Compositions – Compositions containing a single chemical reactant or plural...
Reexamination Certificate
2001-02-16
2004-04-20
Medley, Margaret B. (Department: 1714)
Compositions
Compositions containing a single chemical reactant or plural...
C252S182290, C252S182320, C252S182340, C252S182350
Reexamination Certificate
active
06723255
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions for shortstopping of free radical polymerizations and stabilization of polymers produced therein; the compositions include at least one hydrophilic component and at least one hydrophobic component.
BACKGROUND OF THE INVENTION
In emulsion polymerization processes such as those used to synthesize rubber latices, chain growth is often terminated at a designated conversion to prevent the formation of polymer gel and ensure the quality of the resulting polymer. The termination is accomplished by employing a free radical scavenger, commonly referred to as a shortstopper. The action of a shortstopper is to provide hydrogen atoms which combine with the reactive center to terminate growing polymer chains. It is desirable for a shortstopper to destroy any radical initiator remaining in the latex as well.
It is advantageous for a single shortstopping composition to offer both efficient reaction quenching and effective latex stabilization. This avoids the need for complicated equipment and procedures to introduce first the shortstopper and then the latex stabilizer. However, the chemistry of shortstoppers and that of SBR latices precludes any single molecule from performing both functions.
The efficiency of all shortstoppers, and alkylhydroxylamine shortstoppers especially, depends primarily on the ease of active hydrogen atom removal and the degree of access (lack of hindrance) to the active hydrogen atom by the chain radical. Both of these decrease with increasing substitution and increasing alkyl chain length. Thus diethylhydroxylamine (DEHA) is a less active shortstopper than monoethylhydroxylamine, and less active than dimethylhydroxylamine (DMHA). However, minimizing the number of carbons in the molecule also has the effect of raising its volatility and water solubility. These are the properties least desirable for a latex stabilizer, which must persist in the hydrophobic particles when monomers are stripped from the latex. It is often required that the shortstopper have sufficient volatility to inhibit formation of “popcorn” polymer caused by volatile monomer radicals collecting on the walls of stripping columns, and this is defeated by segregation in the particle.
Nitroxides and phenolic compounds have also been studied as shortstoppers for Styrene-Butadiene Rubber (SBR) emulsion polymerizations and as stabilizers for SBR latexes. These compounds can provide good stability for synthetic rubber latexes during storage but do not perform well as shortstoppers for most free radical emulsion processes. Further, most nitroxides and phenolic compounds are costly or toxic, or both, and lack the ability to inhibit overhead popcorn formation.
In order to provide full functionality, shortstoppers have been formulated as binary mixtures of “stopper” and stabilizer. One such mixture, DEHA and sodium dimethyldithiocarbamate (SDDC), was found to be effective in cost and performance. However, as chemical products and processes have come to be more carefully scrutinized, weaknesses in this formulation were exposed. Upon stripping, SDDC emits CS
2
, a toxic and highly regulated chemical, requiring a scrubber to be installed. In addition, dimethylamine, a potential nitrosamine forming molecule, is emitted. Recently, a formulation containing N-isopropylhydroxylamine (NiPHA) and polysulfides was described. The odor of polysulfides is one drawback to this invention. Another is the lack of overhead popcorn prevention.
The objective of this invention is to offer a shortstopping composition that not only effectively shortstops free radical emulsion polymerization reactions and destroys initiators, but also provides improved stability for the resulting rubber latices without incurring any negative safety, health, or environmental impacts.
