Curable rubber compositions comprising substituted dithiocarbamylurea accelerators

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to novel dithiocarbamylureas which are useful as rubber curing agents.
2. Reference of Interest
U.S. Pat. No. 3,947,511, discloses compounds having the structure X(NHC(O)NRSC(S)NR.sup.1 R.sup.2).sub.n, wherein R and R.sup.1 may be the same or different and are hydrogen, alkyl, cycloalkyl, aralkyl, etc.; R.sup.2 may be alkyl, cycloalkyl, aralkyl, etc.; R.sup.1 and R.sup.2 together may be polymethylene or oxydiethylene, n may be 1 or 2, and if n equals 1, X is C.sub.1 -C.sub.8 alkyl. If n equals 2, X is alkylene, O-- or S interrupted alkylene, alkenylene, alkylenbis(arylene), arylenebis(alkylene), or aryl of up to 13 carbon atoms. A compound typical of the U.S. Pat. No. 3,947,511 is C.sub.2 H.sub.5 NCH(O)NHSC(S)--N(CH.sub.3).sub.2.
It has been found that the urea accelerators of the instant invention exhibit superior performance over the closest known prior art.
Compounds of the instant invention may be employed as rubber curatives, usually in combination with sulfur and optionally with other rubber curing agents such as mercaptobenzothiazole disulfide, N,N-oxydiethylenebenzothiazolesulfenamide and the like. Rubbers which can be cured with the instant compounds include natural rubber, cis- or trans-polyisoprene, polybutadiene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, ethylene-propylene-non-conjugated diene terpolymer and the like.
DESCRIPTION OF THE INVENTION
The compounds of this invention are prepared by the reaction of an S-(dialkylthiocarbamyl)sulfenamide with the appropriate aromatic isocyanate. The reaction is usually done by reacting the two components in a solvent.
Solvents suitable for use in the invention are aliphatic and aromatic hydrocarbons such as hexane, isooctane, benzene, toluene, and xylene, and their halogenated derivatives as chloroform, carbon tetrachloride, 1,1,1-trichloroethane, trichlorotrifluoroethane, and chlorobenzene or ethers. The reactants can also be contacted in melt form if desired. In large-scale preparations, however, the use of an inert solvent is advantageous to aid in control of the reaction.
For most effective utilization of materials, the reactants are usually mixed together in molar equivalents.
The reaction is conveniently carried out at temperatures of 10.degree. to 130.degree. C., preferably 25.degree. to 110.degree. C., most preferably 70.degree.-90.degree. C. Pressure is not critical, and ambient pressure is usually used for the sake of convenience.
The reaction proceeds in the presence or absence of catalysts. Catalysts are advantageous in enabling the use of lower temperatures and/or shorter times. The alkyltin dialkanoates, such as dibutyltin dilaurate, are suitable. Tertiary amines such as trimethylamine, triethylamine, tripropylamine, tetramethylethylenediamine, 1,4-diazabicyclo[2.2.2]octane, and pyridine are also effective catalysts.
The products are recovered by known means, such as filtration from the reaction solvent as they crystallize out, or by evaporation of the reaction solvent. The products may be purified if desired by recrystallization from known organic solvents.
The compounds of the invention have the formula
R.sup.1 --NHC(O)NHSC(S)NR.sup.2 R.sup.3
wherein R.sup.1 is phenyl; phenyl substituted with halogen, C.sub.1 -C.sub.12 alkyl, NR.sup.4 R.sup.5 wherein R.sup.4 and R.sup.5 are the same or different and are H, C.sub.1 -C.sub.6 alkyl; C.sub.1 -C.sub.8 alkoxy, alkylthio, methylenedioxy, COOR.sup.6 wherein R.sup.6, is C.sub.1 -C.sub.12 alkyl; or NHCOOR.sup.7 wherein R.sup.7 is C.sub.1 -C.sub.8 alkyl; R.sup.2 and R.sup.3 are the same or different and are C.sub.1 -C.sub.18 alkyl, C.sub.5 -C.sub.6 cycloalkyl or C.sub.7 -C.sub.9 aralkyl, and R.sup.2 plus R.sup.3 are C.sub.4 -C.sub.6 alkylene, C.sub.3 -C.sub.4 oxydialkylene or thiodialkylene.
