Determination of Styrene in Hydrocarbon Copolymers RAYMOND C. CRIPPEN’ AND CHARLES F. BONILLA2 Johns Hopkins University, Baltimore, M d . A method has been developed which determines, with about 3‘70 or better accuracy, the styrene content of polystyrene and of soluble or insoluble polymers of styrene and butadiene. It presents the advantages of greater speed and less hazard than the conventional carbon-hydrogen method. Butadiene does not interfere. Several substituted styrenes and other aromatics give different reactions. Thus they interfere with a styrene determination. If they are to be determined in their polymers, a separate standardization w-ould be required.
S
tion to benzoic acid and benzaldehyde (1/t, 18,26). This method is not quantitative, however, and materials other than styrene that oxidize to benzoic acid or benzaldehyde under these conditions interfere-for example, toluene and ethylbenzene. Halogenated styrene copolymerized with a nonhalogenated compound can be determined from the halogen content of the polymer (10). Similarly, styrene copolymerized with a compound containing an additional element can be determined by difference (1, 13, 15, 23, 36). The direct chemical quantitative determination of styrene in copolymers with other pure hydrocarbons, however, has not been found in the literature; the carbon-hydrogen analysis ( 4 , 16) is the only available method, and of course, is applicable only when the styrene and other monomer differ in their carbon-hydrogen ratios and when no other constituents than carbon or hydrogen are present Polymeric styrene may also be determined by certain physical methods requiring considerable equipment-fluorescent and absorption spectra (%$,SI),molecular spectra (15,80,$$,%), electron DISCUSSION OF PREVIOUS IYVESTIGATIOUS diffraction (32),and x-ray diffraction (9). However with the widespread use of polystyrene in plastic materials, coatings, and many Many methods have been developed for determining monoother applications, a simple method for the analysis of styrene has meric styrene and pure polystyrene, including halogen absorption, become a necessity. It must be adaptable to a wide variety of nitration, etc. Styrene may be identified in copolymers by osidastyrene-containing materials and, after proper standardization, 1 Present addrese. Research and Development Laboratories, Baltimore must be fairly accurate. The method here described seems to Md. meet most of these conditions. * Present addres-, Columbia Univeisits S e n York. S . T A rapid procedure, lending itself readily to regular routine analysis, was developed from a combination of the A/R-LEAK CONTFR3L colorimetric method of Rowe ,RUBB€R TUBING ASESTQS RUBBER TUHNG el al. ( $ 5 ) for monomeric styrene and the steam-distillation method of Frank et al. ( 11 ), in which the sample is U depolymerized by superheated steam a t about 300’c. The monomeric material is steam-distilled over and absorbed in a known volume of carbon tetrachloride.
ATISFACTORY methods of analysis of monomeric stvi ene are available in the literature (8, 16). Soluble styrene-copolymeric hydrocarbon resins are also relatively easy to analyze by physical means (3, 19, $ 7 ) . Insoluble ones, however, are almost impossible to analyze accurately (6, 7 , 29, 30, 33); the carbonhydrogen determination is the only method used to any great extent (28). This method is uncertain, because a small error in hydrogen content introduces errors more than ten times as great into the final styrene estimation. The carbon-hydrogen determination is also hazardous (51, as styrene-butadiene resins tend to explode in any oxygen atmosphere. Other methods for the analysis of styrene, such as the proposed A.S.T.M. method (b), are long and involved. Thus, an attempt was made to develop a more satisfactory method for the determination of styrene in mixed hydrocarbon resins, especially polystyrene and butadiene-styrene copolymers and particularly insoluble polymrrs such as “popcorn” (17).
n
AUALYTIC4L PROCEDURE
h
-ACE
STEAM GEN€RATOR
SUPGQHEATER
AECWEAY FLASK
UM TRAPS
Figure 1. Diagram of Apparatus 927
Approximately 3 grams of sample are introduced into the depolymerization flask (Figure l ) , 100 ml. of carbon tetrachloride are introduced into the recovery flask, and the entire system is sealed.
ANALYTICAL CHEMISTRY
928 The recovery flask, as well as the trap ahead of the vacuum pump, is cooled with dry ice-acetone mixture. An additional trap prevents oil backing up from the pump or loss of material due to a rapid flow of vapors through the system. The system is evacuated to the vapor pressure of the cold carbon tetrachloride and the steam generator and superheater are turned on. The depolymerization flask should operate in the general neighborhood of 300’ to 400’ C. and 5 to 10 mm. of mercury absolute pressure. -4slow stream of air bubbles to control the boiling rate is admitted to the steam generator by means of a capillary tube, hose, and pinchclamp.
