I -
d
soprene A. J. JOHANSON AND IL. A. GOLDBLATT hruvu2 Stores Research Diaision, Bureau of Agricultural und Industrial Chemistry, Kew Orleans, Lu.
T h e emulsion copolymerization of isoprene, obtained from terpenes, with styrene was investigated. The CQpolymers prepared were evaluated in terms of yield (per cent hydrocarbon conversion), soIubility in benzene, and viscosity in dilute benzene solution. The effects of two catalysts, potassium persulfate and benzoyl peroxide, and of a series of six normal and four tertiary mercaptan (thiol) modifiers in varying amounts were studied. Details of technique and procedure are given. With a fixed amount of potassium persulfate, as catalyst, variation in the amount of each mercaptan used markedly affected the solubility and viscosity and in some cases also the yield of the products. With benzoyl peroxide as catalyst variation in the amount of mercaptan, as well as the ratio of mercaptan to catalyst, affected the solubility, viscosity, and yield. With certain combinations of kind and quantity of modifier and catalyst, copolymers possessing a high degree of solubility and high inherent viscosity could be prepared in good yield.
HE production of synthetic elastomers from isoprene, the fundamental unit of natural rubber, has been the object of numerous investigations (1). The Baruch Committee stated in 194": "If isoprene could be manufactured readily, it might well be the best raw material for the manufacture of a synthetic rubber" (2). Isoprene was prepared on a commercial scale from turpentine during the war (10) and was also produced from petroleum (11). The Naval Stores Research Division has developed a process (6)for the production of isoprene from dipentene, which in turn is readily obtainable from turpentine components. This paper reports the results of an investigation of the emulsion copolymerization of isoprene with styrene to produce synthetic elastomers, by the use of two different types of catalyst, potassium persulfate and benzoyl peroxide, u ith one or another of various normal and tertiary mercaptans (thiols) as polymerization modifiers. POLYMERIZATION PROCEDURE
The composition of the polymerization mixture was similar to that used for GR-S production as reported by Craig (4), except that Craig used butadiene rather than isoprene: Monomers (isoprene f styrene) Emulsifying agent (2.6% soap solution)
Modifier (normal or tertiary mercaptan) C a t a l y s t (potassium persulfate or benzoyl peroxide) T e m p e r a t u r e of polymerization T i m e of polymerization
tive index was talcen as a guide to purity. liti'i fractionation, thc isoprene was stabilized nith p , tert-butylcatechol, and stored in a refrigerator a t 3' C. To remove the inhibitor, the required amount of isoprene was redistilled immediately before each pol3 merization run. The styrene used was the Eastman product stabilized with p , tert-butylcatechol, and before each polymerization run the required amount of styrene was distilled under reduced pressure. The soap was a commercial grade designated as S. I?. flakes, and prior to each run a fresh 2.5% solution was prepared. The potassium persulfate was a C.P. grade, and the benzoyl peroxide was the Eastman product. The various mercaptans were commercial grades of known purity, and included: n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, tert-octyl, tert-dodecyl, tert-tetradecyl, and tert-hexadecyl. Preliminary work was carried out by the Fryling sealed tube technique (8) in an air bath maintained a t 50.0" * 0.5" C. This preliminary work provided considerable information. It was found, for example, that the yield of copolymer was affected by the presence of oxygen, by the amount of benzoyl peroxide used, by the ratio of mercaptan t o peroxide, and by the purity of the isoprene. The polymerizations reported were carried out with 20-gram portions of monomers in 4-ounce screw-cap bottles in a water bath maintained at 50.0' * 0.1" C. For each poiymerization, aftcr addition of the soap solution, catalysts, and freshly distilled styrene in which the desired kind and amount of mercaptan had been dissolved, the bottle wag placed upon the pan of a sensitive triple beam balance and weighed to 0.01 gram. Approximately 1.0 gram more than the required amount of freshly distilled isoprene x-as then weighed into the bot,tle. The evaporation of this extra isoprene by gently warming with an infrared lamp, requiring about 2 minutes, automatically displaced the residual air from the bottle. When the required weight was again reached the bottle was quickly capped. Leakage of isoprene vapor n-as prevented by lining the cap with a neoprene gasket which had been extracted with acetone and covered with a layer of tin foil. The bottles were then placed in individual wire containers, attached to a shaft i n the constant temperature bath, and rotated end over end at 36 r.p.m. for the desired length of time. They were thcn cooled in ice water and 2 ml. of a 1% aqueous solution of hydroquinone were added to cach to prevent further reaction. The latex thus obtained was transferred to a flask; diluted vith water to about 1 2 7 , solids; and after addition of 0.32 gram of phenyl-P-naphthylamine (in 670 alcoholic solution) as an antioxidant, was subjected to steam distillation to remove unreacted monomers. The diluted monomer-free latex was coagulated with sodium chloride solution and very dilute sulfuric acid added
