U.S. patent application number 11/024217 was filed with the patent office on 2005-05-26 for composition and method for inhibiting polymerization and polymer growth.
This patent application is currently assigned to UNIROYAL CHEMICAL COMPANY, INC.. Invention is credited to Abruscato, Gerald J., Benage, Brigitte, Grewal, Ruben S., Sikora, David J..
Application Number | 20050113625 11/024217 |
Document ID | / |
Family ID | 26864311 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050113625 |
Kind Code |
A1 |
Benage, Brigitte ; et
al. |
May 26, 2005 |
Composition and method for inhibiting polymerization and polymer
growth
Abstract
A method for inhibiting the premature polymerization and the
polymer growth of ethylenically unsaturated monomers is disclosed
wherein the method comprises adding to said monomers an effective
amount of at least one hydrogen donor or electron acceptor. In a
preferred embodiment, the hydrogen donor or electron acceptor is
used in combination with a stable nitroxyl free radical.
Inventors: |
Benage, Brigitte; (Wolcott,
CT) ; Abruscato, Gerald J.; (Southington, CT)
; Sikora, David J.; (Middlebury, CT) ; Grewal,
Ruben S.; (Oakville, CT) |
Correspondence
Address: |
Raymond D. Thompson
Uniroyal Chemical Company, Inc.
World Headquarters
Middlebury
CT
06749
US
|
Assignee: |
UNIROYAL CHEMICAL COMPANY,
INC.
|
Family ID: |
26864311 |
Appl. No.: |
11/024217 |
Filed: |
December 28, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11024217 |
Dec 28, 2004 |
|
|
|
09580343 |
May 25, 2000 |
|
|
|
60168623 |
Dec 3, 1999 |
|
|
|
Current U.S.
Class: |
585/324 ; 203/9;
208/48AA; 585/943; 585/950 |
Current CPC
Class: |
Y10S 585/95 20130101;
C08F 2/40 20130101; C09K 15/04 20130101 |
Class at
Publication: |
585/950 ;
208/048.0AA; 203/009 |
International
Class: |
C07C 007/20 |
Claims
What is claimed is:
1. A method for inhibiting the premature polymerization and the
polymer growth of ethylenically unsaturated monomers comprising
adding to said monomers an effective amount of at least one
inhibitor that is an electron acceptor selected from the group
consisting of quinones, quinone imines, quinone methides, and
acetylenes.
2. The method of claim 1 wherein the inhibitor is of the structure
23wherein X and Y are independently selected from the group
consisting of oxygen, NR.sub.110, and CR.sub.124R.sub.125;
R.sub.120, R.sub.121, R.sub.122, and R.sub.123 are independently
selected from the group consisting of hydrogen, alkyl, aryl,
cycloalkyl, heterocyclic, substituted alkyl, substituted aryl,
OR.sub.110, NR.sub.110R.sub.111, SR.sub.110, NO, NO.sub.2, CN,
COR.sub.112, and halogen, or R.sub.120 and R.sub.121 can be taken
together and/or R.sub.122 and R.sub.123 can be taken together to
form one or two ring structures, respectively, either of which can
be of five to seven members; R.sub.124 and R.sub.125 are
independently selected from the group consisting of hydrogen,
alkyl, aryl, cycloalkyl, heterocyclic, substituted alkyl,
substituted aryl, OR.sub.110, NR.sub.110R.sub.111, SR.sub.110,
NO.sub.2, NO, CN, COR.sub.112, halogen, and/or can be taken
together to form a ring structure of five to seven members;
R.sub.110 and R.sub.111 are independently selected from the group
consisting of hydrogen, alkyl, aryl, benzyl, cyclic, heterocyclic,
substituted alkyl or aryl where the substituents are C, O, N, S, or
P, and COR.sub.102, or R.sub.110 and R.sub.111 can be taken
together to form a ring structure of five to seven members;
R.sub.112 is R.sub.102, OR.sub.102, or NR.sub.102R.sub.103; and
R.sub.102 and R.sub.103 are independently selected from the group
consisting of hydrogen, alkyl, aryl, benzyl, cyclic, heterocyclic,
and substituted alkyl or aryl where the substituents are C, O, N,
S, or P, or R.sub.102 and R.sub.103 can be taken together to form a
ring structure of five to seven members.
3. The method of claim 2 wherein X and Y are oxygen.
4. The method of claim 2 wherein X is oxygen and Y is
CR.sub.124R.sub.125.
5. The method of claim 2 wherein X is oxygen and Y is
NR.sub.110.
6. The method of claim 2 wherein X and Y are NR.sub.110.
7. The method of claim 2 wherein X is NR.sub.110 and Y is
CR.sub.124R.sub.125.
8. The method of claim 1 wherein the inhibitor is of the structure
R.sub.126--C.ident.C--R.sub.127 wherein R.sub.126 and R.sub.127 are
independently selected from the group consisting of hydrogen,
alkyl, aryl, cycloalkyl, heterocyclic, substituted alkyl,
substituted aryl, OR.sub.110, NR.sub.010R.sub.111, SR.sub.110,
NO.sub.2, NO, CN, COR.sub.112, and halogen; R.sub.110 and R.sub.111
are independently selected from the group consisting of hydrogen,
alkyl, aryl, benzyl, cyclic, heterocyclic, substituted alkyl or
aryl where the substituents are C, O, N, S, or P, and COR.sub.102
or R.sub.110 and R.sub.111 can be taken together to form a ring
structure of five to seven members; R.sub.12 is R.sub.102,
OR.sub.102, or NR.sub.102R.sub.103; and R.sub.102 and R.sub.103 are
independently selected from the group consisting of hydrogen,
alkyl, aryl, benzyl, cyclic, heterocyclic, and substituted alkyl or
aryl where the substituents are C, O, N, S, or P, or R.sub.102 and
R.sub.103 can be taken together to form a ring structure of five to
seven members.
9. The method of claim 1 wherein the inhibitor is selected from the
group consisting of phenylacetylene,
2,5-di-t-butyl-1,4-benzoquinone, 2,6-di-t-butyl-1,4-benzoquinone,
1,4-benzoquinone, 2-methylanthraquinone, 1,4-naphthoquinone,
2,6-di-t-butyl-4-(phenylmethylene)-2,5-cyclohexadiene- -1-one,
2,6-di-t-butyl-4-(phenylimino)-2,5-cyclohexadiene-1-one, and ethyl
3,4-bis-(3,5-di-t-butyl-4-one-2,5-cyclohexadienylidene)-hexane-1,6-dioate-
.
10. A method for inhibiting the premature polymerization and the
polymer growth of ethylenically unsaturated monomers comprising
adding to said monomers A) at least one first inhibitor that is an
electron acceptor selected from the group consisting of quinones,
quinone imines, quinone methides, and acetylenes, and B) at least
one second inhibitor having the following structural formula:
24wherein R.sub.1 and R.sub.4 are independently selected from the
group consisting of hydrogen, alkyl, and heteroatom-substituted
alkyl; R.sub.2 and R.sub.3 are independently selected from the
group consisting of alkyl and heteroatom-substituted alkyl; and
X.sub.1 and X.sub.2 (1) are independently selected from the group
consisting of halogen, cyano, amido, --S--C.sub.6H.sub.5, carbonyl,
alkenyl, alkyl of 1 to 15 carbon atoms, COOR.sub.7, --S--COR.sub.7,
and --OCOR.sub.7, wherein R.sub.7 is alkyl or aryl, or (2) taken
together, form a ring structure with the nitrogen.
11. The method of claim 10 wherein the first inhibitor is of the
structure 25wherein X and Y are independently selected from the
group consisting of oxygen, NR.sub.110, and CR.sub.124R.sub.125;
R.sub.120, R.sub.121, R.sub.122, and R.sub.123 are independently
selected from the group consisting of hydrogen, alkyl, aryl,
cycloalkyl, heterocyclic, substituted alkyl, substituted aryl,
OR.sub.110, NR.sub.110R.sub.111, SR.sub.110, NO, NO.sub.2, CN,
COR.sub.112, and halogen, or R.sub.120 and R.sub.121 can be taken
together and/or R.sub.122 and R.sub.123 can be taken together to
form one or two ring structures, respectively, either of which can
be of five to seven members; R.sub.124 and R.sub.125 are
independently selected from the group consisting of hydrogen,
alkyl, aryl, cycloalkyl, heterocyclic, substituted alkyl,
substituted aryl, OR.sub.110, NR.sub.110R.sub.111, SR.sub.110,
NO.sub.2, NO, CN, COR.sub.112, halogen, and/or can be taken
together to form a ring structure of five to seven members;
R.sub.110 and R.sub.111 are independently selected from the group
consisting of hydrogen, alkyl, aryl, benzyl, cyclic, heterocyclic,
substituted alkyl or aryl where the substituents are C, O, N, S, or
P, and COR.sub.102, or R.sub.110 and R.sub.111 can be taken
together to form a ring structure of five to seven members;
R.sub.112 is R.sub.102, OR.sub.102, or NR.sub.102R.sub.103; and
R.sub.102 and R.sub.103 are independently selected from the group
consisting of hydrogen, alkyl, aryl, benzyl, cyclic, heterocyclic,
and substituted alkyl or aryl where the substituents are C, O, N,
S, or P, or R.sub.102 and R.sub.103 can be taken together to form a
ring structure of five to seven members.
12. The method of claim 11 wherein X and Y are oxygen.
13. The method of claim 11 wherein X is oxygen and Y is
CR.sub.124R.sub.125.
14. The method of claim 11 wherein X is oxygen and Y is
NR.sub.110.
15. The method of claim 11 wherein X and Y are NR.sub.110.
16. The method of claim 11 wherein X is NR.sub.110 and Y is
CR.sub.124R.sub.125.
17. The method of claim 10 wherein the first inhibitor is of the
structure R.sub.126--C.ident.C--R.sub.127 wherein R.sub.126 and
R.sub.127 are independently selected from the group consisting of
hydrogen, alkyl, aryl, cycloalkyl, heterocyclic, substituted alkyl,
substituted aryl, OR.sub.110, NR.sub.110, R.sub.111, SR.sub.110,
NO.sub.2, NO, CN, COR.sub.112, and halogen; R.sub.110 and R.sub.111
are independently selected from the group consisting of hydrogen,
alkyl, aryl, benzyl, cyclic, heterocyclic, substituted alkyl or
aryl where the substituents are C, O, N, S, or P, and COR.sub.102
or R.sub.110 and R.sub.111 can be taken together to form a ring
structure of five to seven members; R.sub.112 is R.sub.102,
OR.sub.102, or NR.sub.102R.sub.103; and R.sub.102 and R.sub.103 are
independently selected from the group consisting of hydrogen,
alkyl, aryl, benzyl, cyclic, heterocyclic, and substituted alkyl or
aryl where the substituents are C, O, N, S, or P, or R.sub.102 and
R.sub.103 can be taken together to form a ring structure of five to
seven members.
