INDUSTRIAL AND ENGINEERING CHEMISTRY
414
ACKNOWLEDGMENT
The authors me grateful to x-ray data reported here.
Lambert for Obtaining the
LITERATURE CITED
-4nderson, E., J . Bid. Chem., 165, 233-40 (1946). Assoc. of Official Agr. Chemists, “Official arid Tentative Methods of Analysis,” 6th ed., p. 112, Washington, 1946. ENG.CHEM., 7, Aenson, 13. K., and Thompson, T. G., J. IND. 915 (1915). Brauns, F. E., J . Am. Chem. Soc., 61, 2120 (1939). EKG. Buchanan, M . A., Lewis, 11, F., and Kulth, E. F., IND. CHEM..36 907 (1944). Chidester, G.H.,‘ and McGovern, J. N., Paper Trade J., 113, NO.9,34-8 (Aug. 28, 1941). Dickson, A. D., Otterson, H., and Link, K. P., J . Am. Chem. Soc., 52, 775 (1930). Erdtman, H., Suemic Papperstidn., 42, 344-9 (1939) ; Ann., 539,116-27 (1939). Francis, B., Piper, S. €I., and M a l h n , T., PTOC. Rov. SOC.(Lond o n ) , A128, 214 (1930). Frankforter, G. E., and Brown, H. H., Corn. 8th. Intern. Congr. AppL Chem. (.4ppendiz), 25, 359 (1912). Hatch, R. S . , and Holzer, W. F., T A P P I Monograph KO.4, pp. 153-66, 1947. Hibbert, H.. and Phillips, J. B., Can. J . Research, 4 , 1 (1931).
Vol. 41, No. 2
(13) Isenberg, I. H , Buchanan, H. A., and Wise, L. E., Paper Ind. and Paper E7orld, 28, No. 6, 816-22 (September 1946). (14) Jamleson, G. S., “Vegetable F a t s and O h , ” A.C.S. Monogiaph No. 58, 2nd ed., pp. 363, 395, New Yolk, Reinhold PublishingCoro.. 1943. (15) Johnson; C. H., and Cain, R, A., J . $m. Pharm. dssoc., 26, 623 (1937). ( 1 6 ) Kurth, E. F., 11,-D. EXG.CHEM.,25, 192 (1933). (17) Lapworth, A., and Mottram, E. N., J . Chem. Soc., 127, 1628 (1925). - - - ,(18) Leighton, P. A., Craw, R. W., and Schipp, L. T., J . Am. Chem. SOC.,53, 3017 (1931). (18) Lewkowitch, J., “Chemical Technology and bnalysis of Oik, Fats, and Waxes,” 3rd ed., p. 360, London, Macmillan Co.,. 1904. (20) Aratat2. Bur. Stundards ( U . 8.1, Circ. C440, $1. 218 (1942). (21) PatterRon, It. P., and Hibbert, H., J . Am. Chem. SOC.,65, 1862 (1943). (22) Pexv, J. C . , paper presented before 112th Meeting of the -4~1. CHBX.SOC., September 18, 1947. (23) Russell, A., Chem. Revs., 17, 155 (193.5). (24) Technical Association of the Pulp and Paper Industry, “Standards and Suggested Methods” (September 1046). (25) Wolff, H., and Scliolze, E., Chem. Ztg., 38, 369-70 (1914j. \ -
RECEIVED October 13, 1947. Published with approval of t h e hlonographs Publication Committee, Oregon State College, Researoll I’npcr No. 130, School of Science, Department of Chemistry.
From Sodium- Catalyze Copolymerizations W.A. SCHULZE, W. W. CROUCH, AND C. S. LYXCH Phillips Petroleum Company, B a r t l e s d l e , Okla.
A study has been made of the sodium-catalyzed copolymerization of butadiene and styrene with emphasis on the preparation of charge ingredients and sodium catalyst to obtain duplicable results from polymerization runs. A careful control of monomer purity, reaction conditions, and quantity and particle size of the catalyst are required. The process is facilitated by the use of a hydrocarbon diluent to control the heat Qfthe reaction and a wash mill to remove residual catalyst from the copolymers. The products are superior to emulsion-polymerized copolymers in flex life and processing characteristics but are inferior to them in low temperature embrittlement.
