2210
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
modulus, hardness, and plasticity actually do behave in this way. Rebound (Figure 14) behaves similarly except that there is a regular decrease with loading. Rebound also decreases with area (Figure 5 ) and with volume loading of coarse fillers. The foregoing results cover natural rubber and four types of synthetics (GR-S, GR-&I, GR-I, and Hycar). Tests on other GR-A type synthetic rubbers, such as Chemigum and Perbunan, give results similar to those shown for Hycar (19). ACKNOWLEDGMENT
The authors wish to express thcir thanks to the many members of the Witco Research and Technical Service Laboratories who
assisted in obtaining the data and preparing the figures; to their former associates C. Yoran and H. F. Schn-arz; t o P. L. Copeland, of the Illinois Institute, for taking the electron microscope photographs; and to L. R. Sperberg and W. R. Smith for their helpful suggestions and review of the manuscript. LITERATURE CITED
(1) Cohan, L. H., Chem. Eng.News, 23,2078-85 (1945). (2) Colian, L. H., and Mackey, J. F., IND. ENG.CHEaS., 35, 806-8
(1943). (3) Cohan, L. H., and Mackey, J. F., I n d i a Rubber W o r l d , 107, 469-71 (1943). (4) Cohan, L. H.. and Illackey, J. F., Rubber Age, 55, 583-5 (1944).
Vol. 40, No. 11
(5) Cohan, L. H., and Steinberg, hl., IXD. ENG.CHEM.,36, 715 (1944). (6) Cohan, L. H., and Steinberg, M., Rubber Age and Synthetics (London), 25,275-8 (1945). (7) Continental Carbon Go., “Conductivity of Natural and Synthetic Rubber Channel Black Stocks,” Rept. C 1, New York. June 1,1943. (8) Continental Carbon Co., “Physical Properties and Behavior in Rubber of Continental Carbon Blacks,” Rept. R 1, New Pork. 1943. (9) Dobbin; R. E., and Rossman, R. P., IXD.ENG.CHEai., 38 1145-58 (1946). (10) Guth, E. J., J . Applied Phys., 16, 20-5 (1945). (11) Hendrick, 9 . B., ”Structure and Base Exchange Properties of Clays,” presented before Catalysis Conference, Am. -4ssoc A d v . Sei., Gibson Island, Md.; June 1945. (12) Smit.h, W, R., “Carbon Black Behavior,” presented before the High Polyiner Conference Am. Assoc. Adv. Sci., Gibson Island, Md., June 1945. (13) Sweitzer, C. W., and Goodrich, W. C., Rubber Age, 55, 469-78 (1914). (14) Watson, J. H. L., J . Applied Phys., 17, 121-37 (1946). (15) Wiegand, 7%’. B., Can. Chem. and Process I n d . , 28, 151-62, 213. (1944). (16) Wiegand, W. B., India Rubber W o r l d , 105, 2%-2 (1911). (17) Wiegand, W. B., and Ladd, W. A., Rubber A g e , 50, 431-6 (1942). (18) Witco Chemical Co., Carbon Black Manual, New York, 1946. (19) T;Vitco Chemical C o . , New York, Witcarb R, B u l l . 45-2 (1945): 46-2 (1946). RECEIVED January 16,1947.
renew d
J . M . WILLIS, L. B. WAKEFIELD, R. H. POIRIER,
AI\’D E. The Firestone Tire 6% Rubber Company, Akron, Ohio
RI. GLYRIPH
A series of isoprene-styrene copolymers varying in monomer ratio from l O O / 0 to 60/40 has been prepared in the GR-S recipe. Physical tests in a tread recipe show superiority for these polymers over GR-S i n efficiency. A number of activated recipes have been applied to the 75/25 isoprene-styrene ratio a t 50 O C. The use of ferricyanide or acrylonitrile activation offer the most immediate possibilities for plant usage because of the small deviation from conditions for w-hich GR-S plants were designed. Little
difference i n physical properties was noted for polyisoprenes prepared i n a redox system at temperatures ranging from 40 O to 10 C. Isoprene-styrene (75/25) copolymers with varying gel characteristics were prepared in a GR-S system. As the gel varied from low to high temporary to high permanent, the efficiency increased at the expense of cut-growth resistance. Tests o n polymers prepared in the pilot plant have substantiated results obtained on polymers prepared in the laboratory.
0
and study a series of isoprene-styrene copolymers with a fairiv wide range of monomer ratios. Earlier work on the substitution of isoprene for butadiene in GR-S indicated that much slover polymerization rates are obtained with the grades of isoprene available. It has beeD found that, in some cases, even sulfone-purified isoprene givea slower rates than butadiene. Therefore, various methods of activation have been evaluated as means of obtaining standard timc cycles for plant use. In the plant preparation of isoprene analogs of GR-S, it was observed that the modificr charge could be reduced to give a polymer with a Mooney plasticity of 65 (containing gel, however) a-ithout affectini processibility. This lower modifier requirement has bee,i evident throughout the isoprene development. It was necessary, therefore, that attention be directed toward gel-containing isoprene rubbers with particular referexe to physical properties. This paper describes the preparation and properties of polymers made with varying monomer ratioe (ixluding polyisoprene), various activated charges, and a range of gel contents.
