STOPPING AGENTS FOR COLD RUBBER L. B. WAKEFIELD AND R. L. BEBR The Firestone Tire & Rubber Company, Akron, Ohio
A more thorough and searching method of evaluating stopping agents for synthetic rubber polymerization has been developed and used to demonstrate the value of several new compounds in stopping redox systems. The techniqne involves heating the latex in the presence of the particular chemical being tested, with subsequent isolation and analysis of the polymer. The determination of the change in the polymer solubility, intrinsic viscosity, and plasticity in addition t o the presently accepted conversion test made possible the development of materials showing a high degree of stopping activity. The determination of the aged cut growth resistance of compounded and cured stocks has also been used to evaluate those stopping agents which the earlier tests had shown to be of value. Since early work had shown that 2,4-dinitrochlorobenzene was a powerful stopping agent but was undesirably toxic, much of the work reported herein was concerned with the preparation and testing of reaction prodN T H E emulsion polynierizat,ion process leading to the prep-
in which a polymer could be isolat,ed than the previous measurements and would be a fair reflection of t,he relative processability of polymers stopped with different materials. Early work in the field of stopping agents had shown that at 50' C., benzoyl peroxide-initiated systems could he stopped by the same materials that were of value with persulfate systems. Therefore, when later experience proved that hydroquinone, formerly the most common stopping agent, was not sufficiently active to prevent conversion and plasticit,y changes in low temperature redox systems, it was believed that the use of an oilsoluble initiator in the redox recipe was not causing the difficulty. A more logical explanation was found in t,he greater a.verage life of free radicals formed at low temperatures ( 1 ) . This longer life meant that even after no more new radicals were being formed, polymerixation would continue. To destroy t,hese active points, stopping agent,swould be required which had a greater reactivit'y toward free radicals than previously used materials. Some of t,he earliest experience with stopping agents (4) had shown the great effectiveness of 2,4-dinitrochlorobenzene in stopping GR-S systems. The t'oxicity of this compound, however, prevented its use on a commercial scale, since equally effective less dangerous mat,erials were available. When redox recipes were developed for low temperatsure polymerizations, dinitrochlorobenzene was found to be one of the very few effective short,stops. A review of the early work also showed that the reaction product of dinitrochlorobenzene with the sodium salt of mercaptobenzothiazole had also shown good stopping action in GR-S recipes, and since it was virtually nontoxic, it was considered to be worth Iyhile to test it in a redox system. The fact that such derivatives also had a strong stopping action led t,o the belief that the chlorine atom in dinitrochlorobenzene was not the most important part of the molecule, and that other derivatives might be found which would combine high effective stopping action, freedom From toxicity, tendency toward staining, and low cost. The disclosure by Banes and Hund (2, 9) indicated that the addition of small amounts of hydroxylamine to certain alkyl phenols enhanced their value as nondiscoloring st'opping agents.
aration of synthetic rubber, it has been found necessary t o add a polymerization inhibitor, or shortstopping agent to the latex a t the optimum point (60 to 75% conversion). This agent must prevent increases in conversion during monomer recovery operations and latex storage up to the time of coagulation and drying. Since all normal emulsion syst'ems involve the use of an oxidizing agent as the polymerization init,iator, the stopping agent must decompose the remaining initiator as well a s reart with and destroy the polymer free radicals still existing, if further polymerization or cross linking is to be avoided. In a previous report (6) the results of testing a large iiuinber of compounds for inhibitory propert,ies in emulsion polymerization systems of the GR-S type have been given as a part of studies which were undertaken in order to find the best shortstopping agent for plant use. Conclusions drawn from the laboratory tests were based on eonversion changes because it had been found that if there were no change in the conversion, other polymer properties would be held constant. This criterion of stopping action was used for some t,ime until it was found that with low temperature redox recipes, even though no conversion increase occurred, often there was a corisiderable rise in Mooney plasticity during monomer recovery, coagulation, and drying. This was reflected in a highly undesirable loss in processability. This indicat'ion of incomplete destruction of active centers despite the use of relatively large amounts of stopping agent (such as hydroquinone) pointed to the need for further laboratory investigation, making use of methods which would detect as completely as possible an>*sign of incomplete stopping action. Since laboratory tests of processability, although often valuable, are subjective in rlxt,ure and require experienced operators, it was felt that other tests should be relied upon as an indication of change in polymer quality. For this purpose changes in conversion, Williams plasticity, solubility, and intrinsic viscosity were to be determined, with the stopping agent being added at the conversion norinally used in the particular system being studied. It was hoped that these tests would give a clearer indication of the actual condition
838 a
ucts of this material whirh were expected to be equall! effective, but less toxic. Of these derivatives, dinitrophenylbenzothiazyl sulfide, dinitrophenylpyridinium chloride, and dinitrobenzenethiol were found to be the most effective. All but the last material were tested on a pilot plant scale, and i t was shown that by the use of the firstnamed compound, polymers with a significantly superior aged cut growth resistance could be prepared. Toxicity tests on the pilot plant samples are in progress. The results obtained from a study of other derivatives indicated that the presence of nitro groups was not alone sufficient to give stopping activity and also that oil-solubility wan not essential. In some cases a heat softening of the polsmer while in the latex state was observed. This was most noticeable with the combination of 2,5-di-tert-butylhydroquinone and sodium nitrite, by means of which a high initial gel was reduced to zero during the latex aging perind of the test.