18. The method of claim 10 wherein the first inhibitor is selected
from the group consisting of phenylacetylene,
2,5-di-t-butyl-1,4-benzoquinone, 2,6-di-t-butyl-1,4-benzoquinone,
1,4-benzoquinone, 2-methylanthraquinone, 1,4-naphthoquinone,
2,6-di-t-butyl-4-(phenylmethylene)-2,5-cyclohexadiene- -1-one,
2,6-di-t-butyl-4-(phenylimino)-2,5-cyclohexadiene-1-one, and ethyl
3,4-bis-(3,5-di-t-butyl-4-one-2,5-cyclohexadienylidene)-hexane-1,6-dioate-
.
19. The method of claim 10 wherein the second inhibitor is of the
structure 26wherein R.sub.1 and R.sub.4 are independently selected
from the group consisting of hydrogen, alkyl, and
heteroatom-substituted alkyl and R.sub.2 and R.sub.3 are
independently selected from the group consisting of alkyl and
heteroatom-substituted alkyl, and the 27portion represents the
atoms necessary to form a five-, six-, or seven-membered
heterocyclic ring.
20. The method of claim 19 wherein the second inhibitor comprises
one or more nitroxyls selected from the group consisting of:
N,N-di-tert-butylnitroxide; N,N-di-tert-amylnitroxide;
N-tert-butyl-2-methyl-1-phenyl-propylnitroxide;
N-tert-butyl-1-diethylpho- sphono-2,2-dimethylpropylnitroxide;
2,2,6,6-tetramethyl-piperidinyloxy;
4-amino-2,2,6,6-tetramethyl-piperidinyloxy;
4-hydroxy-2,2,6,6-tetramethyl- -piperidinyloxy;
4-oxo-2,2,6,6-tetramethyl-piperidinyloxy;
4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy;
4-ethanoyloxy-2,2,6,6-tetramethyl-piperidinyloxy;
2,2,5,5-tetramethylpyrr- olidinyloxy;
3-amino-2,2,5,5-tetramethylpyrrolidinyloxy;
2,2,4,4-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy;
2,2,4,4-tetramethyl-1-o- xa-3-pyrrolinyl-1-oxy-3-carboxylic acid;
2,2,3,3,5,5,6,6-octamethyl-1,4-di- azacyclohexyl-1,4-dioxy;
4-bromo-2,2,6,6-tetramethyl-piperidinyloxy;
4-chloro-2,2,6,6-tetramethyl-piperidinyloxy;
4-iodo-2,2,6,6-tetramethyl-p- iperidinyloxy;
4-fluoro-2,2,6,6-tetramethyl-piperidinyloxy;
4-cyano-2,2,6,6-tetramethyl-piperidinyloxy;
4-carboxy-2,2,6,6-tetramethyl- -piperidinyloxy;
4-carbomethoxy-2,2,6,6-tetramethyl-piperidinyloxy;
4-carbethoxy-2,2,6,6-tetramethyl-piperidinyloxy;
4-cyano-4-hydroxy-2,2,6,- 6-tetramethyl-piperidinyloxy;
4-methyl-2,2,6,6-tetramethyl-piperidinyloxy;
4-carbethoxy-4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;
4-hydroxy-4-(1-hydroxypropyl)-2,2,6,6-tetramethyl-piperidinyloxy;
4-methyl-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
4-carboxy-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
4-carbomethoxy-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
4-carbethoxy-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
4-amino-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
4-amido-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
3,4-diketo-2,2,5,5-tetramethylpyrrolidinyloxy;
3-keto-4-oximino-2,2,5,5-t- etramethylpyrrolidinyloxy;
3-keto-4-benzylidine-2,2,5,5-tetramethylpyrroli- dinyloxy;
3-keto-4,4-dibromo-2,2,5,5-tetramethylpyrrolidinyloxy;
2,2,3,3,5,5-hexamethylpyrrolidinyloxy;
3-carboximido-2,2,5,5-tetramethylp- yrrolidinyloxy;
3-oximino-2,2,5,5-tetramethylpyrrolidinyloxy;
3-hydroxy-2,2,5,5-tetramethylpyrrolidinyloxy;
3-cyano-3-hydroxy-2,2,5,5-t- etramethylpyrrolidinyloxy;
3-carbomethoxy-3-hydroxy-2,2,5,5-tetramethylpyr- rolidinyloxy;
3-carbethoxy-3-hydroxy-2,2,5,5-tetramethylpyrrolidinyloxy;
2,2,5,5-tetramethyl-3-carboxamido-2,5-dihydropyrrole-1-oxyl;
2,2,5,5-tetramethyl-3-amino-2,5-dihydropyrrole-1-oxyl;
2,2,5,5-tetramethyl-3-carbethoxy-2,5-dihydropyrrole-1-oxyl;
2,2,5,5-tetramethyl-3-cyano-2,5-dihydropyrrole-1-oxyl;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)succinate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylmalonate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)phthalate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)isophthalate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)terephthalate;
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)hexahydroterephthalate;
N,N'-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide;
N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-caprolactam;
N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-dodecylsuccinimide;
2,4,6-tris-[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)]-s-triaz-
ine; and
4,4'-ethylenebis(1-oxyl-2,2,6,6-tetramethylpiperazin-3-one).
Description
[0001] This is a division of U.S. application Ser. No. 09/580,343,
filed May 25, 2000, for which the benefit under Title 35, United
States Code, .sctn. 120 to U.S. Provisional Application No.
60/168,623, filed Dec. 3, 1999, entitled COMPOSITION AND METHOD FOR
INHIBITING POLYMERIZATION AND POLYMER GROWTH has been claimed.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to the inhibition of
polymerization and polymer growth of ethylenically unsaturated
monomers by means of the addition thereto of hydrogen donors and/or
electron acceptors, either alone or in combination with at least
one stable nitroxide free radical compound.
[0004] 2. Description of Related Art
[0005] Many ethylenically unsaturated monomers undesirably
polymerize at various stages of their manufacture, processing,
handling, storage, and use. Polymerization, such as thermal
polymerization, during their purification results in the loss of
the monomer, i.e., a lower yield, and an increase in the viscosity
of any tars that may be produced. The processing and handling of
the higher viscosity tars then requires higher temperature and work
(energy cost) to remove residual monomer.
[0006] Polymerization can also result in equipment fouling,
especially in the case of production of acrylic monomers. Such
polymerization causes loss in production efficiency owing to the
deposition of polymer in or on the equipment being used. These
deposits must be removed from time to time, leading to additional
loss in production of the monomer.
[0007] A wide variety of compounds has been proposed and used for
inhibiting uncontrolled and undesired polymerization of
ethylenically unsaturated monomers. However, many of these
compounds have not been fully satisfactory.
[0008] There are several mechanisms by which polymerization
inhibitors work. One mode of action for polymerization inhibitors
is for the inhibiting species to combine with the propagating
polymer chain such that the polymerization of that polymer chain
stops, i.e., a termination reaction. If such an
inhibitor-terminated polymer chain is capable of participating in a
dynamic equilibrium between a dormant species (the
inhibitor-terminated chain) and an active polymer chain, it would
be considered a "living" or quasiliving polymer. For example, Ivan,
Macromol. Symp. 88:201-215 (1994) describes quasiliving
polymerization as a polymerization in which " . . . only a portion
of chain ends are active (propagating) and these are in equilibria
with inactive (dormant, nonpropagating) chains . . . " Shigemoto et
al., Macromol. Rapid Commun. 17:347-351 (1996) state, "Well-defined
polymers can be prepared by controlled/"living" radical
polymerization in the presence of relatively stable radicals. These
systems employ the principle of dynamic equilibration between
dormant species and growing radicals via reversible homolytic
cleavage of a covalent bond in dormant species." Further, Greszta
et al., Macromolecules 29:7661-7670 (1996) state, "The reversible
homolytic cleavage of dormant species can be accomplished by either
thermal, photochemical, or catalytic activation. The most
successful approaches are as follows: homolytic cleavage of
alkoxyamines and dithiocarbamates, use of various organometallic
species, and catalyzed atom transfer radical polymerization." Such
a "living" polymer is capable of increasing in molecular weight
(growing) through its reaction with additional monomer units of the
same or different types of polymerizable monomers.
[0009] The method by which this "living" polymer grows is termed
the "living" polymerization mechanism, and is depicted below.
M-Inh ---->M*+*Inh (1)
M*+*Inh ---->M-Inh (2)
M*+M'---->M-M'* (3)
M-M'*+*Inh ---->M-M'-Inh (4)
[0010] Reactions (1) and (2) depict the dynamic equilibrium, with
(2) being the termination reaction. Reaction (3) depicts growth of
the polymer chain. Reaction (4) depicts re-termination of the
growing polymer chain with the inhibiting species. The amount of
growth over any period of time is dependent on the relative rate at
which (2) occurs versus (3), as long as (1) occurs to some extent.
The faster (2) is relative to (3), the more time is needed for
significant growth of the polymer. Under the conditions in which
inhibitors are normally used, the concentration of the inhibiting
species should be sufficiently high to cause reaction (2) to be
much faster than reaction (3), otherwise it would not be an
effective inhibiting system for commercial use. However, we have
realized that even at an effective inhibiting amount of the
inhibitor, growth can still occur, given sufficient time and
temperature.
[0011] There are at least two scenarios in which "living" polymer
can remain in a monomer purification train for an excessive amount
of time.
[0012] First, the use of recycle can significantly increase the
amount of time that the "living" polymer can remain in the
purification train. To recycle unused inhibitor that is left in the
purification stream after removal of the monomer, a portion of the
residual stream is added to a feed stream earlier in the
purification train. This residual stream typically contains
inhibitor, small amounts of monomer, impurities in the monomer
stream that have been concentrated by the purification process, and
polymer formed during the production and purification process.
Recycling this polymer will allow it time to grow if it is "living"
polymer and the conditions of the purification train allow the
"living" polymerization mechanism to occur. If this polymer grows
via the "living" polymerization mechanism, excessive polymerization
would cause loss in product yield, increased waste residues from
the process, and potential plugging of equipment due to excessively
high molecular weight polymer in the purification stream.
[0013] Second, occasionally, conditions in the plant/purification
process can result in the formation of polymer within the
purification train that is not dissolved by the monomer stream. If
this polymer is caught in a dead space, or if it attaches to the
metal on the inside of the equipment, it will not be washed out of
the system. Thus, the polymer will remain within the system
indefinitely (potentially for two or more years). If this polymer
grows via the "living" polymerization mechanism, it could coat the
inside of the equipment, causing inefficient separation of the
monomer stream components and/or insufficient heating of the stream
to enable purification. Such a situation would cause loss in
product yield and could potentially cause an unscheduled shut-down
of the plant in order to clean out the undissolved polymer in the
equipment. Such a shut-down results in loss of monomer production
and additional expense to clean out and dispose of the undissolved
polymer.