NE of the most serious shortcomings of GR-S when used in tires has been its low efficiency as evidenced by a much higher running temperature than natural rubber (4,6‘, 7 ) . This is a particular disadvantage in truck tires where thick sections prevent dissipation of the heat. Early workers in the field of synthetic rubber found t h a t isoprene-containing polymers did not have this inherent disadvantage (1). This is consistent with the properties of natural rubber wherein the units of the chain are of the isoprene type (3, 6, 8). One aspect of the work which was undertaken at Firestone involved testing isoprene as a butadiene replacement in an effort to arrive a t a definite conclusion on the relative merits of isoprene-styrene and butadiene-styrene copolymers. TWOstandard experimental types were taken as the basis of this work, X-141 being a 75/25 isoprene-styrene rubber prepared in a dehydrogenated-rosin soap system and X-46 being the same rubber prepared with fatty acid soap. Since it was possible t h a t a 75/25 monomer ratio would not give the best balance of properties, particularly if the end use were in a special purpose compound, it seemed of interest t o prepare
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1948
2211
strength and cut-growth resistance are not so important. further attention in applications where efficiency is more important than tensile strength or cold resistance. It is recognized also t h a t the entire group of isoprene-styrene rubbers was compounded in a standard GR-S recipe with no attention to cold resistance; changes in the recipe might be made t o improve the low temperature characteristics. The series approaches polyisoprene in physical properties as the styrene is decreased from 40 l o 7.5 parts. At the same time cold-resistance and room-temperature rebound approximate the values for GR-S. From this work with the isoprene-styrene ratio it waa concluded t h a t further work should be centered on a 75/25 charge as being higher in properties than 85/15 polymer and better on an economic basis. However, since cold resistance is more important for some applications than tensile strength and cutgrowth resistance it seemed t h a t some attention should be given to the 85/15 sample. Plant runs have now been made with this charge and tests are now under way. Them aterial processed normally in a body stock, after excess stearic acid was added to keep it from sticking to the rolls. Extrusion of the tread stock was satisfactory only after a second milling with extra pine tar. A comparison of a polyisoprene prepared in a GR-S system (X-116 plant batch) with GR-S and smoked sheet completes the monomer ratio picture. These data, presented in Table 111, show t h a t in properties such as running temperature, rebound, and low temperature stiffening, polyisoprene is superior to GR-S and approaches natural rubber. However, its value is reduced by low tensile, elongation, and poor cut-growth resistance. These deficiencies in physical properties exhibited by polyisoprene as compared t o natural rubber when both are composed of the same monomer units have been the subject of much conjecture in the synthetic rubber program. It is felt by many investigators that this is due to the heterogeneity of the synthetic polymer as far as cis and trans configurations and head to head or tail to tail monomer union versus the head to tail
TABLEI. PREPARATION OF ISOPRENE-STYRENE COPOLYMERS These polymers with improved efficiency merit Sample No. Isoprene Styrene
A58 92.5 7.5 DDMQ 0.30 Hours 26 Conversion 76 ML/4/212 b 70 Gel 59 Intrinsic viscosity 0.96 5 Dodecyl mercaptan. b Mooney plasticity, large
419 85 15 0.27 30 79 55 0.5 2.56
420 79 21 0.27 27 75 50 0.4 2.17
48 75 25 0.30' 26 75 49
0.6 2.18
49 70 3g.27 23 75 50 0.7 2.26
422 65 35 0.22 26 75 54 0.3 2.31
424 60 40 0.18 28 78 59 0.4 2.54
rotor a t 212' F.
