Table 111.
If the hydroxyl number is desired, Equation 6 is multiplied by 33.0 to give :
Hydroxyl Content of Polyethers
% % HYdroxyl a. 2.78 HY(Chem- PolyHy- drox 1 Sample ical) ether droxyl Near-?R LG42
1.45 0.05154 2.561 1 . 4 3 0.05210 2.600 0.05158 2.564 r,~t37 2.28 0.0741ii 2 . ~ 2 5 2,s 0.07431 2.616 0.07392 2.599 LG112 3.76 0.11107 2.577 3.75 0.11098 2.574 0.11088 2.572 LB240 7.11 0.19650 2.569 7 . 0 8 0.19504 2.549 7.13 0.19587 2.561 Av. 2.581
1.44 1.46 1.44 2.34 2.33 2.32 3.77 3.77 3.76 7.12 7.06
7.09
2 shows the absorption spectrum of a polyether with a hydroxyl number of 47.5. The concentration was 13.0 grams per liter. The equation devised for the per cent hydroxyl in the case of this polyether was:
% hydroxyl
= 39.2 a,
2.87
- 0.58
(6)
Hydroxyl No. = 1294 a . : . ~- 19.1 (7) The near-infrared procedure has been applied to polyesters of several M e r e n t glycols with various dibasic acids with excellent results. Although the work with polyethers has been more l i i t e d than that with the polyesters, results thus far obtained have been satisfactory. INTERFERENCES
Acids, alcohols, hydroperoxides, and all other hydroxyl-containing compounds absorb in the region from 2.6 to 3.2 microns. Amides, amines, and oximes also interfere. As the comrosition of each polyester or polyether will be known qualitatively, equations can be readily developed to correct for any interferences present. LITERATURE CITED
( I ) Barrow, G. M., J . Phys. Chern. 59, 1129-32 (1955).
(2) Burns, E. A., Muraca, R. F., ANAL.
CAEM.31, 397 (1959). (3) Cannon, C. G., Speetrochim. -4ch 10, 429 (1958). (4) Flett, M. St. C., ZW.,10, 21 (1957). (5) Goddu, R. F., ANAL. CHEM.30,
2009 (1958). (6) Goddu, R. F., Pittsburgh Conference
on Analytical Chemistry and Applied Spectroscopy, March 1958. (7) Goddu, R. F., Delker, D. A., ANAL. CHEM. 30,2013 (1958). (8) Kabssskalian, Peter, Townley, E. R., Yudis, M. D., Zbid., 31,375 (1959). (9) Kaye, W., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1959. (10) &ye, W., Spectroehirn. Acta 6 , 257 (1954). (11) Zbid., 7, 181 (1955). (12) Mitchell, J. A., Bockman, C. D., Jr., Lee, A. V.,ANAL.CHEM.29,499 (1957). (13) Ogg, C. L., Porter, W. L., Willits,
C. O., IND.ENG.CHEM.,ANAL.ED. 17, 394 (1945).
RECEIVED for review March 27, 1959. Accepted June 15, 1959. Pittsburgh Conference on Analytical Chemuirtry and Aplied Spectroscopy, Symposium on dar-Infrsred Spectroscopy, March 1959. Contribution 181.
Terpolymer Rubbers Standardization of Infrared Analysis Radiotracer Methods
by Chemical and
GEORGE B. STERLING, JOHN G. COBLER, DUNCAN S. ERLEY, and FRED A. BLANCHARD The Dow Chemical Co., Midland, Mid. ,A procedure, involving the use of radioactive tracer techniques combined with standard chemical methods, has been developed for standardizing infrared spectroscopic measuhments of a methyl isopropenyl ketonebutadiene-acrylonitrile terpolymer. The technique is generally applicable where a component of the polymer can be synthesized from radioactive materials. The infrared analysis, standardized by this technique, has been applied to the accurate product control of this terpolymer.
