Pslvbutadiene Modified bv Addition of Thiols Containi J
J
C. S. MARVEL, IC. G. CLARICE, .IND H. IC. INSICIP Noyes Chemical Laboratory, University of Illinois, Urbana, I l l .
W. IC. TAFT AND B. G. LABBE Government Laboratories, University of Akron, Akron, Ohio
T
HE purpose of this research was to introduce into polybu-
tadiene polar groups which might improve the oil resistance of t,he polymer without destroying its good low-temperature properties. It is well known that the introduction of nit,rile groups along the chain by copolymerization of butadiene n i t h acrylonitrile gives the desired oil resistance. but this also raises the freesing point'. It was thought that if the oil-resistant groups could be introduced, as in a series of side chains attached to polybutadiene, the tendency to crystallize would be reduced, and the good low-temperature properties of polybutadiene might be retained n-hile oil resistance was increased. Serniuk, Banes, and Su-aney (8)have shown that thiolsaddreadily to polybutadiene, and Serniuk (9) has reported that, the mercaptoacetic acid adduct has improved oil resistance over the untreated polybutadiene. However, the low-temperature properties of the adduct. were not described. In the present work, adducts of polybutadiene and P-mercaptopropionitrile, p-mercaptoethanol, 1-t,hiosorbitol, mercaptoacet'ic acid, and thiolacetic acid were prepared, and their low-temperature and other physical properties !yere investigated. p-~Lercaptopropionitrile was added to polybutadiene latex. The polybutadiene was prepared in an acid-side redox system ( 7 ) , and after stripping the lat,iceP of excess butadiene by bubbling nitrogen through them, the thiol and azobisisobutyronitrile were added to the polymerization bottles. The bottles were tumbled for about 4 days a t 50" C. The latex after being mixed with antioxidant was coagulated and the polybutadiene-thiol adduct isolated. Emulsion systems could not be used successfully for th'olacetic acid or the water-soluble thiols (mercaptoacetic acid, l-thiosorbitol. arid 0-mercaptoethanol). These sulfhydryl derivatives xere added to polybutadiene in dioxane solution Tvith azobisisobutyronitrile as the initiator of the reaction. It was found that, t,he addit,ion had t o be carried out in the absence of air if a noncrosslinked polymer was to be obtained. When any trace of air remained in the reaction system gelation occurred, but under airfree conditions satisfactory addition of 3 to 5% of thiol to polybutadiene was achieved. The difference in behavior between hydrophilic and hydrophobic mercaptans in emulsion addition reactions was also illustrated using a monomeric olefin, I-hexene. n-Decyl mercapt'an was easily added to 1-hexene in emulsion while attempts to add 1-thiosorbitol were unsuccessful. S-n-Hexyl-1-thiosorbitol was made for comparison. The new compounds thus obtained are described in the experimental part,. Polybutadiene-thiol adduct samples containing 3 % of combined p-mercaptoethanol, 2.8yu of 1-thiosorbitol, 2.6 and 12.3% of mercaptoacetic acid, and 3.8% of added 0-mereaptopropionitrile were prepared, compounded, and cured. Their stress-strain, low-temperature, oil-resistance, and hysteresis properties were evaluated according to standard ASTM procedures. I n treadstock recipes, these treated polybutadienes were all shorter (elongation) than the control except for the butadiene-B-mercaptopropionitrile adduct, which showed an elongation of 580%. The tensile values were all favorable as compared to the control.
The treatment with thiols did not appreciablj altei the low-temperature flexibility as shown by the Gehman test Loit-temperature retraction tests indicated t h a t the treatment did not markedly affect the tendency of polybutadiene to crystallize. The oil resistance of polybutadiene was marked11 imp1 oved. but this propertv did not meet t h a t of the standard prepared from 82 parts of lJ-butadiene and 18 parts of acrylonitrile In carcamstock recipes, the superiority in tensile-strength values of the adducts over the original polybutadiene was more pronounced than in the tread-stock recipes. There was no significant change in hysteresis properties as a result of the treatment. I t is noteworthy that the polybutadiene t o which 12.3Yu of mercaptoacetic acid had been added showed no improvement in oil resistance over that to which only 2.6% had been added. The former sample had cross-linked badly in the addition reaction, as shown by its 50% solubility, and it is possible that this caused some unexpected difference in the two materials teyted.
