Compositions – Preservative agents – Anti-oxidants or chemical change inhibitants
Reexamination Certificate
1998-05-26
2001-09-11
Medley, Margaret (Department: 1714)
Compositions
Preservative agents
Anti-oxidants or chemical change inhibitants
C252S403000
Reexamination Certificate
active
06287483
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a method for stabilizing unsaturated organic compounds from polymerization and to a monomeric composition containing a polymerization inhibitor.
2. Background of the Art
The ethylenically unsaturated compounds which can be polymerized by free radical initiation are commonly called monomers. They constitute a major class of industrial chemicals. Because of the presence of the polymerizable double bond, the widespread sources of initiating radicals from peroxides, light and/or thermal generation, such monomers are prone to undesirable and premature polymerization at various stages during their manufacture, purification, storage, shipping, blending and use. Protection of such monomers from such premature polymerization is needed up to the point where polymerization is actually desired. If premature polymerization does occur, the monomer may suffer contamination by polymer, troublesome increase in viscosity, gelation and/or loss of reactivity. Fouling of distillation equipment including heat exchanger surfaces, storage vessels, transfer lines, pumps, shipping containers and application equipment can occur with ensuing costs of cleaning, downtime, loss of material and unnecessary labor costs. Premature polymerization can also constitute a safety hazard since uncontrolled exothermic polymerization can cause ruptured vessels, atmospheric contamination, and in extreme cases, explosions and fires. Deterioration of monomers in shipping and storage may also make necessary the use of costly refrigerated shipping and storage facilities.
A further problem is that of undesired free radical polymerization of unsaturated monomers which occur in commercial products such as hydrocarbon fuels and refinery streams. In these cases, polymerization accompanied by the incorporation of oxygen moieties leads to gum and sludge deposits which can foul carburetors, engines, fuel tanks or fuel lines. In refineries, such monomers in hydrocarbon streams such as cracking products can foul pipelines, valves, pumps, heat exchanges, stills and storage vessels.
Another problem in regard to undesired polymerization of free radical polymerizable monomers is the case of polymerizations which are intentional, but which must be prevented from going too far. For example, the quality of poly(vinyl chloride) suspension polymer and of synthetic rubber made from olefins and dienes is superior (i.e. better molecular weight distribution, stability, and processing properties) if the polymerization is stopped short of complete consumption of the monomers. It is also desirable to have available in a plant conducting vinyl polymerization reactions some rapid and efficient means for stopping a runaway polymerization if other means such as cooling should fail.
It is known that the addition of certain compounds to monomers can retard or even prevent their undesired polymerization, and that when polymerization of the monomer is desired, the inhibitor can be removed or overridden by a deliberately-added polymerization initiator. Various aromatic compounds have been used as such inhibitors in the prior art. Typical ones are 2,6-dinitro-p-cresol (DNPC), hydroquinone, monomethyl ether of hydroquinone (MEHQ), tert-butylphenols, phenothiazine, phenylenediamines and benzoquinones. These are usually used at a level of 50 to 1000 ppm. These inhibitors are not totally effective, and even with such inhibitors present it is often advisable to store such inhibited monomers in a cool place and for limited periods of time. Moreover, these aromatic inhibitors are a cause of serious discoloration problems in the monomers and in polymers deliberately prepared from such monomers. Typically these aromatic inhibitors produce quinoidal chromophoric groups with very visible light absorbance.
Various other polymerization inhibitors are known. For example, U.S. Pat. No. 5,258,138 to Gatechair et al. discloses the stabilization of ethylenically unsaturated monomers from premature polymerization by adding to the monomer a stabilizing amount of a substituted hindered amine in combination with phenothiazine or other related heterocyclic moiety.
U.S. Pat. No. 4,670,131 to Ferrell discloses that fouling of equipment used for processing organic feed streams containing olefinic compounds can be controlled by inhibiting polymerization of the olefinic compounds by the addition of a stable free radical such as a nitroxide to the feedstream.
SUMMARY
In accordance with the present invention a method for stabilizing a polymerizable unsaturated organic compound from premature polymerization is provided. The method comprises:
adding to the unsaturated organic compound an effective amount, sufficient to prevent premature polymerization, of at least one polymerization inhibitor having the formula:
wherein X is —H, —OH, —O•, —NO
2
, or —CH
3
,
R
1
R
2
, R
4
and R
5
are the same or different and each is selected from the group consisting of hydrogen, an aliphatic moiety having from 1 to about 20 carbon atoms, aryl, alkaryl or aralkyl having from 6 to about 12 carbon atoms, alicyclic and heterocyclic, or wherein R
1
and R
2
together or R
4
and R
5
together form part of an alicyclic or heterocyclic moiety having from about 4 to about 10 ring members,
R
3
and optional group R
6
are the same or different and each is preferably selected from the group consisting of hydrogen, an aliphatic moiety having from 1 to about 20 carbon atoms, or wherein R
3
and R
6
together represent oxygen in the form of an oxo (═O) moiety,
and wherein the dotted lines each represent an optional supplemental bond, such that where there is no optional supplemental bond within the ring the R
6
group is present as a ring substituent, z is 1 and Y is —H, —OH, or —O•, and where there is an optional supplemental bond within the ring, there is no R
6
group present as a ring substituent, z is 0 or 1 and where z is 1, Y is O bonded to N in the form of an N→O moiety.
Also provided herein is a composition which includes an ethylenically unsaturated monomer and an effective amount of the polymerization inhibitor described herein.
DETAILED DESCRIPTION
The present method for stabilizing a polymerizable unsaturated organic compound from premature polymerization comprises adding to the unsaturated organic compound an effective amount of a polymerization inhibitor which includes an imidazoline or imidazolidine compound, optionally with hydroxy, oxo, oxyl or oxide substituents, as described more fully below.
The polymerizable organic compound is preferably an ethylenically unsaturated monomer having at least one carbon-carbon double bond capable of undergoing free radical induced polymerization. Particularly advantageous is the stabilization of styrene. The unsaturated organic compound can be neat (i.e., undiluted) or admixed with a solvent such as toluene, benzene, ethylbenzene, styrene or water.
Typical examples of such monomers are olefinic and vinyl aromatic compounds including, but not limited to, styrene, methylstyrene, divinylbenzene, dienes such as butadiene and isoprene; halogenated monomers such as vinyl chloride, chloroprene, vinylidene chloride, vinylidene fluoride and vinyl fluoride; unsaturated acids such as acrylic acid, methacrylic acid and crotonic acid; unsaturated esters such as vinyl acetate, alkyl acrylates and alkyl methacrylates such as methyl methacrylate, ethyl acrylate, methyl acrylate, 2-hydroxyethyl acrylate and methacrylate, ethylene bismethacrylate, trimethylolpropane triacrylate, acrylated epoxy resin and polyethylene glycol diacrylate; unsaturated amides such as acrylamide, N,N-dimethylacrylamide, methylene-bisacrylamide and N-vinylpyrrolidone; unsaturated nitrile monomers such as acrylonitrile; and unsaturated ethers such as methyl vinyl ether; and miscellaneous monomers such as the vinyl pyridines, diethyl vinylphosphonate and sodium styrenesulfonate.
The method of the instant invention involves simply dissolving an effective inhibiting amount of the inhibitor in the monomer pri
DeMassa John M.
Fagan Stephen M.
Dilworth Peter G.
Medley Margaret
Thompson Raymond D.
Uniroyal Chemical Company, Inc.
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