HE sodium-catalyzed polymerization of butadiene is an old 7 ) for the process has been employed in Europe production of synthetic rubber. However, it appears that in spite of the superiority of butadiene-styrene copolymers prepared in emulsion systems over polybutadiene from the same process, little Drogress has been made in admting the sodium-catalvzed reaction to the production of these copolymers. There is some evidence (8)that the process was studied in Russia with results which led to the classification of styrene along with 2-butene and other olefins said to have the property of shortening the Pohmer chains, or modifying polybutadiene. Recently, however, Marvel and co-workers (2, 3) showed that by the use of carefully purified ingredients, the copolymerization of 1,3-butadiene with styrene is effected readily with sodium catalyst to give an elastomeric copolymer of interesting physical properties. They proposed the name S-BE3 €or t h i s product. This material was produced in larger quantities in this laboratory for more thorough evaluation. In the course of this work there arose a number of problems related to the preparation of the charge ingredients and to the polymerization of S-BS. This re&
-
port describes the most satisfactory process developed and presents results of physical tests on the products. The S-BS polymerization process was not adapted to any known type of conventional large scale polymerization equipment. At the start of the polymerization reaction the disper~ed sodium particles became coated with sticky polymer and usually aggregated a t the bottom or in a corner of the reactor in masses of material which grew upward until the whole charge was converted to solid polymer. Agitation of the reaction mixture, which would be required to disperse the catalyst and provide temperature control in a large reactor, would be extremely difficult in the later stages of reaction. Thus, in preparing a 50pound lot of the copolymer, it appeared advantagrous to make the material in a number of small batches in laboratory pressure vessels rather than to attempt to develop an entirely new type of reactor or charge recipe which would permit the reaction in larger For purposes of this study the following modifications of t h e earlier procedure (3) were made:
~I
Larger reaction vessels, either 3 X 11 inch steel bombs or 32glass bottles were used. d low boiling diluent, usually isobutane was used to control the heat of reaction and reduce gel form;tion. The catalyst was prepared in quantities sufficient for a number of charges rather than individually for each charge. A wash mill was used $0 remove sodium and organosodium from the polymers. ounce
PURIFICATION OF CHARGE INGREDIESTS
A typical charge recipe was as follows: Butadiene, 75 parts; styrene, 25 parts; isobutane, 75 parts; and sodium catalyst, 0.30 part. To minimize variations in the purity of the chargc ingredients, they were procured in quantities sufficient for several weeks’ ex-
February 1949
CHARGf CYLINDER
Figure 1.
INDUSTRIAL AND ENGINEERING CHEMISTRY
415
DRY IC&4ETHANOL BATHS
Hydrocarbon Purification System
perimentation. Phillips Petroleum Company special purity 1,a-butadiene and pure grade isobutane were procured in type B cylinders of approximately 70-pounds capacity. The system used for the purification of these ingredients is shown in Figure 1. Each of the liquid hydrocarbons was allowed to flow in turn a t a slow rate to a glass flask where it was vaporized at approximately atmospheric pressure. The vapors passed through a section of 2.5-inch pipe filled with calcium chloride desiccant, condensed in a stainless steel coil immersed in a dry ice-methanol bath, and finally accumulated in a 5-gallon mixing cylinder. Equal weights of butadiene and isobutane were blended in the mixing cylinder and the mixture charged subsequently t o reaction vessels. The hydrocarbons were always drawn from cylinders liquid phase rather than gas phase t o obtain representative samples and reduce variations in purity as cylinders were depleted. Tests of water content of the butadiene by a modified Karl Fisher procedure indicated 0.008% water in a typical sample as received; this was reduced to 0.0015% after drying. Dow Chemical Company 99.5% styrene was employed. It was purified by distilling through a short Vigreux column; the first 10% overhead was discarded to remove water. The distillate was stored in a refrigerator until used and was tested for polymeric material before use. PREPARATION OF CATALYST
To obtain duplicable results in a series of runs, the catalyst was prepared by the procedure of Morton and co-workers (4-6) in batches large enough t o accommodate a number of charges. One hundred fifty grams of clean sodium and 600 grams of dry xylene were heated t o 110' C. in a 2-liter creased flask and stirred at 7,000 t o 10,000 revolutions per minute for 15 minutes. Stirring was stopped when the temperature was 100" C., and the dispersion was allowed t o cool without further agitation. A micrograph of a typical sample of the catalyst is shown in Figure 2. The suspension of catalyst was stored in a cork-stoppered bottle and aliquots removed as required in a graduated pipet. The dispersion was shaken and the sample of catalyst removed quickly by inserting a pipet t o a point near the center of the liquid. Tests t o determine the quantity of sodium removed, which consisted of reacting i t with isopropanol and measuring the volume of hydrogen formed, indicated that satisfactorily representative samples were taken. No reduction in activity with age of the catalyst was observed, although some batches were used over a period of 2 or 3 weeks. During this period the storage bottle was opened a number of times for catalyst withdrawal. POLYMERIZATION APPARATUS AND PROCEDURE
The most satisfactory type of steel reactor bomb is illustrated .in Figure 3. A 13-inch length of 3-inch pipe was threaded at
Figure 2.