T.4BLE
I.
Sample
ADDITION O F
PH
n-DEcYL Time, Hours
>IERC.4PTAA TO I-HEXENE
Yield. Gram-
B.P. '1 Yim,),
C.
EXPERIMENTAL
a miStUrt' O f 102.3 grams (1.9 moles) of acrylonitrile and 148.1 grams (1.9 moles) of thiolacetic acid in a 500-ml. three-necked flask equipped with a stirrer was added 5 ml. of pyridine a t room temperature. The temperature rose to about 90' C. and then began to fall. The mixture was stirred overnight and then distilled. The product was a colorless liquid, boiling point 124" t o 126' C. a t 22 mm.. and the yield was 164.0 grams (65.4%). Infrared analysis of this liquid. presumably p-cyanoethyl thiolacetate. showed bands a t 2246 and 1693 cm.-' which indicate, respectively, the presence of nitrile and thiol ester groups. A mixture of 163.4 grams (1.3 moles) of this ester, 265 ml. of absolute methanol, and 5 ml. of concentrated sulfuric acid was placed in a 500-ml. flask under a column packed rvith glass helices. The column was fitted with a total-reflux, partial take-off distillation head. The reaction mixture waszefluxed until the temperature of the condensing vapors was 54 C. a t which temperature the azeotrope of 35 mole % methanol and 65 mole % methyl acetate (6) was removed slowly. K h e n the temperature rose t o the boiling point of methanol, the reaction mixture was cooled. T o neutralize the acid and t o remove the water thus formed, 19 grams of sodium bicarbonate and 22 grams of anhydrous magnesium sulfate were added. After standing overnight, thc mixture was filtered and the methanol removed a t room temperature under reduced pressure. The product \\-as again filtered and distilled. T h e nitrile boiled a t 44" to 46" c. a t 1 mm..; ngo 1.4863. The yield was 72.9 grams (66.0%). Amperometrir titration for thiol group (assuming the product t o be 8-n~ercapt~propionitrile) showed the product to be 100% pure. ANALYSIS FOR C3H5SS ~->~ERC.4PTOPROPIONITRILE, T O
Calcd. Found
2090
C 41.35 41.65
H
S
7 78 j 8.3
36.79 37 04
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1953 Recent patents (2) describe 0-mercaptopropionitrile as a product of alkaline hydrolysis of the thiolacetic acid adduct of acrylonitrile.
4
2091
THIOLSTO POLYBUTADIENE IN SOLUTIOX TABLE11. ADDITIONOF SUBSTITVTED Wt., Grams
Thiol
Polybutadiene in Dioxane, Grams/Ml.
haobisisobutyronitrile, Gram
Temp., Time, C. Days
S, %
Solubility Inherent (BenT'iscoszene), 70 ity
ADDITIOXO F ~ I - D E C Y L MERCAPTAN TO ~ - H E X E X E . An emulsifier solution was prepared consisting of 50 ml. of redistilled water, 0.5 gram of MP-189-EF (a mixture of electrolyte-free C16 alkanesulfonic 0.49 99 1 6 30 2 0,002 &Mereaptoethanol 0.16" 5/60 acids), and 0.5 ml. of 1 M +I 100 1 6 0.002 5/60 30 2 0.16a sodium acetate. Glacial acetic Mercaptoacetic acid 0.19d 5/80 0.002 30 a 1 04 72 1 2 acid was added to give the de+I 98 1 8 0 l9Cld 5/60 0.002 30 2 sired pH. -4 mixture of 1.3 99 0.6 Thiolacetic acid 0.15 1.6/25 0.002 30 5 grams of ammonium persul+I 96 1.8 6 0.156 5/60 0,002 30 2 0.95 +I 100 fate, 0.65 gram of sodium bi0.15 5/60 0,002 30 2 0. 15c 5/60 0.002 30 2 + f 100 1 . 7 sulfite, and 0.065 gram of copper sulfate was added as initiator. a Infrared analysis showed hydroxyl bands a t 3368 cm. -1 Approximate. experiments were run a t room temperature. To this solution were added Mixture was evacuated three times with water p u m p and C Runs were d r r i e d out with careful exclusion of air. 4.2 grams (0.05 mole) of 1reflushed with nitrogen t o ensure the removal of air or oxygen. hexene and 8.7 grams (0.05 d Infrared analysis showed carboxyl bands a t 1710 cm. -1 8 Infrared analysis showed thiolacetate group bands a t 1693 cm.