e
May 1950
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
This led to the expectation that similar synergistic pairs could be found which might be even more effective in the present problem. The high efficiency of phenylethanolamine, propose& by the same workers, was another starting point for further efforts.
TABLE I. GRrS TYPERECIPE
DISCUSSION
PartR 75 25 180 5.0 0 45 0.3
Butadiene Styrene Water Rubber Reserve Co. standard soap flakes Dodecyl mercaptan (teah.) Potassium persulfate
APPARATUS AND METHODS
The experimental examination of the polymerization-btopping action of the materials under question was carried out &s follows: a 100-gram monomer charge was loaded into a 28-ounce beverage bottle, using either a GR-S-type recipe (3) (Table I ) or a redox recipe (6) (Table 11), placed in a water bath, agitated endover-end, and allowed to polymerize at a definite temperature to the conversion at which the polymer would be isolated in the normal use of that recipe. Butadiene and styrene were used as examples of the most commonly used monomers, and the results obtained arc considered to be representative of those to be found with other materials. The monomer ratio also has been found to have little influence on the results. At the desired conversion, a solution or dispersion of the stopping agents was injected into the bottle through the self-sealing cap liner, by means of a hypodermic syringe and needle. The contents were thoroughly mixed by shaking, and then samples were withdrawn through the needle for solids determination and isolation of a solid sample of polymer large enough for William plasticity (IO) and sol-gel tests. The bottle was replaced in the polymerizer at 50" C. for either recipe for a further aging period of about 20 to 24 hours after which conversion, plasticity, and solubility were again determined. In some cases the dry polymer was subjected to heat aging tests; these involved holding the samples in a 70" C. forced draft oven for a number of days, noting any changes in the polymer's plasticity or solubility. ' The more promising stopping agents were used to prepare amounts of copolymer largc enough to allow compounding and curing tests. This was done either by mixing the product from several identical bottle charges or by using a 5-gallon reactor; in both cases the latex was aged a t 50" C. in the presence of the stopping agent exactly as the initial tests were run. In addition, the cured stocks were aged before testing, so that the final values reflected the protective action of the stopping agent both in the latex and in the dry state.
a39
Hours (50° C.) Conversion, % '
11-12 72
TABLE 11. R.EDOXRECIPE Parts 90 10 200 0.4
Butadiene Btyrene Water Potassium chloride Potassium oleate Dextrose Potassium pyrophosphate Ferrous sulfate Cumene hydroperoxide (100%)
5.0 3.0 0.33 0.28 0.17
Hours (15O C.)
3-5
Conversion, %
TABLE 111.