100 pal t s 200 p a i t s 0.025 t o 0.70 p a i t 0.10 t o 0.70 p a r t 50' C. 12 t o 18 hours
The isoprene used throughout the investigation was derived from terpenes and was either prepared in this laboratory from dipentene (limonene )or obtained from a commercial source. I n all the polymerizations reported, the isoprene used had a purity of 99 to 99.5%. The commercial product, which was about 95% pure, contained considerable formaldehyde and some polymerization inhibitor. This product was washed thoroughly with water to remove the formaldehyde and was then dried with sodium sulfate and fractionally distilled with high reflux ratio at atmospheric pressure through efficient fractionating columns, and the refrac-
Evaporating Excess Isoprene from Polymerization Bottles
2086
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
Interior of Constant Temperature Water Bath Showing Method of Attaching Bottles to Shaft
with vigorous stirring. The coagulated copolymer was washed thoroughly with distilled water, and dried t o constant weight in a vacuum oven at about 50 O C. EVALUATION OF THE COPOLYMERS
The copolymers were evaluated in terms of yield (per cent of hydrocarbon conversion), solubility in benzene, and viscosity, with maximum values as the desiderata. The yield was calculated by subtracting from the weight of the dry product the sum of the weight of the antioxidant used and the calculated weight of the fatty acid obtainable from the soap used. Solubility determinations were made as follows: To an accurately weighed 2.5-gram portion of the copolymer in a 250-ml. ground-glass-stoppered flask were added 200 ml. of benzene. The flask was stoppered, and the contents were allowed to stand a t room temperature for 48 hours in the dark with occasional gentle swirling. The liquid was then filtered through cotton or, when necessary, through cheesecloth before being filtered through cotton. A 10-ml. portion of the filtrate was pipetted into a tared glass evaporating dish and evaporated to constant weight in a current of air a t a temperature of 70“ t o 80”C. The viscosities of dilute benzene solutions containing approximately 0.1 gram of polymer per 100 ml. of solution were measured at 20.0’ * 0.1 C. by means of viscometers of the Ostwald type as modified by Zeitfuchs (13). The technique employed was essentially that described by Croxton (6) except that a thermostatically controlled water bath was used t o maintain the temperature.
2087
constant while the amount of mercaptan was varied in polymerizations run for different periods of time. Of the six normal mercaptans studied as polymerization modifiers, with potassium persulfate as catalyst, the dodecyl dnd tetradecyl mercaptans gave the best results. Viscosity and solubility data from the runs made with ndodecyl mercaptan as modifier for three different periods of time (12, 14, and 16 hours) are shown in Figure 1. The viscosity values of the copolymers from the 12-hour and 14-hour runs were found to be relatively low a t the lowest level of mercaptan, to rise rapidly t o a maximum with increase in mercaptan, and then gradually decrease. The tendency to rise t o a maximum and then decrease was also true of the products from the 16-hour run. The highest values were obtained on samples polymerized for 12 hours. The benzene solubility of the copolymers was high except for those prepared with the smallest quantity of mercaptan. Within the ranges studied the amount of mercaptan had substantially no effect on the yield of copolymers obtained. The yields averaged 73.1% after 12 hours, 80.3% after 14 hours, and 85.0% after 16 hours. In Figure 2 is shown the effect of varying the amount of ntetradecyl mercaptan as modifier with constant amounts of potassium persulfate and other ingredients in polymerizations run for 14 hours. Results were generally similar t o those obtained with the n-dodecyl mercaptan. The viscosity was very low a t the lowest mercaptan level but increased, with increasing mercaptan content, to a maximum and then decreased slightly. The solubility was very low at the lowest mercaptan levels but increased t o about 99% a t the higher levels. Variation in mercaptan level had no significant effect upon the yields, which averaged 78.7% after 14 hours in comparison with an average yield of 80.3% obtained with n-dodecyl mercaptan. Results obtained with the n-octyl and n-decyl mercaptans are given in Table I. The yields were all very low. Variation in quantity of the n-decyl mercaptan, as with the dodecyl and tetradecyl mercaptans, had no significant effect on the yield.