APPARATUS AND PROCEDURE
The isoprene used in this work (except in those runs otherwise designated) was obtained from the Newport Industries Inc., and was freshly distilled before loading. The styrene was commercial grade material which was used "as received." Polymerizations were carried out in 28-ounce crown-capped bottles rotated endover-end in a water bath held a t 50" C. Latex samples for oonversion studies were withdrawn through a hypodermic needle forced through the oil-resistant rubber cap liner. The most accurate value for total solids was obtained by making the initial weighing on the entire sample (including the isoprene) while it was retained i n the hypodermic syringe. After the desired conversion was reached the latex was stabilized with phenyl-&naphthylamine (2% used as a dispersion in Daxad solution), coagulated with either aluminum sulfate or salt and acetic acid, mill washed and dried at 70" C. Evaluation of the copolymers was carried out on samples mill-mixed in a standard tread-stock recipe. MONOMER RATIOS
Preliminary runs were made to determine the modifier requirements for the various monomer ratios. As was t o b e expected from GR-S experience, the charges containing higher isoprene loadings required more modifier. No prefloc was encountered in the preparation of the samples, although the latexes were more viscous than normal Type I (GR-S) latex. All of the copolymers except A58 were nearly gd-free, and it was found that-polymers with Mooney values of 60 to 70, obtained by decreasing the modification, would TABLETI. PHYSICAL TESTDATAON ISOPRENE-STYRENE COPOLYMERS be processible in plant operations. As Sample No. the amount of styrene in the charge A58 419 420 48 49 422 424 C361 was increased, all the copolymers took Cure, Monomer Ratio the pigments with equal ease, somewhat Min. 92.6-7.5 85-15 79-21 75-25 70-30 65-35 60-40 better than did the GR-S control. 300T0 [nodulus. Ib./sq. in. 40 , .. 1000 1000 1025 1025 1125 1200 400 80 ,.. 1400 1375 1350 1500 1575 1700 800 When these copolymers were mixed in 120 ... 1500 1500 1575 1675 1800 1000 160 ... , ,. 1525 1500 1600 1675 1825 1000 the tread recipe, the results shown in T n n d e . ih./aq.in 40 1700 1575 1525 1750 2325 2000 2900 2225 Table I1 were obtained. Except in 1625 1525 1825 2050 2300 2875 3125 120 the case of tensile slabs, all stocks 16f5 1575 . . . 2025 2625 2675 3200 160 1400 1375 2050 1950 2050 2600 2800 3050 were cured 80 minutes at 280' F.; the BO 260 400 400 430 520 450 560 800 Elongation. '76 aging period was 4 days at 212 O F. 80 220 320 320 360 380 400 460 740 120 310 250 290 370 420 410 610 The different ratios resemble each a 160 180 270 360 360 370 420 430 600 other closely in efficiency, and all Ball rebound, % a t 72O F. 40 42 36 31 24 18 12 45 212O F. 66 69 67 66 66 66 66 56 offer a considerable improvement over Cut growth, in./hr. Normal 19.7 2.00 1.37 1 . 3 8 1 . 1 3 0 . 8 8 0.49 0 . 7 3 GR-S in this property; therefore, a Aged 94 15.3 12.7 11.6 9.3 9.2 6.1 4.3 choice among them should be based Flexometer data Load, lb. 225 225 284 on some other property. For the best 228 225 226 256 220 250 Running temp., F. 22 56 57 48 55 49 76 32 550 Blowout time, min. compromise in these values, the 75/25 Dynamic properties" Temp., ratio is probably preferable; if cold (forced vibrator) F. Modulus, lb./sq. in. 122 526 294 282 275 282 310 281 339 resistance were unimportant, then the 212 293 176 164 158 170 154 153 187 60/40 ratio would possess definite su[nt. friction, kilopoisee 122 8.5 5.8 5.75 6.15 6 . 5 5 7 . 5 7.6 8.8 212 4.1 2.73 2.6 2.59 2.75 2 . 5 2.43 4.75 periorities. [In this paper, the effect 100 99 106 112 129 131 151 122 147 Hz b of reduced temperature on the com70.7 46 45 44 47 43 41 82 212 pounded stocks was measured by the 122 52 117 124 139 141 136 166 132 HfC 212 81 154 167 179 166 182 179 232 temperature at which Young's modu-37 -39 -33 -28 -25 -20 -14 -40 t o w temp. index, ' C . lus reached a value of lo4 (listed 5 For a discussion of these tests see (4). as low temperature index in tables).] b Energy absorption a t constant amplitude relative to a natural rubber control. c Energy absorption a t constant force relative t o a natural rubber control. The 85/15 ratio shows the best comhination of properties where tensile O
221 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
T A R L III. E
CO\1€'.4RISOS OF GR-S, 116), d K D ?;.4TVRAL
GR-S-XPOLYISOPHBNE RUBBER
Compounding Formula Polymer Sulfur ZnO Stearic acid E P C black Bardol Pine tar PBNAU Santocure
AMOTJXTOF POTASSIUM FERRICYANIDE. Runs were made with several loadings of potassium ferricyanide, 0.2 part apparently being optimum.
x-I16
Tmiile, Ib ,'%q. in. 20 40 60 60 120 Elongation, V0 20 40 60 80 120 Cure a t 280° F., min. Rebonnd, yo a t 72' F. 212O F. Shore hardness Cut grox\-th, in,/lir. Unaged Aged 2 days a t 212O F. Running temperature, O F. Low temperature index, ' C. 0 Phenyl-0-naphthylamine.
GR-S
~ T A 4 R I ~ 4 T IIONS pII.
25 250 500 775
1050 1350 1400 1400
675 1150 1150 1!00 1100
25 1775 2600 2900 3000
3950 4000 3850 3925 3900
7 80 440 360 390 330 GO 44 62 30
800 890
640 610 580 580 580 40 53 70 -56
4.7 12 9 243 - :2
760 690 650 60
46 3a 50
0.57 1 35 261 -45
R u n No. 12 15 14 13 (control) 17
Run
1.3
0 2
0
0.01 0 03 0,073 0.125
Time, Hours 16 16 16
Min. 0 15 80 45
Run So. 13 42
Parts Alodifier 0 . 2 DDhI 0 1 Sulfole
Coni-ersion,
5%
78.6 65.0 84.5 84.0 62.6
Converbion,
"0
Time, Hours
Conversion,
16 16
84.0 71.7
c/o
CHAAGE I> iri
E&rCLJIFILH. The use of sodium dehydro resinatcl place of soap flakes had little rffect on t h r 16-hour ronversion.