-1 mole) of n-decyl mercaptan. f Positive qualitative test for sulfur. The reaction was carried out a t room temperature in a 200-ml. three-necked flask eaui.a.aed with a stirrer. -4fte; tge-iindicated time, the emulsion was broken with 15 ml. of alum coaguand allowed to stand. The benzene layer yielded a white intraclant, and the entire volume was extracted with 50 ml. of ether. table solid. The ether layer was washed with 50-ml. portions of 0.5 N sodium 48.0 C 5H .78 7 .s1 2 Calcd. for hydroxide, dried, and distilled. The product, n-hexyl n-decyl 53.6 7 34 6.51 Thiosorbitol hexaacetate sulfide, was pale yellow and had a slight disagreeable odor. The 5 66 7 87 S-%-Hexyl thiosorbitol pentaacetate 47.2 results of these experiments are listed in Table I. Thiosorbitol disulfide decaaoetate 5 84 9.17 Found 46.77 The sulfone of this compound, prepared according to the method of Bost and coworkers (I), melted a t 69" C. after reApparently only oxidation of thiosorbitol t o the correspoiidiiig crystallization from ethanol. disulfide, and not addition to the hexene in the oil phase, had OCcurred. -\44.4LYSIS FOR CIBH~~SOZ REACTIONS OF MERCAPTANS WITH POLYBUTADIENE IS EXKLc . H S SION SYSTEMS. Emulsions of polybutadiene were prepared with Calod. 66 29 11.70 11.01 the following recipe: 65 91 11.38 11.30 round
S-n-HEXYLI-THIOSORBITOL. This preparation is a variation of that employed by Farlow and coworkers (3) for the preparation of S-n-dodecyl-I-thiosorbitol. A solution of 4.13 grams of n-hexyl bromide in 12.5 ml. of dioxane was added t o a solution of 5.0 grams of 1-thiosorbitol and 1 gram of sodium hydroxide in 12.5 ml. of distilled water. T h e entire mixture was refluxed for 2.5 hours, cooled, and extracted with ether. T h e ether layer was evaporated to about 10 ml. Distilled water was added, causing the precipitation of a white solid. T h e yield was 3.0 grams. This substance, after recrystallization from hot water, had a melting point of 98" C. -4S.4LYSIS FOR
Calcd. Found
CizHzeOsS
c
H
51.10 51.22
9.22 9.49
S 11.34 11.13
-4n attempt was made to prepare this sulfide from 1.2 grams of I-hexene and 3.2 g r a m of thiosorbitol in a n emulsion containing 3.0 ml. of LIP-635-S and 37 ml. of distilled water, with 0.23 gram of sodium tetradecanesulfinate, 1 ml. of 2.5% ferric sulfate solution, and 30 ml. of air added as initiator. COMPOSITION OF EMULSIFIER, MP-635-S Sodium hexadecanesulfonate Unreacted hydrocarbons Sodium chloride Sodium sulfate About 3% isopropyl alcohol was added t o maintain a homogeneous solution.
49 5% 10 3 0 86 0 4
The reaction mixture was tumbled at 28 r.p.m. at 30' C. in a 4-ounce screw-cap bottle. The mercaptan content was determined periodically by amperometric titration. After 8 days only a small amount of mercaptan remained, so the emulsion was broken and the reaction mixture was extracted with ether, Evaporation of the ether layer yielded no residue. The aqueous layer was evaporated to dryness, treated with excess acetic anhydride in benzene, and gently heated for 2 hours. Twice the volume of water was added, and the entire mixture was shaken
3,0 ml. MP-635-9 0.030 gram Azobisisobutyronitrile 38 ml. Redistilled water 0.04 grain Hooker's lauryl mercaptana 20.0 grams Butadiene a A mixture bf rimary alkyl mercaptans having the average molecular formula ~ 1 2 . e ~ l e . z ~ h .