Preferably R.sup.1 is phenyl; phenyl substituted with Cl, Br, C.sub.1 -C.sub.4 alkyl, NH.sub.2, C.sub.1 -C.sub.4 alkoxy, C.sub.1 -C.sub.4 alkylthio, COOR.sup.6 wherein R.sup.6 is C.sub.1 -C.sub.2 alkyl or NHCOOR.sup.7 wherein R.sup.7 is C.sub.1 -C.sub.2 alkyl.
R.sup.2 and R.sup.3 are the same or different and are C.sub.1 -C.sub.12 alkyl, C.sub.5 -C.sub.6 cycloalkyl or benzyl.
R.sup.2 plus R.sup.3 are tetramethylene, pentamethylene, oxydiethylene or thiodiethylene.
Most preferably R.sup.1 is phenyl or phenyl substituted with Cl, CH.sub.3, CH.sub.3 O, CH.sub.3 S, or NHCOOCH.sub.3.
R.sup.2 and R.sup.3 are the same and are C.sub.1 -C.sub.4 alkyl, cyclohexyl, oxydiethylene or benzyl.
Thus, a sulfenamide having the formula H.sub.2 NSC(S)NR.sup.2 R.sup.3 is reacted with isocyanate having the formula R.sup.1 (NCO).sub.n ; wherein R.sup.1, R.sup.2 and R.sup.3 have the meanings above and n is 1 or 2. It should be noted that if n is 2, the reaction between the sulfenamide and the diisocyanate is carried out at or below 80.degree. C., and subsequently the remaining isocyanate groups are contacted with the appropriate alcohol to hield the compound of this invention wherein R.sup.1 is phenyl substituted with the respective NHCOOR.sup.7 group.
It has been found that compounds of the instant invention provide improved scorch safety at processing temperatures and/or faster cure rates at cure temperatures. Rubber treated with compounds of this invention also have improved physical characteristics, especially in regard to elongation.

The following examples illustrate specific embodiments of the invention without necessarily limiting the scope of the invention:
EXAMPLE 1
N,N-Dimethylthiocarbamylthio-N'-phenylurea (Compound No. 1)
Phenylisocyanate (23.8 g, 0.20 mole) and dibutyltin di-2-ethylhexanoate (0.40 g) were added to a solution of S-(dimethylthiocarbamyl)sulfenamide (27.2 g, 0.20 mole) in toluene (400 ml). The mixture was heated to 85.degree.-95.degree. C. on a steam bath and stirred for 2.5 hours. Then the hot slurry was filtered and the isolated product was dried in a 60.degree. C. oven. Yield: 42.8 g, 83.9% mp 185.degree.-188.degree. C. The product was washed with hot tetrahydrofuran and dried. mp 193.degree.-194.degree. C.
EXAMPLE 2
N-Dimethylthiocarbamylthio-N'-(3-methoxycarbonylamino-4-methylphenyl)urea (Compound No. 7)
Toluene-2,4-diisocyanate (17.9 g, 0.10 mole) and dibutyltin di-2-ethylhexanoate (0.20 g) were dissolved in toluene (100 ml). The solution was heated to 75.degree. C., and then a solution of S-(di-methylthiocarbamyl)sulfenamide (13.6 g, 0.10 mole) in toluene (200 ml) was added slowly, with constant stirring, over a period of 45 minutes. When the addition was complete, the mixture was maintained at 70.degree.-80.degree. C. and stirred for an additional hour. Then anhydrous methanol (15 ml) was added. The slurry was stirred and maintained at 70.degree.-80.degree. C. for one more hour. The slurry was cooled to room temperature and filtered. The white powdery product was dried at 60.degree. C. Yield 30.5 g, 89.2%, mp 180.degree.-185.degree. C. IR and NMR spectra were consistent with the assigned structure.