P
materials are tailored for specific end uses by copolymerising two or more monomers in definite proportions. Because the physical properties exhibited by the synthetic polymers depend largely on exact polymer composition, which generally ditrers from the monomer charge ratio, effort has been devoted to methods for their analysis. Infrared spectroscopy has OLYMERIC
1612
ANALYTICAL CHEMISTRY
proved particularly useful, as it is rapid, above determinations. Furthermore, specific, and accurate; but aamplea of the polymer cannot be redissolved in a known composition are required as solvent after being freed of water by any standards for quantitative work. Thia of the standard techniques such as a m paper describee a novel approach to the tropic distillation of the water, free% development of an infrared method for coagulation, or acid coagulation. The determining the composition of one of insolubility of the isolated polymer ie these tailored producta-a terpolymer thus a deterrent to most methods of of methyl isopropenyl ketone (MIE), chemical analysis. The calculation of butadiene, and acrylonitrile 0. acrylonitrile from a Kjeldahl nitrogen The method could be readily used on determination has been generally acmany products of this type. Cepted. Pepe, Kniel, and Cmba (7) have deCaldulation of the concentration of the scribed an ultraviolet spectrophob monomer units from the elemental metric method for determining methyl analysis (carbon, hydrogen, nitrogen, isopropenyl ketone in polymers. The and oxygen), however, did not agree standard procedure for determining buwith the charged monomer ratios. The tadiene is to determine the amount of unacrylonitrile concentration calculated saturation by iodine monochloride ad& from the Kjeldahl nitrogen value was tion (3,6, 6). These methods are a p about 10% lower than the charged ratio. plicable only if the polymer can be disDetermination of the nitrogen by #e solved in a suitable solvent. This Dumas method gave d t a which were terpolymer, however, is prepared by about 10% higher than the Kjeldahl emulsion polymerization and the h a l method, and agreed reasonably well product is obtained in latex form. T h e with the charged monomer ratio. This latex emulsion is not suitable for the revised nitrogen value, however, failed
~~
- __ -
-
-
1 - - -.
- __
R-CH
= c H - R ' -(trans) -
25
4
3
Figure 1
.
5
6
7
8
9
12
11
10
WAVE LENGTH IN MICRONS
Infrared spectrum of methyl isopropenyl ketone-butadiene-acrylonitrile terpolymer
to improve the calculations of butadiene and methyl isopropenyl ketone based on the elemental analysis. The infrared spectrum obtained from a film cast from the latex (Figure 1) shows the expected absorptions of acrylonitrile (C=N 4.45 microns), methyl isopropenyl ketone (-0 5.90 microns), and butadiene (RCH=CH, 10.98 microns, and truns-Rl-CH=CH-Rz 10.35 microns). Because each of these absorption bands is free of interference from the other components, the terpolymer composition might be determined from the infrared spectrum, if standards of known composition could be obtained. Initial attempts to calculate the terpolymer composition using spectra of two copolymers (butadieneacrylonitrile, and butadiene-methyl isopropenyl ketone) as standards gave results that differed widely from the monomer charge ratio. It was concluded, therefore, that the band intensity ratios did not remain constant in going from a copolymer to the terpolymer, and that terpolymers of known composition would be required w standards for analysis. To obtain such standards it ww necessary to determine any two of the three componente independently, and calculate the third by difference. A Dumas nitrogen could be used to determine the acrylonitrile, but neither the butadiene nor methyl isopropenyl ketone could be determined chemically. However, radioactive tracer analysis can be used to determine the methyl isopropenyl ketone, as it can be synthesized from formaldehyde-GI4. A terpolymer prepared with the methyl isopropenyl ketone-Cl4 can then be analyzed for that component by a measurement of the radioactivity. That, together with the Dumas nitrogen for acrylonitrile, gives sufficient information to determine the polymer composition. PREPARATION OF METHYL ISOPROPENYL KETONE-C"