These ingredients were mixed in a Pounce bottle which x a s tumbled end over end at 28 r.p.m. and 50' C. for 15 houfs. The bottle was then o ened, and the unpolymerized butadiene was stripped out by buPbbling nitrogen through the latex for about an hour. The addition of a small portion of Dow-Corning Antifoam A facilitated this operation. Stripped latices were stored under nitrogen in a refrigerator for several days with no observed deleterious effects on further reactions. T o a bottle of stripped polybutadiene latex prepared as described above containing approximately 10 grams of polymer in 50 ml. of emuision, were added 0.1 gram of azobisisobutyronitrile and the appropriate mercaptan. Then the bottle was again sealed under nitrogen and tumbled a t 50" C. for 2 days. The bottles were opened, a small amount of a n emulsion of phenyl-2naphthylamine was added, and the emulsions were broken by adding alum coagulant (about 25 ml.) and ethanol (about 100 ml.). When 1.1 grams of 6-mercaptopropionitrile was used in such a n experiment, polybutadienes containing sulfur which ne!e soluble in benzene t o the extent of 55 t o 91% were obtained in different trials, Thiolacetic acid (1.1 t o 3.82 grams) also gave products containing sulfur, but their solubilities in benzene were generally only 45 t o 70%. When mercaptoacetic acid (as much as 4.6 grams , @-mercaptoethanol (as much a s 3.9 grams), or 1thiosorbitol )as much a s 9.9 grams) were employed, the polymer obtained was free of sulfur, which indicated t h a t no addition had occurred. I n a few cases, potassium persulfate (0.5 gram) was used in place of the azobisisobutyronitrile, but the results were the same with the water-soluble thiols. Experiments with the watersoluble thiols in emulsions containing 1 gram of added sodium chloride and 1 gram of Daxad-11 were still unsuccessful. An evaluation sample of the adduct of @-mercaptopropionitrile was prepared by making 25 runs of polybutadiene in 4-ounce polymerization bottles using the above recipe a t 50" C. for 15
INDUSTRIAL AND ENGINEERING CHEMISTRY
2092
POLYMERS TABLE 111. EVALUATIOS
PREPARED I11
region showed that the exp e h d functional group had actually been introduced into the molecule. The polymers thus prepared for evaluation are described in Table 111.
SoLUTION
ReacSolubility Added tion (BenInherent Thiol Wt., Time, Yield, zene), Viscos(Calcd.), Sample Thiol Added Grams Days Grams % ity S, % % 37.4 3 253.1 262 &Mereaptoethanol 2.1 1.25 3.0 257.3 100 97 1.9 0.46 2.8 263 1-Thiosorbitol 40.0 4 266 Mercaptoacetic acid 48.0 3 285.0 100 1.4 0.90 2.6 243.8 50" 3.38 12.3 276 Mercaptoacetic acid 46 3 Product was insoluble in benzene and this value is for carbon disulfide. The insolubility was apparently due t o failure t o remove oxygen completely, which evidently increased the amount of thiol added. Evaluation indicated t h a t samples 266 and 276 differed for reasons other than the amount of thiol added.
EVALUATION O F T H E POLYMERS
...
The polymers were comp o u n d e d a c c o r d i n g to the r e c i p e s i n T a b l e IV. I n Tables V, VI, VII, and VI11 are summarized results obtained with tread-type compounds of treated polybutadiene compared with controls when tested for stress-strain ( I I ) , Gehman low-temperature flexibility ( 5 ) )temperature retraction, and oil-resistance properties (4). The stress-strain properties (Table V) of the thiol-treated stocks show that the adducts of mercaptoacetic acid, l-thiosorbitol, and p-mercaptoethanol are all shorter (elongation) than the control polybutadiene, probably because of the higher viscosities of the raw stocks. The elongation of the P-mercaptopropionitrile adduct is higher than the control. The tensile values were all favorable compared with the control. It is noted that the best stress-strain properties were obtained with the thiol-treated polymer having the lowest Mooney and inherent viscosity. The treatment of polybutadiene by the thiols did not alter appreciably the low-temperature flexibility, as shown by the Gehman test (Table VI). The temperature-of-retraction teats (Table V I I ) apparently indicate that the small amount of thiols added did not markedly affect the tendency of the polyhutadiene to crystallize. The oil resistance of the polybutadicne was improved considerably by the addition of minor proportions of thiols, but not to the extent that with the amounts added it >vas equal t o Perbunan 18 (Table VIII). The stress-strain and hysteresis data obtained on compounds of the experimental and control polymcrs (carcass-typr rrcipe) are summarized in Tables I X and X. The superiority of the treated polybutadiene stocks in tensile-strength va1uc.s was
TABLE IV. COMPOUNDING RECIPES Polymer Type Polymer E HPMCFblack black Zinc oxide Red lead Sulfur Altax Stearic acid Circosol-2XH Total
Experimental 100
40 ... 5 .2. . 1.75
... ...