Compounds 2-6 were made essentially according to the above procedures. All such compounds are summarized in Table I as well as additional chemicals (8-14) which can be prepared and used within the scope of this invention ("c" stands for cyclo).
TABLE I__________________________________________________________________________Cpd. No. R.sup.1 R.sup.2 R.sup.3 m.p. .degree.C.__________________________________________________________________________1 C.sub.6 H.sub.5 CH.sub.3 CH.sub.3 193-1942 C.sub.6 H.sub.5 C.sub.4 H.sub.9 C.sub.4 H.sub.9 120-122.53 C.sub.6 H.sub.5 c-C.sub.6 H.sub.11 c-C.sub.6 H.sub.11 173-1764 C.sub.6 H.sub.5 --CH.sub.2 CH.sub.2 --O--CH.sub.2 --CH.sub.2 -- 1655 C.sub.6 H.sub.5 CH.sub.2 C.sub.6 H.sub.5 CH.sub.2 C.sub.6 H.sub.5 202-2036 4-ClC.sub.6 H.sub.4 CH.sub.3 CH.sub.3 177-1807 3-NHCOOCH.sub.3 --4-CH.sub.3 C.sub.6 H.sub.3 CH.sub.3 CH.sub.3 180-1858 2-BrC.sub.6 H.sub.4 --(CH.sub.2).sub.4 --9 4-C.sub.12 H.sub.25 C.sub.6 H.sub.4 --CH.sub.2 CH.sub.2 --S--CH.sub.2 --10 3-[N(C.sub.6 H.sub.13).sub.2 ]C.sub.6 H.sub.4 CH.sub.3 C.sub. 18 C.sub.3711 3-[N(CH.sub.3).sub.2 ]C.sub.6 H.sub.4 --CH.sub.2 CH.sub.2 --S--CH.sub.2 CH.sub.2 --12 3-(NHCOOC.sub.8 H.sub.17)C.sub.6 H.sub.4 CH.sub.3 CH.sub.313 4-COOCH.sub.3 --C.sub.6 H.sub.4 n-C.sub.4 H.sub.9 n-C.sub.4 H.sub.914 3,4-CH.sub.2 O.sub.2 C.sub.6 H.sub.3 C.sub.12 H.sub.25 CH.sub.3__________________________________________________________________________
The compounds of this invention were evaluated as curing agents as demonstrated below. Certain abbreviations or ingredients are used in these examples, namely:
SBR 1712: oil extended (37.5 pph) styrene (23.5%)-butadiene (76.5%) copolymer, ML-4 ca. 55 at 100.degree. C.
Cis-BR: cis-polybutadiene.
Sundex [trademark] 790 oil: aromatic oil.
Circosol [trademark] 4240 oil: aromatic oil.
AO7F: N-phenyl-N'-(1,3-dimethylbutyl-p-phenylenediamine, Flexzone [trademark] 7F, antiozonant.
MST: Mooney Scorch Time measured in minutes at temperature indicated; ASTM D1646.
t.sub.c 90: Time (in minutes) to obtain 90% of cure at temperature indicated; ASTM D2084).
CMT: Cure Meter Torque, 3.degree. arc, 20 minutes; ASTM D2084.
Wax: Sunproof [trademark] improved wax, microcrystalline wax.
EXAMPLE 3
Rubber compounds were prepared on a two-roll mill using the following recipe (all in parts by weight):
______________________________________SBR 1712 89.4Cis-BR 35.0ZnO 3.0Stearic acid 1.5N339 Carbon black 75.0Sundex 790 oil 20.0AO7F 3.0Sulfur 1.9Masterbatch 226.9______________________________________
To the masterbatch were added certain accelerators of the invention, and the compounded rubber was tested for scorching and, after curing for 10 minutes at 177.degree. C., for physical properties.