60
'hEAD
STOCK RECIPE
Polymer Sulfur EPC black Stearic acid Bardol Pine tar Phenyl-8-naphthylamine Zinr oxide Santocure
Parts 100 0 1.7 45 0 2.5 4.0 2 6 0 6 2 4 1.2 160.0
-
stopping agents from the first group are significantly superior in aged cut growth resistance to those made with agents from the second group. There are some indications that aged elongation at break follows the same course, as well as the increase in Williams plasticity values in compounding. The differences among the copolymers in tensile strength are small and irregular, as are the rebound and flexometer data. Alt,ogether, the aged cut growth data were found to be the most sensitive measure of utility among the stopping agents tested. The cut growth data were determined by the use of the Firestone groove cracking machine as described by Prettyman (1). I n the operation of this machine, a series of tests was conducted to establish criteria for use in ascertaining the existence of a significant difference between the cut growth values of two stocks. For this purpose factors were computed for each of the six settings of the machine and for the number of samples
GR-S Studies. A group of stopping agents which had been shown by preliminary tests to be of varying degrees of effectiveness in the GR-S system was examined by the proposed technique in that system. This was done to relate the results to the previous tests, which were in the GR-S recipe. The washed and dried copolymers were mill-mixed in a standard GR-S tread stock (Table 111) cured at 280" F., and tested with the results shown in Table V. The TABLE IV. PREPARATION OF GR-S SAMPLES FOR PHYSICAL TESTING DreDarational and raw Dolvmer Shortstopping Agent, 0.25 Part data are shown in Tabie l?. . p-PhenylThe data in Tabla V indiDinitrophenol + phenylDihydroxy0.1 part Dinitro- Dinitro- Phenylcate that the eight stopping Hydro- benzothiazyl diphenyl hydrpxyl- chlorophenyl ethrqnolquinone sulfide sulfide amine benzene oleate amine agents may be divided into two 73 74 72 72 ' 71 groups: In one are hydroConversion*% Initial 72 ' 76 86 76 77 75 quinone, dinitrophenylbenzoAged 72 Williams plasticity, mm. thiazyl sulfide, dinitrophenyl Initial 2.89 2.98 3.22 3.29 2.91 3.10 3.02 Aged 2.96 3.02 3.31 3.73 2.81 2.88 3.01 oleate, and phenylethanolaRecovery, mm, Initial 0.42 0.47 0.51 0.56 0.48 0.68 0.58 mine; d i h y d r o x y d i p h e n y 1 Aged 0.52 0.48 0.64 0.99 0.40 0.44 0.64 sulfide, phenylphenol plus hyGEI, % Initial 1.1 0.5 0.7 0.4 0.8 1.0 0.9 droxylamine, d i n i t r oc hl or o 1.Q 49 1.0 1.0 1.0 0.9 1.0 Aged benzene, and di-tert-butylhyIntrinsic viscosity 2.30 1.92 2.03 2.02 2.05 1.96 2.20 Initial droquinone are in the other. Aned 1.95 2.16 2.17 1.50 1.99 1.99 2.08 The copolymers made using
- .-
::
~
Diterlbutyl hydroquinone
71 77 2.87 3.20
0.47 0.50 0.6 1.2 1.98 2.07
-
*
840
TABLE V. GR-S
300% modulus, l b /
(51559)
inch Normal 900 Aged 2500 Tensile strength, l b / sq. Inch Normal 3400 Aged 2625 Elongation, % Normal 650 Aged 320 Williams plasticity, mm Raw 3 Compounded 3 Recovery, mm. Raw 0 Compounded 0 Rebound, % sq.
72OF. 212' F .
S T O P P E D WITH ~
r
~M CkT E R I~A L S ~
(Cure, 80 minutes a t 280' F ) Compound No a
GR-S
51734
51735
51736
51737
51738
~
~
51739
51740
51741
800 2360
850
1025 2475
750 2200
750 2150
850 2300
750 2150
3275 2700
3150 2850
3000 2250
3150 2400
3025 2250
3100 2325
3300 2450
3000 2400
720 360
670 350
660 270
590 290
700 310
700 300
680 320
660 320
36 08
3 07
3 14
3 22 3 34
3 41 3 49
3 55 3 88
2 85 3 13
2 93 i 16
3 09 3 34
3 02 3 38
74 59
0 55 0 51
0 51 0 61
0 54 0 64
0 92
0 44 0 57
0 59
0 44
0 51
0 50 0 60
1 10
48 51
49
52
48 50
49 53
47 49
48 85 17.3 296
47 83 18.0 300
48 82 173 314
51 85 21.3 292
3.9
4 7
6 6
7 2
47 53
Stopping agents: 51734. hvdroauinone
Redox Studies. The examination of these compounds a' stopping agents in the GR-S recipe was more or less preliminary to testing them in a low temperature redox system, which was the chief point of interest. It was felt that materials having no power t o stop a high temperature recipe would probably not be of particular use with a redox system, and that this could therefore be used as a screening test. Following the work described above most of the materials included in Table I were rechecked for effectiveness in stopping the polymerization of a 90: 10 butadiene-styrene mixture in an iron-activated redox recipe polymerized at 15" C. The aging period, to simulate plant stripping conditions, was 20 hours a t 50" C.
