude is chosen as the apex. Tlre ~ ' i m n u r nrate of change of differ- ~ ~ t i a itemperature $vas determined "imi the slope of the tangent a t the po,nt of inflection of the descending 1~0rtic11 of the endotherm (Figure 1). I
1696)
3
ANALYTICAL CHEMlSTRY
Table 1.
-
-
*
^ -I
I _ -
Yalui+s oi Parameters Associated with Thermal Degradation
Peak Temp.,
Area, sq. In.
Sample ' c. 1 Laminac 4116 350 4.7 IC 321 350 2 4.3 4.6 IC 730 350 3 IC 1191 4 345 4.3 Glidpol lOOlA 355 4.1 5 Aropol7110 6 3.6 355 4.1 7 hop01 7120 350 Pleogen 1006 8 360 3.7 IC 93i 355 9 4.5 Polylite 8007 10 3.6 35.5 Polylite SO01 360 11 4.0 Laminac 4116, 85yo 4.1 370 J2 4134, 15% Stypol 4051 13 4.1 370 365 IC 401 14 2.8 Vibrin 117 4.6 370 15 375 MR 28C 16 4.2 Select.ron5027 500 17 3.2 2.1 Pleogen 1150 360 18 2.7 360 ED 199 19 380 PLL 4262 1.8 20 375 Vihrin 1008B 21 2.1 380 IC 1154 22 3.9 360 2.6 Aropol7300 23 370 Paraplex 444 7.3 24 Paraplex 49 400 25 3.0 Stypol 405 26 0.5 390 405 Laminac 4134 27 3.6 3.4 Paraplex 43 400 28 1.6 Paraplex 47 370 29 1.2 MX 314 410 30 1.Ob 400 ERL 2i95 31 Parsplex 13 1.8 410 32 Hetron 92 340 0.2 33 Units, divisions of ordinate per division of abscissa. Exothermal decomposit.ion.
Curve
0
~
Maximum Rate of Change of Differential Temp. ai
2% Max:
dAT/dl
-Max.,
so. of
3.0 3.0 2.2 3.0 4.6 3.4 2.0 2.6 2.6
340
1 1 1 1 1 1 1 1 1 2
1.8
2.4 2.6
2.4 6.0 2.3 2.5 2.4 1.8
1.8 0.6 1 .O 1.3 2.0
4.5 2.0
c.
Peaks
335 345 330 335 335 340 330 330 340 350 340 340 360 340 335 370 340 355 340 350 360 340 350 380
3.8 1.7 3.5 0.8 2.5b 4.0 0.7
390 380 350 360 380 350 400
325
2
1
1 1 1
1
1 1 1
2 2 1 4 1 1 1 1 2 1 3 1
5
1
RESULTS
The curves for the differential thermal Supplier Americaii Cyanamid Co. Interchemical Corp. Glidden Co. Archer-Daniels Midland Co. American Petrochemical Co. Reichhold Co. H. H. Robertson Co. Celanese Corp. Pittsburgh Plate Glass Co. Union Carbide Plastics Hooker Electrochemical Co. Rohm and Haas Corp. Naugatuck Chemical analysis of thc poljmiers are shown in Figures 2 and 3. Generally, the overall shapes of the curves illustrated in the figures are grossly similar; however. the rl tails differ. The thermograms, with the exceytion of-26, 29, and 30, display an endothermal trend between room temperature and approximately 250' C., followed by a relatively welldefined endotherm extending from 2.50' to 450' C. Curves 26, 30, 31, 32, and 33, however, show distinct variation in for:n over this temperature range. Tn a number of other cases multiple yeaks are evidmt. as in curves 10, 11, 20, 23, 36, 2h. 30, and 33. Over the
I
y
j
I
I
f
I
SAMPLE TEHP,'C.