The results are summarized in Table II.
TABLE II______________________________________Run No. 1 2 3 4______________________________________Masterbatch 226.9 226.9 226.9 226.9Cpd. No. 1 1.25 -- -- -- 2 -- 1.25 -- -- 3 -- -- 1.25 -- 5 -- -- -- 1.25MST, 135.degree. C., min 35.3 26.3 26.5 38.0t.sub.c 90, 177.degree. C., min 6.0 8.5 9.8 9.5300% Modulus, mPa 7.03 5.31 4.07 5.55Tensile strength, mPa 18.41 17.48 14.07 17.44Elongation, % 630 735 720 705______________________________________
The data indicate that the compounds of this invention provide safe, extended scorch times while providing excellent physical properties at a practical cure rate.
EXAMPLE 4
In similar fashion as in Example 3 a compounded masterbatch was prepared using these ingredients (all in parts by weight):
______________________________________Natural rubber (SMR 5) 100.0N234 Carbon Black 50.0Circosol 4240 oil 5.0A.O. 7F 3.0Wax 1.5Zinc oxide 3.0Stearic acid 2.5Sulfur 2.5Masterbatch 165______________________________________
To 165 parts of the above masterbatch, Cpd. No. 1 (this invention), and Cpd. No. A (disclosed in U.S. Pat. No. 3,947,511) were added, respectively, and then tested. See Table III.
TABLE III______________________________________Run No. 5 6______________________________________Masterbatch 165 165Cpd. No. 1 0.6 -- A -- 0.6MST, 135.degree. C., min 11.0 9.5t.sub.c 90, 177.degree. C., min 2.7 2.4300% Modulus, mPa 11.93 13.17Tensile strength, mPa 23.34 22.37Elongation, % 515 460______________________________________ (Compounded rubber cured for 3 minutes at 177.degree. C.)
The data demonstrate the unexpectedly superior scorch safety, tensile strength and elongation achieved when using the compound of this invention.
EXAMPLE 5
The same masterbatch as in Example 4 was prepared to which certain accelerators were added, as indicated in Table IV. The latter also discloses the test results.
TABLE IV______________________________________Run No. 7 8 9______________________________________Masterbatch 165 165 165Cpd. No. 1 0.6 -- -- 7 -- 0.6 -- B.sup.(1) -- -- 0.6MST, 124.degree. C., min 29.0 30.0 46.3t.sub.c 90, 177.degree. C., min 3.0 3.0 6.6300% Modulus, mPa 10.6 9.7 8.4Tensile strength, mPa 17.9 19.2 15.4Elongation, % 455 510 500______________________________________ Remarks: .sup.(1) 1,3bis[3(dimethylthiocarbamylthio)ureido4-methylbenzene, outside the invention, within the scope of U.S. Pat. No. 3,947,511.
Although compound B has an extraordinary long scorch time, it causes undesirably slow cure rate and inferior modulus and tensile strength.
EXAMPLE 6
A comparison study was undertaken between Cpd. No. 1 of this invention, prior art Cpd. No. A and a well known accelerator, N,N-oxydiethylenebenzothiazolesulfenamide (OBTS) employing the following masterbatch:
______________________________________SBR 1712 84.9Cis-BR 35.0Zinc oxide 3.0AO7F 3.0N339 Carbon black 75.0Sundex 790 oil 20.0Stearic acid 1.5Wax 1.5Sulfur 1.9______________________________________
The compounded stock was cured for 10 minutes at 177.degree. C. before measuring physical properties.
TABLE V______________________________________Run No. 10 11 12______________________________________Masterbatch 228.4 228.4 228.4Cpd. No.: 1 1.2 -- -- A -- 1.2 -- OBTS -- -- 1.2MST, 135.degree. C., min 36.0 20.0 27.8t.sub.c 90, 177.degree. C., min 4.3 3.6 5.8300% Modulus, mPa 7.9 8.7 7.6Tensile strength, mPa 18.1 17.7 18.1Elongation, % 615 540 625______________________________________
The data indicate that the compound of this invention has superior scorch time over the prior art Chemical A and the commonly employed accelerator OBTS while achieving essentially the same physical properties.