b
750 2200
3-Lb. penetration, mils 72' F. 50 Running temp. 80 Deflection, % 16.7 Runningtemp., OF. 279 Aged cut growth, inchedhour 2.7 0
Vol. 42, No. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
0 67
19
48 51
47 50
47 82 22.7 309
46 79 22.0 313
45 82 21.3 300
46 85 22.0 304
7 4
5 2
5.4
7 0
48
51738. dinitroahlorobenaene 51739; dinitrophenyl oleate 5 1740, phenylethanolamine 5 1741, di-teit-butylhydroquinorie
51735' dhitrdphenylbenzothiazyl sulfide 51736: dih droxydiphenyl sulfide 51737, p-pxenylphenol plus hydroxylamiiie
N I T R I T E ?S h U X I 1 , I 4 R Y
tested; for the setting and number of samples used iii the work reported here, a factor of 0.45 vias obtained. This factor is multiplied by the mean cut growth of the two stocks in question, if this product is smaller than the difference between the cut growth values of the two stocks, the difference may be considered significant (5% level). Thus (Table V) the cut growth of the hydroquinone-stopped sample was 3.9 inches per hour, whereas for that stopped with dinitrophenylbenzothiazyl sulfide, the cut growth rate was 4.7 inches per hour. The mean of these values is 4.3 inches per hour; multiplying this by the factor 0.45 gives 1.9, and since this value is larger than 0.8, the difference between the two stocks, they cannot be considered to be significantly different. In this fashion, the stocks given in Table '5' were compared, and the above general grouping arrived at. It should be understood, however that the higher members of the low group are not significantly superior, at the 5% level, to the low tnemhers of the higher group.
TABLEVI. AUXILIARYSTOPPISGAGIGSTSIS 15'' C. REDOX RECIPE
--I
______ I\' 'V
.Testa _..
I11
V T I Conversion, yo 62 63 63 60 61 63 Initial 63 67 67 77 69 64 Aged William plasticity, mm. 2.16 2.32 2.41 2.28 2.41 2.35 Initial 3.62 2.28 2.41 2.22 2.20 Aged 2.85 Recovery, mm. 0.16 0.05 0.05 0.05 0.06 0.07 1nit)ial 0.16 0 SO 0.14 0.11 0.39 0.15 Aged Gel, % 0.57 0.73 0.7.5 0.67 0.77 Initial 0.62 0 77 0.52 0.56 0.77 0.60 0.40 Aged Intrinsic viscosity 1.69 1.59 1.65 1.59 1.68 1.67 Initial 1.61 237 1.54 1.59 1.64 Aged 1.94 a Stopping agents: I 0 3 hydroquinone 11: 0 : 3 di-tevt-butylhydroquinone I11 0 . 3 di-tert-butylhydroquinone 0 . 2 KaNOi IV: 0 . 3 djnitrophenylbenzothiazyl sulfide V, 0 . 3 dinitrophenylbeneothmzylsulfide 0.2
I1
+
- .-- . -.