I 0
1.0
2.0 3.0
4.0
CONCENTRATION, MG.
Figure 3.
u
6.0 Z.0 8.0 STYRENE/SO ML.
5.0
T r a n s m i t t a n c e Curve
I
9.0 100
Cenoo photelometer with blue glass filter and 1 to 10 mg. of styrene per 50 ml.
carbon tetrachloride in a volumetric flask, and 25 ml. of this solution are then diluted to 250 m]. This latter solution represents 1.0 mg. of st rene per ml. Volumes from 1.0 to 15.0 ml. are made up to 15 mf with carbon tetrachloride, treated with nitrating mixture, extracted, and filtered, and light transmittance is determined as previously described,
t1
2o 10
O m
F i g u r e 2.
m
sa, 600 700 WAVE-LEWGTH, MIL LIMICADNS
Spectral
Transmittance Stjrene
800
of Nitrated
8.0 mg. per 50 ml. of solution. Coleman Universal spectropho-
A typical calibration curve with a photoelectric colorimeter is given in Figure 3 and x-ith a spectrophotometer in Figure 4. The deviation from linearity a t high concentrations is confirmed by Rowe (2’5).
tometer
STANDARDIZATIOV WITH POLYMERS
A flame is applied slowly to the sample flask after the flow of steam has started. Water is turned on in the condensers and the sample is melted and evaporated slowly. After it has been distilled, the flame is played over the entire surface of the flask to distill splashes on the walls. Some 100 ml. of water will have been condensed a t this point. The flames are then shut off and the entire system is allowed to cool. The vacuum is broken and the system dismantled for the warming up of the recovery flask and traps. The condenser tubes and flasks are rinsed with the carbon tetrachloride layer in the recovery flask. After shaking, an aliquot of the carbon tetrachloride layer containing about 2 to 8 mg. of styrene is pipetted into a separatory funnel and diluted to 15 ml. with C.P. carbon tetrachloride. Two milliliters of nitrating mixture (equal volumes of concentrated sulfuric acid and freshly boiled and cooled nitric acid) are added, and the separatory funnel is stoppered and shaken vigorously for 10 seconds every 2 minutes over a period of 10 minutes. Fifteen milliliters of distilled water are added, the funnel is shaken, and the water layer is removed. Two additional 15-mI. mater washes are employed and the combined washes are made up with distilled water to 50 ml. in a volumetric flask. This solution is filtered through ashless paper to remove any cloudiness or allowed to stand until the cloudiness settles out. The light transmittance is then read in a photoelectric colorimeter using a blue filter, or better yet, in a spectrophotometer at approximately 365 millimicrons wave length, which corresponds to a minimum in transmittance (Figure 2). The reading is compared to a calibration curve obtained on pure styrene and the corresponding weight of pure styrene is multiplied by an empirical calibration factor of 2.0 to give the amount of styrene in the polymer.
For extreme accuracy, it is essential that an exact technique be used and the same number and type of operations be performed on each sample. STANDARDIZATIOY WITH STYRENE MONOMER
I n the standardization, the method of Rowe et al. ( 8 5 ) is essentially followed. Pure redistilledstyrene monomer(99.5%purityor better, 1.1ml. by volume or 1 gram by weight) is diluted to 100 ml. with C.P.