The literature discloses many variations on the concept of shortstopping compositions for free radical emulsion polymerizations containing hydroxylamines. In U.S. Pat. No. 3,222,334, Demme discloses the use of N,N-dialkylhydroxylamines as shortstopping agents for use in emulsion processes of synthetic rubber latexes involving dienes and monoolefins. Haines et al. in U.S. Pat. No. 3,296,177, disclose bis-oxalate salts of N-monoalkyl and N,N-dialkylhydroxylamines as effective shortstoppers for both hot and cold emulsion polymerization processes for synthetic rubber latices. Albert et al. discloses a process for shortstopping emulsion polymerizations using dithiocarbamate salt/alkylhydroxylamine mixtures in both hot and cold emulsion styrene-butadiene rubber (SBR) processes in U.S. Pat. No. 3,341,487 and the use of N,N-dialkyl-N,N′-methylenebishydroxylamines as shortstoppers for both hot and cold synthetic rubber emulsion processes in U.S. Pat. No. 3,402,138. Albert et al. disclose the use of diethylaniline-N-oxide as a shortstopper for emulsion process synthetic rubber in U.S. Pat. No. 3,567,700.
Haines et al. describe mixtures of N-alkyl-N-arylhydroxylamines as shortstoppers for hot and cold SBR emulsion polymerizations and as popcorn inhibitors in U.S. Pat. No. 3,697,470.
Mixtures of DEHA with a phenolic antioxidant are claimed as shortstoppers for emulsion polymerization processes involving chloroprene by Tsuyoshi et al. in JP 06,298,813.
In U.S. Pat. No. 5,384,372, Lattime discloses the use of N-isopropylhydroxylamine (NiPHA) or its salts as shortstoppers for SER emulsion polymerizations wherein the formation of nitrosamines is suppressed. Maestri et al., U.S. Pat. No. 5,504,168, describe the use of mixtures of isopropylhydroxylamine (or salts thereof) and sodium polysulfide as shortstoppers for free radical emulsion polymerizations; the shortstopping composition is alleged not to yield nitrosamines in the resulting rubber latices.
SUMMARY OF INVENTION
Compositions have been developed for shortstopping free radical emulsion polymerizations and stabilizing polymers produced from the corresponding emulsion processes.
Such compositions include at least one hydrophillic radical scavenger (i.e, shortstopper) and at least one hydrophobic radical scavenger.
The compositions are preferably targeted for applications in the emulsion processes of rubber latexes.
These compositions exhibit excellent performance not only as shortstoppers of free radical emulsion polymerizations but also as stabilizers of the corresponding polymers. Thus, the compositions prevent R
1
and R
2
may each be the same or different, straight, cyclic or branched, and can be hydrogen, C
1-20
-alkyl, hydroxy-C
1-20
alkyl, C
1-10
alkoxy-C
1-10
alkyl, or sulfonated C
1-20
-alkyl groups, with the proviso they may not both be H, or a H and a methyl, and the total carbon number of R
1
and R
2
together is between 2-20.
The salt forms of the hydroxylamines can also be used. These may be based on carboxylic acids such as formate, acetate, propionate, butyrate, isobutyrate, and valerate. An example would be diethylhydroxylamine formate.
Hydroxylamine salts produced from inorganic acids such as mono- or dialkylhydroxylamines hydrochloride, sulfate, phosphate, perchlorate, carbonate, hydrosulfate and hydrophosphate. N-isopropylhydroxylamine hydrochloride will also be effective shortstop.
Whether the hydroxylamine compound is hydrophilic or hydrophobic depends on the total carbon number: R
1
+R
2
. As a rule of thumb, the alkylhydroxylamine is likely hydrophilic if the total carbon number is 0-6, and likely hydrophobic if the total carbon number greater than 6.
Typical examples of the hydrophillic shortstopper useful in the present invention include diethylhydroxylamine (DEHA), N-isopropylhydroxylamine (NiPHA), and dimethylhydroxylamine (DMHA).
The most preferred hydrophilic alkylhydroxylamine is DEHA.
The hydrophobic free radical scavengers of invention can be based on phenol, nitroxide, and hydroxylamine compounds.
Phenolic compounds useful in the present invention have the general formula:
where R
3
and R
5
may be the same or different, and each group could be hydrogen, alkyl, hydroxyl, or alkaryl groups; R
4
could be C
1
-C
20
alkyl,
Buszta Thomas S.
Lou Jianfeng
Nosowitz Martin
Atofina Chemicals, Inc.
Medley Margaret B.
Rudman Gilbert W.
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