Dispersed Sodium Catalyst
both ends and fitted with caps bearing six cap screws; these turn down against a 0.25-inch steel plate which is sealed by a n aluminum gasket. The whole assembly resembles the closures employed in conventional laboratory high pressure hydrogenation bombs. A 0.5-inch pipe collar was welded near the middle of the bomb; after charging this was closed with a plug. T o charge the bomb, the ends were closed and the air displaced by dry nitrogen. The catalyst then was charged as a 20% dispersion in xylene, and the bomb placed in a n ice-salt mixture and cooled. A calcium chloride drying tube in the 0.5-inch opening served to dry the air drawn into the vessel during this operation. Next, the cold bomb was placed on a torsion balance and the monomers charged to it by weight. A liquid stream of a 50 t o 50 mixture of isobutane and butadiene was drawn from the mixing cylinder through a cooling coil in a dry ice-methanol bath, and the cold stream charged at atmospheric pressure from a line inserted down into the open 0.5-inch collar. The styrene was introduced from a pipet while the butadiene-isobutane charging step was in progress. When the required weight of material had been charged, the bomb was closed and taken at once t o the polymerization bath, which was a water bath thermostatically controlled at 40" C. and fitted with a horizontal steel platform arranged t o rock through a n angle of 20' at 45 cycles per minute.
Figure 3.
Polymerization Bomb
Another type reactor employed was a 32-ounce beverage bottle. These were charged substantially as described and closed with Crown caps bearing tinfoil gaskets; the polymerizations were run in the usual way. T o remove the polymer, a hot wire was used t o break the bottom from the bottles. The low cost and ready availability of the bottles made this procedure advantageous since it eliminated the laborious step of cleaning the bombs. Visual examination of the contents during polymerization and the elimination of variables due t o improperly cleaned reactors were further advantages of the glass vessels. All bottles were pressure tested at 100 pounds per square inch before use.
INDUSTRIAL AND ENGINEERING CHEMISTRY
416
TABLE I. EFFECTOF CATALYST CHARGEo s VISCOSITY OF S-BS Catalyst Charge. Parts 0.10 0.20
Inherent Viscosity 6.13
4.27 4.26 3.92 3.33 2.25 1.32
0.30
0.40 0.60 1.0 2.0 5.0
TABLE
Appearance of Polymer Solid Solid Solid Solid Solid Solid Soft and sticky Viscous oil
....
11. E w E c r
OF
ADDITIVES O N VISCOSITY Additire Used, Parts
Additive None Acetone Acetone Acetaldehyde Acetaldehyde Furfural 12-Butadiene
,..... 0.01
0.02
0.76
1.73 0.70
0.02 0.10 0.04
1 .a9
0.037
25 t o 60% of the catalyst, produced a white coating on the etttalyst particles, followed by a n exceptionally fast rate of polymerization to copolymers of high viscosity and gel content. The low concentration of these compounds required to affect the viscosity of the copolymers indicated that the production of S-BSof controlled viscosity would require careful regulation of the purity of the reactants. However, a series of runs, employing a cylinder of commercial butadiene froin the Plains Rutadiene Plant, was made without difficulty.