A number of commercial GR-S synthetic rubber and “popcorn’J polymer samples (cross-linked insoluble polymer of styrene and butadiene) were analyzed by different methods to determine their styrene contents (Table I), and also by the superheated steam d s polymerization method herein described. Attempts were made to secure samples of styrene copolymerized JTith drying oils and other polymerizable substances, but these were unavailable a t the time. However, it was thought that this method could be adapted to such materials by working with the unsaponifiable fraction. One polymer sample containing p-chlorostyrene and one containing 3,5-dimethylstyrene were also run but calibration curves lvere not obtained. The nitration reaction gives different colors in these cases but it is believed that after suitable standardization, the method would apply equally well as with unsubstituted styrene. DISCUSSION
Bs styrene has only one reactive double bond, it polymerizes linearly. Temperatures of about 100” C. or lower are employed. The reverse process, or depolymerization, requires some 75,000 calories per gram mole (12); thus temperatures of 300” to 400 C. are necessary. On heating, the polymer melts a t first, then begins to bubble. I n air at atmospheric pressure, charring occurs Charring is decreased but still appreciable in air a t reduced pressures. Replacing the air with steam makes charring negligible; the steam also minimizes subsequent recombination of the monomer molecules. The color that develops on nitrating is probably due in part to organic compounds formed and in part to oxides of nitrogen. The similarity of the colors obtained with styrene monomer and with the products of disintegration of the polymers here investigated, indicates that monomeric styrene is a principal product and that other interfering compounds do not form. However, slightly high results may be obtained when other materials than butadiene
V O L U M E 21, NO. 8, A U G U S T 1 9 4 9 -~
-__
929 - ---- -
- ____
__ . -
ples on which Photelonieter determinations were also carWith Steam Deyolyiiierization ried out the mean deviation is Without Steam Depolymerization Spectro- Spectroihu&2.7%and the mean is 0.94% Micro Macro Average Kitro- Photelom- photomtometer Deacription SamDle Nominal C-H C-H C-H site eter eter 0s. C--H below the carbon-hydrogen Popcorn (coml 9A ... -0.7 figure. With this equipment, 9B ... -1.37 9C ... -0.64 therefore, the reproducibility 9D fO.4 10.1 is not so good; a correction (+2.1! 10B f0.7 factor a little higher than 2.0 13.4 -0 6 13B 50.3 to.!, would give better agreement. 1 7s:7 74.1 c0,i.i More precise values of the corPopcorn ( B d ) (coml.) Phillips rection factor are not reported 0 0 0 2 -1 ( - 1 32, because it should be deter2B +o 3 3A +o 1 mined by each laboratory for BB +o 47 4 the exact equipment, operating +o 28 5 (-1 28) conditions, and procedures 7 ( - 1 161 used. Popcorn (lab.) Syn. 85/15 83 ... 7 9 5 ... 80.2 82.6 +3 1 Syn. 90/10 40 . . . 87.7 .,. 86’4 RU 5 90.32 +3 6 The need of a correction factor GR-S synthetic of about 2.0 is supported by rrihher BC-60428-A 23.2 . . . 23.5 .., .... 24.0 +o :, BC-60428-B 23.3 . . . 23.8 ... 2i:8 .... 23.9 +O.l Madorsky and Straus ($I), BC-60426-DAl 23.8 ... ... 21.3 +0 3 BC-60426-B 23.4 , . . 24:6 . . . 2217 2. 7. .,2. 5 25.2 t0.B who distilled polystyrene in BC-60426-XBC 23.6 . . . 24.8 .. , 22.9 28.0 24.7 -0 I high vacuum and analyzed tht BC-60424-A 23.5 ... ... , . .... 23.9 +0.4 BC-60424-C 23.5 , . . 2410 ,.. .... 23.8 t0.3 pyrolytic products. Forty per Pure (lab.) Polystyrene 100 99.5 99.7 99.6 98:7 97.2 98.8 -0 u cent of their product vias found Mean, compared t o C-H method -0 94 +o 37 to be styrene monomer and the \Iean deviation, compared t o C - 13 method *2 i =to 74 balance dimer, trimer, etc., and __ __________ -some degradation products. K7all (34) a t atmospheric pressure similarly iound 83% of monomer in the products. The nitrosite method ( 4 ) also requires a correction factor. I t was employed on several of the samples after depolymerization (Table I ) but did not agree well n.ith the other methods and was not utilized further. The equipment required for this procedure can be set up froni standard parts in approximately 0.5 hour. Exclusive of standardization an analysis can be completed within 1hour, which is much less than other methods require. This general procedure may prove useful for the analysis of other types of polymers, after proper standardizat>ion, and may be adaptable t,o microprocedures. T a b l e 1. D e t e r m i n a t i o n of S t y r e n e in Polymers
