Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
1999-12-30
2002-08-20
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S388000, C528S483000
Reexamination Certificate
active
06437091
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to poly(arylene sulfide), (PAS) polymers. In one aspect this invention relates to a process for the curing of poly(arylene sulfide) polymers by a continuous process wherein removal of cured portions of the polymer is timed so as to minimize or avoid the presence of uncured polymer.
BACKGROUND OF THE INVENTION
Poly(arylene sulfide) polymers are generally known in the art and have been found useful due to their high chemical and thermal resistance. Processes for the preparation of such poly(arylene sulfide) polymers have been disclosed in the art. In a typical preparation, at least one dihaloaromatic compound, a sulfur source, and a polar organic compound are contacted under polymerization conditions. Generally, polymers prepared without the addition of molecular weight modifying agents have been found to be more useful for most applications if the polymer is oxidatively cured prior to use for formulating articles. Such curing processes have primarily been conducted in the industry in a batch process in which the cure time and temperature are specified to achieve the desired final polymer properties. Such batch processes are less desirable in a commercial plant since they can create inefficiencies of operation, i.e., require repeated shut-down and start-up of a process and process vessel and thus limit the throughput of the process. It has been disclosed that the curing process can be conducted continuously, but such a process suffers from lack of flexibility in achieving a variety of final product characteristics, and further provides less desirable final polymer characteristics due to the presence of portions of relatively uncured polymer as well as highly cured polymer. It would be desirable to have a method whereby the polymer could be cured in a continuous process while minimizing uncured polymer and providing flexibility to the operator to achieve desired final polymer product characteristics.
OBJECTS OF THE INVENTION
It is an object of this invention to provide a process for curing a poly(arylene sulfide) polymer in which curing process is conducted on a continuous basis wherein the addition of uncured polymer and removal of cured polymer is coordinated such that little or no uncured polymer is present in the continuous cure vessel during the period of removal of product.
SUMMARY OF THE INVENTION
In accordance with this invention, poly(arylene sulfide) polymers are cured in a process comprising achieving and maintaining curing conditions in a cure vessel, then intermittently adding uncured polymer to said cure vessel and intermittently removing polymer from the cure vessel wherein the removal of polymer from the cure vessel is performed at intervals such that the presence of uncured polymer is minimized or avoided.
DETAILED DESCRIPTION OF THE INVENTION
The poly(arylene sulfide) polymer used in this invention can be prepared by any method known to those of skill in the art. Poly(arylene sulfide) polymerizations are generally disclosed in the art. For example, U.S. Pat. No. 3,354,129, which is hereby incorporated by reference, U.S. Pat. No. 3,919,177, and U.S. Pat. No. 4,645,826 all disclose methods of preparing poly(arylene sulfide) polymers. The above-cited patent publications also disclose methods for recovering a useful poly(arylene sulfide) polymer product. Another suitable method of recovering poly(arylene sulfide) polymer products is disclosed in U.S. Pat. No. 4,415,729, which is hereby incorporated by reference. These patent publications all describe the separation of a desired polymer product from reaction mixtures containing various impurities and unreacted polymerization components. The poly(arylene sulfide) polymer is generally prepared by contacting a polymerization reaction mixture comprising at least one dihaloaromatic compound, a sulfur source, and a polar organic compound under polymerization conditions.
Dihaloaromatic compounds which can be employed include p-dichlorobenzene (DCB), p-dibromobenzene, p-diiodobenzene, 1-chloro-4-bromobenzene, 1-chloro-4-iodobenzene, 1-bromo-4-iodobenzene, 2,5-dichlorotoluene, 2,5-dichloro-p-xylene, 1-ethyl-4-isopropyl-2,5-dibromobenzene, 1,2,4,5-tetramethyl-3,6-dichlorobenzene, 1-butyl -4-cyclohexyl-2,5-dibromobenzene, 1-hexyl-3-dodecyl-2,5-dichlorobenzene, 1-octadecyl-2,5-diiodobenzene, 1-phenyl-2-chloro-5-bromobenzene, 1-(p-tolyl)-2,5-dibromobenzene, 1-benzyl-2,5-dichlorobenzene, 1-octyl-4-(3-methylcyclopentyl)-2,5-dichlorobenzene and the like, and mixtures of any two or more thereof. The preferred dihaloaromatic compound for use in this invention is p-dichlorobenzene (DCB) due to availability and effectiveness.
Any suitable sulfur source can be employed in the process of this invention. Suitable sulfur sources are disclosed in U.S. Pat. No. 3,919,177, which is hereby incorporated by reference. Such suitable sulfur sources include, but are not limited to thiosulfates, thioureas, thioamides, elemental sulfur, thiocarbamates, metal disulfides and oxysulfides, thiocarbonates, organic mercaptans, organic mercaptides, organic sulfides, alkali metal sulfides and bisulfides and hydrogen sulfide. It is presently preferred to use an alkali metal sulfide as the sulfur source.
Alkali metal sulfides which can be employed include lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulfide, and mixtures thereof. Preferably, the alkali metal sulfide is used as a hydrate or as an aqueous mixture. If desired, the alkali metal sulfide can be prepared as an aqueous solution by the reaction of an alkali metal hydroxide with an alkali metal bisulfide in aqueous solution. It is preferred to use sodium sulfide or a combination of sodium bisulfide and sodium hydroxide as the sulfur source in this invention.
The polar organic compounds useful are solvents for the dihaloaromatic compounds and the sulfur source used in the production of poly(arylene sulfide) polymers. Examples of such polar organic compounds include amides, including lactams, and sulfones. Specific examples of such polar organic compounds include hexamethylphosphoramide, tetramethylurea, N,N′-ethylenedipyrrolidone, N-methyl-2-pyrrolidone (NMP), pyrrolidone, caprolactam, N-ethylcaprolactam, sulfolane, N,N′-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, low molecular weight polyamides, and the like. The polar organic compound presently preferred is NMP.
It is within the scope of this invention to employ poly(arylene sulfide) polymers that have been produced using other components in the polymerization reaction mixture or during the polymerization. For example, molecular weight modifying or enhancing agents such as alkali metal carboxylates, lithium halides, or water can be added or produced during polymerization. Suitable alkali metal carboxylates which can be employed include those having the formula R′COOM where R′ is a hydrocarbyl radical selected from alkyl, cycloalkyl, aryl, alkylaryl, arylalkyl, and the number of carbon atoms in R′ is in the range of 1 to about 20, and M is an alkali metal selected from lithium, sodium, potassium, rubidium and cesium. The alkali metal carboxylate can be employed as a hydrate or as a solution or dispersion in water. The preferred alkali metal carboxylate is sodium acetate due to availability and effectiveness.
The uncured poly(arylene sulfide) polymers that are cured according to this invention will generally comprise relatively low molecular weight poly(arylene sulfide) polymers; however, the invention process can also be used to cure relatively high molecular weight polymers.
The term low molecular weight poly(arylene sulfide) polymer is generally meant to denote a poly(arylene sulfide) polymer having a melt flow value in the range of greater than 1000 g/10 min. to about 30,000 g/10 min. when measured according to ASTM D 1238, Condition 316/5.
The term high molecular weight poly(arylene sulfide) polymer, as used herein, is generally meant to denote an essentially linear poly(arylene sulfide) polymer having a melt flow value less than about
Fodor Jeffrey S.
South, Jr. Aubrey
Vidaurri, Jr. Fernando C.
Buttner David J.
Owen Polly C.
Philips Petroleum Company
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