negligible for viscosities as low as 0.4 cs. For this instrument,. over a range of 0.4 t o 20,000 cs., Equation 11 reduces to Equation 12. Y
= q / p = Ct
(12)
A charge of only 1.0 ml. is required. It can be used as a dilution viscometer if desired and it is available in 12 different sizes covering a viscosity range of 0.2 to 20,000 cs. This type of viscometer has the same liquid driving head a t all temperatures and consequently the viscometer factor (or C constant in Equation 12) is the same a t all temperatures.
It is used by simply placing the instrument in the bath, pouring in a sample of approximately 1 ml. (the precision of viscosity measurement is independent of the amount charged), waiting 5 or 6 minutes for bath temperature to be attained, and then measuring the efflux time in seconds for the efflux bulb to discharge through the capillary. Viscosity in centistokes is then obtained by multiplying the efflux time in seconds by
the viscometer constant which is the C factor of Equation 12. If absolute viscosity is desired, i t is obtained by multiplying centistokes by density in grams per cubic centimeter, thus obtaining centipoises. More detailed instructions applicable to all capillary-type viscometers are available (1, 7 ) . NOMENCLATURE
B = variable in viscosity equation, stokesecond C = viscometer constant, stokes per second D = capillary diameter, cm. E = kinetic energy factor, stoke-second2 Fy = friction in capillary P, = friction a t capillary entrance F. = friction at capillary exit 9 = acceleration due to gravity, em. per second2 L = capillary length, cm. m = kinetic energy correction coefficient r = capillary radius, cm. t = efflux time, seconds U = velocity of fluid in capillary, cm. per second V = efflux volume, cm. XI - X2 = distance between menisci in viscometer
=
tl
absolute viscosity, poises kinematic viscosity, stokes
’
y = - =
P
=
p
density, grams per cc. LITERATURE CITED
(1) Am. SOC. for Testing
Materials, Philadelphia, Pa., “ASTM Shndards on Petroleum Products and Lubricants.” D 445-53T. (2) Bell, J. D., thesis, “Variationof Kinetic Energy Correction Coefficient with Reynolds Number Capillary Viscometers,” in partial fulfillment for the degree of master of science, Department of Chemical Engineering, Pennsylvania State University, January 1947. (3) Cannon. M. R.. IND.ENG. CHEM.. ANAL.E;, 16, 708’(1944).(4) Cannon, M. R., U. S. Patent 2,805,570 (Sept. 10, 1957). (5) Cannon, M. R., Fenske, M. R., IND. ENQ.CHEM..ANAL.ED. 10.’ 297 (1938). . . ( 6 ) Ibid., 13, 299 (1941). (7) Institute of Petroleum, London, W. 1, England, “Standard Methods for Test; mg Petroleum and Its Products, \ - I
IP71/58.
RECEIVEDfor review August 14, 1959. Accepted November 23, 1959.
Polarographic Determination of Styrene Monomer in Polyester Resins WILLIAM M. AYRES and GERALD C. WHITNACK Chemistry Division, Research Department, U. S. Naval Ordnance Tesf Sfafion, China fake, Calif.
b A quick, precise, polarographic method for the determination of styrene monomer in polyester resins is presented. A solution of the resin in ethyl alcohol is polarographed in a tetrabutylammonium chloride supporting electrolyte (7570 ethyl alcohol). Dissolved oxygen need not b e removed prior to recording the polarogram. Data indicate that the analysis has a precision of about 5 parts per thousand, and the presence of phthalate and fumarate or maleate esters does not interfere.
