Chemistry of hydrocarbon compounds – Product blend – e.g. – composition – etc. – or blending process... – With nonhydrocarbon additive
Reexamination Certificate
1999-09-08
2002-01-29
McAvoy, Ellen M. (Department: 1764)
Chemistry of hydrocarbon compounds
Product blend, e.g., composition, etc., or blending process...
With nonhydrocarbon additive
C585S003000, C585S004000, C203S008000
Reexamination Certificate
active
06342647
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and compositions for inhibiting the polymerization of vinyl monomers, and more particularly relates, in one embodiment, to methods and compositions for inhibiting the polymerization of vinyl aromatic monomers.
BACKGROUND OF THE INVENTION
It is well known that undesirable and costly polymerization is a significant problem during the manufacturing of various vinyl monomers, particularly vinyl aromatic compounds, such as styrene. Many kinds of inhibitors have been used in the past to minimize this problem. For instance, inhibitors such as diethylhydroxylamine, phenyl-p-phenylenediamines, tert-butyl catechol, and phenothiazine have been used to control polymer formation. During the early 1980s, compounds selected from the groups called alkyl-substituted di-nitro-phenols and nitroso-phenols found widespread use in the styrene industry. However, because such compounds also functioned as insecticides or were dangerous to handle, their use has been discouraged by environmental and government agencies.
The literature contains references of N,N-disubstituted hydroxylamines as good free radical scavengers, for example diethylhydroxylamine.
Recently, a new class of compounds called stable free radicals is being investigated to replace the nitrophenol products. The literature is replete with examples of “hindered nitroxides” as excellent free radical scavengers. Perhaps the most well known such nitroxide used for scavenging free radicals is 2,2,6,6-tetramethyl-1-piperidinyloxy. Although stable free radicals effectively inhibit monomer polymerization, their current cost makes them unattractive. It would be desirable if a composition and method could be devised to overcome some of the problems of the commercial polymerization inhibitors.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method and composition to effectively inhibit the polymerization of vinyl compounds, such as styrene.
It is another object of the present invention to provide a method and composition to effectively inhibit the polymerization of styrene that is less expensive than using stable free radicals exclusively.
Still another object of the invention is to permit use of a composition to effectively inhibit the polymerization of styrene that has little or no environmental concerns.
In carrying out these and other objects of the invention, there is provided, in one form, a composition for inhibiting polymerization of vinyl compounds comprising a hindered N,N-disubstituted hydroxylamine having the formula:
[(R
1
R
2
R
3
)C]
2
N—OH
where R
1
, R
2
, and R
3
are independently selected from the group consisting of hydrogen, straight, branched or cyclic alkyl, aryl, aralkyl, and alkaryl moieties; where no more than two of R
1
, R
2
, and R
3
on each C can be hydrogen at a time; where one or more of R
1
, R
2
, and R
3
on one C may be joined to a R
2
, R
2
, and R
3
on the other C to form a cyclic moiety selected from the group consisting of alkylene, and aralkylene moieties; where any two of the R
1
, R
2
, and R
3
on any one C may be joined together to form a cycloalkyl; where any of the above definitions of R
1
, R
2
, and R
3
may contain one or more heteroatoms selected from the group consisting of N, O and S; and where the total number of carbon atoms in the hindered N,N-disubstituted hydroxylamine ranges from 6 to 70.
DETAILED DESCRIPTION OF THE INVENTION
It has been discovered that hindered N,N-disubstituted hydroxylamines are an effective treatment to control styrene monomer polymerization. This treatment protocol is most effective when formulated together with synergists such as 2,5-di-tert-butylhydroquinone, 1,2,3,4-tetrahydronaphthalene, and the like.