EXAMPLE 7
Compound No.'s 4 and 5 were evaluated in 164.5 parts (each) of a masterbatch based on the following recipe:
______________________________________Natural rubber (SMR 5) 100.0Zinc Oxide 3.0Stearic acid 2.0AO7F 3.0Wax 1.5N234 Carbon Black 50.0Circosol 4240 oil 5.0______________________________________
The results are summarized in Table VI.
TABLE VI______________________________________Run No. 13 14______________________________________Cpd. No.: 4 1.2 -- 5 -- 1.6MST, 135.degree. C., min 11.0 14.0t.sub.c 90, 177.degree. C., min 4.2 4.9CMT, 177.degree. C., Mn 3.60 2.67______________________________________
As mentioned previously, the compounds of this invention may be used alone or in combination with known accelerators, however, it has been observed that such combinations unexpectedly have much faster cure rates than when either accelerator is used alone. In most cases, Mooney scorch time is also reduced indicating extraordinarily fast curing conditions.
EXAMPLE 8
Using the masterbatch of Example 6, the following experiments were carried under the conditions of said Example. For results see Table VII.
TABLE VII______________________________________Run No. 15 16 17______________________________________Masterbatch 228.4 228.4 228.4OBTS 1.2 -- 0.5Cpd. No. 1 -- 1.2 1.0MST, 124.degree. C., min 27.8 36.0 26.3t.sub.c 90, 177.degree. C., min 5.8 4.3 4.0300% Modulus, mPa 7.5 7.9 9.4Tensile strength, mPa 18.1 18.1 17.6Elongation, % 625 615 530______________________________________
EXAMPLE 9
Employing the masterbatch and procedure of Example 7, Runs No. 18, 19 and 20 were undertaken with the results indicated in Table VIII.
TABLE VII______________________________________Run No. 18 19 20______________________________________Masterbatch 164.5 164.5 164.5OBTS 0.9 -- 0.45Cpd. No. 1 -- 1.2 0.45MST, 135.degree. C., min 11.0 11.0 11.8t.sub.c 90, 177.degree. C., min 4.3 4.2 3.7______________________________________
The results demonstrate the exceptionally fast cure rate of tire combination of the known sulfenamide accelerator and a compound of this invention.
Also, when using mixtures of the instant compounds with known accelerators similar results are observed regarding especially fast cure rate and/or scorch time when maintaining a CI/KA weight ratio of 4/1-1/3, preferably 2/1-1/2 and most preferably 2/1-1/1, wherein CI stands for "compounds of this invention" and KA means "known curing accelerator."
Suitable benzothiazole sulfenamide accelerators for use with the instant chemicals include N,N-diethyl-2-benzothiazole sulfenamide, N,N-dicyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide, N-cyclohexyl-2-benzothiazole sulfenamide, 2-(4-morpholino)dithiobenzothiazole sulfenamide.
Thiurams which may be used with the compounds of this invention include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram monosulfide, tetrabutylthiuram disulfide, tetrabutylthiuram monosulfide, tetraethylthiuram monosulfide, tetraethylthiuram disulfide, and the like.
Certain mono-isocyanates are useful as intermediates for making the corresponding compounds wherein R.sup.1 is phenyl substituted with, among other things, NHCOOR.sup.7. Such mono-isocyanates have the formula R*NHC(O)NHSC(S)NR.sup.2 R.sup.3, wherein R.sup.2 and R.sup.3 have the above meanings and R* is phenyl or C.sub.7 -C.sub.9 alkylphenyl substituted with an NCO group. Such compounds may also be used as rubber curatives.

Number	Name	Date	Kind
3546185	Coran	Dec 1970
4268640	Matoba	May 1981

Curable rubber compositions comprising substituted dithiocarbamylurea accelerators

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