Formaldehyde-C14 as formalin con-
taining 20 pc. of activity was diluted to 162 grams with nonradioactive formalin (36.94y0 formaldehyde). It was possible to carry out this project with this small amount of radioactivity because of the sensitive method of carbon14 determination used. This limited safety precautions to good ,housekeeping. The diluted f0rma1in-C'~ was added to a three-necked 5-liter flask containing 1440 grams of methyl ethyl ketone. Twenty milliliters of 2 N alcoholic potassium hydroxide solution was added to the flask with constant stirring. The reaction was carried out at 24" to 35" C. until there was no free formaldehyde left when tested by the aniline acetate test. (In this test equal amounts of aniline and concentrated acetic acid are mixed. A few drops of this mixture are added to a fen. drops of the reaction mixture on a spot plate. If formaldehyde is present, a white precipitate is formed.) At this point a small amount of acetic acid was added to neutralize the reaction and the excess methyl ethyl ketone was removed by a simple distillation. The remaiuing crude product was distilled at 66" C. and 4-mm. pressure. The distillate, containing relatively pure 4-hydrosy3-methyl-2-butanone-C", \vas dehydrated with 10% sulfuric acid at 100" C. to form methyl isopropenyl ketoneC'4. The crude methyl isopropenyl ketoneC14 was purified by vacuum distillation. The purified product contained 93.2% methyl isopropenyl ketone and 5,5y0ethyl vinyl ketone as determined by mass spectrometry. Considering the method of synthesis, both of these would be singly labeled. Each has a molecular weight of 84 and a carbon content of 71.570. Because of the unsaturation, each would be polymerizable. They would also appear very similar in the carbonyl region of the infrared spectra. Therefore, the radiopurity of the methyl isopropenyl ketone-Ci4 was considered as equivalent to 98.70/, in further calculations. The specific activity of the methyl isopropenyl k e t 0 n e - 0 ~was determined
Table 1. Polymerization Recipe Weight of monomer, grams 100 Weight of water, grams 110 0 85 Sodium lauryl sulfate, % Sodium bicarbonate, yo 1.0 Potassium persulfate, 7 0 0 75 lertDodecy1 mercaptan, Yo 0 5 Polymerization temperature, C. GO Polymerization time, hours 20 O
Table II. Monomer Charge Ratios Butadiene, Run VCN, % MIK, 70 70 25 20 15 15 10 25
1 2 3 4 5 6
Table 111. C; Run% 80.10 79.72 80.10 81.78 84.09 78.01
1 2 3 4 5 6
15 20 25 15 10 25
60
60 60 70 80 50
Elemental Composition of Rubber Solids H,o N , * I120,cAsh,d 0 , 4 % % % % % 8.65 9.23 9.60 9.66 9 93 9.27
6.30 5.18 4.02 4.22 2.60 6.48
0 . 0 4 1.19 3 . 7 2 0.08 1.19 4 . 6 0 0 06 1.04 5 . 1 8 0.03 0 . 9 6 3 35 0 01 1.01 2 . 3 6 0.11 0.78 5.35
a
Standard microcombustion.
e
Loss in weight at 10.5' C.
* Dumas method.
Ignition at 8.50' C. Difference between 10070 and sum of C, HI N, H 2 0 , and ash. d 6
by measuring the radioactivity of carbon dioxide obtained by dry catalytic combustion of the methyl isopropenyl ketone-C". The carlmn diosidc nas purified by absorption into animonium hydroxide and precipitated by the addition of calcium chloride. Thc precipitate of calciiini c:trhonate was collected and washed thoroughly. The carbon dioxide was reliberated and dried by passing through dry ice traps. The radioactivity of the curbon dioside was counted in an internal GeigerMuller tube (1, $). The specific activity was found to be 193 disintegraVOL. 3 1 , NO. 10, OCTOBER 1959
1613
Table IV. VCN, %
Run
Theor.
Calcd:
1 2 3 4
24.7 19.8 14.9 14.9 9.9 24.8
23.8 19.6 15.2 15.9 9.8 24.5
5
6
Table V.
