1438
Ilel. 41, No. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
numerous and analytical methods so imperfect that a quantitat>ivet,est of such explanations cannot be made a t present on Xapalm or any commercial soap. The study of aluminum dilaurate has shown, however, that thi3 pure soap may be changed from a very inert, insoluble, relatively crystalline modification to a very soluble, almost completely amorphous one, and vice vwsa, with many apparent intermediary modifications and theii mixtures ( I O ) . Here t,hese differences cannot be ascribed to changes of composition or formation of new compounds but probably correspond to variations in the degree and extent of organization and alignment of soap molecules. These forms are mostly thermodynamically unstable but their rate of change is too slon- to be noticed in the dry state and a i least very slow when in contact n-ith h.drocarbons a t room temperature. This suggests that properties of Napalm and other cominerciai products are determined not, only by the obvious factors first mentioned but also by the modifications in which the soap is present. In fact, once the over-all composition is fixed by the raw materials, this may be the most important determinant. CONC LU SIOY
Sapalm, being an industrial product, is not a pure disoap whosc preparation requires delicate laboratory procedures (14). It differs in two respects. In the first place it contains, as pointed out above, about 10% of impurities-water, inorganic, and extractable materials. In the second place, the remaining disoap does not stem from a pure f a t t y acid but from a mixture of fatty and naphthenic acids. The average molecular weight of these, 233, is, hoTTever, only 15% higher than that of lauric acid, and their content of lauric acid has been estimated a t 60%. Hon-ever, as often happens for mixtures of close homologs, the properties become very similar t o those of the individual compound. Thus aluininum dilaurate, n-hose study as a definitc compound is much easier t'han that of Xapalm, serves as an excellent model for t,his product and has already led tmointerpretations which could not a t preseiit be derived from the study of a mixture.
e
ACKYOWLEDGMENT
Of bhe results here reported for Sapalm, the x-ray diffraction data mere obtained by Sidney Ross and Sullivan S. Marsdeu, water and cyclohexane isotherms by George W. Shreve, extraction with acetone by Lockhart B. Rogers, Kjeldahl determinations by Earl B. Working, and transition temperatures and swelling i c iso-octane by Gerould H. Smith. The study of aluminum soaps was conducted under the direction of J. W. McBain. LITERATURE CITED
i l ) Broughton, J., and Bayfield, A , Dept. of Coirm~erce,OTS. PB 4193,31, 71 (1943). (2) Edwards, L. J., U. S. Patent 2,420,233 (1947). ( 3 ) Fieaer, L. F., Harris, G. C., Hershberg, E. B., Morgana, M., Novello, F. C . , and Putnam, S.T., IXD.E m . CHEM.,38, 76s (1946).
(4) Long, K. E., et al., Dept. of Commerce, OTS, PB 4619 (1943). (5) McBain, J. W., etal., Ibid.,5885, 34, 72, 103, 114 (1945). (6) McBain, J . W., Mysels, K. J., and Smith, G. H., Trans. Faladay Soc., 42B, 173 (1946). (7) McGee, C., thesis, Stanford University, 1947; Dept. of Commerce, OTS, PB 3885, 95 (1945). (8) Marsden, S. S.,Myaels, K. J., Smith, G. N.,snd Ross, S., Dept. of Commerce, OTS, PB 31900 (1946) I
(9) Mysels, K. J.,J . Colloid Sci., 2 , 375 (1947). (10) Mysels, IC. J., and McBa.in, J. W., J . P h y s . d Colloid Chem., 52, 1471 (194s). i l l ) Mysels, IC. J., Pomeroy, H. H., and Smith, G. ET.. Dept. of Commerce, OTS, PB 31898 (1946). (12) Shrei-e, G . S., J . Colloid Sci., 3, 259 (1948). (13) Shreve, G . S., Pomeroy, H. H., and Mysele, K . Colloid Chem., 51, 963 (1947). (14) Smith, G. H., Pomeroy, H. H., Mysels, K . J . , and McGee, C., J . d m . Chem. Soc., 70, 1053 (1948). (15) Stimson, H.L., Harpers, 194, 106 (1947). (16) Zentner, R . D., J . Phys. R. Colloid Chem., 51, 972 (!947), S t u d y conducted under c o n t r m t OEMsr-IO57 between Stanford University a n d t h e Office of Emergency Management. recommended by Division 11.3 of t h e S a t i o n a l Defener R c w a r r h Committee, and supervised by J~ W.hIcBain.
RECEIVED January 1 6 , 1948.
