Process for preparing thiosulfate salt polymers

Details Process for preparing thiosulfate salt polymers Process for preparing thiosulfate salt polymers

2001-06-20

2002-07-16

Henderson, Christopher (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S075000

Reexamination Certificate

active

06420505

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an improved polymerization process for preparing pendant thiosulfate (Bunte salt) containing polymers derived from styrenic thiosulfate monomers. The thiosulfate salt monomers may be homopolymerized or copolymerized with one or more ethylenically unsaturated comonomers. In particular, this invention relates to an efficient process wherein a thiosulfate salt monomer is made but not isolated or further purified prior to homopolymerization alone or copolymerization with other monomers.
BACKGROUND OF THE INVENTION
Water soluble polymers formed from thiosulfate salts are useful in a variety of current and potential applications including their use to cross-link or otherwise modify the properties of natural polymer fibers such as wool, cellulosics and leather, and as water-insoluble polymeric sulfur dyes. They are also used in the coating industry and for the manufacture of lithographic printing plates.
H. Bunte first prepared organic thiosulfates or Bunte salts in 1874 with a process which utilized aqueous solutions at an elevated temperature.
RX+Na
2
S
2
O
3
→R—S
2
O
3
−
Na
+
+NaX
This method can also be applied to secondary alkyl halides but not to tertiary halides. Other known methods for the preparation of thiosulfate salts are discussed in U.S. Pat. No. 4,587,296 (P. Moniotte).
Earlier studies have demonstrated that thiosulfate salts can be incorporated into polymers such as poly(epichlorohydrin) by reaction of a chloride group with thiosulfate. Feldstein, in R. W. Feldstein, “Bunte Salt Polymers. Synthesis, Reactivity and Properties”, The American University, 1971, described two synthetic routes to thiosulfate polymers. One method involved the ring opening of glycidyl methacrylate reacted with sodium thiosulfonate, thereby forming a thiosulfate monomer which was then polymerized. The second approach described by Feldstein started with a preformed polystyrene which was chloromethylated and then converted to the thiosulfate salt using magnesium thiosulfate in dimethylformamide (DMF). Feldstein's attempts to isolate a styrenic thiosulfate salt monomer or polymer were unsuccessful.
More systematic work in the area of water-soluble or water-dispersible thiosulfate salt polymers for coatings was described by Thames and coworkers (J. Coat. Technol. 1983, 55, 33-39; Proc. Water-Borne Higher-Solids Coat. Symp. 1985, 12, 5-7). Thames described the synthesis of thiosulfate polymers by using aminoethane thiosulfuric acid in the nucleophilic displacement of alkyl halides, such as epichlorohydrin in DMF/water; or by reacting thiosulfates with either the epoxide ring of glycidyl-containing monomers or with acid chlorides. The polymers obtained by these processes were of low molecular weight. Additionally, their synthesis involved the use of undesirable solvents such as tetrahydrofuran (THF) or dimethylformamide (DMF) and required multiple purification steps.
The most common commercial applications for thiosulfate polymers involve thiosulfate terminated polyethers. In particular, the patents of both Gruning U.S. Pat. No. 4,895,917 and Vandenberg U.S. Pat. No. 3,706,706 describe the modification and use of preexisting polymers with sodium thiosulfate to form thiosulfate polymers. U.S. Pat. Nos. 5,985,514 and 6,136,503 describe two general approaches to manufacturing thiosulfate salt polymers. In the first approach, a thiosulfate salt monomer is made in a water/alcohol mixture, isolated, purified, and then redissolved with a second monomer to make a copolymer. This approach has the disadvantage of high waste generation, low yield, and a long and somewhat difficult reaction sequence. In the second approach to thiosulfate salt polymers, a preformed homopolymer or copolymer containing a halogenated substituent is either purchased or made in an organic solvent. It is then precipitated and isolated, and then redissolved in DMF/water in order to react with sodium thiosulfate and form a thiosulfate salt polymer. Again, this approach has several disadvantages including the use of undesirable organic solvents, such as toluene, THF, dimethyl sulfoxide (DMSO) and DMF, high waste generation, and a limited number of available starting commercial polymers.
In general, the undesirable proclivity of thiosulfate salts to react with activated double bonds such as acrylic and methacrylic acid derivative monomers has limited their usefulness with this class of monomers. Further, the use of an unpurified monomer generally prevents the conversion of the monomer by free radical polymerization to a thiosulfate salt polymer or limits the size of the polymer to low molecular weight oligimers.
It is, therefore, highly desirable to provide simpler and more robust methods for the preparation of thiosulfate salt monomers and their subsequent incorporation into polymers. It is particularly desirable that such methods be environmentally friendly and cost effective.
SUMMARY OF THE INVENTION
This invention provides a method of preparing a thiosulfate salt containing polymer comprising reacting at least one thiosulfate salt with at least one halogenated styrenic monomer to form a styrenic thiosulfate salt monomer represented by Formula (1);
wherein X is a cationic counter ion; R
1
is a substituent; and R
2
is a divalent linking group; and polymerizing the styrenic thiosulfate salt monomer in the presence of an initiator.
The present invention provides a simple and robust process for the production of vinyl aromatic hydrocarbon (also known as styrenic) thiosulfate salt monomers which can then be utilized in a polymerization process without purifying the intermediate thiosulfate salt monomer(s). This process utilizes environmentally friendly solvents, it reduces manufacturing costs, and it improves the throughput and yield of the monomers and the final polymerized materials. Thiosulfate salt polymers are considerably easier to prepare and purify with the current invention than with processes described in the prior art. Because the inventive process is commercially viable, it will increase the availability and variety of homopolymers and copolymers containing thiosulfates.
DETAILED DESCRIPTION OF THE INVENTION
The initial step of the process of the invention comprises reacting at least one thiosulfate salt with at least one halogenated styrenic monomer to form a styrenic thiosulfate salt monomer represented by Formula (1).
X is a proton or a cationic counter ion. Preferably X is a metal ion, particularly an alkali metal ion, or an ammonium ion. Examples of suitable cationic counter ions include sodium, potassium, magnesium, ammonium, barium, lithium, calcium, cesium, zinc, diazonium, iodonium, pyridinium, phosphonium, sulfonium, or 2-benzyl-2-imidazoline. Preferred cationic counter ions are sodium, potassium, and ammonium.
R
1
is any suitable substituent which does not interfere with either the process of preparing the monomers or the final polymerization process. In one suitable embodiment R
1
is either a hydrogen or halide atom; a substituted or unsubstituted alkyl group having 1 to 16 carbon atoms, more preferably having 1 to 8 carbon atoms; a substituted or unsubstituted aryl group having 6 to 16 carbons (such as a phenyl or naphthyl group), more preferably having 6 to 10 carbon atoms; a substituted or unsubstituted heteraryl group of 4 to 16 atoms; or a cyano group. Preferably R
1
is either a hydrogen or an alkyl group having 1 to 4 carbon atoms, such as a methyl, ethyl, or butyl group.
R
2
is a divalent linking group. Preferably R
2
is a substituted or unsubstituted linear, branched or cyclic alkylene group having 1 to 8 carbon atoms that can have one or more oxygen, nitrogen, or sulfur atoms in the chain, or a substituted or unsubstituted arylenealkylene group having 7 to 16 carbons. More preferably R
2
is a substituted or unsubstituted linear, branched or cyclic alkylene group having 1 to 8 carbon atoms and most preferably having 1 to 4 carbon atoms, such as methylene, ethylene, isopropylene, etc.
When reference in this application i

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