Emulsion Polymerization of Myrcene J
d
A . J. JOHANSON, F. L. MCKESNON, AND L. A. GOLDBLATT A-acal Stores Research Division, Bureau of Agricultural and Industrial C h e m i s t r y , L-nited States Department oJ Agriculture, New Orleans, La.
A series of synthetic rubbers was prepared by the emulsion polymerization and copolymerization of myrcene, 2-methyl-6-methylene-2,7-octadiene,derived from turpentine. The polymers and copolymers, all of which were relatively soft, were compounded, milled, and vulcanized, and the vulcanizates were tested for tensile strength and elongation. The polymers obtained from myrcene alone were low in tensile strength and elongation. The copolymers prepared from myrcene and styrene had relatively low tensile strength, generally less than 1200 pounds per square inch, but had ultimate elongations ranging up to 1100%. Tercopolymers prepared from myrcene and styrene with butadiene possessed much higher tensile strengths, ranging up to about 2300 pounds per square inch, and had elongations ranging up to 500%.
A
S ONE phase of a wartime investigation to determine the possibility of producing synthetic rubbers from turpentine derivatives, the emulsion polymerization and copolymerization of myrcene derived from turpentine have been studied. A process had been previously developed ( d ) for the production of myrcene, 2-methyl-6-methylene-2,7-octadiene, in good yield, by the vapor-phase thermal isomerization of @-pinene,one of the major components of gum turpentine, according to the equation:
400" C.
___c
H @-Pinene
Me-
/I
C--Me
Myrcene
Myrcene possesses the conjugated diolefinic structure characteristic of isoprene which polymerizes and copolymerizes to form rubberlike products of high molecular weight. Myrcene tends to undergo polymerization thermally during its separation by fractional distillation from the. accompanying close-boiling terpene impurities. This results in considerable loss by polymerization a h e n grades are prepared with a purity above about 97%. In the present study, samples of myrcene, typically of 96% purity, prepared by the previously developed process, were subjected to emulsion polymerization and copolymerization. The products obtained were compounded, milled, and vulcanized, and the vulcanizates were then tested for tensile strength and elongation. The variables involved in the preparation and evaluation of the products included monomer ratio, kind and quantity of catalyst, quantity of modifier, kind and quantity of emulsifying agent, and time and temperature of the polymerizations.
TYPIC4L POLYMERIZATION FORJIUW
Three series of polymerizations are reported: (1) with myrccne alone, (2) with myrcene and styrene, and (3) with myrcene, styrene, and a third monomer, butadiene. The following formula is typical: 100 parts of monomers, 180 parts of water, 5 parts of soap, 0.3 part of potassium persulfate, and 0.15 part of dodecyl mercaptan (dodecanethiol). The polymerization time in these experiments ranged from 16 to 28 hours, and two temperaturcb were used, 50' or 60 a C. POLYMERIZATION PROCEDURE
The polymerizations were carried out on a 10-gram scale essentially according to the method of Fryling (1). With this method, the extent of polymerization can be roughlyfollowed by observing, a t intervals, the decrease in meniscus height of the contents.of the tube. The decrease when myrcene is used is about 1 mm. for each 147, of hydrocarbon conversion as compared t o about 1 mm. for each 673 conversion when butadiene is used. The various ingredients were added to the carefully cleaned polymerization tubes in the following order: soap solution, catalyst, freshly distilled monomer (or monomers) with the desired amount of modifier dissolved in the myrcene. Each tube was then sealed with a hand blowtorch. When all the tubes of a given run had been thus charged and sealed, they were placed in a water bath t o bring the contents t o the desired reaction temperature, the meniscus heights were measured, and the tubes were rotated end over end at that temperature in an air bath for the desired length of time. In order t o stop the polymerization a t the end of the period, a small amount of hydroquinone (0.005 to 0.02 gram, depending upon the amount of catalyst used) was added as a 1% aqueous solution t o the finished latex in each tube. The latex was then transferred to a flask, diluted with water, and steam-distilled to remove unreacted monomers. An alcoholic solution of phenyl@-naphthylamine sufficient t o provide about 2% concentration of the amine in the dry polymer was added as an antioxidant. The latex was coagulated with sodium chloride and dilute sulfuric acid, added u ith vigorous stirring. The coagulated polymer was washed with distilled water and dried t o constant weight a t 50' to 60' C. in a vacuum oven, and the yield was determined. CORIPOUNDING, RIILLIR'G, VULCANIZING, AND TESTING PROCEDURES
Eight grams of the dried finished polymers were then compounded, milled, vulcanized, and tested for tensile strength and per cent elongation. In compounding, two formulas were used. Formula I consisted of 100 parts of polymer, 50 parts of carbon (Kosmobile 77, an easy processing channel black), 5.0 parts of zinc oxide, 1.50 parts of sulfur, 1.00 part of Thiotax (2-mercaptobenzothiazole), and 0.25 part of diphenyl guanidine. Formula I1 consisted of 100 parts of polymer, 50 parts of Kosmobile 77, 5.0 parts of zinc oxide, 2.0 parts of sulfur, and 1.5 parts of Thiotax. The polymers were soft and, therefore, no softening agent was added.