Tread GR-Sa 100 40 ... 5 ... 2 3 1.5
...
PolyBDb 100 40 ... 5
.2. . 3 1.5
...
148.75 181.5 151.5 a GR-S X-672, 41' F. GR-S. Polybutadiene, made a t 50' C. in the Mutual recipe.
Vol. 45, No. 9
Carcass, All Polymers 100
30'
. 2. ..5 2 1
..I
__ 20 155.5
hours, The latices were mixed and stripped of butadiene by bubbling nitrogen through the mixture for 1 hour and then by reducing the pressure with a water pump for 2 hours. The mixed latex was then recharged into 25 bottles. For each 50 ml. of emulsion, 1 ml. of a solution of 1.25 grams of azobisisobutyronitrile in 25 ml. of 8-mercaptopropionitrile was added. The bottles were sealed and tumbled a t 50' C. for 2 days. The latices were mixed, a small amount of emulsion of phenyl-2-naphthylamine was added, and the polymer was coagulated by adding 600 ml. of alum coagulant and 2400 ml. of methanol. The polymer was washed and dried. The yield was 262.6 grams. The infrared absorption of the polymer showed bands a t 2246 cm.-l, indicating the presence of nitrile group. It was soluble to the extent of 80% in benzene, and the inherent viscosity in benzene was 2.4. The sulfur analysis (1.4'%) indicates that this polymer contains 3.8% pmercaptopropionitrile added to the polybutadiene. This is sample 261 in Tables V through X. ADDITIONOF SUBSTITUTED THIOLSTO TABLE V. STRESS-STRAIN TESTS AT 77" F. POLYBUTADIEKE IK DIOXANE SOLUTIOS. To solutions of polybutadiene in dioxane (Jlicrotechnique, tread-type recipe) were added initiator and thiol. The Curine bottles were flushed with nitrogen, sealed, Timeat 300% Tensile and tumbled end over end a t the tem292O Modulus, Strength Williams perature indicated. ,4t the end of the F., Lb./Sq. I,b./Sq.' Elong., Set, Tisc. Plasticreaction period, phenyl-2-naphthylamine Samplo Thiol Added Min. Inch Inch % % ' 3IL-4* ityb equivalent t o about 10% of the weight of 261 &Mereaptopropionitrile 700 2480 580 11 50 69 0.166 the polymer was added, and the polymer 50 ... 190 6 91 262 8-Mercaptoethanol 1600 0.198 190 7 50 113d 263 1-Thiosorbitol 1850 ... 0.126 was precipitated by pouring the solution ... 170 75 Mercaptoacetic acid 1800 3 .. 0 190 276 into 4 volumes of distilled water. The 50 2460 2890 230 4 82 0.167 266 Mercaptoacetic acid results of these experiments together with 50 4940 770 17 910 49 0.116 GR-S ....... 75 520 7 29 1580 660 PolyBD ......... ... the variations in procedures are summarized in Table 11. a 212O F. Load. 3000 grams; 3-minute value PREPARATION OF EVALUATION SAMPLES Questionable. IS SOLUTION.Polybutadiene was preCrumbled. pared in the Mutual recipe ( I d ) and, withe 200% modulus. out adding any antioxidant, was coagulated, washed, and dried before preparing a solution. For each sample, 230 grams TABLE T'I. GEHlf.%s I~OW-TEI\IPER.ZTURC TESTY of polybutadiene (solubility 95 to 100% (Tread-type recipe) and inherent viscosity about 2) was disCuring solved in 3500 ml. of redistilled dioxane, Time together with 0.5 gram of azobisisobutyrTemperature, - * C. at 292O F., Freeze onitrile and the indicated amount of Tz TS Tin Tm Pointn Sample Thiol Added >Tin. thiol. The same precautions to remove oxygen were taken here as in the previous 62 70 30 57 71 8-llercaptopropionitrile 50 261 63 5 72 69 50 34.5 60 8-Meroaptoethanol 262 experiments. After 3 or 4 days of 67 74 73 50 62.5 33 1-Thiosorbit ol 263 tumbling, about 40 grams of phenyl-25 0 43 59 62 6 7.5 70 Mercaptoacetic acid 276 65 75 70 62 50 37 Mercaptoacetic acid 266 naphthylamine was added, and the 40 49 $5 3 53 22.5 60 ..... .... ... GR-S polymer was coagulated by pouring the 55.5 63 73.5 76 36 60 . .... PolyBD dioxane solution into 14 liters of distilled Temperature a t which relative stiffness, compared t o t h a t a t 77' F., is equal to subscript. water. The polymer was washed and dried. Examination in the infrared a
I
.
