sulfur-modified polychloroprene in alkaline aqueous emulsion is prepared by incorporating one or more organic polysulfides which act as peptizing agents during the polymerization of the chloroprene. The sulfur-modified polychloroprenes obtained have stable viscosities.
|
1. A method of preparing sulfur-modified polychloroprene by copolymerization of chloroprene and an ethylenically unsaturated copolymerizable monomer with sulfur, in alkaline aqueous emulsions and in the presence of a free-radical initiator, at least one organic polysulfides polysulfide selected from the class consisting of:
(a) di- and tetra-alkylthiuram disulfides in which the alkyl group contains from about 3 to 5 carbon atoms; (b) benzothiazyl disulfide; (c) benzyl polysulfides in which the number of sulfur atoms is equal to or greater than 3; (d) 2,4,5-trichlorophenyl trisulfide; and (e) benzanilide disulfide and the said polysulfide is being introduced before the initiation of the polymerization in proportions of between about 0.1 and 2 parts to 100 parts, by weight, or chloroprene charged, and the ethylenically unsaturated copolymerizable monomer being present at up to about 20% by weight of chloroprene.
2. A method according to
3. A method according to
4. A method according to any of
5. A method according to
6. A method according to claim 2 1, wherein the copolymerizable monomer is a member selected from the class consisting of vinyl aromatic compounds, acrylic acids, aliphatic conjugated diolefins, vinyl ethers, and vinyl ketones.
7. A method according to
8. A method according to
9. A method according to
10. A method of preparing sulfur-modified polychloroprene by copolymerization of chloroprene with sulfur, in alkaline aqueous emulsion and in the presence of a free-radical initiator, comprising introducing at least one organic polysulfide selected from the class consisting of:
(a) benzothiazyl disulfide; (b) benzyl polysulfides in which the number of sulfur atoms is equal to or greater than 3; (c) 2,4,5-trichlorophenyl trisulfide; and (d) benzanilide disulfide, and the said polysulfide is introduced before the initiation of the polymerization in proportions of between about 0.1 and 2 parts to 100 parts, by weight, of chloroprene charged. 11. A method according to
A method according to claim 10, wherein the free-radical initiator is a member selected from the class consisting of hydrogen peroxide, cumyl peroxide, dibenzoyl peroxide, a ferricyanide and a persulfate. 15. A method according to claim 11, wherein the copolymerizable monomer is a member selected from the class consisting of vinyl aromatic compounds, acrylic acids, aliphatic conjugated diolefins, vinyl ethers, and vinyl ketones. 16. A method according to claim 10, wherein the polymerization is conducted at a temperature of between about 10°C and 80°C 17. A method according to claim 10, wherein the amount of sulfur is between about 0.1 to 0.6% by weight of chloroprene. 18. A method according to claim 10, wherein the pH is at least about 10. 19. A method according to claim 10 wherein the organic polysulfide is benzothiazyl disulfide. 20. A method according to claim 10 wherein the organic polysulfide is benzyl polysulfides in which the number of sulfur atoms is equal to or greater than 3. 21. A method according to claim 10 wherein the organic polysulfide is 2,4,5-trichlorophenyl trisulfide. 22. A method according to claim 10 wherein the organic polysulfide is benzanilide disulfide. |
|||||||||||||||||||||||||||||||||
carred carried out in alkaline aqueous emulsion in known manner in the presence of free-radical producers, such as hydrogen peroxide, the organic peroxides, cumyl peroxide, dibenzoyl peroxide, alkaline-metal or ammonium ferricyanides and, preferably alkaline-metal or ammonium persulfates.
As emulsifying agents there can be employed any of the usual compounds or mixture of usual compounds, such as water-soluble salts of acids derived from crude dimutated hydrogenated or partially polymerized rosins derived from pine oleoresin, wood, or tall oil. The emulsion generally contains a certain amount of dispersing and stabilizing agents, such as the fatty alcohol sulfates, alkyl sulfates and sulfonates, the alkaline salts of alkyl aryl sulfonic acids and, more particularly, the alkaline salts of methylene-bis-naphthalene sulfonic acid. Small amounts of a conventional chain transfer agent can also be added.