[0014] It is significant that there has been no indication that
previously used inhibitors would lead to the formation of "living"
polymer when used as polymerization inhibitors. However, a newly
utilized class of inhibitors, the stable nitroxyl radicals, is
known to allow this "living" polymerization mechanism to occur.
These nitroxyl radicals are highly efficient polymerization
inhibitors under normal use, providing better performance than most
other inhibitors on the market, but their incapacity to prevent
"living" polymerization has hindered their full utilization.
Accordingly, there is a need for compositions that can be used in a
purification train, preferably in combination with nitroxyl
radicals, to prevent polymer growth that occurs via a "living"
polymerization mechanism.
[0015] Nitroxyl radicals are known to facilitate polymerization via
a "living" free radical process to give polymers of narrow
polydispersity.
[0016] Georges et al., Macromolecules 26(11):2987-2988 (1993)
synthesized narrow molecular weight resins by a free-radical
polymerization process with polydispersities comparable to those
that can be obtained by anionic polymerization processes and below
the theoretical limiting polydispersity of 1.5 for a conventional
free-radical polymerization process. The process comprised heating
a mixture of monomer(s), free-radical initiator, and a stable free
radical, e.g., 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO).
[0017] Hawker et al., Macromolecules 29(16):5245-5254 (1996)
prepared and evaluated a variety of initiating systems for the
preparation of macromolecules by nitroxide-mediated "living" free
radical procedures. The systems were divided into two classes,
unimolecular initiators in which alkylated TEMPO derivatives
dissociate to provide both the initiating radical and the stable
radical, and bimolecular systems in which a traditional free
radical initiator, such as BPO or AIBN, is used in conjunction with
TEMPO. For the unimolecular initiators it was found that an
.alpha.-methyl group is essential for "living" character, while a
variety of substituents could be placed on the phenyl ring or the
.beta.-carbon atom without affecting the efficiency of the
unimolecular initiator. It was found that the rate of
polymerization is approximately the same for both the unimolecular
and corresponding bimolecular systems; however, the unimolecular
initiators afforded better control over molecular weight and
polydispersity.
[0018] The inventors are unaware of any art on the use of compounds
to prevent polymer growth that occurs via a "living" polymerization
mechanism since this growth phenomenon is not known to have
previously been observed. Hindered nitroxyl compounds are known to
be very active inhibitors of free radical polymerizations of
unsaturated monomers such as styrene, acrylic acid, methacrylic
acid, and the like. Nitrophenols, nitrosophenols, phenylenediamines
(PDA's), hydroxylamines, quinones and hydroquinones are also known
to have a similar capacity.
[0019] U.S. Pat. No. 2,304,728 discloses that a vinyl aromatic
compound may effectively be stabilized against polymerization by
dissolving therein a monohydric halo-nitrophenol having the general
formula: 1
[0020] wherein one X represents a halogen and the other X
represents a member of the group consisting of hydrogen and halogen
and nitro substituents.
[0021] U.S. Pat. No. 3,163,677 discloses a process for the
preparation of N,N,O-trisubstituted hydroxylamines and
N,N-disubstituted nitroxides of the formulae: 2
[0022] wherein R.sub.1, R.sub.2, and R.sub.3 are each an alkyl
radical having 1 to 15 carbon atoms. (As used herein, the
designation N--O* denotes a stable free radical wherein the
asterisk is an unpaired electron.) The N,N,O-trisubstituted
hydroxylamines can be used to make the N,N-disubstituted
nitroxides, which are stable free radicals and are said to be
useful as polymerization inhibitors.
[0023] U.S. Pat. No. 3,334,103 discloses that nitroxides can be
prepared from the corresponding heterocyclic amine wherein the
nitrogen atom of the nitroxide group is attached to other than a
tertiary carbon of an aliphatic group (i.e., the nitrogen atom
forms a part of a heterocyclic nucleus). These nitroxides are said
to have useful properties similar to those described for the
N,N-disubstituted nitroxides of U.S. Pat. No. 3,163,677.
[0024] U.S. Pat. No. 3,372,182 discloses that a great variety of
N,N-disubstituted, stable, free radical nitroxides not otherwise
readily available can be prepared by a simple and convenient
process that comprises pyrolyzing in an inert reaction medium
virtually any hydroxylamine that is susceptible to cleavage of the
O--C bond, e.g., tri-t-butylhydroxylamine.
[0025] U.S. Pat. No. 3,422,144 discloses stable, free radical
nitroxides of the formula: 3
[0026] wherein R is selected from the group consisting of tertiary
alkyl, aryl, alkaryl, haloaryl, carboxyaryl, alkoxyaryl,
alkylthioaryl, pyridyl, and dialkylaminoaryl, and R' is tertiary
alkyl. These nitroxides are said to be useful as traps for reactive
free radicals both in the counting of free radicals and for
inhibiting oxidation and free radical polymerization.
[0027] U.S. Pat. No. 3,494,930 discloses free radicals of the
nitroxide type for use as initiators of free radical reactions,
collectors of free radicals, polymerization inhibitors or
antioxidants. They are constituted by nitrogenous bicyclic
compounds in which one of the bridges comprises solely the
nitroxide radical group and, in particular, by aza-9-bicyclo
(3,3,1) nonanone-3-oxyl-9, and by aza-9-bicyclo(3,3,1) nonane
oxyl-9.
[0028] U.S. Pat. No. 3,873,564 discloses compounds and a method for
assaying enzymes by adding to a medium containing an enzyme a
stable free radical compound having a stable free radical
functionality which, when subjected to an enzyme-catalyzed
reaction, changes the environment of the free radical
functionality. By following the change in the electron spin
resonance spectrum as affected by the change in environment, the
type of enzyme and the activity of the enzyme can be determined.
The compounds found useful are normally stable nitroxide radicals
with an enzyme labile functionality. Other compounds include two
cyclic nitroxide containing rings joined by a chain having an
enzyme labile functionality.
[0029] U.S. Pat. No. 3,966,711 teaches that 2,2,7,7-tetraalkyl- and
2,7-dispiroalkylene-5-oxo-1,4-diazacycloheptanes substituted in the
4-position by mono- or tetravalent radicals are powerful
light-stabilizers for organic polymers. They are said to possess
higher compatibility than their 4-unsubstituted homologues, from
which they can be synthesized by reactions known for N-alkylation.
Preferred substituents in the 4-position are alkyl, alkylene,
alkenyl, aralkyl, and esteralkyl groups. The 1-nitroxyls derived
from the imidazolidines by oxidation with hydrogen peroxide or
percarboxylic acids are also said to be good light stabilizers.
[0030] U.S. Pat. No. 4,105,506 discloses a process for the
distillation of readily polymerizable vinyl aromatic compounds and
a polymerization inhibitor therefor. The process comprises
subjecting a vinyl aromatic compound to elevated temperatures in a
distillation system in the presence of a polymerization inhibitor
comprising 2,6-dinitro-p-cresol.
[0031] U.S. Pat. Nos. 4,252,615 and 4,469,558 disclose a process
for the distillation of readily polymerizable vinyl aromatic
compounds and a polymerization inhibitor therefor. The process
comprises subjecting a vinyl aromatic compound to elevated
temperatures in a distillation system in the presence of a
polymerization inhibitor comprising 2,6-dinitro-p-cresol. Also
disclosed is a distillation method and apparatus for use with this
inhibitor.
[0032] U.S. Pat. No. 4,434,307 discloses the stabilization of vinyl
aromatic compounds against undesired polymerization by adding to
the vinyl aromatic compounds small amounts of at least one
N,N-diarylhydroxylamine and at least one mono- or ditertiary alkyl
catechol and/or at least one mono- or ditertiary
alkylhydroquinone.
[0033] U.S. Pat. No. 4,439,278 discloses an improvement in methods
for preparing and processing ethylenically unsaturated aromatic
monomer. The improvement comprises employing 3,5-dinitrosalicylic
acid or a derivative or isomer thereof as a process inhibitor. The
process inhibitor is present in a concentration of about 50 to 3000
ppm, preferably about 250 to 2,000 ppm, and most preferably about
500 to 1,000 ppm.
[0034] U.S. Pat. No. 4,466,904 discloses a compound and a process
for utilizing the compound to prevent the polymerization of vinyl
aromatic compounds, such as styrene, during heating. The compound
includes effective amounts of phenothiazine, 4-tert-butylcatechol
and 2,6-dinitro-p-cresol respectively, as a polymerization
inhibitor system in the presence of oxygen resulting in a less
viscous polymer tar and in the effective inhibition of
polymerization to temperatures as high as 150.degree. C.
[0035] U.S. Pat. Nos. 4,466,905 and 4,468,343 disclose a compound
and a process for utilizing the compound to prevent the
polymerization of vinyl aromatic compounds, such as styrene, during
heating. The composition includes effective amounts of
2,6-dinitro-p-cresol and either a phenylenediamine or
4-tert-butylcatechol respectively, to act as a polymerization
co-inhibitor system in the presence of oxygen.
[0036] U.S. Pat. No. 4,480,116 discloses an improvement in methods
for preparing and processing readily polymerizable acrylate
monomers. The improvement comprises employing
phenyl-para-benzoquinone, 2,5-di-phenyl-para-benzoquinone, and
mixtures thereof as process inhibitors. The process inhibitors are
present in a concentration of about 50 to 3000 ppm, preferably
about 250 to 2000 ppm, and most preferably about 500 ppm.
[0037] U.S. Pat. No. 4,558,169 discloses a process for preparing
vinyltoluene comprising passing ethyltoluene through a
dehydrogenation zone to form vaporous crude vinyltoluene, adding
from about 50 to about 100 parts per million by weight of a
polymerization inhibitor such as a nitrated phenol to the vaporous
crude vinyltoluene at a temperature between about 200.degree. and
about 300.degree. C., condensing the vaporous crude vinyltoluene,
maintaining the pH of the aqueous phase of the condensed crude
vinyltoluene at a value between about 5.5 and about 6.5 sufficient
to maintain the inhibitor in the organic phase of the condensed
crude vinyltoluene, adding a second portion of polymerization
inhibitor to the condensed crude vinyltoluene until the inhibitor
concentration totals about 500 parts per million by weight relative
to the vinyltoluene content of the crude vinyltoluene, filtering
the condensed crude vinyltoluene to remove seed polymer, and
distilling the condensed crude vinyltoluene to recover
substantially pure vinyltoluene; and apparatus for carrying out
said method.
[0038] U.S. Pat. No. 4,665,185 discloses a process for the
efficient preparation of nitroxyls of sterically hindered amines by
the oxidation of the amine using a hydroperoxide in the presence of
a small amount of a metal ion catalyst, at moderate temperature for
a short period of time, to give the nitroxyl in high yield and
purity.
[0039] U.S. Pat. No. 4,692,544 discloses certain substituted diaryl
amines that are used to inhibit the polymerization of ethylenically
unsaturated monomers; for example, unsaturated carboxylic acids and
derivatives thereof.