Run NO.
13 43
Time, Parts Ernulaifier 5 soap flakes 5 sodium dehydro resinate
Hours 16
16
Conversioxi,
70
64.0 82.8
VARIATIOX I N SOURCE OF I ~ O P R E N E. Isoprenc from several A comparison of fwshly distilled Xexport Industries isoprene [this was the material uscd in t,he majority of runs) with various other grades indicated that only the Standard Oil sample gave a more rapid reaction rate.
, sources was tried in the basic recipe.
Run
Isoprene 29 Newport 13 Newport 30 Ncwport 31 Standard Oil Phillips (puye) 32 Sulfone DurifiedQ 49 41 Recycle Obtained through courtesy of C.
so.
Treatment Distilled Distilled NaOH washed NaOH washed S a O H washed S Distilled a O H washed
Time, I-Iours
CO!lversion,
7 ''
8.Marvel, University of Illinois.
ACRYLOXITRIL~ ACTIVATION. The replacement of part of the styrene in a modified GR-S charge with a n equal weight, of' acrylonitrile was also investigated. It was felt that t,he use of over 2.0 parts might adversely affect the resulting polynicr, s o this was taken as the upper limit.
500-C.
The water, potassium persulfate, potassium ferricyanide, and sodium hydroxide were a g d a t 50" C. for 60 minutes. I n each set of runs one factor in the system r a s varied.
Time, Hours 24 24 19 16 24.5
PH 6.0 11.2 11.8 12.0 12.2
CHANGE IN MODIFIER. The subetitut,ivn of Sulfolo (a mixturr of tert)iary mercaptans) for dodecanethiol (dodecyl mercaptan i in the basic ferricyanide recipe gave a reduced reaction rate.
* 26 180 5 0.25 0.20 0.075 ( p H = 1 2 . 0 )
Parts, SaOH
23 24 25 26 16 27 60 18 16 60" 28 Only IGSsOa and I i i F e ( C K ) i in 675 solution.
ACTIVATED RECIPES
*"
:7c
77.6 79.0 76.5 84.0 68.3
A high pH of 12.0 gave tho maximum con-
.I.inp,
XO.
-_
Standard Recipe
Conversion,
AGISG PoThssImi FERRICYANIUE. Jn all but one of these runs, the total amount of water, potassium persulfate, potassium ferricyanide, and sodium hydroxide w x e aged for Chc time indicated a t 50" C. I n run 28 below, the ferricyanide and persulfate were aged for 60 minutes in 6 % aqueous solution. This latter procedure has been recommended by several workers investigating the ferricyanjde activation of GR-S. Howevei,, the optimum conditions were apparently attained when thch whole solution was aged for 15 minutes.
-3%)
Along &th the improved propert,ies obtained from isoprene polymers it would be desirable to reduce polymerization time as much as possible. It is evident, however, that a superior polymer would not be discarded because the polymerization time was longer than that of a GR-S system. Thus a study of the various possible methods of activating the isoprene-styrene peared to be in order. I t was shown that an activating system consisting of potassium ferricyanide (0.2 part) and excess caustic (0.075) pave an 84Yc conversion in 16 hours against S9.570 in 24 hours for a control. Much more activation was found when a p-methoxyphenyl diazothio-p-naphthyl ether (MDK) and a redox charge were employed. (LIDK is one of a number of diazothioethers developed as activators by workers in the Goverhineiit Synthetic Rubber Program.) FERRICYASIDE i%C'PIrATI0N. The major portion of this study was devoted to ferricyanide activation, with various factors affecting the reaction being invest,igated. The basic recipc used was R S follows:
Time, Hours 16 16 16 16 16
version rate.
0 01 0 24 1
possibility. The development of satisfactory methods for determinat,ion of those polynior characteristics might go a long way toward expIai!iing the differences in polyisoprene and natural rubher.
Isoprene Styrene Water Soap flakes KzSzOs KaFe(CN)e NaOH DDM Temperature
Parts, KaFe(CN)a 0.05 0.10 0.15 0.20 0.30
R u n No. 20 19 16 13 (control) 47
100 2.0 3.0 2.5 45 4.0 2.5 0.6 1.2 Smoked Shret
Vo1. 40, No. 11
Isoprene Scyrene Acrylonitrile Water liZSZOS Soap flakes DDM
Recipe 75 Variable Variable 180 0.5 5 0,2
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1948
TABLE IV. Run
PROPERTIES OF ISOPRENE-STTRENE COPOLYMERS (75/25) PREPARED AT 50" C. PHYSICAL 2 Acrylonitrile Acti(2-361 vation GR-S 2 .O Pts. 15l/a 82
h70.
Polymerization system Time hours convkrsion,
70
Modulus 300%, lb./sri. in.