Chemical Analysis of Standards
1 2 :3 i
5 6
14.8
18.7 24.6 27.5 17.7 12.5 28.7
U.8 24.8 14.9 9.9 24.8
Butadiene, % Theor. Calcd. 59.3 59.3 59.4 69.3 79.2 49.6
55.3 54.6 56.3 65.4 76.7 45.8
Rubber Composition by Chemical and Radiotracer Analysis
!:CN Run
Mm, % Theor. Calcd.
by Dumas N Analysis, yo Theor. Calcd. 24.7 19.8
ii.9
14.9 9.9 24.8
MIK by Radioactivity Measurement, % Theor. Calcd.
23.8 19.6. 15.2 15.9 9.8 24.5
14.8
14.6 18.6 22.2 14 0 10.0 23.8
19.8
24.8 14.9 9.9 24.8
tions per minute per milligram (DPM/ mg.1. PREPARATION OF TERPOLYMER STANDARDS
Citrate of magnesia bottles were charged with water, sodium lauryl sulfate, and sodium bicarbonate. The solution was cooled to just above 0' C. and the tert-dodecyl mercaptan was then added, followed by the acrylonitrile and methyl isopropenyl ketone. The bottles were purged with nitrogen znd the potassium persulfate was added. The calculated amount of butadiene plus 1 to 2 grams in excess was added last. The bottles were allowed i o warm slightly; the excess butadiene vaporized and purged any traces of remaining oxygen. The bottles were capped and placed in a constant temperature bath at 60" 6. equipped with 3 mechanism which rotated the bottles at 40 r.p.m. The t,ernary rubber samples were poiymerized for 20 hours. Table I ~ O W Sthe polymerization recipe and Table I1 the ratios of the monomers for the various runs. After polymerization the emulsion intex was steam distilled to remove the yolatile products. The distillate was anaiyzed for carbon-1 4 and acrylonitrile. The radioactivity found (0.07 to 0.17% of the original radioactivity) indicated iittic or no ioss of methyl isopropenyl >?tone to the distilhtc. A portion of each latex was freeze coagulated, washed, and vacuum dried at 60' C. The dried samples were then ssored under nitrogen to prevent excessive oxidation until analyzed by chemical methods and by radioactivity measxenients. The remainder of the latex was rescrwd [or the infrared spectro5cOi)rC examinations.
Butadiene by Difference, % Theor. Calcd. 59.3 59.3 59 4 69.3 79.2 40.6
60.2 59.8 60.6 68.6 79.1 49.4
culated from the elemental analysis is given in Table IV. Acrylonitrile was calculated from the nitrogen value, methyl isopropenyl ketone from the oxygen value, and butadiene as the difference between 100% and the sum of the acrylonitrile, methyl isopropenyl ketone, and ash. The theoretical composition of the polymer calculated from the ratio of monomers added is also given in Table JY. These values have been corrected for the amount of acrylonitrile found in the steam distillate and for the ash content of the rubber solids. In general, the acrylonitrile content, calculated from the per cent of nitrogen, agrees with the value calculated from the ratio of monomers added. However, the methyl isopropenyl ketone content, calculated from the per cent of oxygen, is ccnsistently higher than the calculated amount of monomer added. Because the amount of butadiene was obtained by difference [100% - (MIK VCN ash)], this value is consistently too low.
+
+
RADIOACTIVITY MEASUREMENTS OF RUBBER
The dried rubbers mere oxidized with Van Slyke-Folch reagents (8). The carbon dioxide was purified and the activity determined in the procedure described under preparation of methyl isopropenyl ketone-Cl4. The per cent methyl isopropenyl ketone in the rubber mas calculated by the following equation: NC X = F=
5 . 1 8 NC X lo-"
CHEMICAL ANALYSIS OF STANDARDS
where = yG MIK in the rubber N = DPM/mg carbon by gss counting C = yo carbon in rubber C = DPM/mg. MIK
The elemental composition of the rubber solids is given in Table 111. The eoniposition of the rubbers cal-
Table V shows the final analysis of the rubber standards by the combined chemical-radiotracer method.