[0040] U.S. Pat. No. 4,720,566 discloses compositions and methods
of inhibiting acrylonitrile polymerization, particularly in quench
columns of systems producing acrylonitrile, comprising adding to
the acrylonitrile an effective amount for the purpose of (a) a
hydroxylamine having the formula 4
[0041] wherein R and R' are the same or different and are hydrogen,
alkyl, aryl, alkaryl or aralkyl groups, and (b) a
para-phenylenediamine or derivative thereof having at least one
N--H group. Preferably the phenylenediamine is a
para-phenylenediamine having the formula 5
[0042] wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same
or different and are hydrogen, alkyl, aryl, alkaryl, or aralkyl
groups with the proviso that at least one of R.sup.1, R.sup.2,
R.sup.3 or R.sup.4 is hydrogen.
[0043] U.S. Pat. No. 4,774,374 discloses a vinyl aromatic
composition stabilized against polymerization comprising (a) a
vinyl aromatic compound and (b) an effective amount of a stabilizer
system in which the active ingredient consists essentially of an
oxygenated species formed by the reaction of oxygen and an
N-aryl-N'-alkyl-p-phenylenediamine.
[0044] U.S. Pat. No. 4,797,504 discloses compositions and methods
of inhibiting acrylate monomer polymerization at elevated
temperatures comprising adding to the acrylate monomer an effective
amount for the purpose of (a) a hydroxylamine having the formula
6
[0045] wherein R and R' are the same or different and are hydrogen,
alkyl, aryl, alkaryl or aralkyl groups, and (b) a
para-phenylenediamine or derivative thereof having at least one
N--H group. Preferably the phenylenediamine is a
para-phenylenediamine having the formula 7
[0046] wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same
or different and are hydrogen, alkyl, aryl, alkaryl, or aralkyl
groups with the proviso that at least one of R.sup.1, R.sup.2,
R.sup.3 or R.sup.4 is hydrogen.
[0047] U.S. Pat. No. 4,912,247 discloses a composition and method
of use for inhibiting the polymerization of acrylate esters during
elevated temperature processing and during storage and handling
thereafter. It comprises the combination of a Mannich reaction
product, which is prepared from a substituted phenol, an aldehyde
and ethylenediamine, and either phenylenediamine or derivatives
thereof and/or phenothiazine or derivatives thereof.
[0048] U.S. Pat. No. 4,929,778 discloses methods and compositions
for inhibiting the polymerization of styrene monomer during
elevated temperature processing thereof or during storage or
shipment of styrene containing product. The compositions comprise a
combination of (a) a phenylenediamine compound having at least one
N--H bond and (b) a hindered phenol compound. The methods comprise
adding from 1-10,000 ppm of the combination to the styrene medium,
per one million parts of styrene.
[0049] U.S. Pat. No. 5,128,022 discloses methods and compositions
for inhibiting the formation of polymers in petroleum or
petrochemical processes that subsequently foul heat transfer
surfaces. The compositions comprise a combination of
N-Phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediam- ine (PDA) and an
organic acid. The methods comprise adding from 1 to 2500 ppm PDA
and 1 to 3500 ppm organic acid to the system experiencing the
fouling problem.
[0050] U.S. Pat. No. 5,254,760 teaches that the polymerization of a
vinyl aromatic compound, such as styrene, is very effectively
inhibited during distillation or purification by the presence of at
least one stable nitroxyl compound together with at least one
aromatic nitro compound.
[0051] U.S. Pat. No. 5,446,220 discloses methods for inhibiting the
polymerization of vinyl aromatic monomers in oxygen-free processing
systems. These methods comprise adding from 1 to about 10,000 parts
per million parts monomer of a combination of a dinitrophenol
compound, a hydroxylamine compound and a phenylenediamine compound.
Preferably, 2-sec-butyl-4,6-dinitrophenol or 4,6-dinitro-o-cresol
are used in combination with bis-(hydroxypropyl)hydroxylamine and
N,N'-di-sec-butyl-p-phenylenediamine.
[0052] U.S. Pat. Nos. 5,545,782 and 5,545,786 disclose that
nitroxyl inhibitors in combination with some oxygen reduce the
premature polymerization of vinyl aromatic monomers during the
manufacturing processes for such monomers. Even small quantities of
air used in combination with the nitroxyl inhibitors are said to
result in vastly prolonged inhibition times for the monomers.
[0053] European Patent Application 0 178 168 A2 discloses a method
for inhibiting the polymerization of an
.alpha.,.beta.-ethylenically unsaturated monocarboxylic acid during
its recovery by distillation by using a nitroxide free radical.
[0054] European Patent Application 0 325 059 A2 discloses
stabilizing vinyl aromatic compounds against polymerization by the
addition of an effective amount of a polymerization inhibition
composition comprising (a) a phenothiazine compound; and (b) an
aryl-substituted phenylenediamine compound.
[0055] European Patent Application 0 398 633 A1 discloses a method
of inhibiting acid monomer polymerization comprising adding to the
monomer (a) a manganese source compound and (b) a phenylenediamine
compound having at least one N--H bond therein.
[0056] European Patent Application 0 594 341 A1 discloses methods
and compositions for inhibiting the polymerization of vinyl
aromatic monomers under distillation conditions. The compositions
comprise a combination of a phenylenediamine compound and a
hydroxylamine compound.
[0057] European Patent Application 0 765 856 A1 discloses a
stabilized acrylic acid composition in which the polymerization of
the acrylic acid is inhibited during the distillation process for
purifying or separating the acrylic acid as well as during
transport and storage. The compositions comprise three components:
(a) acrylic acid, (b) a stable nitroxyl radical, and (c) a
dihetero-substituted benzene compound having at least one
transferable hydrogen (e.g., a quinone derivative such as the
monomethyl ether of hydroquinone (MEHQ)). During the distillation
process, transport, and storage, components (b) and (c) are present
in a polymerization-inhibiting amount. During the distillation
process, oxygen (d) is preferably added with components (b) and
(c). According to the specification, examples of suitable nitroxide
free radical compounds include di-t-butylnitroxide;
di-t-amylnitroxide; 2,2,6,6-tetramethyl-pipe- ridinyloxy;
4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;
4-oxo-2,2,6,6-tetramethyl-piperidinyloxy;
4-dimethylamino-2,2,6,6-tetrame- thyl-piperidinyloxy;
4-amino-2,2,6,6-tetramethyl-piperidinyloxy;
4-ethanoyloxy-2,2,6,6-tetramethyl-piperidinyloxy;
2,2,5,5-tetramethylpyrr- olidinyloxy;
3-amino-2,2,5,5-tetramethylpyrrolidinyloxy;
2,2,5,5-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy;
2,2,5,5-tetramethyl-1-o- xa-3-pyrrolinyl-1-oxy-3-carboxylic acid;
and 2,2,3,3,5,5,6,6-octamethyl-1,- 4-diazacyclohexyl-1,4-dioxy.
[0058] WO 97/46504 concerns substance mixtures containing: (A)
monomers containing vinyl groups; and (B) an active amount of a
mixture which inhibits premature polymerization of the monomers
containing vinyl groups during their purification or distillation
and contains: (i) between 0.05 and 4.5 wt %, relative to the total
mixture (B), of at least one N-oxyl compound of a secondary amine
which has no hydrogen atom at the .alpha.-C atoms; and (ii) between
99.95 and 95.5 wt % relative to the total mixture (B), of at least
one nitro compound. The publication also discloses a process for
inhibiting the premature polymerization of monomers, and the use of
mixture (B) for inhibiting the premature polymerization of
monomers.
[0059] WO 98/02403 relates to inhibiting the polymerization of
vinyl aromatic compounds by using a mixture of a phenol and a
hydroxylamine. It is said that the process is useful in
ethylbenzene dehydrogenation effluent condenser systems and
styrene-water separator vent gas compressor systems and that it
effectively inhibits polymerization of monomers, preventing the
formation of a polymer coating on condenser and compressor
equipment, thus reducing the necessity for cleaning of equipment
surfaces.
[0060] WO 98/14416 discloses that the polymerization of vinyl
aromatic monomers such as styrene is inhibited by the addition of a
composition of a stable hindered nitroxyl radical and an oxime
compound.
[0061] WO 98/25872 concerns substance mixtures containing: (A)
compounds containing vinyl groups; (B) an active amount of a
mixture which inhibits premature polymerization of the compounds
containing vinyl groups and contains: (i) at least one N-oxyl
compound of a secondary amine which does not carry any hydrogen
atoms on the .alpha.-carbon atoms; and (ii) at least one iron
compound; (C) optionally nitro compounds; and (D) optionally
co-stabilizers. The publication also discloses a process for
inhibiting the premature polymerization of compounds (A) containing
vinyl groups, and the use of (B) optionally mixed with nitro
compounds (C) and/or co-stabilizers (D) for inhibiting the
premature polymerization of radically polymerizable compounds and
stabilizing organic materials against the harmful effect of
radicals.
[0062] U.K. Patent Number 1,127,127 discloses that acrylic acid can
be stabilized against polymerization by the addition thereto of a
nitroxide having the essential skeletal structure: 8
[0063] wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are alkyl
groups and no hydrogen is bound to the remaining valencies on the
carbon atoms bound to the nitrogen. The two remaining valencies
that are not satisfied by R.sub.1 to R.sub.4 or nitrogen can also
form part of a ring (e.g., 2,2,6,6
tetramethyl-4-hydroxy-piperidine-1-oxyl).
[0064] CS-260755 B1 is directed to the preparation of
4-substituted-2,2,6,6-tetramethylpiperidine nitroxyls as olefin
stabilizers.
[0065] SU-334845 A1 is directed to the inhibition of the radical
polymerization of oligoester acrylates using iminoxyl radical
inhibitors of a given formula.
[0066] SU-478838 is directed to the inhibition of the radical
polymerization of oligoester acrylates and the prevention of
oligomeric peroxides using a binary polymerization inhibitor
comprising quinone.
[0067] FR 2,761,060 relates to the prevention of premature
polymerization of styrene during its production by dehydrogenation
of ethylbenzene by injecting into the process effluent a radical
inhibitor based on an oxyl-tetramethylpiperidine derivative.
[0068] The foregoing are incorporated herein by reference in their
entirety.
SUMMARY OF THE INVENTION
[0069] In accordance with the present invention, inhibiting systems
have been developed in which a component that is a hydrogen donor
or electron acceptor or a combination of two or more of such
components is used in the purification train, either alone or,
preferably, in combination with a nitroxyl radical to prevent
polymer growth via a "living" polymerization mechanism. When the
component is used in combination with the nitroxyl radical, the
effectiveness of the nitroxyl radical inhibitor can be preserved
and utilized without risking high molecular weight polymer
formation and/or coating of the internal parts of the purification
train owing to excessive polymer growth over time.