Modulus 40070, lb./sq. in.
Tensile, lb./sq. in.
Elongation, 7C
Ball rebound, ';a room temp. 212O F. Dynamic properties (forced vibrator) Modulus, lb./sq. in.
Cure, Min. 20 40 60 80 20 40 60 80 20 40 * 60 80 20 40 60 80 60 60 Iemp., 0
Internal friction, kilopoises Energy ahs. H L b
Hf Statio modulus, Ih./*q. in.
2213
8
9
13
16
Redox 1.5 68
MDN Activation 4 77
p H = 12.0 KFCa 16 84
I/Sin GR-S 24 89.5
200 775 925 1000 350 1200 1400 1475 1300 2226 2125 2300 920 610 510 520
260 1050 1325 1425 350 1600 1925 2100 1875 2075 2000 2550 1020
260 1100 1350 1450 400 1700 2000
25 350 700 800 25 650 1125 1300 25 2150 2575 2750 510 760 650 620
275 1050 1250 1350 376 1700 1925 2075 2100 2350 2450 2375 940 490 440 440
475 1200 1425 1500 1750 1850 2125 2300 2775 2400 2400 2250 830 470 430 400
38 48
25 56
26 58
...
327 167 7.9 3.75 137 64 121 238 138 95
327 180 7.9 3.06 122 52.7 114 159 172 120
308 174 5.76 2.64 99 45~5 103 148 200 120
265 220 11.7 6.02 201 103 62.1 208 277 128
...
.. .
460 410 460
1800, 2500 2225 2000 880 530 430 370
28 52
25 56
27
12
KFCa pH = 0 Aged 60 Min. KFC 24 16 77.5 78.5
2,
29
30
KFCa Newport Distilled 16 80.2
KFCa Newport Washed
950 1175 1300 300 1475 1800 1900 1650 2250 2150 2150 990 520 450 420
250 1025 1275 1350 400 1600 1900 2050 2075 2750 2300 2450 980 560 460 440
26 49
27 56
19 50
302 161 6.05 2.5 104 43 113 164 157 112.5
339 176 6.4 2.81 110 ' 48.5 95.1 153 190 120
200
250 1050 1200 1275 450 2000 2025 2250 1550 2225 2350 950 380 430 440
42
31 KFCa Std, Oil Isoprene 16 87.7
KFCC Sulfole Mod. 16 72
425 1625 1950 2025 1860 2250 2250 2250
250 1150 1300 1350 450 1725 1950 2150 2050 2100 2200 2180 840 480 440 400
300 975 1250 1250 550 1675 1875 1975 2350 1975 1875 2175 860 460 400 390
27 55
26 56
26 61
445 210 7.9 3.77 137 65 68.2 145
274 153 5.42 2.41 94 41.5 123 174 144 101
257 152 5.23 2.15 90.5 36.8 135 158 164 113
16
78.8
I?
122 212 122 212 ,122 212 122 212 122 212
385 210 7.09 4.35 122 75 81.1 167 226 138
285 174 5.98 2.81 102.5 48.5 124 156 150 120
403 201 7.71 3.9 133 67.1 81.2 163 226 128
200
138
KaFe(CN) activation. b At constant amplitude relative to natural rubber control. 0 A t constant force relative t o natural rubber oontrol.
It is seen that the 2.0 parts of acrylonitrile give apporximately the same activation as the ferricyanide recipe. Run NO. 2 10 .ll
Parts, hcrylonitrile 2.0 1.0 0.5
Time, Hours 15.5 17.5 19.5
Conversion,
% 82.0 80.5 81.0
SIDN AND REDOXACTIVATION.The very rapid activator systems, redox and p-methoxyphenyl diazothio-p-naphthyl ether, were also evaluated for isoprene-styrene a t 50" C. The recipes used are given below: Isoprene Styrene Water Soap flakes NaOH (5%) NasPOa.lZH20 KaFe(CN)s
MDh-
Sulfole Run
No. 9 40 8
39
MDN 75 25 200 5 1 3 1 0 0.3 0 2 0.2
Isoprene Styrene Water Soap Rakes Nad'zOi Fe ( N H4)zSOd.6Hz0 Benzoyl peroxide Sorbose
Description MDN MDN Redox Redox
Time, Hours 4 4 1.6 1.5
Redox 75 25 200 5 0.2 0 35 0 5 0.6 Yield,
%
77 51 68 42
The most notable fact about these very rapid runs is the nonreproducibility of conversion rates. This is in agreement with the observations made in the course of the redox development for butadiene-styrene systems. CATALYST VARIATIONS IN GR-S RECIPE. The effect of several catalysts in the standard GR-S recipe was tested. The loading recipe was as follows:
Isoprene Styrene Water
75 25 180
Soap Rakes Catalyst DDM
5 Variable 0.2
The results indicate that organic peroxides and hydroperoxides are inferior t o potassium persulfate for this purpose. Run No. Catalyst 16 KzSzOs 48 KzSzOs 21 Uniperoxa 22 Cumene hydroperoxide b a Union Oil Go. b Hercules Powder Company.
