Method of preparing sulfur-modified polychloroprene

Abstract

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.

What is claimed is: 
     
       1. A method of preparing sulfur-modified polychloroprene by copolymerization of chloroprene .Iadd.and an ethylenically unsaturated copolymerizable monomer .Iaddend.with sulfur, in alkaline aqueous emulsions and in the presence of a free-radical initiator, at least one organic .[.polysulfides.]. .Iadd.polysulfide .Iaddend.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.]. .Iadd.being .Iaddend.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.Iadd., and the ethylenically unsaturated copolymerizable monomer being present at up to about 20% by weight of chloroprene.Iaddend.. .[.   
     
     
       2.  A method according to claim 1, wherein up to about 20% by weight of the chloroprene is replaced by an ethylenically unsaturated copolymerizable monomer..]. 
     
     
       3. A method according to claim 1, wherein there is also .[.subsequently.]. added .Iadd.in combination with said polysulfide .Iaddend.a tetramethyl or tetraethyl thiuram disulfide or tetrasulfide in an amount of less than 0.25 part per 100 parts, by weight of chloroprene. 
     
     
       4. A method according to .[.any of.]. claims 1.[., 2.]. or 3, wherein the amount of sulfur is between about 0.1 and 0.6% by weight referred to the .[.chlorprene.]. .Iadd.chloroprene .Iaddend.and copolymerizable ethylenically unsaturated monomer. 
     
     
       5. A method according to claim 1, 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. 
     
     
       6.  A method according to claim .[.2.]. .Iadd.1.Iaddend., 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 claim 1, wherein the polymerization is conducted at a temperature of between about 10° and 80° C. 
     
     
       8. A method according to claim 1, wherein the amount of sulfur is between about 0.1 and 0.6% by weight of chloroprene. 
     
     
       9. A method according to claim 1, wherein the pH is at least about 10. .Iadd. 
     
     
       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. .Iaddend. .Iadd.11. A method according to claim 10, wherein up to about 20% by weight of the chloroprene is replaced by an ethylenically unsaturated copolymerizable monomer. .Iaddend. .Iadd.12. A method according to claim 10, wherein there is also added in combination with said polysulfide a tetramethyl or tetraethyl thiuram disulfide or tetrasulfide in an amount of less than 0.25 part per 100 parts, by weight of chloroprene, the said tetramethyl or tetraethyl thiuram disulfide or tetrasulfide being introduced at the same time before the initiation of the polymerization. .Iaddend. .Iadd.13. A method according to claim 10, wherein the amount of sulfur is between about 0.1 and 0.6% by weight referred to the chloroprene and copolymerizable ethylenically unsaturated monomer. .Iaddend.   
     
     
        .Iadd.     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. .Iaddend. .Iadd.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. .Iaddend. .Iadd.16. A method according to claim 10, wherein the polymerization is conducted at a temperature of between about 10° C. and 80° C. .Iaddend. .Iadd.17. A method according to claim 10, wherein the amount of sulfur is between about 0.1 to 0.6% by weight of chloroprene. .Iaddend. .Iadd.18. A method according to claim 10, wherein the pH is at least about 10. .Iaddend. .Iadd.19. A method according to claim 10 wherein the organic polysulfide is benzothiazyl disulfide. .Iaddend. .Iadd.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. .Iaddend. .Iadd.21.  A method according to claim 10 wherein the organic polysulfide is 2,4,5-trichlorophenyl trisulfide. .Iaddend. .Iadd.22. A method according to claim 10 wherein the organic polysulfide is benzanilide disulfide. .Iaddend.