Up to 20% of the weight of the chloroprene monomer can be replaced by another copolymerizable monomer. Among the monomers which are copolymerizable with chloroprene are the vinyl aromatic compounds, such as styrene, the vinyl toluenes, and vinyl naphthalenes, the acrylic and methacrylic acids, as well as their ester and nitrile derivatives, such as ethyl acrylate, methyl methacrylate and acrylonitrile, the aliphatic conjugated diolefines, such as 1,3-butadiene, isoprene, 2,3-dichloro-1, 3-butadiene and 2,3-dimethyl-1, 3-butadiene, and the vinyl ethers and ketones, such as methyl vinyl ether, vinyl acetate and methyl vinyl ketone.
The concentration of the monomer or monomers in the emulsion is generally between about 30 and 60% by weight, referred to the total weight of the emulsion.
The amount of sulfur may vary from about 0.1 to 0.6% by weight, referred to the chloroprene monomer or the mixture of monomers.
The polysulfides which can be employed in the method of the invention are introduced into the reaction medium at the same time as the other reagents, but before the start of the polymerization.
The polymerization temperature may vary from about 10°C to 80°C, but it is preferably between about 40°C and 60°C
The pH of the emulsion during the polymerization is greater than about 10 and preferably between about 11 and 13.
The final conversion content does not present any particular limit and it may vary from about 50 to 90%, and, preferably, from about 75% to 85%.
The polymerization can be stopped at any time by addition of a conventional polymerization-inhibiting agent.
The residual monomer is eliminated by flash distillation and the resulting rubber is isolated from the resulting latex by any known means.
The process of the invention has an appreciable economic advantage due to the fact that it is carried out in a single step without increasing the duration of the polymerization. Furthermore, the amount of peptizing agent necessary can be decreased to one-third of its value as compared with the conventional two-step processes of the prior art.
The chloroprene polymers obtained have a Mooney viscosity of between about 20 and 100 and, preferably, between about 35 and 70. This value is stable and does not change during the storage of the latex or the treatment of the rubber. The value desired can be fixed by the man skilled in the art by means of a few preliminary tests as a function of the amount of sulfur, the nature and concentration of peptizing agent, as well as the polymerization conditions. The polychloroprenes can be vulcanized with the vulcanization systems customarily employed for sulfur-modified polychloroprenes, without addition of accelerators derived from thiourea, and in the same manner as the polychloroprenes peptized in conventional manner by thiurams. The vulcanized products have excellent mechanical properties. They are superior to the polychloroprenes peptized or modified in accordance with the prior art with respect to the values of compression-set and tear-strength. Therefore, they are particularly suitable for the manufacture of technical parts such as joints and damping members.
In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are given. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims. In the examples which follow, and throughout the specification, the quantities of material are expressed in terms of parts by weight, unless otherwise specified.
A sulfur-modified polychloroprene latex is prepared by means of an aqueous emulsion system of the following composition:
| ______________________________________ |
| Parts |
| ______________________________________ |
| chloroprene 100 |
| resin acid: dismutated rosin |
| 4 |
| sulfur 0.20 |
| tetrabutylthiuram disulfide 1 |
| water 100 |
| sodium hydroxide (100%) 0.64 |
| sodium salt of methylene-bis-alkyl- |
| 0.70 |
| naphthalene sulfonic acids |
| Catalyst solution to be added to the emulsion system: |
| sodium persulfate 1 |
| water 99 |
| ______________________________________ |
The polymerization is effected at 50°C in a nitrogen atmosphere at a pH of 12.9 and the catalyst solution is added continuously at a rate so as to obtain a uniform rate of polymerization (the total amount introduced is about 5 parts by weight of the weight of the emulsion system). After 4 hours and 15 minutes the conversion of the monomer is 80%. The polymerization is stopped by adding 0.01 part of p-tertiarybutyl catechol and 0.01 part of phenothiazine in the form of an emulsion. The latex is then treated with steam to eliminate the residual monomer and then cooled. After isolation of the polymer by coagulation on a cold drum, the measurement of the Mooney viscosity (ML 1+4 at 100°C) gives a value of 50.