O
The viscosity function (lnqr/c), where ?r is equal to the viscosity of the solution relative t o that of the solvent, and where cis the concentration (grams of solute per 100 ml. of solution), was taken in conjunction with the solubility as an index of the average molecular weight and chain length (7, 9). [Cragg ( 3 ) has proposed the term “inherent viscosity” for the quantity (InqJc), which is usually very nearly but not quite the same as the intrinsic viscosity, lim[ (lnqr)/c] .]
\-I4
I2 H O U R S 14 H O U R S IOHOVRS
c+o
The importance of size and length of the chain molecules and of their solubility on the behavior of polymers is generally recognized. As pointed out by Fuller (9): “The length of the molecules which are present in a polymer is of critical importance t o certain properties such as mechanical strength. . . .netted [cross-linked] chain molecule systems are invariably insoluble.” RESULTS WITH POTASSIUM PERSULFATE A S CATALYST
NORMAL MERCAPTANS.I n this group the quantities of isoprene, styrene, soap solution, and potassium persulfate were held
0 0 Cl 0 X X
SOLUBILITY
0.02
HOURS
-
VISCOSITY
____
0.03
0.04
0.03
0.00
5 - DODECYL MERCAPTAN, ( C R A M S )
Figure 1. Effect of n-Dodecyl Mercaptan as Modifier with Potassium Persulfate as Catalyst 15.0 grama of isoprene, 5.0 grams of styrene, 48.8 ml. of 2.5% aoap solution, 0.86 gram of potarsium persulfate
2088
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE
I. EFFECTOF
n-OCTYL AND 12-DECYL hIBRCAPTANS AS MODIFIERSWITH POTASSIUM PERSULFATE AS CATALYST^
Nu.
Modifier n-Octyl n-Decyl mercaptan, mercaptan. gram gram
.. ..
Yield,
%
Viscosity (lnvr/c)
Solubility, (in Benzene),
%
2.18 100.0 2.13 100.0 2 2.09 100.0 a 2.44 99.0 % 2.56 99.1 5 6 0:02 2.96 99.4 7 0.04 2.45 100,o 8 0.06 2.05 100.0 5 15.0 grams isoprene, 5.0 grams styrene, 40.0 ml. 2.5% soap Bolution, 0.06 gram KzSzOe, polymerized 14 hours. L
0.02 0.04 0.06 0.08 0.10
.. ..
.. .. ..
42.1 65.4 49.7 55.8 58.2 53.6 53.3 53.5
AND Y LTZ-OCTADECYL MERTABLE 11. EFFECTOF ~ - H E X A D E C CAPTANS AS MODIFIERS WITH POTASSIUM PERSULFATE AS CATALYST'
Modifier n-Hexan-OotaPolymeridecyl mer- decyl merzation captan, captan, Time, gram gram Hours
L -
Yield,
Viscosity (Inw/c)
No. % 1 0.06 12 69.8 2 0.06 14 77.7 3 0:06 14 75.5 U 15.0 grams isoprene, 5.0 grams styrene, 40.0 ml. 0.06 gram KzSz08.
..
..
~
Solubility (in Benzene),
0.82 0.77 0.76 2.5% soap
% 17.5 12.4 16.1
solution,
TABLE111. EFFECTOF tert-OcTYL MERCAPTAN AS MODIFIER WITH POTASSIUM PERSULFATE AS CATALYST" Modifier, tert-Octyl Mercaptan, 80. Gram
0.02 0.04 a 15.0 g r a m gram KzSzOs.