B
polyester resins are used as inhibitors for solid propellant grains, a rapid and precise method of analysis was needed for styrene monomer in such mixtures. Current methods require either a vacuum distillation prior to analysis or a n accurate knowledge of all interfering constituents present, so that corrections may be applied (1, 2, 5 ) . Although the spectrophotometric method of Hirt (2) appears rapid and precise, the presence of phthalate and maleate or fumarate esters requires a two-component analysis for styrene ECAUSE
358
ANALYTICAL CHEMISTRY
and phthalate and then a correction for the absorption of the fumarate or maleate component of the polyester. The reduction of styrene a t the dropping mercury electrode has been reported by Laitinen and Wawzonek (4) to occur a t a half-wave potential of -2.35 volts referred to the saturated calomel electrode (S.C.E.). This potential is considerably more negative than the reduction potentials of phthalates (6) and maleates or fumarates (S), and should enable the measurement of the diffusion current of styrene in the presence of these esters. APPARATUS A N D MATERIALS
A Sargent Model XXI Recording Polarograph was used throughout these studies to obtain and record the polarographic data. I n the initial phases a Cary Model XI recording spectrophotometer was used for the spectrophotometric data. A semimicro vacuum distillation apparatus was used to purify the commercial styrene and to check the styrene content of the polyester resins. The polyester resins used were: Selectron 5119 (Pittsburgh Plate Glass Co.. Pittsburgh, Pa.), Vibrin 121
(Naugatuck Chemical Co., Naugatuck, Conn.), and Marco 28C and 28V (Celanese Corp. of America, New York, N. Y.). Solvents were: 95% ethyl alcohol (LAC Chemicals, Culver City, Calif.), absolute methanol (Mallinckrodt, analytical reagent), and chloroform, B and A Reagent (Allied Chemical and Dye Corp., New York, N. Y.). T h e supporting electrolyte used in the polarographic analysis was tetrabutylammonium chloride. A special polarographic grade of this material was purchased from Southwestern Analytical Chemicals, Austin, Tex. Five milliliters of a n aqueous 0.1M tetrabutylammonium chloride solution was added to 15 ml. of 95% ethyl rtlcohol containing the styrene. Thus, the styrene was polarographed in a solution that was approximately 75% ethyl alcohol. Redistilled mercury (c.P. grade) was used as the anode in all beakers for polarographic analysis. A capillary with a drop time of about 4 seconds per drop a t -2.50 volts (vs. mercury pool) in the supporting electrolyte was used in all work. The total pressure applied to the dropping mercury was 91.5 cm. On open circuit and a t zero applied potential the values for m and 1 were 5.37 mg. and 8.25 seconds per drop, respectively.
The potential of the mercury pool in 0.025M tetrabutylammonium chloride was +0.0185 volt. The resistance of the polarographic cell was about 1000 ohms, and in this study constituted a negligible correction to the Em. The styrene (Thalco Co., Los Angeles, Calif.) was vacuum distilled a t 22-mm. pressure. The distilled styrene had a refractive index of 1.5464 at 20.0" C. and analyzed better than 99% by a spectrophotometric method at 291 mp ( 2 )* Polarograms of the samples were obtained in a constant temperature bath at 30" =k 0.2' C. Small borosilicate glass beakers (30-ml.) were used as polarographic cells. A rubber stopper, to which was attached the dropping mercury electrode and the contact electrode, was placed over the top of the bcakers. PROCEDURE
A 250- t o 500my. sample of the polyester resin is added to a 100-m1. volumetric flask containing 50 nil. of 95% ethyl alcohol. T h e flash and contents are placed on a shaker for 1 hour. T h e solution is diluted to the mark with 95y0 ethyl alcohol and a 5-ml. aliquot is added t o a 30-nil. polarographic beaker containinq 10 ml. of 95% ethyl alcohol and 5 ml. of 0.1.11 tetrabutylammonium chloride solution. The final solution is stirred, placed under the dropping mercury electrode, and polarographed from -2.00 to about - 2.80 volts. Dissolved oxygen need not be removed prior to recording the polarogram. Duplicate polarograms are produced for each sample and the average wave height is referred to a standard graph for styrene content. Preparation of Standard Graph. T h e standard graph for styrene is obtained from ficshly distilled commercial styrene. A 95y0 ethyl alcohol solution of styrene is prepared so t h a t each milliliter of solution contains 1 t o 2 mg. of styrene. Aliquots of this solution are then added t o 5 ml. of 0.1 Ai tetrabutylammonium chloride solution and additional 95% ethyl alcohol to make the final volume 20 ml. The final solution for each point is polarographed a t a sensitivity of 0.100 pa. per mm. Analysis of Sample.
RESULTS AND DISCUSSION
The data in all tables were obtained in approximately 75y0 ethyl alcohol solutions of 0.025M tetrabutylammonium chloride. To determine the precision and reliability of the procedure, several commercial samples of polyester resins were analyzed for styrene monomer content by the proposed method. The results (Table I) indicate that the polarographic analysis of styrene has a precision, shown by a standard deviation obtained from five values of each commercial sample, of about 5 p.p.t. I Phthalate esters and/or maleic anhydride appeared t o have little or no effect
Table
1.
Analysis of Commercial Samples of Polyester Resins
A. VIBRIN-121 343.6 315.1 351.5 321.4 340.2
13.10 11.95 13.20 12.05 12.90 ~~
~~
C. MARCo-28C
176.8 161.6 178.0 163.0 174.0
51.4 51.3 50.6 50.7 51.1
220.9 245.7 250.0 213.9 249.6
32.0 32.7 31.9 32.9 32.9
406.9 ~~.~ 393.0 379.4 399.7 421.4
B. SELECTRON-5081 328.9. 248.8 233.3 253.0 259.3
7 .. 8.. 0 6.02 5.50 6.16 6.35
116.0 130.0 132.8 114.2 132.4
52.5 52.9 53.1 53.4 53.0
D. MARCO-28V
105.2 81.4 74.4 83.2 85.4 ~~
8.60 9.60 9.86 8.48 9.80
~
10.40 10.30 10.00 10.46 10.60
140.4 139.2 134.8 141.2 143.2
34.5 35.4 35.5 35.3 34.0
Per Cent A B C D Average found, X 51.00 32.5 53.0 34.9. Standard deviation, (est.) 0.35 0.49 0.33 0.66 Standard deviation of mean of 5 0.16 0.22 0.15 0.29 Confidence range (95% level) 5 1 . 0 =k 0 . 4 1 32.5 zk 0.56 5 3 . 0 zk 0 . 4 2 34.9 =k 0.81 Table II.