[0070] More particularly, the present invention is directed to a
method for inhibiting the premature polymerization and the polymer
growth of ethylenically unsaturated monomers comprising adding to
said monomers an effective amount of at least one inhibitor that is
a hydrogen donor or an electron acceptor.
[0071] It is also advantageous to add a transition metal ion to the
monomers. The preferred transition metal ion is copper, especially
Cu(I)naphthenate.
[0072] In a preferred embodiment, the present invention is directed
to a method for inhibiting the premature polymerization and the
polymer growth of ethylenically unsaturated monomers comprising
adding to said monomers A) an effective amount of at least one
first inhibitor that is a hydrogen donor or an electron acceptor
and B) at least one second inhibitor having the following
structural formula: 9
[0073] In another aspect, the present invention is directed to a
composition comprising A) at least one first inhibitor that is a
hydrogen donor or an electron acceptor and B) at least one second
inhibitor having the following structural formula: 10
[0074] In formula (I), R.sub.1 and R.sub.4 are independently
selected from the group consisting of hydrogen, alkyl, and
heteroatom-substituted alkyl and R.sub.2 and R.sub.3 are
independently selected from the group consisting of alkyl and
heteroatom-substituted alkyl; and X.sub.1 and X.sub.2 (1) are
independently selected from the group consisting of halogen, cyano,
COOR.sub.7, --S--COR.sub.7, --OCOR.sub.7, (wherein R.sub.7 is alkyl
or aryl), amido, --S--C.sub.6H.sub.5, carbonyl, alkenyl, or alkyl
of 1 to 15 carbon atoms, or (2) taken together, form a ring
structure with the nitrogen, preferably of five, six, or seven
members.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0075] As stated above, the present invention is directed to
inhibiting systems in which at least one hydrogen donor or electron
acceptor is used in the purification train, preferably in addition
to at least one nitroxyl radical, to prevent polymer growth that
occurs via a "living" polymerization mechanism.
[0076] The hydrogen donor compounds can, for example, be
hydroxylamines, oximes, phenols, catechols, hydroquinones, thiols,
anilines, dihydroanthracenes, and the like. Such compounds can
include a metal species which facilitates the reduction/oxidation
reactions that can accompany growth inhibition through deactivation
of the growing radical chain. More particularly, the hydrogen donor
compounds are preferably chosen from compounds having the
structural formulae I through V. 11
[0077] In structural formulae I through V:
[0078] R.sub.100 and R.sub.101 are independently selected from the
group consisting of hydrogen, alkyl, alkylidene, benzylidene, aryl,
benzyl, COR.sub.102, COOR.sub.102, CONR.sub.102R.sub.103, cyclic,
heterocyclic, and substituted alkyl or aryl where the substituents
are C, O, N, S, or P, or R.sub.100 and R.sub.101 can be taken
together to form a ring structure of five to seven members;
[0079] R.sub.102 and R.sub.103 are independently selected from the
group consisting of hydrogen, alkyl, aryl, benzyl, cyclic,
heterocyclic, and substituted alkyl or aryl where the substituents
are C, O, N, S, or P, or R.sub.102 and R.sub.103 can be taken
together to form a ring structure of five to seven members;
[0080] R.sub.104, R.sub.105, R.sub.106, R.sub.107, R.sub.108, and
R.sub.109 are independently selected from the group consisting of
hydrogen, alkyl, aryl, cycloalkyl, heterocyclic, substituted alkyl,
substituted aryl, OR.sub.110, NR.sub.110R.sub.111, SR.sub.110,
NO.sub.2, NO, CN, COR.sub.112, halogen (as used herein, halogen
includes fluorine, chlorine, bromine, and iodine), and/or any two
adjacent groups can be taken together to form ring structure(s) of
five to seven members, provided that at least one of R.sub.104,
R.sub.105, R.sub.106, R.sub.107, R.sub.108, and R.sub.109 is OH or
NHR.sub.110;
[0081] R.sub.110 and R.sub.111 are independently selected from the
group consisting of hydrogen, alkyl, aryl, benzyl, cyclic,
heterocyclic, substituted alkyl or aryl where the substituents are
C, O,
[0082] N, S, or P, and COR.sub.102, or R.sub.110 and R.sub.111 can
be taken together to form a ring structure of five to seven
members;
[0083] R.sub.112 is R.sub.102, OR.sub.102, or
NR.sub.102R.sub.103;
[0084] R.sub.113, R.sub.114, and R.sub.115 are independently
selected from the group consisting of hydrogen, alkyl, aryl,
cycloalkyl, and heterocyclic moieties; and
[0085] R.sub.116, R.sub.117, R.sub.118, R.sub.119, R.sub.120,
R.sub.121, R.sub.122, and R.sub.123 are independently selected from
the group consisting of hydrogen, alkyl, aryl, cycloalkyl,
heterocyclic, substituted alkyl, substituted aryl, OR.sub.110,
NR.sub.110R.sub.111, SR.sub.110, NO.sub.2, NO, CN, COR.sub.112,
halogen, and/or any two adjacent groups can be taken together to
form ring structure(s) of five to seven members.
[0086] The electron accepting compounds can, for example, be
quinones, quinone imines, quinone methides, and acetylenes. Such
compounds can include a metal species which facilitates the
reduction/oxidation reactions that can accompany growth inhibition
through deactivation of the growing radical chain. More
particularly, the electron accepting compounds are preferably
chosen from compounds having the structural formulae VI or VII.
12
[0087] In structural formula VI:
[0088] X and Y are independently selected from the group consisting
of oxygen, NR.sub.110, and CR.sub.124R.sub.125;
[0089] R.sub.120, R.sub.121, R.sub.122, and R.sub.123 are
independently selected from the group consisting of hydrogen,
alkyl, aryl, cycloalkyl, heterocyclic, substituted alkyl,
substituted aryl, OR.sub.110, NR.sub.110R.sub.111, SR.sub.110, NO,
NO.sub.2, CN, COR.sub.112, and halogen, or R.sub.120 and R.sub.12,
can be taken together and/or R.sub.122 and R.sub.123 can be taken
together to form one or two ring structures, respectively, either
of which can be of five to seven members;
[0090] R.sub.124 and R.sub.125 are independently selected from the
group consisting of hydrogen, alkyl, aryl, cycloalkyl,
heterocyclic, substituted alkyl, substituted aryl, OR.sub.110,
NR.sub.110R.sub.111, SR.sub.110, NO.sub.2, NO, CN, COR.sub.112,
halogen, and/or can be taken together to form a ring structure of
five to seven members;
[0091] R.sub.110 and R.sub.111 are independently selected from the
group consisting of hydrogen, alkyl, aryl, benzyl, cyclic,
heterocyclic, substituted alkyl or aryl where the substituents are
C, O, N, S, or P, and COR.sub.102, or R.sub.110 and R.sub.111 can
be taken together to form a ring structure of five to seven
members;
[0092] R.sub.112 is R.sub.102, OR.sub.102, or NR.sub.102R.sub.103;
and
[0093] R.sub.102 and R.sub.103 are independently selected from the
group consisting of hydrogen, alkyl, aryl, benzyl, cyclic,
heterocyclic, and substituted alkyl or aryl where the substituents
are C, O, N, S, or P, or R.sub.102 and R.sub.103 can be taken
together to form a ring structure of five to seven members.
[0094] In structural formula VII:
[0095] R.sub.126 and R.sub.127 are independently selected from the
group consisting of hydrogen, alkyl, aryl, cycloalkyl,
heterocyclic, substituted alkyl, substituted aryl, OR.sub.110,
NR.sub.110R.sub.111, SR.sub.110, NO.sub.2, NO, CN, COR.sub.112, and
halogen wherein R.sub.110, R.sub.111, and R.sub.112 are defined as
for formula VI.
[0096] In the foregoing, alkyl (or substituted alkyl) groups
preferably contain 1 to 15 carbon atoms, e.g., methyl, ethyl,
propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl,
dodecyl, tridecyl, tetradecyl, pentadecyl, and the like, and
isomers thereof, e.g., t-butyl, 2-ethylhexyl, and the like. It is
more preferred that the alkyl (or substituted alkyl) groups be of
one to five carbon atoms (e.g., methyl, ethyl, propyl, butyl,
pentyl, and isomers thereof). Substituents on the substituted alkyl
groups can be any moiety that will not interfere with the hydrogen
donating or electron receiving functions of the compounds. Aryl
groups are preferably of from 6 to 10 carbon atoms, e.g., phenyl or
naphthyl, which, in addition, may be substituted with
non-interfering substituents, e.g., lower alkyl groups, halogens,
and the like.
[0097] Exemplary hydrogen donating compounds include, but are not
limited to, diethylhydroxylamine, cyclohexanoneoxime,
dibenzylhydroxylamine, 2,4-dinitro-6-sec-butylphenol,
N-phenyl-N'-(1,4-dimethylpentyl)-para-phen- ylenediamine,
2,5-di-t-butylhydroquinone, 2,5-di-t-amylhydroquinone,
methylhydroquinone, 4-t-butylhydroquinone, 4-t-butylcatechol,
octanethiol, 2,6-di-t-butyl-4-ethylphenol/Cu(I)naphthenate,
dihydroanthracene, N-t-butyl-2-benzothiazole-sulfenamide,
N-methyl-4-nitroaniline, and the like.
[0098] Exemplary electron accepting compounds include, but are not
limited to, phenylacetylene, 2,5-di-t-butyl-1,4-benzoquinone,
2,6-di-t-butyl-1,4-benzoquinone, 1,4-benzoquinone,
2-methylanthraquinone, 1,4-naphthoquinone,
2,6-di-t-butyl-4-(phenylmethylene)-2,5-cyclohexadiene- -1-one,
2,6-di-t-butyl-4-(phenylimino)-2,5-cyclohexadiene-1-one, ethyl
3,4-bis-(3,5-di-t-butyl-4-one-2,5-cyclohexadienylidene)-hexane-1,6-dioate-
, and the like.
[0099] An effective growth inhibiting system can consist of one or
more of any of the compounds described above with or without one or
more nitroxyl compounds.
[0100] As stated above, in one preferred aspect, the present
invention is directed to a method for inhibiting the premature
polymerization of ethylenically unsaturated monomers comprising
adding to said monomers, in addition to at least one first
inhibitor that is a hydrogen donor or an electron acceptor, an
effective amount of at least one second inhibitor that is a stable
hindered nitroxyl compound having the structural formula: 13
[0101] wherein R.sub.1 and R.sub.4 are independently selected from
the group consisting of hydrogen, alkyl, and heteroatom-substituted
alkyl and R.sub.2 and R.sub.3 are independently selected from the
group consisting of alkyl and heteroatom-substituted alkyl; and
X.sub.1 and X.sub.2 (1) are independently selected from the group
consisting of halogen, cyano, COOR.sub.7, --S--COR.sub.7,
--OCOR.sub.7, (wherein R.sub.7 is alkyl or aryl), amido,
--S--C.sub.6H.sub.5, carbonyl, alkenyl, or alkyl of 1 to 15 carbon
atoms, or (2) taken together, form a ring structure with the
nitrogen.