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
September I953
TABLE VII. TEMPERATURE-OFRETRACTION TESTS AT 100% ELONGATION (IO) (Tread-type recipe)
Sample 261 262 263 276 266 GR-S PolyBD
Thiol Added &Mereaptopropionitrile ,¶-Mereaptoethanol I-Thiosorhitol Mercaptoacetic acid Mercaptoacetic acid
......... .........
TABLE VIII.
Curing Time at 292O F. Min. 50 50 50 50 50 60 60
10 68 60 62 64 62 52 72
Retraction, % 30 50 58 48 44 33 41 29 55 48 44 26 47 41 62 51
70 37 22 17 35 9 33 38
Difference' TRIOTR7o 31 38 45 29 53 19 34
OIL RESISTANCE5
__
(Tread-tvue recipe) . .
Sample 261 262 263 276 266
GR-S
Pol BD Pergunan 180
Thiol Added &Mereaptopropionitrile 8-Mercaptoethanol I-Thiosorbitol Mercaptoaoetic acid Mercaptoacetic acid
......... ......... .........
No: 1 No: 2 No. 3 Oil 19 13 9 12 9 13 33 0
Oil 44 26 26 37 30 30 69 6
100%
60/40
Iso-
octane/ Oil octane Toluene 60 205 135 44 115 77 44 95 64 82 48 120 73 48 115 115 69 192 174 91 218 19 13 82 160-
Special Solvent Mixturea 205 105 95 120 115 I99 218 77
2093
uble substituted thiols p-mercaptoethanol, l-thiosorbitol, and mercaptoacetic acid goes well in dioxane solution. If care is exercised to remove all of the air, the reaction initiated by aaobisisobutyronitrile gives adducts of high benzene solubility. If air is present during the addition some cross-linking appears to occur and insoluble products are formed. Water-soluble thiols have not been successfully added t o polybutadienes in emulsion. Addition of the water-insoluble P-mercaptopropionitrile did take place in emulsion. These adducts of polybutadiene containing 2.8 to 12.3% of P-mercaptopropionitrile, I-thiosorbitol, p-mercaptoethanol, and mercaptoacetic acid all have low-temperature properties near those of polybutadiene itself. The oil resistance of polybutadiene is improved in every case. However, the improvement brought about by the addition of the nitrile group is less than might have been expected for the properties of the butadieneacrylonitrile copolymer. None of the adducts were as good in oil resistance as Perbunan 18. The preparations of P-mercaptopropionitrile and n-hexyl n-decyl sulfide and sulfone are recorded. ACKNOWLEDGMENT
This work was performed as a part of the research project sponsored by the Reconstruction Finance Gorp., Office of Synthetiu Rubber, in connection with the government synthetic rubber program. The authors are indebted t o Helen Miklas and Elizabeth P. Leighly for the infrared data and their interpretations; to S. R. Detrick, Jackson Laboratory, E. I. du Pont de Nemours & Co., for the emulsifiers MP-189-EF and MP-635-S which were used in this work; and to A. V. Willett of the Organic Chemicals Department of E. I. du Pont de Nemours & Co. for a generous supply of 1-thiosorbitol. All microanalyses reported here were done by iMicro-Tech Laboratories, Skokie, 111.