Yield,
%
Viscosity (lnvr/c)
14 66.7 14 69.9 14 71.6 14 74.1 14 76.3 69.2 16 16 70.6 16 73.6 16 75.8 isoprene, 5.0 grams styrene, 40 ml.
0.005 0.01 0.02 0.04 0.06 0.005 0.01
Polymerization Time, Hours
Solubility (in Benzene),
% 3.46 97.5 3.38 99.9 2.62 99.5 1.78 99.2 1.40 99.1 3.35 98,s gx.2 3.60 2.72 99.3 1.91 100 .o 2.5% soap solution, 0.06
With the n-octyl mercaptan, on the other hand, the yield inGreased regularly with increase in mercaptan level. All the viscosity values were fairly high. On the three lower levels of n-octyl mercaptan the viscosity remained practically constant and was also nearly constant at the higher levels with somewhat higher values obtained. With n-decyl mercaptan, on the other hand, viscosity decreased regularly with increase in mercaptan level. The solubility of all these copolymers in benzene was practically complete. Use of the higher normal mercaptans, n-hexadecyl and noctadecyl, as modifiers, in quantities of 0.02, 0.04, and 0.06 gram per 20 grams of monomers, gave approximately the same yields as those obtained with the n-tetradecyl mercaptans. Here, again, variation in modifier level seemed t o have no significant effect on the yield. The viscosity and solubility values were all extremely low. Typical results obtained are indicated in Table [I but t o conserve space only the data for the 0.06-gram level of these mercaptans are included. TERTIARY MERCAPTANS. Data obtained with the use of led-octyl mercaptan as modifier in polymerizations of 14- and 16-hour duration are shown in Table 111. Variation in quantity of this mercaptan was found to have a pronounced effect upon the yield. As with the n-octyl mercaptan, the yield increased regularly with increase in quantity, but gave distinctly higher yields than those obtained with the normal mercaptan. The viscosity tended to decrease with increase in the modifier level. At the lower levels the viscosities were very high; a value of 3.60 was the highest obtained with any mercaptan when potassium persulfate was the catalyst. The benzene solubility of all the rsamples was generally high, ranging from 97.5 to 100%.
Vol. 40, No. 11
The results obtained with various levels of tert-dodecyl mercaptan, in 12-, 14-, and 16-hour periods, are shown in Table IV. Here, again, the yield increased with increase in modifier level. This tendency was noted for all three polymerization times. The yields were somewhat higher than those obtained with the tert-octyl mercaptan but averaged a few per cent lower than with n-dodecyl mercaptan. I n no case did the yield exceed that obtained with the normal mercaptan a t a comparable polymerization time. As with the tert-octyl mercaptan, viscosity decreased regularly with increase in modifier level. The solubility of the products was very high, ranging from 98.9 to 99.7%. Results obtained with the use of tert-tetradecyl mercaptan aa modifier a t a few representative levels are shown in Table V. Once more, the yields were found to increase with increasing