Parts 0.3 0.3 0.02 0.25
Time, Hours 24 16 16 26.5
Conversion,
%
89.5 71.3 31.5 81.5
The amounts of catalyst used in these runs have been shown to give approximately equivalent rates using a butadiene-styrene monomer system. The investigation on activating systems has shown potassium ferricyanide and acrylonitrile to be effective in accelerating the polymerization rate enough to allow the use of less pure isoprene without a n undue increase in time cycle. If, however, i t is important to use the very impure monomer or to operate at lower temperatures, more potent activating systems are to be found in a redox or p-methoxyphenyl diazothio-p-naphthyl ether formula. PHYSICAL PROPERTIE& The physical properties obtained on a number of the above polymers when compounded in a tread stock recipe are presented in Table IV. The particular polymers in the list tested which show the most improvement in physical properties are:
1. The polymer from Sulfole modified, ferric anide activated charge (Run 42) which shows very low internal giction and relative energy absorption.
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
2214
Vol. 40, No. 11
Four systems were chosen and applied to a 75/25 isoprene styrene charge (Table VI). TABLEV. PHYSICAL PROPERTIES OF REDOXPOLYISOPRENES Polymer No. Temperature, Conversion,
O
GR-S 50 75
C.
,,
Gel, %
..
[rll
Williams plasticity 3.1 Y,a t 212O F., nim. 0.45 Recovers, mm. 300y0 modulus, Cure, 1nin.Q lb./sq. in. 40 625 60 1025 80 1225 120 1450 Tensile, lb./sq. in.
3.9 1.88
4.2 1.66
82-19 30 61.5 4.7 2.98
A2-18 40 63.2 59.6 4.00
4.7 2.37
4.6 1.02
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . 1200 1150 1250 1428
1300 1000 1428 1300
800 900 850 1025
1475 1450 1150 1375
1225 1075 1100 1225
750 610 510 480
240 230 240 250
260 200 210 230
200 200 190 200
240 220 170 230
170 170 150 160
80
80
0.17 2.16
0.88 10.1
0.48 8.2
0.28 13.2
80
281
274
264
267
264
266
EO
17 78.0
41 ' 89.4
38 88.3
34 90.6
41 90.3
...
Elongation at break, 7%
40 60 80 120
Blowout time, min. 650-lb.load % 1,4 addition (9) 5 At 280" F.
4.0 1.84
A2-20 A2-21 20 20 52.0 65.3 0.8 1.1 2.76 3.32
2650 3400 3000 3025
40
60 80 120
Cut growth, in./hr. Normal Aged Running temp., O F. 250-lb.load
A2-16 10 56.7 0.7 2.44
1 . 5 4 Broke l5.Q 25.0
42
2. The polymer made in the redox system (Run 8) which combines fairly high tensile with low internal friction and relative energy absorption.
I t seems logical to compare the physical properties of a number of polyisoprenes prepared in a redox system with those of the Isoprene-styrene copolymers. These data (Table V) also indicate the effect of polymerization temperature. The charging recipe for this series of runs was as follows: Isoprene Water Benzoyl peroxide NaaPaOi Sorbose Fe(NH4)&30r)n.6HzO Sodium oleate MP-189-S
I n a n effort to study the gel characteristics of the polymers, a small sample (3 to 5 grams) of each was passed 10 times through a cold, hand-tight mill, and the properties for the original and milled rubbers were dctermined. The Williams plasticity valuee of the unmilled polymers were also obtained for comparison with a standard GR-S control. The gel produced with decreased dodecyl mercaptan concentrations readily dispersed on milling, as did the gel formed at normal modification and high conversion, the reductions being 60.8 to 16.7% and 63.6 to 1.97YG,respectively. The pel from dodecyl mercaptan-free charges, whether produced by benzoyl disulfide or by the use of excess alkali, was more permanent, decreasing from 70 to 50% in both instances. As a rule, a substantial increase in intrinsic viscosit,v accompanied the gel breakdown. The polymers were compounded in the standard tread recipe and tested against a GR-S control (Table VII1). The isoprene rubbers exhibitcd favorable high temperature (212 O F.) rebound, 10.i~ heat generation, good blowout time, loa internal friction, and relative energy absorption properties in comparison with a GR-S control; room-temperature rebound and crack-groirth resistance were poor. The high resilience at 212 F., and the low-running temperature, internal friction, and energy adsorption indicated stocks of improved efficiency. As a rulc, the properties for the gel-containing isoprene copolymers were comparable to those for the isoprene analog of GR-S. Slight advantages in rebound at 212" F., blowout time, and heat generation accompanied the partly soluble polymers The rubbers from charges with benzoyl disulfide and excese sodium hydroxide showed longer blowout time and lower runninp temperature than the other polvmers of the group; elongatinrt and crack-growth properties were not promising. Ths properties of the gel-containing isoprene rubbers seemed, in general, t o progress from t h e ~rl-frccrubher to the sample@ containing a tight gel
LOO 200 0.25 0.20 0.60 0.25 1.0 4.0
AB the temperature was lowered, the expected improvement in
physical properties failed to materialize. The only significant change was the drop in gel from the 40" to the 30" C. polymer. Compared to GR-S, these rzdox polyisoprenes exhibit improved efficiency as shown by lower runninp temperature and longer blowout time. However, they are inferior in per cent elongation, tensile strength, and resistance to cut groiT-th. Since the increased amount of 1,4 addition (9) in the polyisoprenes has not added anything t o the physical properties, it appears t h a t this factor alone is not significant in the preparation of a superior synthetic elastomer. Attempts to determine these values on isoprene-styrene copolymers led t o anomalous results, as the relative ratio of isoprene to styrene in the copolvmer is not readily determined. EFFECT OF GEL COXTENT
In the early work with butadiene-styrene systems it was shown that the gel increased with decreasing modifying agent, with increasing conversions above 77%, with high p H systems, and with the use of nonmodifying promoters. As the examination of isoprene as a butadiene replacemcnt has followed the pattern established in the investigation of GR-S, the butadiene backqround was again used when a study of the gel content of isoprene rubbers versus physical properties was made.