more pronounced in the carcass-type recipe than i t was in the tread-type recipe. The hysteresis tests (Table X) failed to show any significant improvement from the thiol treatment. The trend in the results obtained with samples 266 and 276 may indicate t h a t increasing the thiol content of the product was not favorable, or may only indicate that this highly gelled sample was poor in this respect. SUMMARY
I t has been found possible t o modify the properties of polybutadiene by the addition of substituted thiols in amounts ranging from 2.8 to 12.3% of its weight. The addition of the water-sol-
LITERATURE C I T E D
TABLE IX. STRESS-STRAIN TESTSAT 77' F. (Microtechnique, carcass-type recipe) Curing 300% Time ModuTensile at lus Strength, 280' F., Lb./Sq. Lb./Sq. Thiol Added Min. Inch Inch j3-Mercaptopropionitrile 40 440 1040 910 @-Mereaptoethanol 40 690 1-Thiosorbitol 40 900 1120 860 Mercaptoacetic acid 40 550 Mercaptoacetic acid 40 820 1140 40 810 2070 30 580 590
(1) Bost, R. W., Turner, J. O., and Norton, R. D., J . Am. Chem. SOC.,54, 1986 (1932). (2) Crouch, W. W., and Werkman, R. T., U. S.
Patents 2,630,448, 2,630,452 (March 1953). (3) Farlow, M. W., Hunt, Madison, Langkammer, C. 430 3 lM., Lazier, W. A., Peppel, W. P., and Signaigo, 330 4 F. K., J . Am. Chem. SOC.,70, 1392 (1948). 370 5 (4) Garvey, B. S., Jr., Am. SOC.Testing Materials, 380 3 D 471431'. 350 2 GR-S ......... 540 6 (5) Gehman, S. D., Woodford, D. E., and ......... 290 1 PolyBD Wilkinson, C. S., IND.ENG.CHEM,, 39. 1108 (1947). TABLE HYSTERESIS D.4TAa (6) International Critical Tables, Vol. 111,p. 319, New York, McGraw-Hill (Carcass-type recipe) Book Co., 1928. Curing Time a t 280' F., Minutes (7) Marvel, C. S., and Meinhardt, N. A., 30 60 90 -~ SO 60 90 30 60 90 30 60 60 J . Polymer Sci.. 6, 773 (1951). Shore A Initial (8) Serniuk, G. E., Banes, F. W., and Sample hardness compression Heat rise, F. Set, % Swanev. M. W.. J . Am. Chem. SOC.. 261 41 43 43 33.1 28.1 28.1 33 20 22 24 9.1 7.3 70, 1864 (1948)'. 27.2 26.7 52 52 28.1 262 55 17 16 15 9.3 4 2.6 (9) Serniuk, G. E., U. S. Patent 2,589,151 25.6 24 21 20 7 6 4.3 27.9 25.2 263 60 58 59 (1952). 42.9 36.7 35.0 6 8 b 68c 9Sd 276 40 40 41 13 13 11 619 i.'e i.'s (10) Smith, 0. H., Hermonat, W. A,, Haxo, 27.7 25.8 25.6 266 55 55 55 GR-S 48 49 51 26.8 23.7 22.4 19 12 12 1 6 . 4 4.2 2.9 H. E., and Meyer, A. W., Anal. XP-998 50 51 51 25.6 20.7 21.2 17 11 9 1 1 . 4 2.4 1.6 Chem., 23, 322 (1951). 18 4.7 3.2 PolyBD 42 42 41 30 27.1 27.6 27 15 18 (11) Vanderbilt Rubber Handbook, 9th ed., a Obtained in Goodrich Flexometer a t 212' F. with stroke of 17.5% and load of 143 lh./sq. inch, and New York, R. T. Vanderbilt, 1948. frequency of 1800 flexures/min. Heat rise measured a t end of 30 minutes, except as shown. (12) Wilson, J. W., and Pfau, E. S., IND. Sample broke a t end of 8 miqutes. Sample broke a t end of 15 minutes. ENG.CHEM.,40,530 (1948). Sample 261 262 263 276 266
Elong.,
Set,
%
%
x.
A,
~
Sample broke a t end of 20 minutes. e A 71.5/28.5 butadiene-styrene copolymer made a t 41' F. to 155 ML-4, compounded by the same recipe as used for GR-6.
RECEIVED for review Maroh 7, 1953. ACCEPTED June 15, 1953.