A test is carried out under the same operating conditions as in the above example, but without adding thiuram during the polymerization. After the termination of the polymerization, the polymer, isolated on a sample of latex, has a viscosity of 170. One part of tetraethylthiuram disulfide is then introduced into the latex; the latex is stirred for four hours at 45°C and treated by the customary method. The Mooney viscosity of the polymer obtained is 155 and the material is very unstable upon storage.
PAC (Peptization process of the prior art)The test is again carried out by this time without thiuram and the amount of sulfur is increased to 0.6 parts. After the termination of the polymerization, 1.6 part of tetraethylthiuram disulfide is added. The latex is stirred for 4 hours at 45°C and treated in accordance with the customary method. The Mooney viscosity of the polymer obtained is 50.
PAC (Modified non-peptized polymer in accordance with the prior art)The test is again carried out replacing the tetrabutylthiuram disulfide by 0.4 part of diisopropyl xanthogen disulfide. The amount of sulfur is 0.6 part. The polymer isolated after the termination of the polymerization has a Mooney viscosity of 50.
The polychloroprene obtained in accordance with each of Example 1 and Comparative Tests B and C mixed with the following components:
| ______________________________________ |
| Parts by weight |
| ______________________________________ |
| polychloroprene 100 |
| magnesium oxide 4 |
| zinc oxide 5 |
| stearic acid 0.5 |
| phenyl-β-naphthylamine |
| 2 |
| SRF black 75 |
| aromatic extending oil (DURTREX 729 FC of |
| 15 |
| Shell Oil) |
| ______________________________________ |
Vulcanization is carried out at 153°C, for 40 minutes. The properties of the vulcanized products are entered in Table I below:
| TABLE I |
| ______________________________________ |
| Compression Set-ASTM standard 395-61-Method B-after 96 |
| hours at 100°C-Tear strength-ASTM Standard D 624-73- |
| Angular Test Piece C |
| Tear |
| Polychloroprene |
| Compression Set % |
| strength in kg/cm |
| ______________________________________ |
| Example 1 54 63 |
| Comparative Test B |
| 63 54 |
| Comparative Test C |
| 64 44 |
| ______________________________________ |
A polychloroprene is prepared in the same manner and using the emulsifying system described in Example 1, above. The nature and quantity of the thiuram or of a mixture of thiurams in accordance with the invention is varied. The amount of sulfur, the polymerization temperature and the degree of conversion of the monomer are also varied (the polymerization time is 4 to 5 hours). These changes and the viscosity values measured on the polymer obtained are set forth in Table II, below. In Table II the following abbreviations are employed:
TETD--tetraethylthiuram disulfide
TITD--tetraisopropylthiuram disulfide
TBTD--tetrabutylthiuram disulfide
DPTD--dipentamethylene thiuram disulfide
DPTT--dipentamethylene thiuram tetrasulfide
The results obtained and set forth in Table II show that the method of the invention makes it possible to obtain stable Mooney viscosity values within the range of about 30 to 65. Example E in Table II, given by way of comparison, shows that the thiuram tetrasulfide used does not operate as peptizing agent in the method of the invention.