level of modifier, being geneially a few per cent higher than those obtained with the tert-dodecyl mercaptan, and a t the higher levels of mercaptan approximately the same as the average yield obtained with n-dodecyl or n-tetradecg-1 mercaptan. The viscosities were high, in general, but the highest values Fere lower than the highest obtained by the use of terl-dodec) 1 mercaptan For each polynierization time, as the modifier level vias increased, t h e viscosity rose to a maximum value a t the 0.02-gram level and then decreased. The solubility values were relatively high excepi for those polymers prepared with the lowest levels of modifier. The effects produced by variation in quantity of terl-hexadccyl mercaptan as modifier were also studied. Within the range investigated, 0.02 t o 0.06 gram, the lield for each polymerizatiou time was found t o be independent of the modifier level. I n thie respect, this mercaptan behaved like the higher normal mercaptans rather than the other tertiary 'mercaptans studied. Foi each polymerization time the solubility increased regularly,with increase in modifier content, from relatively low values at the lowest modifier levels to complete solubility at the higher levels The viscosity, like that obtained with tert-tetradecyl mercaptan, increased with increasing modifier content t o a maximum value and then decreased. This was true for all three times of polymerization, the maximum value being reached in each case ai
TABLE Iv. EFFECTOF
tert-DoDEcYL MERCAPTAN AS MODIFIER WITH POTASSIUM PERSULFATE AS CATALYSTn Modifier, trrt-Dodecyl PolymerizaSolubility Mercaptan, tion Time, Yield, Viscosity (in Benzene), No. Gram Hours % (Innr/c) % 1 0.01 12 65.6 3.54 98.9
70.0 12 2.69 99.5 12 71.2 1.64 99.5 12 72.2 1.16 99.2 14 71 .9 3.52 99.7 14 74.8 2.89 98.9 14 76,9 1.76 99 .o 14 76.6 1.32 99.4 14 78.6 0.88 99.0 73.3 16 3.40 98.9 75.7 16 11 3.19 99.2 79 16 12 ...7 2.21 99.4 16 13 81.1 1.76 99.7 a 15.0 grams isoprene, 5.0 grams styrene, 40.0 mi. 2.5% soap solutiou. 0.06 gram KaSzOs. 2 3 4 5 6 7 8 9 10
0.02 0.04 0.06 0.01 0.02 0.04 0.06 0.12 0.01 0.02 0.04 0.06
TABLE v. EFFECTOF
No.
tert-TETRADECYL hfERCAPT.4N AS 1 I O D I FIER WITH PoT.4SSIUM PERSULFATE A S CATALYST5 lLIodifier, Polyt e i tmerizaTetradecyl tion Solubility, Mercaptan, Time, Yield, Viscosity (in Benzene), Gram Hours % (lnv?/r) %
a 15.0 grams isoprene, 5.0grams styrene, 40.0 ml. 2.5% soap solution, 0.06 gram K z S Z O ~ .
November 1948 TABLEVI.
INDUSTRIAL AND ENGINEERING CHEMISTRY
EFFECTOF tWt-HEXADECYL MERCAPTAN AS MODIPOTASSIUM PERSULFATE AS CATALYST@
FIER WITH
Polymerization Time,
Yield,
Hours 12 14 16
71.8 79.6 84.0
No.
%
Viscosity (lnw/c)
Solubility (in Benzene).
%
99.2 3.38 3.19 98.6 99.4 2.86 3 0 15.0 grams isoprene, 5.0 "rams styreno, 40 ml. 2.5% soap solution, 0.00 gram K&Oa, 0.04 grain tert-hoexadecyl rnercapran. 1 2
2089
TABLE VII. EFFECTOF VARIATION IN ISOPRENE-STYRENE RATIO WITH POTASSIUM PERSULFATE AS CATALYST^ Modifiers, Monomers Mercaptan, Isoprene, Styrene, No. Gram grams grams n-Dodeoyl 1 0.03 17.0 3.0