3614
ANALYTICAL CHEMISTRY
X
Because some of the carbonyl groups in the methyl isopropenyl ketone may have been modified during polymerization and subsequent treatment, what is measured and reported as methyl isopropenyl ketone is in reality per cent of the terpolymer derived from charged methyl isoprqpenyl ketone. INFRARED
Theory. The Beer-Lambert lav: states that A , = a,bCx, where A , is the absorbance of component 2, a, is its absorptivity, b is the sample thickness, and Cx is its concentration. For a single terpolymer film such as the butadiene acrylonitrile-methyl isopropenyl ketone material under consideration then, the following relations hold: A B = U B ~ Cfor B butadiene AVCN= avc~bCvcNfor acrylonitrile
(1) (2)
A Y I K = ~ M I K ~ CforMmethyl I~ isopropenyl ketone (3)
Because the film thickness is not readily measured, it is preferable to solve for the ratios of the components so that the thickness cancels. If Equations 2 and 3, respectively, are divided by Equation 1, the following relations are found.
The constants, Kv and KM, must be determined from standards of known composition. It was to evaluate these constants that the radioactive standards were prepared. Once the constants are known, unknown samples may be calculated as follows. Relations 4 and 5 are solved for C V C N and C Y I K , respectively, and substituted in the equation CB CVCN CYIK = 100%. Tllis yields expressions for the concentrations in terms of Kv, KY, and the sample absorbances.
+
cB(%)
+
=
Experimental. Films of each latex, prepared and analyzed by the methods outlined above, were cast on glass plates and allowed to dry. The latex film mas then stripped from the plate and suspended on a frame in the sample beam of the spectrometer. Their spectra were scanned from 2.5 to 13 microns on a double-beam infrared spectrometer designed and built in the Dow Infrared Instrument Laboratory (4). Band absorbances
were measured by the base line technique and combined with the known composition data to obtain the K factors for subsequent analyses. Absorption bands at 4.45 and 5.9 microns were used for acrylonitrile and methyl isopropenyl ketone, respectively. No correction was made for the ethyl vinyl ketone impurity in the methyl isopropenyl ketone, as its absorption coefficient is probably very close to that of methyl isopropenyl ketone. The methyl isopropenyl ketone percentage then, represents the total of methyl isopropenyl ketone plus ethyl vinyl ketone. For butadiene, the sum of the two bands at 10.35 microns (trans) and 10.90 microns (vinyl) gave more consistent results than the 10.35 micron band alone, probably indicating some variation in the ratio of 1,4-addition to 1,2-addition of butadiene in the polymerization process. Using the sum of the two bands gives a firstader correction for such variations. (It k here assumed that the ratio of trans- to Cis- 1,4 polymerized butadiene i: essentially const.ant.) The K factors thus determined appear in Table VI. The values for K M vary considerably more than those for Kv. However, the composition measurements for acrylonitrile, are probably more accurate than those for methyl isopropenyl ketone, so a greater fluctuation is expected. Another source of error may be in variations of the spectrometer zero which would affect the deep C 4 absorption of methyl isopropenyl ketone much more than the weaker C=N. Unknown latex samples were prepared and their infrared spectra scanned in the same manner as the standards. Although the film thickness does not enter into the calculation directly, more accurate results are obtained if the thickness is held within reasonable limits. For this reason the film thickness was adjusted by stretching, or the 6lms were recast, until the absorbance of the C=O absorption at 5.9 microns
-
Table VI.
K Factor Determinations
Ye
% ButsMIK dlenea (C14 (DifDu- Trac- ferer) ence) K v Ky Run mas 1 23.8 14.6 60.2 0.356 2.96 0.364* 3.01* 2 19.6 18.6 59.8 0.341 3.24 0.365 3.54 3 15.2 22.2 60.6 0.353 3.52 0.366 3.47 4 15.9 14.0 68.6 0.350 3.29 0.345 3.26 5 9.8 10.0 79.1 0.358 3.31 0.362 3.35 6 24.5 23.8 49.4 0.354 3.01 0.338 2.95 Av. (1.354 3.24 a Butadiene figure corrected for a small percentage of inorganic material found in $dyer. b Fdm of each standard were cast in dudicate. K factors obtained from both SlmS are given. Table VII.