J
L. H, PERRY Union Buy S t u t e Chernical Company, Cambridge 4 2 , Muss.
S o m e tert-butyl peroxides have been found to be suitable catalysts for the solvent preparation of polyisoprene and the resinous copolymer of styrene-isoprene, In both systems these peroxides gave high yields and were superior to benzoyl peroxide. The polyisoprene shows promise of being useful as a replacement of natural rubber i n cheinical reactions. The resinous copolymer possesses the properties of a modified polystyrene.
T
HE purpose of this paper is t o describe the preparation of polyisoprene and of a resinous copolymer of styrene-isoprene
by polymerization in solvent, using organic peroxides derived from tert-butyl alcohol. Solvent or bulk polymerizations are ideally suited for the preparation of clear polymers free from impurities since the system rcquires no modifying agents other than the solvent medium. A serious problem, however, espe-
cially for diolefins, is the fact that such polymerrzatiur?s are verj~10~57, and fen-, if any, catalysts arc suitable. Attempts to accelerate the reaction by higher temperatures serve only to decompose the catalyst a t a faster rate than it can be efficiently used. Recent studies ( 5 ) shoaed that tert-butyl peroxides have the property of decomposing slonly a t temperatures up t o 150" C, Since the range 80' t o 150' C. is most favorable for pronioting rapid iolvent polymerization of diolefins, this research was started tc determine the value of several representative tert-butyl peroxides as catalysts in the preparation of the following twc polynicis. POLYI SOPRESE
The solvent polymerization of isoprene was studied to determine whether R polyisoprene, free from adulterants, could b E prepared. Previous polyisoprenes, which have been tested in
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July 1949
1439
,
BO
a W E
2a I
TERT-BUTYL HYDROPEROXlVE
LL
0 Q
J
w > -I w
z v
I
(L &I
a
20 80
so
100
110
0
Figure 1.
Effect of Temperature on Polymerization of Isoprene
48 hours, 50% toluene, 48% isoprene, and 2 % peroxide
~
chemical reactions such as cyclization, chlorination, and hydrochlorination, were prepared in emulsion and required milling, just as does natural rubber, to render them satisfactory ( I ) . An important purpose of this research was to prepare a polymer which could be used directly without milling and would contain little, if any, cross linking. Starting Materials. S e n p o r t Industries Inc. furnished the isoprene which was synthesized from turpentine. Immediately before use the isoprene was distilled to remove inhibitor and polymers. The freshly distilled material contained better than 95% conjugated double bonds (measured by maleic anhydride adduct) and had the following constants: n",O1.4210, d:E.,J 0.683. The following peroxides mere used without further purification: 60% tertbutyl hydroperdxide was a commercial grade containing approximately 60% tert-butyl hydroperoxide and 40% di-tert-butyl peroxide. tert-Butyl hydroperoxide was a specially prepared peroxide from which all di-tert-butyl peroxide had been removed; it contained 82% tert-butyl hydroperoxide, and the remainder was bdieved to be tert-butyl alcohol. Ditert-butyl peroxide, tert-butyl perbenzoate, and di-tert-butyl diperphthalate were commercial grade; benzoyl peroxide was C.P. grade. All solvents were technical grade and mere used without further treatment. Polymerization Procedure. The polymerizations were carried out on three different scales: (a)200-cc. bombs, ( b ) 3-gallon reactor, ( c ) 250-gallon reactor. The bombs were constructed of carbon steel, and the larger reactors of stainless steel. The procedure consisted in adding the ingredients to the reactor and heating the closed reactor a t a controlled temperature for a given time. The small bombs were cylindrical and had an inside diameter and depth of 2 and 4.5 inches, respectively. The bombs were sealed by bolted covers and were designed to withstand a pressure of 500 pounds per square inch. When desired, pressure gages could be attached t o the covers. The bombs were heated by immersion in a diethylene glycol bath thermostatically controlled within 1O C. The bath tempei ature, which corresponded closely t o that of the polymer~zingmixture, m-as used as the temperature of the reaction. The only time a t which these two temperatures differed appreciably was at the start of the reaction, when the exothermic nature of the polymerization raised the temperature of the reacting mixture 2' to 3 O C. above that of the bath for about 30 minutes. Before each run the bombs were carefully washed and scrubbed down to clean metal with steel wool. The polymerization ingredients were previously mixed in small bottles, then added to the bombs which were closed immediately. At the conclusion of polymerization, the bombs were cooled in tap
30
80
SO
PER CENT PEROXIDE CONSUMED
TEMPERATURE ."C.
Figure 2.