N*NO"
VI, 0 . 3 diphenyl-p-phenylenediamine
+
STOPPING XGEXT. The fiist group of conipounds tested included hydroquinone, as a standard, and three other materials arising from previous work in the GR-S recipe These materials are listed in Table VI together with the raw polymer data. In this case, the dry polymers were further aged by heating for 2 days at 70" C. in a forced draft oven, and Williams plasticity again determined. Williams plasticity, 2 91 mm. Recovery, mm. 0 46
2 28
1 80
2 08
2 41
7 74
0 16
O 01
0 00
0 19
I 11
Here the addition of an auxiliary stopping agent has had an observable effect in only one of the two cases in which it was used. Conversion increases i-cere very small even without sodium nitrite, but the substituted hydroquinone plus sodium nitrite actually caused a softening on aging; in the benzothiazyl sulfide compound, nitrite was of no effect. The phenylenediamine compound mas not particularly interesting, since it allowed too great a conversion and plasticity increase. The gel value, however, remained practically unchanged. NITROCOUPOUNDS.A group of dinitrochlorobenzene derivatives furnished a more interesting picture, with some promise of eventual utility. The compounds are given in Table VII. Of these, dinitrochlorobenzene, dinitrophenyl oleat.e, and clinitiophenylpyridinium chloride were highly effective in preventing conversion and plasticity increases; dinitrobenzenet.hio1 held the conversion constant, but allowed the Williams plasticity value to rise. A comparison of the fourth and fifth compounds shows that the presence of two nitro groups considerably improved the inhibitory power of phenylethanolamine, but that it still was not sufficiently powerful to prevent further reaction. Following these laboratory tests, some of the materials were checked on a pilot plant scalc in 5-gallon reactors, using a redox recipe similar to t.hat mentioned and carrying out the tests in an exactly similar manner, aging the st'opped charge 24 hours at 50" C. Some of the materials gave unexpected difficulties at this point; in particular, diiiitrophcnylpyridinium chloride caused prefloc, though the plasticity remained constant. The polymers finally isolated from the aged latices were compounded in a standard tread stock recipe and compared with a GR-S control.
May 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE VIII. PILOT PLANTTESTSOF STOPPING AGENTS
TABLEVII. DINITROCHLOROBENZENE AND DERIVATIVES AS STOPPIXG AGENTSFOR 15 C. REDOXRECIPE O
'
Conversion, % Initial hged Williams plasticity, mm. Initial Aged Recovery, mm. Initial Aged Gel, ,% Initial Aged Intrinsic viscosity Initial Aged
Stopping Agent, 0.3 P a r t DinitroDiniDinitro- DiMDini- phenyltrotropyri- Phenyl- phenyltrochloro- phenyl dinium ethinol- ethanol- benbenzene oleate chloride amine" amine zenethiol 61 67
67 68
59 61
60 94
57 73
59 60
2.16 2.17
2.39 2.49
4.34 4.82
5.20 6.79
5.00 6.22
4.63 5.36
0.05 0.12
0.10 0.17
2.09 2.45
2.63 1.83
2.22 3.92
1.80 0.14
0.62 0.77
0.72 0.60
.. ..
..
1.59 1.55
1.69 1.69
,
.. ..
,
,.
.. ..
Stopping Agentsa (0.3 Part) R u n No. 1009
Conversion, % Initial 57 Aged 59 Williams plasticity, mm Initial 3 10 Aged 3 33 Recovery, mm. Initial 0 47 Aged 0 68 Cnl " l b ,
*,-. ,
..
84 1
G7
1017 56 61
1040
1043
57 69
1049
53 57
51
Pre5oc
3.35 3.20
1.92
..
2.88 4.05
2.36
0.60 0.32
0.00
0.26 1.19
0.03
..
..
Ingal 0.6 15.7 , . 0.9 .. Aged 1.1 0.6 ,. 55 .. Intrinsic viscosity Initial 2.10 1.90 ,. 1.06 .. Aged 2.06 1.88 1.67 .; a Stopping agents: 1009, dinitroohlorobenzene, 1017, dinitrophenylbenzothiazyl sulfide 1040, dinitrophenyl oleate, 1043, Santovar-0 f NaNOz (0.2 part), lb49, dinitrophenylpyridinium chloride
..
..
t .
TABLE IX. PHYSICAL TESTDATAON PILOTPLANT SAMPLES
0.2 part.
(Cure, 80 minutes a t 280° F.) Stock N0.a
The stopping agents tested and the raw polymer properties are included in Table VI11 and tensile data in Table IX. The gel and intrinsic viscosity data for the mixture of Santovar-0 (2,5-di-tert-butylhydroquinone) and sodium nitrite suggest that the combination was not acting as a true stopping agent, but that the low gel and high plasticity of the polymer finally isolated results from a latex heat softening process. In Table I X the aging period was 4 days at 212' F.; it is the aged data which are most significant in this study. The materials may be separated into two groups on the basis of these data; in one is dinitrophenylbenzothiazyl sulfide; in the other are dinitrochlorobenzene, dinitrophenyl oleate, di-tert-butylhydroquinone plus sodium nitrite, and dinitrophenylpyridinium chloride. The material in the first group is outstanding in respect ut growth resistance, whereas its tensile strength and elongation are substantially the aame as the best of the second group, so that altogether it represents a worth-while advance, SUMMARY AND CONCLUSIONS
.
