Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Statutory Invention Registration
2000-06-26
2003-12-02
Jordan, Charles T. (Department: 3641)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S330800
Statutory Invention Registration
active
H0002092
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for preparation of polychloroprene having reduced odor and to polychloroprene compositions prepared by that process.
BACKGROUND OF THE INVENTION
Polychloroprene is prepared on a commercial scale by free radical initiated emulsion polymerization of 2-chloro-1,3-butadiene (i.e. chloroprene), optionally in the presence of comonomers. Generally, the polymerization is conducted in an aqueous medium in the presence of an anionic soap system, although for certain specialty types of polychloroprene either a nonionic or cationic surfactant is used. A water soluble redox catalyst is normally employed and provides rapid reaction rates at relatively low polymerization temperatures.
In practice, chloroprene monomer and any optional comonomers are added to an aqueous phase containing a surfactant. The mixture is then subjected to high shear, which causes the monomer droplets to be reduced to a few microns in size. Surfactant and monomer distribute between the monomer droplets and surfactant particles (micelles) that are suspended in the aqueous medium. Initiator and optional additives, for example sulfur or chain transfer agents such as mercaptans or dialkyl xanthogen disulfides, are also present in the aqueous or organic phase. Free radicals formed in the aqueous phase migrate to the micelles, where polymerization takes place. When monomer conversion has reached the desired level, a shortstop agent is added which terminates the polymerization reaction. The resultant polymer composition is a polychioroprene latex comprising polymer dispersed in water.
By-products, residual additives and monomers may be removed from the latex by steam stripping. During productionlof dry polychloroprene, additional quantities of these residual additives are removed or reduced during isolation of the dry polymer, for example by water washing polymer film isolated using the freeze roll process and then drying. Such processes are disclosed in U.S. Pat. Nos. 2,467,769 (Morrow et al.); 2,187,146 (Calcott et al.); and 2,384,277 (Calcott et
The presence of by-products in polychloroprene latex, for example chloroprene dimers and other unidentified low molecular weight materials, can have an undesirable effect on the odor and physical properties of elastomeric materials prepared from the latex. Even rigorously stripped latexes can retain an undesirable odor. In the past, various methods have been utilized to reduce the odor of polychloroprene latex or solid polychloroprene, for example by addition of reodorants such as vanillan, o wintergreen, terpineol, anisic aldehyde, oil of cloves, camphor, and coumarin, as disclosed in J. C. Carl, Neoprene Latex, 67, E. I. du Pont de Nemours & Co. (1962). Addition of reodorants does not eliminate undesirable odor in the finished product, but rather masks it.
The presence of minor odors associated with polychloroprene latexes has caused these products to be excluded from use in a number of product formulations, even though performance properties are excellent. For example, polychloroprenes are not utilized in manufacture of adhesives for certain food packaging applications due to odor and taste problems caused by the presence of residual reodorants. An effective process for eliminating taste and odor-producing components of polychloroprene without addition of reodorants would permit use of high performance polychloroprene adhesives in food packaging applications.
SUMMARY OF THE INVENTION
The present invention is directed to a process for producing a polychloroprene composition of low odor which comprises mixing a stabilized polychloroprene latex having a chloroprene monomer content of 0.8 weight percent or less with a compound selected fro m the group consisting of ozone, hydrogen peroxide, alkali metal salts of halogen oxo acids, alkali metal salts of peroxy acids and mixtures thereof
The present invention is further directed to a polychloroprene latex of low odor prepared by a process which comprises mixing a stabilized polychloroprene latex having a chloroprene monomer content of 0.8 weight percent or less with a compound selected from the group consisting of ozone, hydrogen peroxide, alkali metal salts of halogen oxo acids, alkali metal salts of peroxy acids and mixtures thereof.
In addition, the present invention is directed to a solid chloroprene polymer of low odor prepared by a process comprising isolating a solid chloroprene polymer from a stabilized polychloroprene latex, wherein said stabilized polychloroprene latex is prepared by a process comprising mixing a polychloroprene latex having a chloroprene monomer content of 0.8 weight percent or less with a compound selected from the group consisting of ozone, hydrogen peroxide, alkali metal salts of halogen oxo acids, alkali metal salts of peroxy acids and mixtures thereof.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the present invention are polychloroprenes (i.e. polymers having polymerized units of chloroprenee) characterized by low odor, low residual monomer content and excellent curing profile. The polychloroprenes can be in the form of latexes (i.e. polymer dispersed in aqueous media) or solids. The polychloroprene latexes can be used to manufacture dipped goods that exhibit many of the elastomeric properties of natural rubber, but which have lower odor and are less allergenic. The latexes may also be used to form adhesives that have low odor and provide excellent adhesion and tack. The isolated, solid form of the polymer can be used in manufacture of a variety of elastomeric articles, such as hoses, belts, gaskets, elastomeric thread, closed cell foam, and other general purpose rubber goods. The isolated polymer may also be dissolved in solvents to form adhesive compositions.
The compositions of the invention are prepared by a process that comprises treating a stabilized polychloroprene latex with an oxygenating substance that reduces its odor without compromising important physical properties, such as elongation at break. By “stabilized” is meant that free radical polymerization reactions in the polychloroprene latex have been terminated, for example by treatment with a short-stopping agent. Stabilized latexes that have been treated with oxygenating agents according to the present invention are characterized by marked reduction in odor compared to freshly prepared, untreated latexes. In addition, films prepared from samples of treated latex have a reduced odor when compared to films prepared from untreated latex. Such solid polychloroprene compositions of the invention are prepared from the treated latex using techniques such as coagulation, extrusion, or freeze roll isolation.
Polychloroprene latex is produced in a free radical emulsion polymerization reaction. The polymerization reaction is most commonly carried out in aqueous emulsion at temperatures of between 0C. to 80° C., in the presence of initiators such as potassium persulfate or cumene hydroperoxide. In a first step, chloroprene monomer or a mixture of chloroprene monomer and any optional copolymerizable monomers is added to a stirred reaction vessel. Such copolymerizable comonomers include, but are not limited to styrene; the vinyltoluenes and vinylnaphthalenes; 1,3-butadiene; isoprene; 2,3-dimethyl-1,3-butadiene; 2,3-dichloro-1,3-butadiene; methyl vinyl ether; vinyl acetate; methyl vinyl ketone; acrylic and methacrylic acids; ethyl acrylate; methyl methacrylate; methacrylamide; and acrylonitrile. Any such comonomer present will be added in an amount that will result in incorporation of up to 65 weight percent of one or more of the comonomers in the polymer produced during the polymerization reaction. That is, the polychloroprene component of the latex produced will comprise at least 35 weight percent copolymerized units of chloroprene. Generally, the amount of comonomer or comonomers used will be an amount that results in incorporation of up to 20 weight percent copolymerized units in the isolated, solid polymer. However, useful polychloroprene latexes can comprise chloroprene c
Bauman Stevan Charles
Christell Lance Alan
DuPont Dow Elastomers L.L.C.
Felton Aileen B.
Jordan Charles T.
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