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TABLE I. COPOLYMERIZATION OF MYRCENE A N D STYRENE USINGVARYING AMOUNTS OF
Catalyst Potassium Persulfate, Gram
CATALYST WITH
Modifier Dodecyl Mercaptan, Gram
A N D WITHOUT
Yield,
Curing Time, Min.
MODIFIER"
Tensile Ultimate Strength, Elongation, Shore Lb./Sq. In. % Hardness 1000 450 57
from the tensile strips and measuring hardness with a Shore durometer. DISCUSSION OF RESULTS
The results showed that myrcene NO. % with or without other monomers poly0.03 0.0 84.9 30 475 54 0.03 0.015 86.5 40 1035 merizes to form soft rubberlike prod88.1 0.06 0.0 500 53 30 1135 ucts. 0,015 90.7 360 56 0.06 40 1050 0.12 89.3 425 56 0.0 1135 60 When myrcene was polymerized alone, 0.12 0.015 87.7 475 52 900 40 . 0.24 0.0 91.5 325 56 1135 80 the products obtained were unusually soft and the vulcanizates were low in 5 7.5 grams of 96% myrcene, 2.5 grams of styrene 18 ml. of water 0.5gram of Ivory soap, polymerized 24 hours a t 60° C. Polymers compounded accord& t o Formula I ' a n d cured at 260° F. tensile strength and elongation. A typical yield after 24 hours a t 60 O C. was 78.5% of hydrocarbon polymer, which, TABLE 11. COPOLYMERIZATION OB MYRCENE AND STYRENE WITH BENZOYL PEROXIDE AS CATALYST" when compounded and vulcanized, gave C a t a1ys t a tensile strength of 600 pounds per Benzoyl Time of Curing Tensile Ultimate square inch and an ultimate elongation Peroxide, Polymerization, Yield, Time, Strength, Elongation, Shore KO. Gram Hours % Min. Lb./Sq. In. % Hardness of 30070, The milling characteristics 1 0.03 16 53.0 15 . 920 700 43 were poor. 2 0.03 28 64.8 15 930 600 47 3 0.06 28 73.5 15 1140 700 44 Somewhat better products were ob-' tained when myrcene was copolya 7 5 grams of 96% myrcene 2.5 grams of styrene, 18 ml. of water, 0.5 gram of sodium stearate, 0.015 gram of dodecyl mercaptan, polymerized a t 60" C. Polymers compounded according to Formula merized with styrene, as shown by I1 and cured a t 280' F. the data in Table I. Increasing the amount of catalyst increased the yield , somewhat, but the addition of a modiAll ingredients were weighed to an accuracy of 0.25%. In prefier (dodecyl mercaptan) had no significant effect on liminary work Formula I was used with a curing temperature of yield. Neither the quantity of catalyst nor the use of modifier 260' F. , Substantially the same results were obtained with Forsignificantly affected the physical properties of the commula I1 and a curing temperature of 280 o F., which more nearly pounded and vulcanized polymers. The yields ranged from simulates the vulcanizing conditions used for GR-S tread stock. 84.9 to 91.5%; tensile strengths were typically about 1000 The compounded mixtures were cured for various periods of time, pounds per square inch; and the elongations were generally over but only the times leading t o the best results are reported in the 400%. tables. The best compounding formula and optimum curing Other copolymerizations of myrcene and styrene showed that conditions were not determined. addition of dodecyl mercaptan in excess of 0.02 gram produced The %gram batches were mixed on a special mill with rolls 4 materially softer polymers which were difficult to mill. Varying inches in diameter, the distances between the guides being 1 the soap-Le., using Ivory soap, S.F.flakes, pure sodium stearinch (2.5 em.) in all cases. Speeds of the front and back rolls ate, or potassium stearate-or varying the p H of the soap soluwere 10 and 15.2 r.p.m., respectively. The milling was carried tions between 8.5 and 11.5 had no significant effect on the yield out a t atmospheric temperature. During the first 5 minutes or properties of the products. Substitution of myrcene of 99% all the chemicals were added to the rubber in the following order: purity for myrcene of 96% purity increased the rate of polymerisulfur, Thiotax, zinc oxide, and carbon black. The samples were zation somewhat, but did not improve