There were two main objects of this work. One was to develop a method for investigating stopping agents which would be more thorough and complete than hitherto used, giving a closer correlation with plant scale results. This goal has been substantially gained, though there still remain the differences in behavior caused by the use of different methods of agitation. The second object was t o develop stopping agents which were more effective in low temperature polymerization systems; this work has been only partially completed, for it is felt that more progress can still be made in this direction. Several of the materials tested were found to be outstanding in their effectiveness in stopping polymerization in redox systems. Of these, dinitrophenylbenzothiazyl sulfide was possibly the best, with dinitrophenylpyridinium chloride and dinitrobenzenethiol close seconds. These .three ma,terials probably depend on different mechanisms for their effectiveness. The benzothiazyi sulfide may well owe its action to an activation of a point on the ring by the nitro groups, wher'eas the pyridinium compound is known to react in the presence of base to give a form of glutaconaldehyde, leaving behind dinitroaniline. The different forme of these materials are undoubtedly highly active toward free radicals, and the resulting adducts would be greatly stabilized by resonance. The thiol could react in the same manner as an overactive mercaptan modifier (9), acting as a chain terminator instead of a transfer agent. The relative inactivity of dinitrophenylethanolamine may arise from the fact that the activity of the parent phenylethanolamine is due to the assumption of a quinoid form, which would be made difficult by the presence of two nitro groups, and the inactivity of the phenylethanolamine
Normal Modulus a t 300%, lb./sq. inch Tensile strength, lb./sq. inch Elongation, % Aged 4 days @ 212O F. Modulus ,at 300y0, lb./sq. inch Tensile strength, lb./sq. inoh Elongation % Rebound, dl, 72' F. 212' F.
Cut growth. inches/ hour
,51559
51768
51769
51770
51771
__ 51772
, 900
525
525
500
725
475
3450 670
2175 680
2750 760
2300 750
2925 700
3100 800
2300
1825
1750
1775
2025
1650
2400 310
2355 370
2550 410
1775 300
2200 330
2700 440
39 50
37 45
43 45
31 41
39 47
31 41
3.8
9.2
3.4
12.8
8.4
8.8
itself in redox systems indicates that quinoid forms are too weak to be of value. The solubility of the compounds appears to have no direct bearing on the stopping power, as dinitrophenylpyridinium chloride is very soluble in water, but compounds such as dinitrophenylbenzothiazyl sulfide and dinitrophenyl oleate are insoluble. It seems most probable, therefore, that in most of the compounds studied the stopping action results from a specific reactivity for free radicals and not a destruction of the initiator. The presence of nitro groups is essential, but not sufficient of itself to ensure stopping power; they probably activate a point or another group within the molecule, and reaction occurs a t this point. BIBLIOGRAPHY
(1) Bamford and Dewar, Proc. Roy. SOC. ( L o n d o n ) , 192, 309, 329 (1948). (2) Banes and Hund, private communication of Standard Oil De-.
velopment Co. to Rubber Reserve Co. (Oct. 11, 1945). (3) Craig (to B. F. Goodrich Co.), U. S. Patent 2,362,052 (Nov. 7, 1944). (4) Kluchesky and Bebb, private communication of Firedone Tire & Rubber Co. to Rubber Reserve Co. (June 15, 1945). (5) Kluchesky and Wakefield, IND. ENQ.CHEM.,41, 1768 (1949). (6) Mitchell, Spolsky, and Williams, Ibid., 41, 1592 (1949). (7) Prettyman, Ibad., 36,29 (1944). (8) Schulze and Crouch (to Phillips Petroleum Co.) U 8. Patent 2,425,840 (Aug. 19, 1947). (9) Standard Oil Development Co., Brit. Patent 612,252 (Nov. 10, 1948). (10) Williams, IND.ENG.CHEM.,16, 362 (1924). RECEIVED September 26, 1949. Presented before the Division of Rubber Chemistry a t the 116th Meeting of the AMERICANCHEMICALBOCIETY, Atlantic City, N. J. This investigation was carried out under the sponsorship of the Office of Rubber Reserve, Reconstruction Finanoe Corporation, in connection with the government synthetio rubber program.