~
ACKNOWLEDGMERT
set
301
Thanks for assistance are due to B. L. Harris, D. A. Edivards, and J. Grossman; and for samples to The Goodyear Tire and Rubber Company a t Skron and a t Houston, C. S. Marvel of the University of Illinois, Phillips’ Petroleum Company a t Borgrr. and Humble Oil Company a t Baytown, Texas, COMPREHENSIVE BIBLIOGRAPHY (11 -Ufrey, T.,
and styrene are pyrolyzed, such as stearic acid in GR-S synthetic rubber. Leaching the polymer with sodium hydroxide and then water minimizes the effect in this case. Similarly, in oils work may be done with the unsaponifiable portion and the method adapted to styrenated oils. The empirical correction factor of 2.0 was obtained by comparison of the carbon-hydrogen and colorimetric analyses of the samples in Table I. After applying this factor, the styrene content by apectrophotometer of the 23 samples averages 0.37% higher than the corresponding carbon-hydrogen figure, or the mean of the two carbon-hydrogen figures if both micro- and macromethods were employed. Thus a correction factor slightly below 2.0 would give better agreement for the partjcular equipment and conditions used. However, the mean deviation is +0.74% and adequate acriirocy is afforded by the round number of 2.0. For the 16 sam-
and Harrison, J. G., Jr., J . Am. Chem. Soc., 68, 299.301 (1946). ( 2 ) Am. SOC.Testing Materials, Vol. 111-B, p. 969, D 833-48T (1946). ( 3 ) Barnes, R. B., Liddel, U., and Williams. T’. Z., IXD.EN(. C H E Y . , A N ~ LED., . 15, 681 (1943). (4) Bond, G. R., Jr., I h i d . , 19,390-2 (1947). ( 5 ) Bonilla, C. F., Edwards, D. E., Grossman, J., and Crippen, K. C., Rubber Reserce Corp. Rept., CD-850 (1946). (6) Brajnikoff, B. J., Plastics, 6, 276-84 (1942). (7) Ibt‘d., 6, 316-28 (1942). (8) Coghill, R. D., and Sturtevant, J. M., “Identification of Organic Compounds,” pp. 139, 140, 150, 168, New York, McGraw-Hill Book Co., 1936. (9) Dzhelepov, B. S., Phus. 2. Sowiejetunion, 11, 157-67 (in German); J. Ezptl. Theoret.Phys. (U.S.S.R.),7,61-7 (1937). (10) Fieser, L., and Fieser, H., “Organic Chemistry,” pp. 548, 650, 917,918, New York, D. C. Heath Co., 1946. (11) Frank, J. C., -4mos, J. L., and Straubel, ,4.F. (to Dow Chemical Co.), U. 8 . Patent 2,359,212 (1944). (12) Gilman, Henry, “Advanced Treatise in Organic Chemistry,” pp, 743-50, New York, John \%%ley& Sons, 1943. (,13) Glavis, F. J., Ryden, L. L., and Marvel, C. S., J . A m . Chem. SOC., 59, 707-11 (1937). (14) Goff, J. H., P a p e r Trade J . , 122, KO.5,41-3 (1946). { IA) Horio. M.. .Ifem. (‘d. Eng. Kuoto, I m p . L‘nia-., 7, 177--248(18331.
ANALYTICAL CHEMISTRY
930 (16) Kamm, Oliver, “Qualitative Organic Analysis,” 2nd. ed., pp. 41, 141,194,195,267,New York, John Wiley & Sons, 1937. (17) Kharasch, M. S., Jensen, E. V., and Nudenberg, N., Rubber Reserve Corp. Rept. CR-870, CR-950 (1945). (18) Kunke, W. F., J. Assoc. Agr. Chemists, 28,723-5 (1945). (19) Lebas, G., Trans. Faraday Soc., 15, Pt. 3,231-7 (1920). (20) Ley, H., and Dirking, H., Ber., 67B, 1331-8 (1934). (21) Madorsky, S. L., and Straus, S., Ind. Eng. Chem., 40, 848-52 (1948). (22) Pestemer, M., and Wiligut, L., Monatsh., 66, 119-28 (1935). (23) Quiliro, A., and Fleischner, E., Atti acad. Lincei, 7, 1050-6 (1928). (24) Ramart-Lucas, Mme., and Amagat, P., BUZZ. SOC. chim., 51, 965-8 (1932). (25) Rowe, V. K., Atchison, G. J., Luce, E. N., and Adams, E. M., J . Ind. Hug. Toxicol., 25, 348-53 (1943). (26) Simonds, H. R., and Ellis, C., “Handbook of Plastics,” pp. 770-1, New York, D. Van Nostrand Co., 1943. (27) Smoker, E. H., and Burchfield, P. E., IND. ENG.CHEM.,ANAL. ED.,15, 128-9 (1943). (28) Snell, F. D., and Biffen, F. M., “Commercial Methods of Analysis,” pp. 143-5, New York, McGraw-Hill Book Co., 1944.