2 3 4 5
0.03 0.03 0.03 0.03
Yield,
%
Viscosity (hr/c)
Solubility (in Benzene),
%
16.0 15.0 14.0 13.0
4.0 5.0 6.0 7.0
76.05 77.55 79.85 81.35 82.4
2.71 2.71 2.85 2.76 2.49
99.6 99.9 99.7 99.4 98.3
17.0
3.0
74.8
2.73
91.9
n-Tetradeovl
0.06
6
the 0.04-gram level of modifier. The data obtained a t this level 7 0.06 10.0 4.0 76.65 2.56 100.0 8 0.06 15.0 5.0 79.5 2.67 98.7 are given in Table VI. 9 0.06 14.0 6.0 81.4 2.75 98.2 10 0.06 13.0 7.0 83.4 2.47 98.4 EFFECTOF MONOMER VARIATION WITH POTASSIUM PERSULFATE tert-Dodeoyl AS CATALYST.The effects produced by variation in the monomer 11 0.015 17.0 3.0 70.5 3.45 96.3 ratio between the limits of 85% isoprene to 15% styrene and 12 0.015 16.0 4.0 72.2 3.36 98.5 13 0.015 15.0 5.0 72.6 3.44 98.9 65% isoprene to 35% styrene, through 5% intervals, with the 14 0.015 14.0 6.0 74.7 3.27 96.9 n- and tert-dodecyl and tetradecyl mercaptans as modifiers in 15 0.015 13.0 7.0 75.7 3.45 95.1 tert-Tetradeovl quantities that appeared to give satisfactory yields, viscosities, .~ . ~" 16 0.02 17.0 3.0 74.7 3.30 95.4 and solubilities with the usual 75-25 ratio are shown in Table 17 0.02 16.0 4.0 76.3 3.32 99.0 VII. Potassium persulfate was used as the catalyst and the 18 0.02 15.0 5.0 76.6 3.39 98.8 19 0.02 14.0 6.0 76.7 3.29 98.9 polymerization time was constant a t 14 hours. With each mer20 0.02 13.0 7.0 79.3 3.37 98.8 captan the yield of copolymer increased with increase in the pera 40.0 ml.2.5% s o a p solution, 0.06 gram K2Sz08,polymerized 14 hours. centage of styrene; the over-all increases ranged from 4.6 to 8.6%. The change in yield was greater in the two series produced TABLEVIII. EFFECTOF ~ - D O D E C Y MERCAPTAN L AS MODIFIER with normal mercaptans than in those prepared with the tertiary ~ I T H BENZOYL PEROXIDE AS CATALYST^ mercaptans. Change in monomer ratio, within the range studied, Catalyst, Modifier, Solubility appeared to have little or no effect on the viscosity. All the n-Dodecyl (in Benzo 1 PeroxiL, Mercaptan, Yield, Viscosity Benzene), viscosities were relatively high, but the tertiary mercaptans gave No. Gram Gram % (lnsr/o) % the highest values. Solubility was relatively high, the values 42.4 1.38 99.2 ranging from 98.2 t o 100% for the samples prepared by use of 60.1 1.06 99.6 41.7 0.71 98.6 the normal mercaptans, and from 95.1 t o 99% for those made with 42 .O 1.57 99.4 55.2 1.38 99.7 the tertiary mercaptans. ~
~
~~
~
~
48.8 32.4 49.3 53.5
RESULTS WITH BENZOYL PEROXIDE AS CATALYST
As preliminary experiments indicated that the rate of polymerization is slower with benzoyl peroxide than with potassium persulfate as catalyst, polymerizations with benzoyl peroxide were continued for 18 hours. The amount of catalyst as well as t,he amount of modifier was varied. 100
$? 90
0-1
w>. 80
n
z
-4 W
70
W
N
z eo
50
W
m
z
*c d
m 2.0
40
3
-1
0 v)
30
1.21 1.78 0.90 0.83
99.1 100.0 99.4 98.9
0 15.0 grams isoprene, 6.0 grams styrene, 40.0 ml. 2.5% soap solution, polymerized 18 hours.