Relation betkeen Polymer Formed and Peroxide Consumed
Polymerization formula, pounds: isoprene, 900; carbon tetrachloride, 915; di-tert-butyl diperphthalate, 28. Total time 90 hours, temperature 100' C.
water for 15 minutes and opened and the contents transferred t o glass bottles. The procedure in the larger reactors was similar. Both reactors were heated by steam jackets and were equipped with slowmoving, paddle-blade stirrers to ensure even distribution of heat. The temperatures were controlled by adjusting the steam pressure. Testing of Polymers. The yield fiom a polymerization was calculated from the percentage of solids in the product solution. Approximately 0.5-gram samples were placed in weighing bottles which were heated in a vacuum oven for 3 hours a t 90" C., then the residue was weighed and calculated as polymer. The intrinsic viscosities were determined in benzene, at concentrations of less than 1% by weight, according to the method of Kraemer (a). To obtain solution free from foreign particles the polymer solution was diluted with carbon tetrachloride and filtered. The filtered solution was evaporated to dryness in a vacuum oven, the residue dissolved in benzene, and the viscosity measured at 25" C. Discussion of Results. The polymerization of isoprene wlth peroxides derived from tert-butyl alcohol was studied in carbon tetrachloride, in toluene, and without solvent. Depending on the various factors, 60 t o 90% yields of polyisoprene with intrinsic viscosities ranging from 0.15 to 0.70 were obtained. All of the tert-butyl peroxides gave comparable results and differed from one another only in degree. I n general there was a tendency for the di-tert-butyl peroxide to cause gelling most readily and tert-butyl hydroperoxide the least; the peresters were intermediate. This behavior was in direct reverse t o the comparative strengths of the peroxides as oxidizing agents. For example, iodine is readily oxidized by tert-butyl hydroperoxide but 1s unaffected by di-tert-butyl peroxide. Polymerizations in carbon tetrachloride with tert-butyl peroxides as catalysts gave high yields of low-molecular-weight
TABLEI. EFFECTO F PEROXIDES ON P O L Y M E R I Z d T I O K a O F ISOPRENE IN CARBON TETRACHLORIDE AND TOLUENE CC14 Soln. Toluene Soln. Yield, Intrinsic Yield, Intrinsic % % viscosity viscosity 607, tert-butyl hydroperoxide 73 0.18 68 0.39 tert-Butyl hydroperoxide 87 0.15 69 0.32 Di-tert-butyl peroxide 53 0.16 47 0.61 tert-Butyl perbenzoate 84 0.20 63 0.39 Di-tert-butyl diperphthalate 83 0.22 Insol. gel 42 0.29 Benzoyl peroxide 50 0.13 a I n 200-00. bombs by heating the following m i x.ture for 48 hours a t 100' C.: solvent SO%, isoprene 48.5%, and peroxide l.5Yo.
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
1440 100
20
80
90
Figure 3.
io
100
TEMPERATURE
,*C.
Effect of Temperature on Copolymerization of Styrene-Isoprene
Polymerization formula: styrene 31.570, isoprene 10.570, naphtha 56%, peroxide 2%; time 48 hours
100
a"
i
h
0.43
cc w a
70
I
60
0
0
------+ 3 :
zc
33
PER CENT CARBON TETRACHLORIDE IN FORMULA
Figure 4.