TABLE VI. POLYMERIZATION DETAILS Run No.
Isoprene Styrene Water KzSzOa Soap flakes DDM
4-104 Isoprene Control 75 25 180 0.3 5
0.25 ... ...
NaOH
Benzoyl disulfide Hours a t 50° C. Conversion, yo
4-105 Normal Conver ion 78 25 180 0.3 5
4-107 High Con-
version 75 25 180 0.8
.0.03 ..
23 79
23 80
5
4-108
High pH 7.5 25 180 0.3
Benzoyl Disulfidr 75 25 180 0.3 5
5
0.20
... ...
,..
0.5
is
40 92
'
4-106
I
80
...
...
0.5 23 83
TABLE 1'11 Run No.
4-104 GR-S Control
Gel, % Swelling index Intrinsic v i s cosityQ
.. .. ..
Gel, % Swelling index Intrinsic viscosity
,.
.. ..
4-105 Xormal Conversion
4-107 IIigh Conversion
Excess Caustic
4-108 Benzoyl Disulfide
Cnmilled 0.88 60.8 .., 81 2.18 1.39
63.6 Q9 1.11
70.6 43 1.17
72.2 42 1.12
Milled 0.65 16.7 ... 85 1.42 2.34
1.97 2.06
50.8 93 l.Q3
51.6 82 1.47
5.2 2.9
4.8 2.3
Iso-
prene Control
...
4-106
Williams Plasticity Unmilled Y3(1000C.) 3.1 2.8 4.8 3.8 Recovery, 1 0.3 0.2 2.6 0.8 min. a For a discussion of intrinsic viscosity see ( 2 ) .
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1948
TABLE VIII. TREAD STOCKPROPERTIES (All cures at 280’ F.) 4-104 4-105 Normal Cure GR-8 Isoprene ConMin.’ Control Control version 40 650 1500 1950 60 1050 1825 2200 1950 80 1250 2250 120 1425 40 2725 2125 2250 60 3150 2000 2200 80 2860 1900 2075 120 2860 2000 1950 10 720 340 350 60 600 320 290 80 510 290 280 L20 430 280 260
Run No.
300% modulus.
Ib./sq. in.
...
Tensile strength. ib./sq. in. Elongation, % ’
Rebound ’3’ a t 72; F: a t 212’ F. Cut growth Normal, in./hr. Aged 4 days at 212O F., in./hr. Firestone flexomekr 250-lb. load Running temp. O F. 500-lb. load Blowout time, min. Condition Forced vibrator data (80‘ cure) Dynamic mod.. lb./sq.in. Internal friction. kilopoises Energy abs. Hx5 Energy aba. Hfb
Static modulus, lb./sq. in. h
...
4-107 High copversion 1800 2150
Caustic
...
...
...
2200 2250 2050 2150 350 320 270 260
4-106
4-108
Excess
Benzoyl Disulfide
... .. .. ..
... .., ...
43 55
32 66
34 72
28 67
34 72
35 72
80
0.5
1.2
1.8
1.9
4.3
3.5
80
4.8
13.5
32.6
-20.9
43.6
49.7
80
283
237
236
224
228
80
17 Lar,ge cavity
72 Large cavity
406 210 8.7 4.7 150 75 90.5 167 201 120
379 215 6.25 3.1 107.5 53.5 74 114 256 164
Temp., F. 122 212 122 212 122 212 122 212 122 212
\>
234
93 63 Shattered
403 233 5.96 3.12 102.5 53.9 62.5 97.5 258 164
LITERATURE CITED
123 100 Shattered
431 230 7.39 3.17 127 54.6 67.2 99 258
If34
Grateful acknowledgment is made for the assistance of ,J. L. Dum in obtaining a portion of the physical testing data presented in this paper. Thanks are also extended to B. L. Johnson for physical chemical data and t o the Firestone Tire & Rubber Company for permission to publish this paper.