Figure 2 . Graphic method for estimation of area of endotherm a. Minimum of endotherm
bc. l i n e d r o w n t a n g e n t to curve a t e obc. Triangle of Dert Rt ef. Slope a t point of inflection, a
temperature intervai of 250" to -ijooC. the evolution of dense w h t e ana yellow vapors. vigorous boiiing, and, in many cases, the forniation of rororless needle-shaped crystals, as we11 as the ignition of volatile products, i\erp observed. Table I gives the areas, peak temperatures, num'ber of peaks. maximum rates of change in differential temperature,
.r
tl0C
^I
2
B E 9: 0;' w
-a
i
I-
w z
a w Y
L
I 0
w z
1
0
.
1
I00
a
I
I
200
I
wo
r
I
,
400
I
500
L . ? .
0
SAMPLE TEWP.,*C.
Figure 2.
100
I
.
I
.
I
200 300 403 SAMPLE TEMP,.C.
,
,
500
Differential thermal analysis curves
Samples, 2.0 grams each. Heating rate, 15O C per minute. Downward direction, endothermal. Upward direction, exothermal
i.Laminac 41 16
2. IC 312 3. IC 730 4. IC 1191 S. Glidpol lOOlA 4. Aropol 71 10 7. Aropol7 120 8. Pleogen 1006
9. IC 937 10. Polylite 8007 1 1. Polylite 8001
12. Laminic 4116, 85%; 4\35, 15% 13. Stypol 4051 14. IC 401 15. Vibrin 117 16. MR 28C 17. Sledron 5027 17. Pleagen 1150 19. ED 199 20. PLL 4262
and -01 responding temperaturrs for the cmdothrrni representing the thermal degradation. The areas vary b e t w e n 0.2 arid 4.1 sq. inches: peak temperatures, from 350" to 450" C.; maximum rates of change of differential temperature, from 0.6 to 6.0 (for curw 26 the 1-alue is infinite); and the number of peaks, from 1 to 5. Table I1 shows the polymers subtlividrd into four groups. This classification is based on the relative values of the above parameters with respect to Laminac 4116. For group 1 , the values are Ivithin '20% of Laminac; group 2, 21 to 40%; group 3, 41 to 60%; and group 4, greater than The limits of the peak temperatures and temperatures at the maximum rates of change in differential temperature, with the esception of group 4, are within 15 to 5% of each other, respectively. In general, the curves within each group are similar to one another except for those in group 4 where no systematic pattern is obsenred. Curve 31, for E R L 2795, an epoxy resin, is different from the polyesters, exhibiting an exotherm at 375' C. DISCUSSION
Among the factors that influence the t h e r m ' s' rctra obtained by dnfferential thtt .;nxlysis are: the hemical P F 'icin, structure of t n c l reacting I' m c : the nature the bonds
Figure 3.
21. 22. 23. 24. 25. 26. 27.
28. 29. 30. 31.
IC 1154 Aropol 7300 Paraplex 444 Paraplex 49 Stypol 405 Laminac 41 34
involved in reaction. I':tr:tnit'ters, such as the areas undrr the differential thermal analysis hands, maximum rates of change i n difftwntial temperature and rtspwtivc~tcmpc~rature,which are functioiis of the thrrmocliemistq, and kinetics of reaction, may be used for the characterization of the resins. On the basis of the closeness of these parameters to those of Laminac, the polsmers were divided into 4 groups. Lsminac 4116 was chosrn as the reference material because of special interest in this compound with regard to its physicochemical behavior as compared to other similar polymers. I n addition, its ingredients are known, namely, maleic and phthalic anhydrides, propylene glycol, and styrene. There appears to b a general differ-
Group 1