Effect of Diethyl Phthalate and Maleic Anhydride on Polarographic Styrene Analysis
Diethyl Phthalate Added, blg.
Maleic -4nhydride Added, Mg.
2.67 5.34 2.67 5.34
...
2.67 2.67
1,05 2.10 2.10 1.05
... ...
Styrene, hlg. Added Found 6.75 6.75 5.57 5.57 5.57 5.57 5.57 5.57
Table 111. Half-Wave Potentials and Diffusion Currents for Millimolar Solutions of Styrene, Diethyl Phthalate, and Maleic Anhydride in Admixture
Ei/z Z'S.
Compound Styrene Diethyl phthalate Maleic anhydride
S.C.E., Volts -2.53 - 3 .92 - 1.41
id,
pa.
3.02 8 42 3,13
6.68 6.80 5.64 5.70 5.54 5.44 5.44 5.54
99.0 100.7 101.2 102.3 99.4 97.7 97.7 99.4
Table IV. Half-Wave Potentials for Reducible Constituents of Some Polyester Resins
Resin
E l / , us. Mercury Pool, Volts 1st 2nd 3rd 4th wave wave wavea wave
Vibrin
...
...
121
-1.22
5081
-1.22 -1.75
28C
-1.19 -1.80 -2.12 -2.47
28V
-1.19 -1.76 - 2 . 1 3 - 2 . 4 7
Selectron Rlarco
on the styrene determination (Table 11). Half-wave potentials and diffusion currents for styrene, diethyl phthalate, and maleic anhydride are shown in Table 111. The data indicate a 500to 600-mv. separation between these compounds in the tetrabutylammonium chloride solution. Oxygen reduced a t a much lower potential than any of the polyester resin constituents and did not interfere in the determination for styrene. Table IV shows the half-wave potentials obtained with some polyester resin formulations. All samples contained styrene monomer and maleate or fumarate esters (first and fourth waves). However, no trace of a phthalate ester was observed in Vibrin 121, although well defined waves were observsd for
Styrene Recovery, yo
Marco
-2.45
-2.13 -2.48
Selectron 5119 a
-1.19
- 1 . 7 5 - 2 . 1 2 -2.47
Second wave of phthalate ester.
phthalates in the other three samples. The phthalate esters, oxygen, and maleate or fumarate esters reduce a t considerably more positive potentials than styrene. The half-wave potentials of the reducible materials are about 100 to 200 mv. more positive in solutions containing the resin. I n preliminary work a n attempt was made t o determine the styrene content of the polyester resin spectrophotometrically. Styrene has a characteristic absorption spectrum in the ultraviolet with well defined peaks a t 291 and 282 VOL. 32, NO. 3, MARCH 1960
359
nip. Standard curves for styrene in chloroform, methanol, and 95% ethyl alcohol were prepared. Samples of the Vibrin and Selectron polyester resins were dissolved in each of these solvents and the styrene content of the samples was determined from the standard curves. As both phthalate and maleate-fumarate absorb in the region below 300 mp, with absorbance increasing with decreasing wave length, high results were obtained. From these results it was concluded that the spectrophotometric method
would require extensive and time-consuming corrections and the method was abandoned in favor of the more rapid polarographic technique. ACKNOWLEDGMENT
The authors express their thanks to Mary M. Williams for samples of the polyester resins used in this study.
(1955).
LITERATURE CITED
(1) Boundy, R. H., Boyer, R.
rene, Its Polymers, Copolymers and Derivatives," pp. 185-9, Reinhold, New York, 1952. (2) Hirt, R. C., Schmitt, R. G., Staffor, R. W., ANAL.CHEM.27, 354-6 (1955). (3) . . Kolthoff. I. M.. Lineane. J. J.. "Polarography," 2nd ed.; pp: 712-13; Interscience, New York, 1952. ( 4 ) Laitinen, H. A., Wawzonek, S. A,, J. Am. Chem. SOC.64, 17658 (1942). (5) McGovern, J. J., Grim, J. M., Teach, w.c., ANAL.CHEX 20, 312-14 (1948). ( 6 ) Whitnack, G. C., Reinhart, Joan, Gantz, E. St. C., Ibid., 27, 359-62
F.,"Sty-
RECEIVEDfor review August 10, 1959. Accepted November 9, 1959.