[0102] In a particularly preferred embodiment, the stable hindered
nitroxyl compound has the structural formula: 14
[0103] wherein R.sub.1 and R.sub.4 are independently selected from
the group consisting of hydrogen, alkyl, and heteroatom-substituted
alkyl and R.sub.2 and R.sub.3 are independently selected from the
group consisting of alkyl and heteroatom-substituted alkyl, and the
15
[0104] portion represents the atoms necessary to form a five-,
six-, or seven-membered heterocyclic ring.
[0105] Accordingly, one of the several classes of cyclic nitroxides
that can be employed in the practice of the present invention can
be represented by the following structural formula: 16
[0106] wherein Z.sub.1, Z.sub.2, and Z.sub.3 are independently
selected from the group consisting of oxygen, sulfur, secondary
amines, tertiary amines, phosphorus of various oxidation states,
and substituted or unsubstituted carbon atoms, such as
>CH.sub.2, >CHCH.sub.3, >C.dbd.O, >C(CH.sub.3).sub.2,
>CHBr, >CHCl, >CHI, >CHF, >CHOH, >CHCN,
>C(OH)CN, >CHCOOH, >CHCOOCH.sub.3,
>CHCOOC.sub.2H.sub.5, >C(OH)COOC.sub.2H.sub.5,
>C(OH)COOCH.sub.3, >C(OH)CHOHC.sub.2H.sub.5,
>CR.sub.5OR.sub.6, >CHNR.sub.5R.sub.6,
>CCONR.sub.5R.sub.6, >C.dbd.NOH,
>C.dbd.CH--C.sub.6H.sub.5, >CF.sub.2, >CCl.sub.2,
>CBr.sub.2, >CI.sub.2, >CR.sub.5PR.sub.13R.sub.14R.sub.15,
and the like, where R.sub.5 and R.sub.6 are independently selected
from the group consisting of hydrogen, alkyl, aryl, and acyl and
R.sub.13, R.sub.14, and R.sub.15 are independently selected from
the group consisting of unshared electrons, alkyl, aryl, .dbd.O,
OR.sub.16, and NR.sub.17R.sub.18, where R.sub.16, R.sub.17, and
R.sub.18 are independently selected from the group consisting of
hydrogen, alkyl, and aryl. Where R.sub.5 and/or R.sub.6 are alkyl,
it is preferred that they be a lower alkyl (i.e., one having one to
five carbon atoms, e.g., methyl, ethyl, propyl, butyl, pentyl, and
isomers thereof).
[0107] Where R.sub.5 and/or R.sub.6 are aryl, it is preferred that
they be aryl of from 6 to 10 carbon atoms, e.g., phenyl or
naphthyl, which, in addition, may be substituted with
non-interfering substituents, e.g., lower alkyl groups, halogens,
and the like.
[0108] Where R.sub.5 and/or R.sub.6 are acyl, it is preferred that
they be acyl of the structure 17
[0109] where R.sub.19 is alkyl, aryl, OR.sub.20, or
NR.sub.20R.sub.21, and where R.sub.20 and R.sub.21, are alkyl,
aryl, or 18
[0110] where R.sub.22 is alkyl or aryl. Where R.sub.19, R.sub.20,
R.sub.21 or R.sub.22 are alkyl, they are preferably alkyl of from 1
to 15 carbon atoms, more preferably lower alkyl of from 1 to 5
carbon atoms, as described above. Where R.sub.19, R.sub.20,
R.sub.21, or R.sub.22 are aryl, they are preferably aryl of from 6
to 10 carbon atoms, as described above.
[0111] Another of the several classes of cyclic nitroxides that can
be employed in the practice of the present invention can be
represented by the following structural formula: 19
[0112] wherein Z.sub.1 and Z.sub.2, which may be the same or
different, are nitrogen or substituted or unsubstituted carbon
atoms, such as .dbd.C(H)--, .dbd.C(CH.sub.3)--, .dbd.C(COOH)--,
.dbd.C(COOCH.sub.3)--, .dbd.C(COOC.sub.2H.sub.5)--, .dbd.C(OH)--,
.dbd.C(CN)--, .dbd.C(NR.sub.5R.sub.6)--,
.dbd.C(CONR.sub.5R.sub.6)--, and the like, and where Z.sub.3,
R.sub.5, and R.sub.6 are as described above.
[0113] The cyclic nitroxides employed in the practice of the
present invention can also be derived from five-membered rings.
These compounds are of the structure: 20
[0114] wherein Z.sub.2 and Z.sub.3, which may be the same or
different, are sulfur, oxygen, secondary amines, tertiary amines,
phosphorus of various oxidation states, or substituted or
unsubstituted carbon atoms, such as, >CH.sub.2, >CHCH.sub.3,
>C.dbd.O, >C(CH.sub.3).sub.2, >CHBr, >CHCl, >CHI,
>CHF, >CHOH, >CHCN, >C(OH)CN, >CHCOOH,
>CHCOOCH.sub.3, >CHCOOC.sub.2H.sub.5,
>C(OH)COOC.sub.2H.sub.5, >C(OH)COOCH.sub.3,
>C(OH)CHOHC.sub.2H.sub.5, >CR.sub.5OR.sub.6,
>CHNR.sub.5R.sub.6, >CCONR.sub.5R.sub.6, >C.dbd.NOH,
>C.dbd.CH--C.sub.6H.sub.5, CF.sub.2, CCl.sub.2, CBr.sub.2,
CI.sub.2, >CR.sub.5PR.sub.13R.sub.14R.sub.15, and the like,
wherein the several R groups are as described above.
[0115] The cyclic nitroxides employed in the practice of the
present invention can also have the structure: 21
[0116] wherein Z.sub.4 and Z.sub.5, which can be the same or
different, can be nitrogen or a substituted or unsubstituted carbon
atom, such as .dbd.C(H)--, .dbd.C(CH.sub.3)--, .dbd.C(COOH)--,
.dbd.C(COOCH.sub.3)--, .dbd.C(COOC.sub.2H.sub.5)--, .dbd.C(OH)--,
.dbd.C(CN)--, .dbd.C(NR.sub.5R.sub.6)--,
.dbd.C(CONR.sub.5R.sub.6)--, and the like, where R.sub.5 and
R.sub.6 are as described above.
[0117] Another class of cyclic nitroxides that can be employed in
the practice of the present invention is of the structure: 22
[0118] wherein Z.sub.2 and Z.sub.3, which may be the same or
different, are sulfur, oxygen, secondary amines, tertiary amines,
or substituted or unsubstituted carbon atoms, such as,
>CH.sub.2, >CHCH.sub.3, >C.dbd.O, >C(CH.sub.3).sub.2,
>CHBr, >CHCl, >CHI, >CHF, >CHOH, >CHCN,
>C(OH)CN, >CHCOOH, >CHCOOCH.sub.3,
>CHCOOC.sub.2H.sub.5, >C(OH)COOC.sub.2H.sub.5,
>C(OH)COOCH.sub.3, >C(OH)CHOHC.sub.2H.sub.5,
>CHNR.sub.5R.sub.6, >CCONR.sub.5R.sub.6,
>CR.sub.5OR.sub.6, >C.dbd.NOH, >C.dbd.CH--C.sub.6H.sub.5,
CF.sub.2, CCl.sub.2, CBr.sub.2, CI.sub.2,
>CR.sub.5PR.sub.13R.sub.14R.sub.15, and the like, where the
several R groups are as described above.
[0119] Further, two or more nitroxyl groups can be present in the
same molecule, for example, by being linked through one or more of
the Z-type moieties by a linking group E, as disclosed in U.S. Pat.
No. 5,254,760, which is incorporated herein by reference.
[0120] As stated above, for all the nitroxyl structures above,
R.sub.1 and R.sub.4 are independently selected from the group
consisting of hydrogen, alkyl, and heteroatom-substituted alkyl and
R.sub.2 and R.sub.3 are independently selected from the group
consisting of alkyl and heteroatom-substituted alkyl. The alkyl (or
heteroatom-substituted alkyl) groups R.sub.1 through R.sub.4 can be
the same or different and preferably contain 1 to 15 carbon atoms,
e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl,
nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,
and the like, and isomers thereof, e.g., t-butyl, 2-ethylhexyl, and
the like. It is more preferred that R.sub.1 through R.sub.4 be
independently selected lower alkyl (or heteroatom-substituted lower
alkyl) of one to five carbon atoms (e.g., methyl, ethyl, propyl,
butyl, pentyl, and isomers thereof). Where heteroatom substituents
are present, they can, for example, include halogen, oxygen,
sulfur, nitrogen, and the like. It is most preferred that all of
R.sub.1 through R.sub.4 be methyl.