| TABLE II |
| __________________________________________________________________________ |
| Sulfur-parts |
| Thiuram Operating conditions |
| Mooney viscosity |
| Examples |
| by Weight parts by Wt. |
| T (°C.) |
| Conversion % |
| ML 1 + 4 - 100°C |
| __________________________________________________________________________ |
| 2 0.1 TBTD |
| 2 40 60 60 |
| 3 0.6 TITD |
| 0.6 40 80 47 |
| 4 0.2 TBTD |
| 0.8 50 70 66 |
| TETD |
| 0.2 |
| 5 0.6 TBTD |
| 0.1 45 70 39 |
| TETD |
| 0.1 |
| 6 0.2 TBTD |
| 1.3 30 80 62 |
| TETD |
| 0.2 |
| 7 0.2 DPTD |
| 0.5 40 80 75 |
| 8 0.2 DPTD |
| 0.8 40 80 57 |
| 9 0.2 DPTD |
| 1 40 80 30 |
| E 0.2 DPTT |
| 1 50 80 170 |
| __________________________________________________________________________ |
The thiuram sulfide employed in the foregoing examples is replaced by a different polysulfide. 0.2 part of sulfur is used. The polymerization is carried out at 50°C and is terminated when the conversion of the monomer into polymer reaches 80%. The total time of the polymerization varies from 4.5 to 5 hours. The results are entered in Table III, below. Examples, F, G, H are given by way of comparison.
| TABLE III |
| ______________________________________ |
| Examples 10 F 11 12 G H 13 |
| ______________________________________ |
| Polysulfide (parts by weight) |
| Benzothiazyl disulfide |
| 1 |
| Mercaptobenzothiazol 1 |
| Benzanilide disulfide 0.5 |
| Benzyl polysulfide 1.1 |
| Benzyl disulfide 1.1 |
| Benzoyl disulfide 1 |
| 2,4,5-trichlorophenyl- 1 |
| trisulfide |
| Mooney viscosity |
| 43 170 41 65 150 180 52 |
| (ML 1 + 4 - 100°C) |
| ______________________________________ |
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but is recognized that various modifications are possible within the scope of the invention claimed.
Branlard, Paul, Merle, Jean-Pierre
| Patent | Priority | Assignee | Title |
| Patent | Priority | Assignee | Title |
| 2234215, | |||
| 2264173, | |||
| 3392134, | |||
| 3492276, | |||
| 3704283, | |||
| 3984609, | Jul 10 1970 | Distugil | Process for the instantaneous peptization of polychloroprene latex |
| 4121033, | Nov 08 1976 | CITICORP NORTH AMERICA, INC | Chloroprene-sulfur polymerization with di(O-alkylthionothiolcarbonoxy)sulfides |
| FR1376314, | |||
| FR1392446, | |||
| FR1393099, | |||
| FR1398602, | |||
| FR1457004, | |||
| FR2076922, | |||
| FR2089811, |
| Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
| Oct 20 1988 | Distugil | (assignment on the face of the patent) | / | |||
| May 07 1994 | Distugil | Enichem Elastomeres France SA | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 007041 | /0145 |
| Date | Maintenance Fee Events |
| Feb 04 1991 | ASPN: Payor Number Assigned. |
| Date | Maintenance Schedule |
| Oct 09 1993 | 4 years fee payment window open |
| Apr 09 1994 | 6 months grace period start (w surcharge) |
| Oct 09 1994 | patent expiry (for year 4) |
| Oct 09 1996 | 2 years to revive unintentionally abandoned end. (for year 4) |
| Oct 09 1997 | 8 years fee payment window open |
| Apr 09 1998 | 6 months grace period start (w surcharge) |
| Oct 09 1998 | patent expiry (for year 8) |
| Oct 09 2000 | 2 years to revive unintentionally abandoned end. (for year 8) |
| Oct 09 2001 | 12 years fee payment window open |
| Apr 09 2002 | 6 months grace period start (w surcharge) |
| Oct 09 2002 | patent expiry (for year 12) |
| Oct 09 2004 | 2 years to revive unintentionally abandoned end. (for year 12) |