Differential thermal analysis curves
Vibrin 10088
Paraplex 4; Paroplex 47
MX314 ERL 2795
32. Paraplex IS 33. Hetron 92
clitia1 tlic~rnid:inalysis pattern for tlrc, tlrroniposition of the polycstcw i i i groups 1, 2, and 3. The p o l y t i ~ ~ ! ~ delectron 502T of group 3 is kn0n.n t o c,ontain the same basic ingrcrlic,nts :I< Lamina($4116. Deviations of it. tlifft*i.csntial thrrninl analysis rurvv froiii tli:it of Lsnnin:tc. 4116 may be dur t o tlic> nirthod of preparation and thcs c ~ m wqucnt structure of the poljmlr. The endothermal trend, observrd at this lwginning of rach different ial tlicmiogram, from room teniprrature u p to 200' C., ma\- hv attributed to thc lo\vrr tliermal conductivity of the rrushtd polymer as compared with that of th(. rf~fewnwcompound. The results ctf :I t,hermogravimetric investigation of Laminac 41 16 (1) indicate decomposition does not ocrur in this region. For the c a w of Laminac 4116, 3 Ion order tsothei-m occurs a t 200" C. There is eyidenre to indicate that this csot,herm is due to the formation of an
Table It. Characterization of Polymers Group 2 Group ?,
Group 4
Curve Sample 1 Laminac 4116 2 4 8 9 12 13 16
Curve Sarrple Ciirvp Sample Curve Samplc 3 I C 730 5 CiidpollOOlA 14 IC401 IC312 6 Aropol 7110 1 1 I'oLylite 8001 20 PLL 4262 IC 1191 7 Aropol 7126 IT SPlcdron 502i 21 Vibrin 100813 Pleogen 1006 10 Polylite 8007 18 I'lrogen 1150 26 Stypol 405 30 hfX 314 IC937 15 Vibrin 117 10 1:1) 199 22 IC 1154 31 ERL2795 Laminac 4116, 85% 4134, 15'/b 2.( .\ropol 5900 32 Paraplex 13 St.ypol4051 24 l'araplex 444 33 Hetron MR 28C 2.5 Paraples 49 27 Larninnc 4134 28 Paraplex 43 L'r) Paraple\ 1 7
V O t . 31, NO. 10, OCTOBER 1959
1699
unstablc hvdroperoxide (1) which immediately undergoes rearrangement and degradation. The endothermal bands :it approximately 350' C. undoubtedly r c w i t from decomposition of the polymers, as the evolution of dense vapors, vigorous boiling, and, in many cases, ignition of volatile products were observed. The marked dissimilarity in the thermal behavior of Hetron 92, curve 33, from the other polymers is indicative 2f a difference in structure, constituents, and/or chemical bonding. I n this case, it i s known that the polymer, containing
,wtls,n-chlorinc bonitc,, iZt?., rs iron1 the ottif'r polyesters. F J x I T2595, , an epoxy resiii. is the or 13 poi) T which under-
is) Freeman, E. S., CarroL
goes exotherrial decomuosition. Degradation of ai. oi the polymers is comFlete a t 450' C.,leavine; a carbonaceous residue. On the basis of Drevious work ( I ) , it is assumed that part of the residue reacts with oxygen, influencing the shape and slope of the ascending portion ofthe endotherm.
(4) Hogan, V.,Gordon, S., Campbell, C., ibid., 29,306 (1957). (5) Morita, H., Ibid., 28,H (1956). (6)Murphy, C. B., Palm, J. A., Doyle,
.A
~ 3 . J,
'.bm62,394 (1958). I ' ;ordon, S., Campbell, C., 'iiEM.
'k,r ANAL.
29, 1102 (1955).
9. C., Curtiss, E. M., J. Polymer Sa. 28,447 (1958). (7)Ibid., 28,453 (1958). (8)Smothers, W.J., Chiang, Y., Wilson, A., Unw. rlrknnsas Inst. Sci. and Techml., Research Ser. No. 21 (1951).
LITERATURE CITED
(1) Anderson, D. A., Freeman, E. S., J. A p p l . Polymer Sei., in press.
RECEIVED for review November 28, 1958. Accept.ed June 12, 1959.
Influence of Amino Acids upon the Anthrone Reaction of Uronic Acids j.