tensile strength nor elongathen milled for an additional 7 minutes to disperse the chemicals and finally sheeted 5 times with an opening of 0.011 TABLE 111. COPOLYMERIZATION O F MYRCENE A S D STYREVE WITH T7ARI4TION I N inch between the rolls. While there is MONOMER RATIO" some doubt as to the degree of dispersion of compounding ingredients in these soft Monomers Curing Tensile Ultimate Myrcene, Styrene, Yield, Time, Strength, Elongation, Shore samples, it was at least possible in most No. grams grams % Min. Lb /Sq. I n % ' Hardness cases to obtain a pheet that was smooth 40 965 175 62 0 5 80 4 1 9 5 40 930 300 53 83 1 2 9 0 10 and shiny. 300 52 84 0 40 780 3 8 5 15 The cures were made in a specially con40 890 350 52 83 1 4 8 0 * 2 0 475 54 83 3 40 1000 5 7 5 2 5 structed mold to produce vulcanizates 3 85 4 40 1030 575 50 6 7 0 3 0 600 54 85 8 40 925 7 6 5 3 5 inches long, 0.625 inch wide, and 0.030 575 58 85 1 40 925 4 0 8 6 0 inch thick. The mold consisted of three a 18 ml. of water, 0 5 gram of sodium stearate 0 06 gram of potassium persulfate, 0 015 gram of separate 6 X 6 inch pieces: two polished dodecyl mercaptan, polymerized 22 hours a t 50° C. Polymers compounded according t o Formula I and cured a t 260' F. stainless steel outer plates and a thinner center plate with three rectangular openings. Ten vulcanizates . were obtained TABLE Iv. COPOLYMERIZATION O F RfYRCEYE AND STYRENE WITH BUTADIENE* from each &gram batch. Time of The stress-strain measurements were Monomers Po!yUltimate ButamerizaCuring Tensile Elongamade on a standard Scott tensile tester. Myrcene, Styrene, diene, tion, Yield, Time, Strength, tion, Shore For cutting the small tensile strips a No. grams grams grams Hours % Min. Lb./Sq. In. % Hardness special dumbbell with a 0.125-inch 90 2370 400 69 16 90.1 1 0.1 2.5 7.4 375 63 18 88.3 90 2470 2 0.5 2.5 7.0 narrow section was used. Although 75 2070 425 63 18 89.2 3 1.0 2.5 6.5 75 2590 400 62 6.0 18 87.8 4 1.5 2.5 there was not enough raw polymer to 75 2270 500 61 18 86.3 5 2.5 2.5 5.0 make a standard vulcanized block for a 18 ml. of water, 0.5 gram of sodium stearate, 0.03 gram of potassium persulfate, 0.05 gram of dodetermination of hardness, a n approxidecyl mercaptan, polymerized a t 50° c. Polymers compounded according to Formula I1 and cured a t mate figure was obtained by stacking 280° F. up the pieces of vulcanizates remaining I
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tion of the vulcanizates. Data given in Table I1 show that the substitution of benzoyl peroxide for potassium persulfate as catalyst greatly decreased the polymerization rate, had no significant effect on the tensile strength, but markedly increased the elongation of the vulcanizates. An elongation of as much as 1100% was obtained on an undercure of sample 1. Varying the ratio of myrcene to styrene between the limits of 95% myrcene to 5 7 , styiene and 60% myrcene to 40y0 styrene did not greatly alter tensile strength, as shown by the data in Table 111. With increased styrene content, however, there was a slight tendency toward increased yield and a greater tendency toiyard increased elongation. The copolymers also tended to become harder and tougher with inci ease in styrene content. llyrcene was also found to copolymerize readily with substituted styrenes such as a-methylstyrene and &chlorostyrene. Hon ever, the products showed but little superiority in tensile strength and elongation over the niyrcene-styrene copolymers. Distinctly better products mere obtained when myrcene and
styrene were copolymerized with butadiene as a third component (Table IV). Variation in the myrcene content from 1 to 25% did not greatly alter either the yield or the physical properties of the vulcanizates. In each case the tensile strength was in excess of 2000 pounds per square inch with an elongation of approximately 4007,. ACKYOWLEDGMERT
The authors wish to acknowledge the assistance of Dorothy