(29) Staudinger, H., arid Hmm, W., Ber., 67B, 1159-64 (1934). (30) Staudinger, H., Heuer, W., and Husemann, E., Trans. Faraday SOC.,32, 323-35 (1936). (31) Titeica, R . , Ann. 11, 44&70 (1936). (32) Trillat, J. J., Kolloid-Z., 69, 378-89 (1934). (33) Valyi, I., Janssen, A. G., and Mark, H., J.Phys. Chem., 49,46171 (1945). (34) Wall, L. A., paper presented before Division of Cellulose Chemistry, High Polymer Forum, at the 112th Meeting of AM, CHEM.SOC., New York, 1947. (35) Williams, D., J . Chem. P h y s . , 4, 460 (1936). (36) Wulff, Carl, Dorrer, Eugen, and Hopff, Heinrich (to I. G. Farbenindustrie, Ger. Patent 627-037 (March 6, 1936). RICEIVED August 21, 1948. Presented before t h e Division of Paint, Varnish, and Plastics Chemistry, Plastics Group, a t the 114th Meeting of t h e ~ZMERICAN CHEMICAL SOCIETY. Washington, D. C. Investigation carried out under the sponsorship of the Office of Rubber Reserve, Reconstruction Finance Corporation, in connection with t h e government synthetic rubber program. Presented in partiaI fuIfiIIment for t h e degree of master of science in engineering in t h e Department of Chemical Engineering a t t h e Johns Hopkins University, Baltimore, Rld., J u n e 1948.
Spectrophotometric Determination of Cobalt as Cobalt(l1) Chloride in Ethanol
*
Determination of Water in Ethanol GILBERT H. AYRES AND BETTY VINING GLANVILLE The University of Texas, Austin, Tex.
A photometric method has been developed for estimation of cobalt based upon the intense blue color of cobalt(I1) chloride in ethanol solution. The solutions show minimum transmittancy at 655 mp. The color is stable with respect to time, but the transmittancy is decreased considerably by rise in temperature; the temperature effect is completely reversible. The system shows some deviation from Beer’s law. The optimum range for the spectrophotometric measurement with the instrument and procedure used is between 100 and 400 p.p.m. of
S
I K C E 1737, when J. Hellot first observed color changes in cobalt(I1) chloride, this substance has been the subject of extensive study on account of the varied colors exhibited by the solid and by solutions of varying concentration and temperature in many different solvent media. Dilute aqueous solutions, which are pink (spectrophotometrically, reddish purple), change to violet-blue on heating, corresponding in general to changes in color in passing from the hexahydrate to lower hydrates and anhydrous salt. Solutions of cobalt(I1) chloride in sufficiently concentrated hydrochloric acid, and in certain salts such as the chlorides of calcium, magnesium, zinc, tin(II), and mercury( 11), are blue in color; solutions in many organic solvents are deep blue in color at room temperature, and many of these change through violet to rpd at lower temperatures (5, pp. 632-6). [All the following report is concerned with cobalt only in compounds in which i t is bivalent, except in the analytical methods used for checking the proposed method; the bivalent state of the cobalt is not specifically designated hereafter.] Winkler (9) observed that cobalt chloride is soluble in ethanol to give a blue solution; although a 1 t o 2500 solution is distinctly blue, a 1 to 10,000 solution is colorless when cold, but blue when hot, (The ethanol used by Winkler was obviously
cobalt, with an accuracy of 0.5%. The effect of diverse ions has been studied. The method has been tested by comparison with other methods (gravimetric and titrimetric) in the assay of a cobalt salt and in the analysis of a standard steel. Water modifies the color of the cobalt chloride-ethanol solutions; this effect is the basis of a method for estimating water in ethanol, for which the optimum range is about 1 to 5 % water and the maximum accuracy is 0.3 to OS$%& depending upon the concentration of cobalt chloride used.
not absolute, for a 1 to 10,000 solution of cobalt chloride in absolute ethanol is very distinctly blue even a t room temperature; a 1 to 10,000 solution in 95yoethanol is visually almost colorless.) Winkler found that the addition of water to the blue alcoholic solution caused the color to change through violet t o red; hence the blue solution could be used to detect the presence of water. Many of the studies involving color changes of cobalt chloride in various solvents have been concerned with deducing the composition of the colored solute, and various theories have been proposed to account for the observed effects. It is not the purpose of the present investigation to study the mechanism of the color reactions, but rather to test the application of the cobalt chloride-ethanol color to determination of small amounts of water in ethanol, and to establish a colorimetric method for cobalt based on the intense blue color of the cobalt chloride-ethanol system. REAGENTS
All chemicals were reagent grade; maximum limits of impurities likely to interfere are give? below. Cobalt chloride hexahydrate. Impurities: nickel, 0.15%; copper, 0.002%; iron, 0.001%.