R. HELBERT
and K. D. SROWN
Veterans Administration Hospital, Downey, I//., and Marquette University School of Medicine, Milwaukee, Wis.
b The influence of 12 amino acids upon the anthrone color of the uronic acids has been investigated under various experimental conditions. Tryptophan alone produces a anthrone color and this color is additive with the glucuronic acid color and the mannurone color at 550 mp, but nonadditive with the idurone color at the same wave length. Methionine alone produces no anthrone color, but causes color enhancement with all uronic xids; cysteine alone likewise produces no anthrone color, but, depending upon experimental conditions, may cause either depression or enhancem e n t of uronic acid color. The remaining amino acids are without etfect. The magnitude of the observed effects varies with such exDerimental factors as tewperature, heating time, and concentration. ~~~REVIOU n-ork S
with a uronic acid polymer (3) indicated an anomaIUS coior reaction with anthrone. Chro- i ? ~ atuqraphic ana1ysc.s indicatcd the w-csmc" of small amounts of amino tc*itfs. In view of the reported behavior -G) of tryptophan with anthrone, ~ a r ~ i c i h rin~ vthe presence of carboI: drrttcs, tiir subject of the present incl>tig.:tticn scemcd pertinent. Morew c r , At is often desirable to determine (ironic :;rids or their polymers in the presence of amino acids or proteins. a
1700
ANALYTICAL CHEMISTRY
MATERIALS AND PROCEDURE
Most of the uronic acids used were obtained from noncommercial sources. The glucuronic, galacturonic, and amino acids were of best quality commercially available, and were used as received. Anthrone solutions were prepared by dissolving 0.160 gram in 100 ml. of 27.5 f 0.1N sulfuric acid, allowing about 60 minutes for complete solution. Uronic and amino acid solutions were prepared by dissolving solid sample in 27.5N sulfuric acid. About 30 minutes was allowed to effect complete solution of the uronic acids. All of the amino acids dissolved rapidly and were used within 30 minutes after solution. Basic Procedure. Four milliliters of anthrone solution were pipetted into uniform borosilicate glass test tubes, followed by uronic acid and/or amino arid solutions to make a final volume of 6 mi. For convenience, concentration has been expressed throughout as micrograms per 6 ml. As all reactants \$ere dissolved in 27.5N sulfuric acid, no heat of mixing was evolwd. Test samples were then heated in a boiling-water bath or, if l o w r tenipcratures were desired, in a thermostatically controlled water bath. Aftm heating, samples were quickly transferred to a cold-water bath (4" f 1" C.)for 3 minutes. Heating and cooling time was measured to *2 seconds. The test tubes containing the reacting solutions were spaced in wire racks in the heating and cooling baths to facilitate uniform heat transfer. After removal from the coldwater bath, test wmples were held at
room temperature (23" f 2" C.) i i i a light-proof cabinet for 20 f 2 hours. Photometric readings were made with a Beckman DU spectrophotometer. EXPERIMENTAL RESULTS AND DISCUSSION
Uronic Acids. The spectra of cidurone, Lgulurone, and D-mannurone after reaction with anthrone are deliieated ;TI Figure 1 . Analogous spectra and other information about D-glucuronic and D-galacturonic acids have been published (2). Idurone was obtained and used as the 1,Z-O-isopropylidene derivative. The available quantity of gulurone permitted examination a t only one temperature. The color response of the idurone- or niannurone-anthrone complex to changes in heating temperature (Figure 1) is similar t o that previously observed (2) with galacturonic acid. -Vannurone is unique among the uronic acids in t h a t its spectrum a t 100" has no maximum ?letween 500 and 600 mu. Solutions n i t h this kind of spectrum display no red coloration which can he readily drtected visually. On the other hand, the spectrum of mannurone reacted with snthrone a t 70" has a well-defined maximum a t 550 mp, and such solutions have a distinctly obsrrvablr red coior. The absorbances a t 550 mp for equal quantities of the various uronic acids relative to glucuronic acid are: Dglucuronic, 100; D-mannurone, 55; Lgulurone, 125; bidurone, 130; D-