Effect of Carbon Tetrachloride on Copolymerization of Styrene-Isoprene Polymerization formula: styrene 36 7 ~isoprene . 12 Yo, carbon tetra-
chloride 0-30y0, naphtha 50.5-20.570, tert-butyl time 48 hours, temperature 100°
8.erbenzoate
Vol. 41, No. 7
The temperature of polymerizabion had a marked effect on the rate of reaction catalyzed by tert-butyl peroxides. Figure 1 shows typical results of a series run with tert-butyl hydroperoxide. On the other hand, polymerizations with benzoyl peroxide were affected only slightly by similar temperature changes. The benzoyl peroxide was undoubtedly decomposed so rapidly that it was used much less efficiently than the tmtbutyl hydroperoxide. If the temperature of the reaction mixture were lowered t,o permit slower decomposition, the benzoyl peroxide n-ould give better yields, but the act,ual building up of the chains n-ould be so slow as to make the process uneconomical. The intrinsic viscosities of polymers formed a t various temperatures differed only slightly. A large amount of peroxide amounting to 5 to 6%, based on polymer formed, was required in all t'he isoprene polymerizations. To s h d y the reason for this and to obtain an idea of the nature of polymerization, a series of samples was withdrawn periodically from a large scale polymerization. Examination of t,hese samples revealed that over the range 20 to 85% polymerization, the intrinsic viscosity varied only from 0.24 t o 0.27. Examination also showed t,hat a given amount of peroxide catalyzed the formation of a given amount of polymer during the ent,ire reaction (Figure 2 ) . Since t'he breakdown of each peroxide group was accompanied by polymerization of a given number of polymer chains during all stages of the reaction, it is believed that the peroxide was not wasted through side reactions. The 5 to 6% of catalyst was evidently required because of the low molecular weight of the polymer and the large number of chains that had t'o be init,iated. The polgisoprenes, prepared by solvent polymerization with tert-butyl peroxides, were clear, colorless mat,erials. They were readily soluble in carbon tetrachloride or toluene at concentrations as high as 50%, in contrast to m:lled natural rubber or commercially available, emulsion-prepared polyisoprene, which can only be used at very low concentrations. Furthermore the solutions of solvent-polymerized isoprene are exceptionally stable and may be stored indefinitely without effect, on the color or viscosity. For t,hese reasons these polyisoprenes should lend themselves readily to such chemical reactions as chlorination, cyclization, and hydrochlorination. COPQLY3IERIZhTIOS O F STYRESE-ISOPRENE
1.57~;
polyisoprene. Because of the strong modifying action of the solvent, there was little tendency for the polymers to gel. One drawback t o carbon tetrachloride was the fact that polymers prepared in it contained chlorine which split off relatively easily during subsequent use of the products. Table I lists typical results of polymerizations catalyzed by tert-butyl peroxides and benzoyl peroxide. Table I includes a similar series of results obtained with toluene as solvent; here the controlling action of the solvent was one of dilution alone. As a result the intrinsic viscosities were higher and the poly-merizations had to be stopped sooner t o prevent gelation. A third series was run in the absence of solvent and produced polyisoprenes with intrinsic viscosities as high as 0.70 when 60% tert-butyl hydroperoxide or tert-butyl perbenzoate was used. The nonsolvent polymerizations were much more rapid than those modified by solvents, and only 24 houra was required for a 6574 conversion a t 100" C. Beyond this point insoluble gels Lwre formed. The nonsolvent polymerizations were difficult t o control, and reacions that vere carried out under similar conditions gave soluble polyisoprenes ranging in intrinsic viscositv from 0.30 t o 0.65 as well as gels. The pressure of these polymerizations ranged from 80 pourlds per square inch at the stai t to 35 at the end.
Resinous polymers were prepared which consist of an approximate mole ra.tio of 2 parts styrene to 1 isoprene. These resins, like the soluble polymers just described, have relatively low molec-. ular weights and are free of cross linking. For the most part the procedures and starting materials were identical t o those already described. I n addition to the chemicals previously listed, the folloxing were used: Styrene 3 - 9 9 from Dow Chemical Company was freshly distilled just prior to use. The naphtha was . h s c o tcxtile spirits (boiling from 63' t o 93' C.) obtainect from American Mineral Spirits Company. Yields and intrinsic viscosities were calculated and the resin solutions mere taken doim to dryness and the melting points: determined. The capillary method was used, and the melting point vas taken as that temperature a t which the findy powdered resin started to coalesce.
TABLE 11. EFFECT OF
P E R O X I D E S O N ~ O P O L Y M E R I Z A T I O NOF ~
STYRESE-ISOPRENE Yield,
Intrinsic Viscosity 98 0.13 60% tert-butyl hydroperoxide 98 0.12 tert-Butyl hydroperoxide 99 0.33 Di-tert-Bu t yl peroxide 94 0.13 tert-Butyl perbenzoate 51 0.18 Benzoyl peroxide a I n 200-cc. "bombs by heating t h e following mixture Sor 48 hours at 120° C.: styrene 31.5'%, isoprene 10.5%, naphtha 56%, peroxide 2 % . CI /o
July 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