The hindered N,N-disubstituted hydroxylamines are expected to be useful in inhibiting the polymerization of a variety of vinyl monomers including, but not necessarily limited to, styrene, acrylonitrile, acrylic acid, methacrylic acid, vinyl chloride, acrylates, methacrylates, vinyl ethers, butadiene, isoprene, and the like. It is particularly expected that suitable vinyl aromatic monomers that may be polymerization inhibited by the compositions and methods of this invention include, but are not necessarily limited to, styrene, substituted styrene such as &agr;-methylstyrene, divinylbenzene, vinyltoluene, vinyl naphthalene, and isomers thereof. Preferably, the aromatic monomer is styrene. By “substituted styrenes” is meant styrene substituted with alkyl, aryl, aralkyl, alkaryl hydrocarbon moieties optionally containing oxygen, nitrogen and sulfur, and mixtures thereof. In one non-limiting embodiment, these hydrocarbon substituents have from 1 to 20 carbon atoms, preferably from 1 to 8 carbon atoms, and most preferably from 1 to 4 carbon atoms.
Hindered N,N-Disubstituted Hydroxylamines
Hindered N,N-disubstituted hydroxylamines expected to be effective in the method of this invention include, but are not limited to, those of the formula:
[(R
1
R
2
R
3
)C]
2
N—OH
where R
1
, R
2
, and R
3
are independently selected from the group consisting of hydrogen, straight, branched or cyclic alkyl, aryl, aralkyl, and alkaryl moieties; where only one of R
1
, R
2
, and R
3
on each C can be hydrogen at a time; where one or more of R
1
, R
2
, and R
3
on one C may be joined to a R
1
, R
2
, and R
3
on the other C to form a cyclic moiety selected from the group consisting of alkylene, and aralkylene moieties; where any two of the R
1
, R
2
, and R
3
on any one C may be joined together to form a cycloalkyl; where any of the above definitions of R
1
, R
2
, and R
3
may contain one or more heteroatoms selected from the group consisting of N, O and S; and where the total number of carbon atoms in the hindered N,N-disubstituted hydroxylamine ranges from 6 to 70. Preferably, the total number of carbon atoms in the hindered N,N-disubstituted hydroxylamine ranges from 8 to 20, and where the hydrocarbon groups (alkyl aryl, aralkyl, alkaryl, and cyclic moieties) may contain oxygen moieties. In another preferred embodiment of the invention, R
1
, R
2
, and R
3
independently and individually contain from 1-10 carbon atoms, preferably from 1-8 carbon atoms, more preferably from 1-6 carbon atoms and most preferably from 1-4 carbon atoms. This definition of the hindered N,N-disubstituted hydroxylamines is understood to include structures having functional groups and substituents including, but not necessarily limited to, ether groups, hydroxyl groups, amine groups, carbonyl groups, cyano groups, ester groups, sulfone groups, sulfoxide groups, sulfide groups, and the like.
Some specific, non-limiting examples of suitable hindered N,N-disubstituted hydroxylamines include, but are not necessarily limited to, compounds of the following structures:
Synthesis of Compounds of Structures X and XI
It is believed that a novel Michael-type addition preparation method for making hindered hydroxylamines of the structure such as X and XI has been discovered. This method has two embodiments, the first of which may be described as Synthesis A:
where X and Y are hydrogen or the same or different electron withdrawing group and include, but are not necessarily limited to: —NO
2
, —C═N,
where R
4
, R
5,
R
6
, R
7
, R
8
, R
9
, and R
11
can independently be the same as R
1
, R
2
and R
3
, except that both R
4
and R
5
may be simultaneously hydrogen; and as long as both X and Y are not simultaneously hydrogen, that is, at least one of X or Y must be an electron withdrawing group.
In one example using Synthesis A, R
4
and R
5
are both methyl and X and Y are cyano.
The second embodiment may be described as Synthesis B:
where X, Y and R
4
and R
5
are as above and R
10
is —C(R
7
)
3
, where R
7
is as defined above.
An example of using Synthesis B would be as follows:
Synergists
Suitable synergists that may optionally be included in the polymerization inhibitor composition of this invention include, but are not limited to substituted alkyl-dihydroxyarenes (e.g., alkylphe
Roof Glenn L.
Shahid Muslim D.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
McAvoy Ellen M.
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