NORMAL MERCAPTANS.Of five normal mercaptans studied as polymerization modifiers with this catalyst, the dodecyl and tetradecyl mercaptans, as with potassium persulfate, gave the best results. Representative data obtained using n-dodecyl mercaptan are given in Table VIII. All the yields were low, less than 58%, even after 18 hours, and were affected both by the amount of modifier and by the ratio of the quantity of modifier to quantity of catalyst. For a given level of catalyst the yield tended t o increase with increasing quantity of modifier to a maximum value and then to decrease and the viscosity to decrease with increasing amount of modifier. None of the viscosity values was very high. On the other hand, the solubilities were generally above 99%. Better results were obtained with n-tetradecyl mercaptan. Here, again, the yields of copolymer varied with the ratio of modifier to catalyst and a t all catalyst levels tended to increase with increase in quantity of modifier. At the lower levels yields were all low, but at the higher levels values in excess of 75 and even 80% were obtained. All the viscosity values, in contrast to those of the preceding series with n-dodecyl mercaptan, were relatively high, even when large quantities of catalyst and modifier were employed. The viscosity generally tended to decrease with increasing mercaptan content. The solubility values were high except in instances when the amount of modifier used was small compared to the amount of catalyst. These trends are illustrated by representative data given in Table IX. Polymerizations were also carried out with n-decyl, n-hexadecyl, and n-octadecyl mercaptans as modifiers a t leveh of mercaptan and benzoyl peroxide corresponding approximately to
Vol. 40, No. 11
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
2090
Softness arid the acconipanj irig btickiness arid compact ncss MERCAPTAN AS ~ I O I J I - tended to increase with increasing quantity of modifier, a tendTABLE IX. EFFECTOF n-TETRADECYL FIER WITH B E X ~ O Y PEROXIDE L AS ChTAI.YSTa ency more pronounced with the tertiary than with the normal Catalyst, Modifier, Solubility mercaptans. With each series of mercaptans the softncss of the Benzoyl n-Tetradeoyl (in Yield, Visoosity Benzene), Peroxide, Mercaptan, copolymer varied inversely with the carbon content of the merNo. Gram Gram % (hr/c) 74 captan. The softening tendency of the modifiers was more 40 1 3.67 94.1 0.02 1 0.04 pronounced when benzoyl peroxide rather than potassium per2 0.04 55.4 2.62 99.2 0.08 2.09 99.2 3 0.04 62.7 0.12 sulfate was used as the catalyst. At the lowest mercaptan levels, 4 0.08 24.4 3.72 98.4 0.02 5 0.08 66.1 3.17 97.1 0.08 however, the products obtained with benzoyl peroxide were hard 73.3 0.12 2.63 99.2 6 0.08 and tough. Increase in percentage of styrene tended to increase 0.06 62.7 3.03 76.8 7 0.12 8 0.12 75.3 2.96 98.7 0.10 hardness and toughness. 0.14 80.6 2.55 99.0 9 0.12 15.0 grams isoprene, 5.0 grams styrene, 40.0 ml. 2.5% soap solution, polymerized 18 hours. Q
those used for the n-dodecyl and n-tetradecyl mercaptans and under the same conditions. However, none of these mercaptans seemed promising. The products prepared with n-decyl mercaptan were practically completely soluble in benzene and had viscosities ranging u p t o 3.33, but the yields were very poor, below 35y0. With the n-hexadecyl and n-octadecyl mercaptans the yields were somen-hat higher, ranging up to 54%, but the solubilities were generally poor and the viscosities mediocre. TERTIARY MERCAPTAKS.The effect produced by variation in quantity of tert-octyl, tei-t-dodecyl, tert-tetradecyl, and tei-t-hexadecyl mercaptans with different quantities of benzoyl peroxide was investigated. Of these the tert-dodecyl mercaptan gave the best results and several copolymers possessing high solubility and viscosity were obtained in good yield with this mercaptan. Representative data obtained with this mercaptan are given in Table X. At each catalyst level the yield increased with increase in amount of modifier, rapidly at first; then more slowly. Except a t the lowest mercaptan levels the viscosity values were all relatively low and at each catalyst level decreased with increasing mercaptan content. The solubility was high in all cases.
CONCLUSION
Isoprene-styrene copolymers possessing a high degree of solubility in benzene and high inherent viscosity can be prepared in good yield under a variety of conditions with respect to catalyst and modifier by emulsion polymerization. With potassium persulfate as catalyst best results were obtained with certain levels of the n-dodecyl and tetradccyl mercaptans and of the tertoctyl, dodecyl, tetradecyl, and hexadecyl mercaptans as modifiers. With benzoyl peroxide a3 catalyst best results were obtained iyith the n-tetradccyl mercaptan. ACKNOWLEDGMENTS
The authors wish to express their appreciation to Barbara E. Hillery for assistance in the polymerization work and in the solubility and viscosity determinations, and to Dorothy Tvl. Oldroyd for fractionation of the isoprene. LITERATURE CITED
Barron, H., “Modern Synthetic Rubbers,” 2nd ed., pp. 52-66, New York, D. Van Nostrand Co., 1943. Baruch, B. IW., Conant, J. B., and Compton, K. T., “Report oi the Rubber Survey Committee,” p. 68, Sept. 10, 1942. Cragg, L. H., J . CoZloid Sei., 1 ( 3 ) , 2 6 1 (1946); Rubber Chem. Technol., 19, 1092 (1946).