Infrared Analysis of Pilot Plant Latex
Butadiene,
Sample % A 59 B 6 0 c 59 D 60.5 E 59.0 F 61
G 6 0 H 61 I 58
J K L
59 6 0 61
VCN, %
21 20 21.5 20.5 21 19 20 20
22 21 19 19.5
MIK, % 20 20
19.5 19 20 20 20 19 20 20
21 19.5
was between 0.7 and 1.0. In som2 cases where films could not be removed easily from glass, they were cast on silver chloride p l a h and s c ~ n n e ddirectly. Table VI1 shows a typical set of analyses on a series of pilot plant runs in which
Table VIII. Reproducibility of Analysis of a Typical Latex Film ButaNo. diene VCN, k hlIK, %
5% 1
2 3 4 5 6
60.4 60.3 60.5 61.1 60.0 602
19.6 19.3 19.2 i9.5 19.8 19.2
20.0 20.4 20.3 19 4 203 20 6
the monomer charge was 60% butadiene acrylonitrile, and 20% methyi isopropenyl ketone. Because infrared absorption was the only analytical method used to analyze the pilot plant s%mples,thcre wcre no direct data indicating the accuracy of tne method. However, considering the probable errors in the K factors and errors in measurement on the spectra it wems probable t h s t the butadiene prrcentages are within =kayoof tlic nc.tud value and thc acrylonitrile and nwtliyi isopropenyl ketone figures within f1%. Six analyses of a single mmple shonn in Tab!e VI11 indicate that the reproducibility of the method is within tht: estimated error. LITERATURE CITED
(1)Brown, S. C., Miller, W. W., Rev. Sn’. Znstr. 18,496 (1947). (2)Eidinoff, M. L., ANAL. CHEM.22, 529 (1950). (3) Govans, W.J., Clark, F. E., Ztrid., 24, 529 (1952). (4) Hekche;, 1,. W.,Ruhl, H. D., Wright, N., J. Opt. Soc. Am. 48,36 (1958). (5) Kemp, A. R., Peters, H., ANAL. CHEM.15,453 (1913). (6) Kobeko, P. P., Moskvina, E. J., J. A w l . Chem. 19, 1143 (1946). (7) Pep, J. J., Kniel, I., Czuba, M., Jr., ANAL.CHEM.27,755 (1955). (8)Van Slyke, D. D., Plazin, J., Weisiger, J. R., J . BioZ. Chem. 191,239 (1951). RECEIVEDfor review March 23, 1959’ Acce ted July 1, 1959. Division of Rubber &emistry, ACS, Los Angeles, Calif., May 1959.
Qua ntita tive Determination of Reduc ing Suga rs after Separation by Paper Chromatography ATHINEOS J. PHlLlPPU laboratory of Physiology, University o f Athens, Athens, Greece .A method is described for the quantitative determination of reducing sugars after chromatographic separation. The experimental error of the method amounts to 0.8 to 5.470, depending upon the quantity of the sugar.
M
methods have been described recently for the quantitative
ANY
determination of reducing sugars after separation by paper chromatography. The method now proposed has the advantages of simplicity, accuracy (the coefficient of variation being 0.8 to 5.4% depending upon the quantity of the sugar), and sensitivity; as little as 20 y of glucose, galactose, and fructose and 40 y of lactose can be determined.
EXPERIMENTAL
From 0.001 to 0.001 ml. of the aliquot containing the reducing sugars to be determined is dropped on two separate filter papers. After a simultaneous development, the regions of the spots are identified by spraying one of the filter papers with the detection solvent of Bryson and Mitchell (1). The correVOL. 31, NO. 10, OCTOBER 1959
1615