RI. Oldroyd in the purification of the myrcene used, of Barbara E. Hillery in the polymerization work, and of Elsie T. Field in the compounding and physical testing of the polymers. LITERiTURE CITED
(1) Fryling. C . F., ISD. ESG. CHEM.,AXAL.ED.,16, 1-4 (1944). (2) Goldblatt, L A.. arid Palkin, S.,J . Am. Chem. Soc., 63, 3517-22 (1941). RECEIVED February 27, 1 9 4 i
Production of 2-Methylfuran by VaporPhase Hy rsgenation of Furfural E,. W. BURNETTE', I. B. JOHSS2, R . E'. HOLDRES3, AND R. R.I. HIXOS Iowa State College, A m e s , Iowa
Twenty-three catalysts and catalyst carriers have been studied for the production of 2-methylfuran by vaporphase hydrogenation of furfural. Copper chromite dispersed on activated charcoal has been found to he the most efficient catalyst for the hydrogenation. The reaction is conducted at a hydrogen pressure of 1 atmosphere and a temperature of 200-230" C. In the laboratory, 90-95% yields of 2-methylfuran were obtained in one pass of furfural through the catalyst at a rate of 20-30 grams per hour. Yields and catalyst life were somewhat lower in a large unit designed for 1 pound of furfural per hour.
T
HE preparation of 1,3-pentadiene was undertaken in this laboratory in 1942 when the impending natural rubbei shortage directed research toward the finding of a satisfactory substitute. The large s u p p l ~of furfural potentially available made this chemical attractive as a starting material (I). 81though other paths are possible, the following three steps were considered the most direct and feasible:
HC-CH 11
HC bCHO
Y
2H2
HC-CH
'
Cu-Cr HC
I
CCH,
Y
2H2
HZC-CHz
Ni
H2L hHCHa
+
Y
HiC=CHCH=CHCHa
-1
-HzO
I +J
Guinot ( 5 ) has patented a process which covers essentially the reactions outlined, but the claims, particularly of the last t a o steps, were not substantiated in this laboratory. The project was discontinued after the first two steps had been norked out on a laboratory scale because it was then apparent i
2 8
that the over-all process naa impractical as a source for rubber. However, the results of the investigation indicated that it might be possible to produce methvlfuian successfully on a large scale. The purpose of this paper is to report data on the catalytic hydrogenation procedure that was used. The primary object of almost all previous work on the hydrogenation of furfural has been the production of furfuiyl or tetrahydrofurfuryl alcohol. Many of the previous M orkers have reported the simultaneous formation of methylfuran, but in only a few cases has the amount formed been of any consequence (9, 1 2 ) . In two instances methylfuran has been sought as the sole product of the hydrogenation ( 5 , I O ) . Thermochemical data indicate that the hydrogenation proceeds with the evolution of a considerable quantity of heat. I n practice the reaction s a s found to be so exothermic that care had to be taken to prevent inactivation of the catalyst. The heat of reaction in the liquid phase at 25" C. was found as follows: The heat of formation of furfural used is the value given by Landrieu et al. (8). These investigators showed that the heat of combustion of furan derivatives is about 284 kg.-cal. per mole lower than the corresponding benbene compounds. Using this figure and the heat of combustion of toluene, from the International Critical Tables ( 7 ) ,the heat of formation of methylfuran was calculated to be 27.0 kg.-cal. per mole. The heat of reaction is then:
Present address, General Aniline and Film Corporation, Easton, Pa. Present address, Monsanto Chemical Company, Dagton 7, Ohio. Present address, Tulane University. New Orleans 1.5, La
Products Methylfuran ( 1 ) Water ( 1 )
Heat of Formation, Kg.-Cal./Mole -27.0
. -68.4
-Q.5 4. _.
Reactant Furfural ( 1 )
-49.2
Heat of reaction
--46.2
At 25" C. the heat of reaction in the g& phase is found to be -35.2 kg.-cal. per mole from the following molar latent heats: water 10,500 calories: methylfuran 8800; and furfural 10,300.