O F tert-DODECYL ?VIERCAPTAN AS TABLEx. EFFECT WITH BENZOYL PEROXIDE AS C.4TALYSTa
No.
Catalyst, Benzoyl Peroxide, Gram 0.02 0.02 0.02 0.04 0.04
Modifier, tert-Dodecyl Mercaptan, Gram 0.02 0.04
Yield,
%
Viscosity (lnvr/c)
;\IODIFIER
Solubility (in Benzene),
%
99.3 2.17 100.0 1.43 98.7 0.83 0.08 99.2 2.12 0.02 99.7 1.33 0.06 1.14 98.8 0.04 0.08 99.5 1.31 0.08 0.04 99. 3 1.19 0.06 0.08 98.0 0.90 0.10 0.0s a 16.0 grams isoprene, 6.0 grams styrene, 40.0 ml. 2.5% soap solution, polymerized 18 hours. 56.1 6 1 .9 65.6 52.7 74.9 76.6 60.2 69.7 74.1
Polymerization products obtained with tert-octyl mercaptan as modifier, and benzoyl peroxide as catalyst, possessed high solubility (above 99.0y0) but were very low in yield (less than 40%) and in viscosity (less than 1.0). tort-Tetradecyl mercaptan also gave polymers with substantially complete solubility but with somewhat better yields (up to 6870) and viscosities (up t o 1.7). Use of terthexadecyl mercaptan gave polymers in substantially the same yield and solubility as did tert-tetradecyl mercaptan but with distinctly higher viscosities (up to 2.83). With all four tertiary mercaptans investigated, a t each level of benzoyl peroxide used, the yield tended to increase with increasing mercaptan content, but the viscosity tended to decrease. PHYSICAL CHARACTER1STICS
The copolymers obtained varied widely in appearance and in rubberlike characteristics. They ranged from very tough, spongy, dry, and hard at one extreme to weak, compact, sticky, and soft even to the point of plastic flow, a t the other extreme.
Craig, David (to B. F. Goodrich Co.), U. 5.Patent 2,362,052 (Kov. 7, 1944). Croxton, F. C., IND. ENG.CHEX.,ANAL.ED.,14, 593 (1942). Davis, B. L., Goldblatt, L. A., and Palkin, S.,IND. ENG.CHEM.. 38, 53 (1946).
Flory, P. J., J. Am. Chem. SOC.,65, 372 (1943). Fryling, C. F., IND. ESG.CHEX.,AXAL.ED.,16, 1 (1944). Fuller. C. S.. Bell Telephone Swstem Tech. Publs., Mononraph B1405, 5 , 8 (1946).
Palmer, R. C., IND.ENG.CHEM.,34,
1034 (1942);
35, 1025
(1943).
Rubber Age, 52 (3), 244, 247 (1942). Zeitfuchs, E.R., ’Vatl. Petroleum N e w s , 31, 109 (1941). RECEIVED June 16, 1947. Based upon a paper presented before the Division of Rubber Chemistry and the High Polymer Forum a t the 110th Meeting of the .kMERICAN CHBMICAI, SOCIETY, Chicago, 111.
Corrections The editors regret that the title “Pyrolysis of Hydrocarbons” [IND.ENG. CHEu., 40, 1660 (1948)l incorrectly describes the subject matter of the article appearing thereafter. The review article by Vladimir Haensel and Melvin J. Sterba covers pyrolytic and catalytic decomposition of hydrocarbons. The article as originally submitted contained an adequate title. The editors apologize for the incorrect title substituted during editing of the review.
....*..
I n the biographical sketch of Stephen I?. Perry [IxD. EKG. CHERI.,40, 1554 (1948)] it is stated that Mr, Perry served on the Aviation Gasoline Advisory Committee. He was not actually a member of this committee or of its Isomerization Subcommittcv, although he was active in the work of the subcommittee.