tert-Butyl peroxides were satisfactory catalysts for the preparations of resins by the copolymerization in solvent of styrene and Ssoprene. By proper adjustment of the various factors, it was possible t o prepare clear, colorless polymers in 100% yields. AB indicated by the ready solubility of these resins, little if any cross linking was encountered by carrying the polymerizations t o completion. In general, the polymerizakions were analogous t o those using isoprene alone. All of the tert-butyl peroxides promoted the polymerizations and were superior t o benzoyl peroxide (Table 11). The effect of temperature was also similar, both with the tert-butyl peroxides and with benzoyl peroxide (Figure 3). The intrinsic viscosities were similar to those found with isoprene alone but tended t o be affected to a greater degree. Unlike the solvent polymerization of isoprene, these resinous copolymers could be prepared in high yields without a modifying eolvent such as carbon tetrachloride. Benzene, toluene, or naphtha was used t o produce better than 95% yields of resins that were almost identical. Carbon tetrachloride, in addition t o reducing the size of the polymer, had a curious effect on the yield, in t h a t small amounts tended to retard the reaction and then promote i t as the amount was increased (Figure 4). Again, carbon tetrachloride was not a desirable solvent since i t left reactive chlorine in the resin. B y varying the ratio of styrene t o isoprene, the chemical makeup and physical properties of the resin could be altered over a considerable range. Below a mole ratio of 1.4 parts of styrene to 1 of isoprene, t h e nature of isoprene predominated and the polymer became rubbery. I n the other direction, as the styrene content was increased, the resin approached the properties of polystyrene. As the isoprene content was increased, the melting point dropped and the intrinsic viscosity rose (Figure 5). During preparation of these resinous copolymers, the exothermic nature of the reaction was so slight that constant heat could be applied throughout the polymerization. Thus in a typical run in the 5-gallon reactor, the temperature of the reactants rose only 2 ” C. above normal for 30 minutes after the start of reaction, while a constant steam pressure was maintained in the jacket. Another indication of the ease of control is apparent from Figure 6 which shows t h a t the resin, once formed, is unchanged by polymerization conditions. Therefore the time of polymerization is not critical, except t h a t i t should be sufficient to consume all monomers. The hydrocarbon resins produced by this method act, in general, like modified polystyrenes and show promise of finding use in rubber, textile, and coating industries. The resins are soluble in aliphatic and aromatic hydrocarbons, chlorinated solvents, esters, and ketones except acetone. Films of the resin possess good adhesion and are moderately flexible even without addition of plasticizers.
0 MELTING PONT 0 INTRiNSlC VISCOSITY
60
MOLES OF STYRENE PER MOLE OF I S O P R E N E
Figure 5.
Effect of Styrene-Isoprene Ratio on Resin
Polymerization formula: monomers 42 Yo, naphtha 56 %, tertbutyl perbenzoate 2%; time 48 hours, temperature 100’ C.
loo
t
P E R CENT YIELD
c z eo w
u
*
O
F
* O t
I
I TIME ,HOURS
Figure 6.
Effect of Extended Heating on Intrinsic Viscosity of Resin
Polymerization run at 130’ C. on 31.5% styrene, 10.5% isoprene, 52.5% naphtha, 3 % benzene, and 2.5% tert-butyl hydroperoxide
tions offered during this work. H e is grat,eful t o J. W. Battle who efficiently assisted during this research and t o Union Bay St’ateChemical Company for permission t o publish these results. LITERATURE CITED
ACKNOWLEDGMENT
(1) D’Ianni, J. D., Naples, F. J . , Marsh, J. W., and Zarney, J. L. IND.ENG.CHEM.,38, 1171 (1946). (2) Kraemer, E. O., Ibid., 30,1200 (1938) (3) Milas, N. A , , and Surgenor, D. M., J. Am. Chem. Soc., 68, 205, 643 (1946); Milas, N. ii., and Perry, L. H., Ibid., 68, 1938
The author wishes t o thank Newport Industries Inc. for the uee of certain of its facilities and for the many valuable sugges-
(1946). RECE!YED April 28, 1948. Presented before t h e Division of Rubber Chemist r y a t the 113th Meeting of the AMERICAN CHEMICAL SOCIETY, Chioago, Ill.
Forty years ago [J.Im. ENG.CHEX., 1, 263 (1909)j the Bureau of Soils of the Department of Agriculture (in connection with a hearing before U. S. House of Representatives) conducted a survey to determine whether the following tenets of soil fertility (prescribed by the bureau) were being taught in agricultural colleges: 1. “That all soils contain enough mineral plant food in available form for maximum crops. . . . 2. T h a t the real cause of infertility is the accumulation in the soil of poisonous excreta from plant roots. 3. T h a t it is not ever necessary t o add fertilizers for the purpose of increasing the plant food in the soil. , , 4. T h a t soil fertility can be maintained indefinitely by practicing a system of [crop] rotation. . ,” The survey showed t h a t only two of 104 representatives of colleges endorsed the views of the bureau without qualification. About 50% recognized t h a t there might be some truth in the doctrines worthy of discussion; t h e other 50% indicated either t h a t they would not teach these views or t h a t they were strongly opposed t o them. Today’s thinking confirms the trend suggested by the results of the survey. , , (see pages 1314-1337).
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