[0121] Examples of suitable nitroxide free radical compounds that
can be used in combination with the hydrogen donor or electron
acceptor in the practice of the present invention, include, but are
not limited to:
[0122] N,N-di-tert-butylnitroxide;
[0123] N,N-di-tert-amylnitroxide;
[0124] N-tert-butyl-2-methyl-1-phenyl-propylnitroxide;
[0125]
N-tert-butyl-1-diethylphosphono-2,2-dimethylpropylnitroxide;
[0126] 2,2,6,6-tetramethyl-piperidinyloxy;
[0127] 4-amino-2,2,6,6-tetramethyl-piperidinyloxy;
[0128] 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0129] 4-oxo-2,2,6,6-tetramethyl-piperidinyloxy;
[0130] 4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy;
[0131] 4-ethanoyloxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0132] 2,2,5,5-tetramethylpyrrolidinyloxy;
[0133] 3-amino-2,2,5,5-tetramethylpyrrolidinyloxy;
[0134] 2,2,4,4-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy;
[0135] 2,2,4,4-tetramethyl-1-oxa-3-pyrrolinyl-1-oxy-3-carboxylic
acid;
[0136]
2,2,3,3,5,5,6,6-octamethyl-1,4-diazacyclohexyl-1,4-dioxy;
[0137] 4-bromo-2,2,6,6-tetramethyl-piperidinyloxy;
[0138] 4-chloro-2,2,6,6-tetramethyl-piperidinyloxy;
[0139] 4-iodo-2,2,6,6-tetramethyl-piperidinyloxy;
[0140] 4-fluoro-2,2,6,6-tetramethyl-piperidinyloxy;
[0141] 4-cyano-2,2,6,6-tetramethyl-piperidinyloxy;
[0142] 4-carboxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0143] 4-carbomethoxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0144] 4-carbethoxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0145] 4-cyano-4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0146] 4-methyl-2,2,6,6-tetramethyl-piperidinyloxy;
[0147]
4-carbethoxy-4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;
[0148]
4-hydroxy-4-(1-hydroxypropyl)-2,2,6,6-tetramethyl-piperidinyloxy;
[0149]
4-methyl-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
[0150]
4-carboxy-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
[0151]
4-carbomethoxy-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxy-
l;
[0152]
4-carbethoxy-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
[0153]
4-amino-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
[0154]
4-amido-2,2,6,6-tetramethyl-1,2,5,6-tetrahydropyridine-1-oxyl;
[0155] 3,4-diketo-2,2,5,5-tetramethylpyrrolidinyloxy;
[0156] 3-keto-4-oximino-2,2,5,5-tetramethylpyrrolidinyloxy;
[0157] 3-keto-4-benzylidine-2,2,5,5-tetramethylpyrrolidinyloxy;
[0158] 3-keto-4,4-dibromo-2,2,5,5-tetramethylpyrrolidinyloxy;
[0159] 2,2,3,3,5,5-hexamethylpyrrolidinyloxy;
[0160] 3-carboximido-2,2,5,5-tetramethylpyrrolidinyloxy;
[0161] 3-oximino-2,2,5,5-tetramethylpyrrolidinyloxy;
[0162] 3-hydroxy-2,2,5,5-tetramethylpyrrolidinyloxy;
[0163] 3-cyano-3-hydroxy-2,2,5,5-tetramethylpyrrolidinyloxy;
[0164]
3-carbomethoxy-3-hydroxy-2,2,5,5-tetramethylpyrrolidinyloxy;
[0165]
3-carbethoxy-3-hydroxy-2,2,5,5-tetramethylpyrrolidinyloxy;
[0166]
2,2,5,5-tetramethyl-3-carboxamido-2,5-dihydropyrrole-1-oxyl;
[0167] 2,2,5,5-tetramethyl-3-amino-2,5-dihydropyrrole-1-oxyl;
[0168]
2,2,5,5-tetramethyl-3-carbethoxy-2,5-dihydropyrrole-1-oxyl;
[0169] 2,2,5,5-tetramethyl-3-cyano-2,5-dihydropyrrole-1-oxyl;
[0170] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)succinate;
[0171] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipate;
[0172] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)sebacate;
[0173]
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)n-butylmalonate;
[0174] bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)phthalate;
[0175]
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)isophthalate;
[0176]
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)terephthalate;
[0177]
bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)hexahydroterephthalate-
;
[0178]
N,N'-bis(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipamide;
[0179]
N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-caprolactam;
[0180]
N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-dodecylsuccinimide;
[0181]
2,4,6-tris-[N-butyl-N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)]-s-
-triazine;
[0182] 4,4'-ethylenebis(1-oxyl-2,2,6,6-tetramethylpiperazin-3-one);
and the like.
[0183] As used herein, the abbreviation TEMPO stands for
2,2,6,6-tetramethyl-1-piperidinyloxy. Thus, 4-amino-TEMPO is
4-amino-2,2,6,6-tetramethyl-1-piperidinyloxy; 4-hydroxy-TEMPO is
4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (also known in the
art as HTEMPO); 4-oxo-TEMPO is
4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy; and so on.
[0184] It is preferred that one member of the combination employed
in the practice of the present invention be 4-amino-TEMPO,
4-oxo-TEMPO, 4-hydroxy-TEMPO, or TEMPO.
[0185] Blends of two or more of the foregoing, e.g., 4-amino-TEMPO
and 4-oxo-TEMPO, can also be employed.
[0186] Such stable nitroxide free radical compounds can be prepared
by known methods. (See, for example, U.S. Pat. Nos. 3,163,677;
3,334,103; 3,372,182; 3,422,144; 3,494,930; 3,502,692; 3,873,564;
3,966,711; and 4,665,185; which are incorporated herein by
reference.) They are suitable for use over a wide range of
temperatures, but distillation temperatures employed with the
ethylenically unsaturated monomers that are stabilized by the
process of the present invention typically range from about
60.degree. C. to about 180.degree. C., preferably from about
70.degree. C. to about 165.degree. C., and, more preferably, from
about 80.degree. C. to about 150.degree. C. Such distillations are
generally performed at an absolute pressure in the range of about
10 to about 1,200 mm of Hg.
[0187] The ethylenically unsaturated monomer, the premature
polymerization and polymer growth of which is an object of the
present invention, can be any such monomer for which unintended
polymerization and/or polymer growth during its manufacture,
storage, and/or distribution is a problem. Among those monomers
that will benefit from the practice of the present invention are:
styrene, .alpha.-methylstyrene, styrene sulfonic acid,
vinyltoluene, divinylbenzenes, polyvinylbenzenes, alkylated
styrene, 2-vinylpyridine, acrylonitrile, methacrylonitrile, methyl
acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate,
acrylic acid, methacrylic acid, butadiene, chloroprene, isoprene,
and the like.
[0188] The ethylenically unsaturated monomers will not necessarily
be stabilized indefinitely by the presence of the inhibitor(s),
especially when the monomers are heated as in distillation, but
they can be considered to be stabilized as long as A) there is a
measurable increase in the time for which they can be heated before
the onset of polymerization and/or polymer growth in a static
system, B) the amount of polymer made at a constant temperature
remains constant over time in a dynamic system, and/or C) the rate
of polymer growth is significantly slower than when the growth
inhibiting system is not present.
[0189] Those skilled in the art will understand that, if desired,
free radical scavengers can also be included in the practice of the
present invention. For example, air or O.sub.2, as disclosed in
U.S. Pat. Nos. 5,545,782 and 5,545,786, can be added, as can the
aromatic nitro compounds disclosed in U.S. Pat. No. 5,254,760, the
dihetero-substituted benzene compounds having at least one
transferable hydrogen, e.g., a quinone derivative such as the
mono-methyl-ether of hydroquinone disclosed in European Patent
Application 0 765 856 A1, the iron compounds disclosed in WO
98/25872, and other inhibitors, e.g., phenolics and certain
inorganic salts, well-known to those skilled in the art.
[0190] The polymerization inhibitor(s) can be introduced into the
monomer to be protected by any conventional method. They can, for
example, be added as a concentrated solution in suitable solvents
just upstream from the point of desired application by any suitable
means. In addition, individual inhibiting components can be
injected separately into the distillation train along with the
incoming feed and/or through separate and multiple entry points,
provided there is an efficient distribution of the inhibiting
composition. Since the inhibitors are gradually depleted during the
distillation operation, it is generally advantageous to maintain
the appropriate amount of them in the distillation apparatus by
adding them during the course of the distillation process. Adding
inhibitors can be done either on a generally continuous basis or
intermittently, in order to maintain the inhibitor concentration
above the minimum required level.
[0191] The total inhibitor concentration should be from about 1 to
about 2000 ppm versus the monomer being inhibited; preferably from
about 5 to about 1000 ppm, depending on the conditions of use.
[0192] The ratio of the first component, or blend A (electron
acceptor or hydrogen donor compound or blend thereof) to a second
component, or blend B (nitroxyl or nitroxyls), based on the total
of both components is from about 1 to 100 wt % A: about 99 to 0 wt
% B; preferably, about 25-75 wt % A: about 75-25 wt % B; more
preferably about 50-75 wt % A: about 50-25 wt % B.
[0193] The advantages and the important features of the present
invention will be more apparent from the following examples.
EXAMPLES
Procedure for Polymer Growth Reboiler Test Preparation of Feed
Solution
[0194] Tert-butylcatechol (TBC) is removed from commercially
available styrene by distillation under vacuum. Removal of TBC is
verified by caustic titration. The desired amount of inhibitor(s)
is added to this TBC-free styrene either directly or by first
making a concentrated solution of the inhibitor in TBC-free styrene
followed by further dilution with TBC-free styrene.
Procedure for Polymer Growth Dynamic Reboiler Test:
[0195] A quantity of the Feed Solution containing inhibitor or
blend of inhibitors at the desired charge (stated as a wt/wt total
inhibitor to styrene) is added to a round-bottom flask (the Pot). A
known quantity of insoluble polymer capable of growing via a living
mechanism is placed inside the Pot and submersed in the Feed
Solution in the Pot. The insoluble polymer can be retained in the
Pot by any suitable means. Typically, the insoluble polymer is
securely wrapped in a piece of filter paper or wire mesh and
suspended by a wire within the Pot. Conversely, the Bottoms Stream
line (as described below) can be covered with filter paper or mesh
to prevent insoluble polymer from being removed from the Pot. The
Pot is placed in a hot oil bath, and the Feed Solution in the pot
is heated to the desired temperature (usually 130.degree. C) and
brought to reflux by adjusting the pressure/vacuum. Once the Pot
contents are at temperature, a continuous stream of fresh Feed
Solution is begun at a rate that will add the volume of the initial
Pot solution to the Pot over a period of time called the "residence
time" (typically one hour). At the same time at which the fresh
Feed Solution flow is begun, the Bottoms Stream flow is also begun.
The Bottoms Stream is solution in the Pot that is removed at the
same rate as the fresh Feed Solution is added. The equal flows of
Feed and Bottoms Streams causes the quantity in the Pot to remain
constant over the time of the experiment while allowing continuous
replenishment of inhibitor. This procedure simulates the way
inhibitors are used in a distillation train of a plant producing
vinyl monomers. The experiment continues with flow in and out of
the Pot for a specified length of time (usually 7 hours). Samples
are collected hourly from the Bottoms Stream. These samples are
analyzed for polymer content via the methanol turbidity method. The
amount of polymer in the samples is an indication of effectiveness
of the inhibitor system being tested.
[0196] After running for the specified length of time, the vacuum
is released and, if used, the filter paper bag of polymer is
removed. The Pot solution is filtered to recover any insoluble
polymer that may have escaped from the bag. Any filtered polymer
and the polymer in the filter paper bag are allowed to dry open to
the atmosphere for at least 18 hours. The polymer can be further
dried by placing it in a vacuum oven at 40-50.degree. C. under full
vacuum for 1-2 hours. The polymer is then weighed. Percent growth
is determined by the following equation: 1 % growth = weight of
final insoluble polymer - weight of initial insoluble polymer
weight of initial insoluble polymer .times. 100
[0197] Lower percent growth numbers indicate increased
effectiveness of the system to inhibit polymer growth via a
"living" mechanism.
[0198] Preparation of Insoluble Polymer Capable of Growing
[0199] Tert-butylcatechol (TBC) was removed from commercially
available styrene and from commercially available divinylbenzene
(DVB) by distillation under vacuum. Removal of TBC was verified by
caustic titration. TBC-free styrene (50 g), ethylbenzene (49 g),
TBC-free DVB (1 g), and 4-oxo-TEMPO (0.01 g) were combined. The
mixture was stirred at 130.degree. C. until the mixture polymerized
to a gel (about 3 hours). The gel-like system was cooled to about
60.degree. C., and 2 liters of ethylbenzene were added. The
resulting mixture was stirred for 2 hours at 50.degree. C.,
filtered by vacuum filtration until the gel was mostly dry, and
remaining solvent was removed by evaporation under full vacuum at
50.degree. C. A hard, white polymer was obtained (25 g, 49%
yield).