2275 2100 2100 1825 310 280 260 210
YO 80
440 250 6.3 2.94 108 50.5 55 83 258 172
The polymers appear to be inferior to GR-S in low temperature properties, tensile, elongation, and resistance t o cut growth. Further attention is being given to 76/25 and 85/15 isoprene-styrene ratios using activation with potassium ferricyanide and gel-containing isoprenestyrene polymers are being given a complete evaluation. ACKNOWLEDGMENT
...
1800 2375 1650 1600 , 260 210 210 200
2215
467 262 6.4 2.9 111 50 49.7 71.5 301 20 1
At constant amplitude relative t o natural rubber control. A t constant force relative to natural rubber oontrol.
(1) Cole, 0. D., Fickes, L. A., and Harrison, S.R., Firestone Research Laboratory, unpublished work on “Evaluation of Special Tire T y p ~ Polymers,‘’ Nov. 14, 1944. (2) Cragg, J . Colloid Sci., 1, 261 (1946). (3) Davis, C. C., and Blake, J. T., “Chemistry an6 Technology of Rubber,” A.C.S. Monograph 74, p. 114, New York, Reinhold Publishing Corp., 1937. (4) Dillon, J. H., et al., J . Applied Phys., 15, 309 (1944). (5) Gehman, S. D., Chem. Revs., 26, 203 (1940). (6) Gehman, S. D., etal., IND.ENO.CHEM.,35, 964
.--
(11148). --, -
(7) Havenhill, R. S., and Rankin, J. J., I n d i o Rubber W o r l d , 107, 365 (1943). ( 8 ) Hourvink, R., India-Rubber J.,92, 457 (1936). (9) Saffer, A., private communication, Firestone Tire & Rubber Co. to Office of Rubber Reserve, April 25, 1946. RECEIVEDJune 10, 1947. Presented before the Cleveland Meeting of the Division of Rubber Chemistry, ANERICAN CHEMICAL SOCIETY, M a y 26,1947.
PILOT PLANT COPOLYMERS i), number of the more promising laboratory recipes were repeated on the b-gallon ecale in the pilot plant, using the 75/25 isoprene-styrene ratio in these runs. The results of phgsical tests on the polymers (Table IX) served to substantiate the conclusions drawn from laboratory scale work. A variety of time cycles can be had depending on the activation chosen, thus making the isoprene-styrene monomer system adaptable to autoclaves with different heat transfer surfaces. These polymers were compounded in a treodstock recipe and for all tests, except tensile. were cured 60 minutes a t 280O” F. against 80 minutes for the GR-S control, for preliminary remlts showed them to be faster curing. Compared to the GR-S control, they exhibit superior efficiency as measured by reduced running temperatures, increased blowout times, and better rebound at 212” F. They have very acceptable tensile strengths but are somewhat deficient in cut growth and cold properties. The redox activated polymer appears to be slightly better than the rest of the group on the basis of tensile, Pfficieacy, and cut growth.
CONCLUSIONS
Isoprene-styrene copolymers and polyisoprene may be of interest in those applications where improved dynamic modulus and lower internal friction are the predominant, factors in product performance.
TABLEIX. PILOT PLANTISOPRENE-STYRENE COPOLYMERS Run No.
A264 Low GR-9 Modifier System High Gei 22.5 25 50 50 75 75 72 88 12.7 76.2 0.96 0.52 A263 In
milling
300% modulus, Ib./sq. in. Tensile, Ib./sq. in.
Elongation, To
‘
Cure, Min. b 20 40 60 80 20 40 60 80 20 40 60 80
Rebound, % e 72’ F. 212O F. Flexometer Data 0 Running temp., 9 P. Blowout time, min. Cut growthe Normal, in./hr. Aged 4 days a t 212’ F., in./hr. Low temp. index, C. 0
A266 A272 KsFe(CN)o AotiI/S/AN vated 75/23/2 17 14 50 50 75 75 74 69 53.7 36.9 1.69 2.96
A294 Redox Activated 7.5 40 75 51 60.9 0.54
C-361 GR-8 Control
.. .. 56 0.0
.
7.6 0.95
57.4 0.76
50.7 1.6R
,..
..
...
350 1550 2000 2175 1900 2550 2425 2175 880 450 360 a00
650 1950 2350
350 1600 2000
25 1875 2125
2750 2300 2350 2250 740 350 300 280
1700 2475 2425 2250 830 430 360 300
50 2075 2125 2175 920 320 300 280
625 1875 2275 2425 2225 2600 2375 2500 760 400 300 300
30 66
29 68.5
30 66.5
27 70
36 70
46 66
242 35
243 58
228 37
240 42.5
235 41
282 15.8
1.62 45.6
5.22 Broke
2.22 30.6
3.40 Broke
2.43 13.6
1.38 6.4
-28.5
- 28
-29.5
-25
- 30
-40
...
...
Intrinsic viscosity. b At 280° F. All cures 60 min. a t 280° F. versus 80 min. for C-361 control.
...
,..
...
... 50
500 1076 1376 100 2150 2900
3076 700 800 620 560