S-BS
OF
Inherent VlSCObltY 2.80 1.74
1. T X
The reactions were run for a period of about 20 hours t o obtain conversions in the range of 90 to 100%. At the end of that time, isobutane and unreacted butadiene were ventcd off, the reactors opened, and the Copolymers transferred to a 11 ash mill where sodium and organosodium compounds n e i e rcmoved. The red or bron-n color of the copolymers, as taken from the reactors, disappeared rapidly on contact TI ith the atmosphere, and aftrr washing for a few minutes, a n hite product was obtained. ‘I‘here was no evidence during the washing process of the vigorous reaction which occurs when larger particles of metallic sodium come into direct contact with water. The copolymer was washed for 5 t o 10 minutes; after this 1.570 phenyl-@-naphthylamine was milled into it. It then was sheeted off the mill and dried for 24 hours in a mechanical convection oven. CONTROL OF VISCOSITY
The control of the viscosity of S-BSwas found to be a difficult problem. Viscosities of the products were affected by a number of variables, including the quantity and particle size of the catalyst charged, rate of agitation, monomer ratio, reaction temperature, extent of conversion, and the presence in the charge of modifying impurities. Even when all these factors were controlled, there remained differences in the viscosity of various batches of product; these were attributed to fortuitous differences in the distribution of the catalysts in the reaction mixtures. The effect of varying the catalyst chargc is shown in Table I. Varying the catalyst charge is the most effective way of eontrolling the viscosity of the copolymers, and with each new batch of catalyst or monomers used, preliminary tests were made to determine the amount of catalyst required to produce material in the viscosity range desired. Certain compounds, including aldehydes, ketones, and 1,2butadiene were found t o behave as modifiers for the polymerization. Butenes and 4-vinyl-1-cyelohexene (butadiene dimer) in low concentrations apparently had little effect on the reaction. The addition of methanol, in quantities sufficient to react with
PHYSICAL PROPERTIES
Fifty pounds of S-BS were prepared and blended, and a sample of 100 parts copolymer was compounded with 50 parts Wyex carbon black, 3.0 parts zinc oxide, 10.0 parts Asphalt No, 6 softener, 2.50 parts sulfur, 1.00 part Santocure, and 1.50 parts stearic acid. Phybical properties, after curing for 30 minutes at 308’ F., are shown in Table 111 with data for natural r u b b ~ r and GR-S compounded and cured in the same way. Although this sample of S-RS had a relatively high Moonep viscosity (RIL-4 at 212 F.) of 69, processing eharacleristics were rated equal to natural rubber and superior to GR-S. Additional tests with a number of other samples confirmed the superior processing properties and flex life of this material over equivalent samples of GR-S. Other properties such as tensile strength, elongation, abrasion resistance, and aging characteristics of the copolymers prepared by the tmo processes were found t o be approximately equal. The most notable deficiency of 5-135 appears to be its low temperature embrittlemcnt. Compounded stocks were found t o bccome brittlc at temperatures wound -40” F. compared t o -5d” F. for natural rubber and -70’ F. for GR-S tested in the same way. Recently, Juve et al. ( 8 ) described the evaluation of foul samples of S-BS,prepared by hlarvel and eo-workers by various polymerization procedures, with an undiluted 75 to 25 butadienestyrene recipe. Results showed these samples also to be supe rior to GR-S in processing quality and in balance of flex crack growth and hysteresis, and to have higher brittle points than GR-S. Confirmation of these observations with another sample of S-BSpiepared in this laboratory by a somewhat different procedure provides further evidence that these properties are inherent with this type of polymer, regardless of variations in the procedure by which it is prepared. ACKNOWLEDGMENT
The authors acknowledge the assistance of C. S. hIarve1, W. J. Bailey, and G. E. Inskeep of the University of Illinoi.: for many helpful suggestions in starting this work. LITERATURE CITED
(1) DeBell, J. M., Goggin, W. C., and Gloor, W. E., “Gerinttn Plastics Practice,” p. 436, Springfield, Mass., DeBell and Rich-
ardson, 1946. ( 2 ) Juve, A. E., Goff, hI. M., Schroeder, C. H., Meyer, A. W., and Brooks, M. C., IND. ENG.CHEM.,39, 1490 (1947). (3) Marvel, C. S., Bailey, W. J . , and Inskeep, G. E., J. P o l g . Sci., I, 275 (1946). (4) Morton, A. A., Darling, B., and DaiTidson, J., IND. EKG.CIIEM., A x . 4 ~ .ED., 14. 734 (1942). ( 5 ) Morton, A. A,, Davidson, Y B., and Kewey, H. A, J . Am. Chem. LCOC., 64, 224C) (1942).
PROPERTIES OF COMPOUNDED S-BS TABLE 111. PHYSICAL Rubber
300% Modulus Lb./Sq. 1;.
Lb./Sq. In.
Elongation, 70
Hysteresis Heat, O F.“
Resilience, %‘cb
S-BS GR-S Smoked sheet
1040 1190 1270
2920 3250 4090
590 695 620
64.2 71 .o 42.4
54.7 69.3 74.0
a 6 C
d
Tensile,
Vol. 41, No. 2
Flex LifeC
64.1 9.Q
> 50
Heat rise in O F. on flexing i n a Goodrich flexometer a t 200’ F. Resilience a8 measured on a Yerzley Oscillograph. Flex life in thousands of flexures t o a standard crack growth on a De Mattia flexing machine. .4brasion loss in g r a m as measured on a Goodyear angle abrader.
Bbrasion Loss, G.d 3.30 4.57 3.57
((3)
Morton, A. A., and Richardson, G. M., Ibid., 62, 123
(7)
Talalay, A,, and Magat, M., “Synthetic Rubber froin illcohol,” pp. 144-97, New York, Interscience E’ublishers, Inc., 1945.
(1940).
(8) Ibid., p. 173. RECEIVBD January 15, 1948.