Procedure for Multi-Pass Reboiler Test
[0200] Preparation of First Pass Feed Solution:
[0201] Tert-butylcatechol (TBC) is removed from commercially
available styrene by distillation under vacuum. Removal of TBC is
verified by caustic titration. The desired amount of inhibitor(s)
is added to this TBC-free styrene either directly or by first
making a concentrated solution of the inhibitor in TBC-free styrene
followed by further dilution with TBC-free styrene.
[0202] Procedure for Reboiler Test (A Dynamic Test):
[0203] A quantity of the Feed Solution containing inhibitor (blend)
at the desired charge (stated as a wt/wt total inhibitor to
styrene) is added to a round-bottom flask (the Pot) and heated to
the desired temperature (usually 130.degree. C.) and brought to
reflux by adjusting the pressure/vacuum. Once the Pot contents are
at temperature, a continuous stream of fresh Feed Solution is begun
at a rate that will add the volume of the initial Pot solution to
the Pot over a period of time called the residence time (typically,
one hour). At the same time that the fresh Feed Solution flow is
begun, the Bottoms Stream flow is also begun. The Bottoms Stream is
solution in the Pot that is removed at the same rate as the fresh
Feed Solution is added. The equal flows of Feed and Bottoms Streams
cause the quantity in the Pot to remain constant over the time of
the experiment, while allowing continuous replenishment of
inhibitor. This procedure simulates the way inhibitors are used in
a distillation train of a plant producing vinyl monomers. The
experiment continues with flow in and out of the Pot for a
specified period of time. Typically, the First Pass runs for 10
hours, the Second Pass runs for 9 hours, the Third Pass runs for 8
hours, etc.
[0204] Samples are collected hourly from the Bottoms Stream. These
samples are analyzed for polymer content via the methanol turbidity
method. The amount of polymer in the samples is an indication of
effectiveness of the inhibitor system being tested. "Average
Polymer Make" is the average of the polymer content values for
samples taken after 4 hours running.
[0205] The material left in the Pot at the end of the run is
quickly removed and cooled, to stop any further polymerization. The
material is then concentrated, if necessary, under reduced pressure
at 40.degree. C. until the polymer content is >5 wt %. A sample
of this polymer solution is then analyzed by Gel Permeation
Chromatography (GPC) to determine the weighted average molecular
weight (M.sub.w) of the polymer.
[0206] Preparation of Second and Third Pass Feed Solutions:
[0207] The Bottoms Stream from the previous Pass is collected
except for the material in the Pot at the end of the run. The
amounts of inhibitor(s) in the First Pass Feed Solution and the
Bottoms Stream from the First Pass are determined by appropriate
analytical method(s), e.g., gas chromatography. An amount of
inhibitor(s) is added to the collective Bottoms Stream from the
First Pass to increase the level of inhibitor(s) in the Bottoms
Stream to a level equal to that found in the First Pass Feed
Solution. An equivalent amount of inhibitor(s) is added to the
collective Bottoms Streams for subsequent Passes.
[0208] Evaluation of the Results
[0209] The difference in the "Average Polymer Make" made in one
Pass versus subsequent Passes is an indication of the ability of
the inhibiting system to prevent or allow polymer to grow. For
example, an increase in the amount of polymer made going from one
Pass to the next which is roughly equivalent to the amount of
polymer made during the First Pass is an indication that the
inhibiting system effectively prevents polymer growth during
recycle. Conversely, an increase in the amount of polymer made
going from one Pass to the next that is dramatically greater (about
10 times or more) than the amount of polymer made during the First
Pass is an indication that the inhibiting system does not
effectively prevent polymer growth during recycle.
[0210] The difference in the M.sub.w of the polymer made in one
Pass versus subsequent Passes is an indication of the ability of
the inhibiting system to prevent or allow polymer to grow. Any
significant increase in M.sub.w of the polymer made in one Pass
versus the previous Pass is an indication that the inhibiting
system does not prevent polymer growth. The closer to zero the
increase in M.sub.w, the better the growth inhibiting ability of
the system.
[0211] The effectiveness of hydrogen donor systems and their blends
with nitroxyls is shown in Tables 1 and 4. The effectiveness of
electron-accepting systems and their blends with nitroxyls is shown
in Table 2. Examples of Synergistic Blends of Donor and Acceptor
systems are shown in Table 3. The first two examples in each of
Tables 1-3 are baseline examples of nitroxyl inhibitors used
alone--conditions that are known to allow polymer growth via a
"living" mechanism. Under these Polymer Growth Test baseline
conditions, about 700% growth was observed. All other examples in
Tables 1-3 gave less than 700% growth, indicating that those
systems provided some growth inhibiting activity.
[0212] The first example in Table 4 is also a baseline example of a
nitroxyl inhibitor used alone--conditions that are known to allow
polymer growth via a "living" mechanism. Under these Multi-Pass
Test baseline conditions, the average polymer make increased
100-fold and the molecular weight (M.sub.w) of the polymer made
increased nearly 10-fold over three passes. The other examples in
Table 4 gave minor increases in average polymer make (versus the
baseline example) and essentially no change in molecular weight of
the polymer over three passes, indicating that those systems
provided significant growth inhibiting activity.
1TABLE 1 Performance of Hydrogen Donor Systems Using Polymer Growth
Test Method Growth (% increase in Inhibitor Charge(s) weight of
insoluble Inhibitor System (ppm vs styrene) polymer after 7 hrs.)
4-oxo-TEMPO (baseline) 300 684 4-hydroxy-TEMPO (baseline) 300 736
4-oxo-TEMPO/diethylhydroxylamine 300/3000 20
4-oxo-TEMPO/diethylhydroxylamine 300/600 76
4-oxo-TEMPO/cyclohexanoneoxime 300/3000 382
4-oxo-TEMPO/dibenzylhydroxylamine 300/600 388 4-oxo-TEMPO/DNBP
150/1500 -2 DNBP 1500 20 DNBP/PDA 900/600 11 DNBP/PDA (air) 900/600
(8 cc/min) -13 4-oxo-TEMPO/2,5-di-t-butylhy- droquinone 300/3000
175 4-oxo-TEMPO/2,5-di-t-butylhydroquinone 300/600 197
4-oxo-TEMPO/2,5-di-t-amylhydroquinone 300/900 173
4-oxo-TEMPO/2,5-di-t-amylhydroquinone 300/600 275
4-oxo-TEMPO/methylhydroquinone 300/600 420 4-oxo-TEMPO/4-t-butylhy-
droquinone 300/300 464 4-oxo-TEMPO/4-t-butylcatechol, 300/3000 56
4-oxo-TEMPO/octanethiol 300/3000 220 4-oxo-TEMPO/octanethiol
300/1500 420 4-oxo-TEMPO/2,6-di-t-butyl-4-methylphenol/Cu(I)naphth-
enate 300/3000/150 416 4-oxo-TEMPO/dihydroanthracene 300/3000 524
4-oxo-TEMPO/N-t-butyl-2-benzothiazole-sulfenamide 300/3000 532
4-oxo-TEMPO/N-methyl-4-nitroaniline 300/3000 538 PDA =
N-phenyl-N'-(1,4-dimethylpentyl)-para-phenylenediamine DNBP =
2,4-dinitro-6-sec-butylphenol
[0213]
2TABLE 2 Performance of Electron Acceptor Systems Using Polymer
Growth Test Method Growth (% increase in Inhibitor Charge(s) weight
of insoluble Inhibitor System (ppm vs styrene) polymer after 7
hrs.) 4-oxo-TEMPO (baseline) 300 684 4-hydroxy-TEMPO (baseline) 300
736 4-oxo-TEMPO/phenylacetylene 300/3000 540
4-oxo-TEMPO/2,5-di-t-buty- l-1,4-benzoquinone 300/3000 96
4-oxo-TEMPO/2,5-di-t-butyl-1,4-benzo- quinone 300/600 180
4-oxo-TEMPO/2,6-di-t-butyl-1,4-benzoquinone 150/1500 358
4-oxo-TEMPO/1,4-benzoquinone 300/600 136
4-oxo-TEMPO/2-methylanthraquinone 300/600 235
4-oxo-TEMPO/1,4-naphthoquinone 300/600 308 4-oxo-TEMPO/2,6-di-t-bu-
tyl-4-(phenylmethylene)-2,5- 150/1500 14 cyclohexadiene-1-one
2,6-di-t-butyl-4-(phenylmethylene)-2,5-cyclohexadiene-1-one 1500 40
4-oxo-TEMPO/2,6-di-t-butyl-4-(phenylimino)-2,5- 300/2900 396
cyclohexadiene-1-one 4-oxo-TEMPO/ethyl 3,4-bis-(3,5-di-t-butyl-4-o-
ne-2,5- 300/600 525 cyclohexadienylidene)-hexane-1,6-dioate
[0214]
3TABLE 3 Performance of Synergistic Blends of Donors and Acceptors
Using Polymer Growth Test Method Growth (% increase in Inhibitor
Charge(s) weight of insoluble Inhibitor System (ppm vs styrene)
polymer after 7 hrs.) 4-oxo-TEMPO (baseline) 300 684
4-hydroxy-TEMPO (baseline) 300 736
4-oxo-TEMPO/2,5-di-t-butylhydroquinone 300/600 197
4-oxo-TEMPO/2,5-di-t-butyl-1,4-benzoquinone 300/600 180
4-oxo-TEMPO/2,5-di-t-butylhydroquinone/2,5-di-t-butyl-1,4-
300/150/450 112 benzoquinone
4-oxo-TEMPO/2,5-di-t-butylhydroquinone/2,5- -di-t-butyl-1,4-
300/60/540 128 benzoquinone
[0215]
4TABLE 4 Performance of Hydrogen Donor Systems Using the Multi-Pass
Test Method Average Polymer Inhibitor System/Pass Make (wt %)
M.sub.w of Polymer 300 ppm
4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (4-oxo-TEMPO) Pass 1
0.052 3,910 Pass 2 1.45 17,000 Pass 3 7.45 31,700 45 ppm
4-oxo-TEMPO; 420 ppm PDA; 900 ppm DNBP; 3 cc/min air Pass 1 0.026
1,430 Pass 2 0.150 1,330 Pass 3 0.363 1,760 48 ppm 4-oxo-TEMPO;
1125 ppm DNBP Pass 1 0.146 3,840 Pass 2 0.485 4,340 Pass 3 0.640
4,120 PDA = N-phenyl-N'-(1,4-dimethylpentyl)-para-phenylenediamine
DNBP = 2,4-dinitro-6-sec-butylphenol
[0216] In view of the many changes and modifications that can be
made without departing from principles underlying the invention,
reference should be made to the appended claims for an
understanding of the scope of the protection to be afforded the
invention.
* * * * *