Determination of Traces of Oxygen in Sodium Metal by Infrared Spectrophotometry H. J. deBRUlN Research Establishment, Australian Atomic Energy Commission, lucas Heights, New South Wales, Australia
b Current research with liquid metal systems required the development of an analysis with accuracy and reproducibility greater than those of the conventional alkyl halide method. Improved procedures to a lower limit of 20 p.p.m. with an accuracy to *20% are detailed. A Wurtz reaction, employing n-amyl chloride, is followed by the application of the infrared pressed disk technique to the solid reaction products, which contain the oxygen impurity. The carbonate absorbance band a t 11.38 microns, due to the conversion of the original sodium monoxide to carbonate by atmospheric carbon dioxide, follows the LambertBeer law between 0 and 300 p.p.rn. A simple method is suggested for handling of samples, contained in glass ampoules.
C
methods for the determination of traces of oxygen in sodium ( I O , f5) have been ayplied nith varying success (2, 6, 12). Among the available physical methods, the plugging indicator (5) relies on the formation of a saturated solution of the oxide in the metal a t a known temperature. Solubility data, however, are very conflicting ( I , 9, I I ) , and the formation of supersaturated solutions tends to produce low results. The relatively recent distillation method (7) does not yet appear t o give consistent results ( 2 ) . In current research with liquid metal systems the alkyl halide method of White et al. (15) was required t o be reliable between 0 and 100 p.p.m. of ovygen by weight. Only minor changes were introduced in the Wurtz reaction 360
HEMICAL
ANALYTICAL CHEMISTRY
stage. It had already been shown ( I S ) that large amounts of halide interfered considerably in the acidimetric titration of the oxide which mas used in the original method. It also became obvious that the infrared pressed disk technique could be applied to the reaction products ITith advantage. The transparent sodium halide contained traces of oxide, which were easily converted to the absorbing carbonate ( 3 ) . The final procedure which employed infrared sl.ectrophotometry was used in a n effort t o eliminate difficulties associated with the acidimdric estimation. REAGENTS
Analytical reagent grade n-amyl chloride was kept over anhydrous calcium chloride to remove alcohol and water contamination. Analytical reagent grade n-hexane n as kept over freshly cut sodium metal. The Wurtz reagent, consisting of a mixture of 60% n-amyl chloride in n-hexane, !vas stored over anhydrous calcium chloride. Traces of amyl alcohol and water were removed by passing the solvent over an 18-inch colunin containing activated alumina before entering the reaction vessel (Figure 1). Alumina, especially prepared for chromatography, n as activated by heating it for 2 hours a t 300" C., before filling the column of the reaction apparatus. After four determinations the column was recharged. I n this way no moisture could be detected in the outcoming solvent by the Karl Fischer method. Sitrogen, nith an oxygen content of less than 10 p.p.m., was passed through two KaK bubblers and a liquid nitrogen trap before entering the reaction vessel as a blanket gas.
-411 connecting tubes were copper. Moisture was not detectable by Karl Fischer techniquw (less than 5 p.p,m.). Standard sodium carbonate solution (0.25 mg. per ml.) was made from analytical reagent grade sodium carbonate, which had been heated to constant neight in a muffle furnace a t 300" C. For the standard sodium chloride solution (0.192 gram per nil.)>analytical reagent grade sodium chloride dried for 24 hours at 150" C. in a vacuum oven iyas used. Traces of hydrochloric acid, adsorbed on the sodium chloride will interfere when carbonate-chloride mixtures are made up in the preparation of the standard curve. Liquid paraffin (British Pharmacopoeia, 1952) to which sodium metal had been added n ac: heated t o approaimately 150" C. It was rapidly etirrcd for 2 hours, forming a finely divided sodium suspension. The paraffin n a s then cooled to b e h e e n 80" and 90" C. and filtered through a Whatman No, 1 filter paper, after nhich it was stored over freshh- cut sodium metal lumps in a hard glnsq desiccator under vacuum. The tcnipcrature of the paraffin was maintaincxd constant a t about 50" C., by placing the desiccator on an elmtrically heatrd sand bath. APPARATUS
The Wurtz reaction was carried out in the apparatus shown in Figure 1. This was built inside a dry box, 40 X 30 X 24 inches. Nitrogen passed a t the rate of approximately 100 cc. per minute via the apparatus into the dry box. This procedure was essential because of considerable diffusion of air through the Perspex panels. As a result the moisture content of the box could not be reduced below 500 p.p.m. A copper refluv condenser was used to avoid the introduction of external cooling IT-hich
