Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-01-11
2003-03-25
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S50200C, C528S373000, C528S387000, C528S397000
Reexamination Certificate
active
06538102
ABSTRACT:
The invention relates to a process for preparing linear or branched sulfur-containing polymers, such as polyarylene sulfides, in particular polyphenylene sulfide (PPS).
The preparation of polyarylene sulfides and the properties of these polymers are known per se to the skilled worker. The monomers used comprise dihalogenated aromatic hydrocarbons, in particular dichloro-benzene (DCB) and sulfides, in particular sodium sulfide. The monomers are reacted in a high-boiling, polar aprotic solvent, such as N-methylpyrrolidone (NMP). The polymer is then isolated.
Typically, hydrous sulfide is firstly reacted with the polar aprotic solvent, and the mixture substantially dewatered by distillation, resulting in solvent losses and also losses of hydrogen sulfide.
These processes have serious space-time yield disadvantages, however. The dewatering is frequently protracted, since foaming has to be suppressed and it is desirable to minimize losses of the aprotic polar solvent. Overall, the known processes give cycle times of 10 hours or even longer, even using reaction temperatures up to 280° C. There is also a restriction on monomer concentration, since the charge of sulfide or sulfide hydrate at full concentration in the solvent at the start is easily precipitated during addition of the dihalogenated aromatic hydrocarbon.
There are also known processes in which hydrous sulfide is added to the reaction mixture and the water introduced with the sulfide is distilled off during the reaction. Na
2
S easily precipitates during this process and is removed from the reaction mixture.
EP-A-0 737 705 describes a two-stage process for preparing polyarylene sulfides. It uses an excess of the dihalogenated aromatic hydrocarbon in the first stage of the reaction, and the resultant prepolymer, which contains halogen end groups, is reacted with small amounts of sulfide in the second stage. This application satisfactorily achieves the object of short reaction times, but carries out the dewatering batchwise as in the prior art, which has the disadvantages described.
EP-A-0 374 462 describes a process for preparing polyarylene sulfides from dihalogenated aromatic hydrocarbons and from sulfides. The dihalogenated aromatic hydrocarbon, together with the polar solvent, forms an initial charge in the process. Sulfide is metered in, to some extent continuously, without prior dewatering. The sulfide source used comprises a mixture of 66.6 mol % of sodium sulfide and 33.4 mol % of sodium hydrogensulfide with 5 mol of hydrate water per sulfide equivalent. The amount of hydrogensulfide metered in is a stoichiometric excess of 20 mol %, based on the dihaloaromatic compound of the initial charge, resulting in emanation of H
2
S together with the hydrate water during the metering phase. Although the process disclosed avoids the disadvantages of batchwise dewatering of mixtures of solvent and sulfide, it gives solvent losses and considerable monomer losses. The space-time yield for the single-stage reaction is also unsatisfactory, with a cycle time of 12 hours.
EP-A-0 215 259 describes a process for preparing polyarylene sulfides from dihaloaromatic compounds and alkali metal sulfide in N-methyl-caprolatcam. One half of the reaction mixture forms an initial charge at gentle reflux. The second half of the mixture is then metered in. The sulfide used comprises a mixture of anhydrous sodium sulfide and anhydrous sodium hydrogensulfide. A dewatering precedes the actual polymerization reaction. The average reaction time in the stirred reactor cascade is 12.5 hours. Hydrogen sulfide emanates in this process, too, and has to be disposed of.
WO-A-97/47676 describes a process for preparing sulfur-containing polymers, in particular polyarylene sulfides, from a sulfide and from an aromatic dihalogen compound in a solvent, where a mixture made from aromatic dihalogen compound and sulfide is polymerized, aromatic dihalogen compound and sulfide are added to the polymerized mixture, and the reaction mixture is polymerized further. The process requires an additional polymerization step prior to the further addition of the monomers. This increases cycle times.
In the light of the prior art mentioned, the object on which the invention was based was to provide an improved process which prepares sulfur-containing polymers, in particular polyarylene sulfides, over a wide range of molar masses (e.g. M
w
=from 10,000 to 200,000 g/mol), and which avoids the disadvantages of batchwise dewatering of mixtures made from polar solvent and sulfide and, respectively, overcomes the restriction on monomer concentration during the preparation of polyarylene sulfides.
Surprisingly, it has now been found that sulfur-containing polymers, in particular polyarylene sulfides, can be prepared at high space-time yield at reaction temperatures of not more than 250° C. and with short reaction times (less than 5 hours), and specifically without batchwise dewatering of a mixture made from sulfide and from polar solvent. According to the invention, the sulfide is fed continuously or to some extent continuously to the polymerization reactor, but not in the form of a salt melt or aqueous solution but rather in the form of its solution in the polar solvent.
The invention consequently provides a process for preparing sulfur-containing polymers from at least one sulfide and from at least one aromatic dihalogen compound in at least one solvent, where
a) a mixture or solution made from the sulfide and from the solvent is prepared in a first reaction vessel,
b) the solution or mixture prepared in step (a) is placed in a second reaction vessel with the aromatic dihalogen compound, and
c) the sulfide and the aromatic dihalogen compound react in the second reaction vessel while addition proceeds, to form the sulfur-containing polymer.
It has also been found that the loss of hydrogen sulfide during the reaction can be substantially suppressed and the loss of solvent reduced if the mixture prepared in step (a) is brought into contact with the vapor mixture emanating from the second reaction vessel before the mixture is passed to the second reaction vessel.
The novel process represents a marked improvement in the cost-effectiveness and environmental compatibility of the preparation process for sulfur-containing polymers, in particular polyarylene sulfides, over a wide range of molar mass, from 10,000 to 200,000 g/mol. The loss of monomers and solvent from the reaction system during the reaction is avoided or minimized.
The invention also provides a process for preparing sulfur-containing polymers from at least one sulfide and from at least one aromatic dihalogen compound in at least one solvent, where
a) a mixture made from a sulfide and from a solvent is prepared in a first reaction vessel,
b) the sulfide and an aromatic dihalogen compound react in a second reaction vessel to form a sulfur-containing polymer,
c) the pressure in the second reaction vessel is to some extent or completely released during the reaction, and the emanating vapor mixture is brought into contact with the mixture prepared in step (a).
The mixture prepared in step (a) may be metered simultaneously with the aromatic dihalogen compound and, if desired, with further solvent continuously or to some extent continuously into the second reaction vessel.
In one preferred embodiment of the invention a stoichiometric excess of from 3 to 100 mol %, preferably from 5 to 75 mol % and particularly preferably from 10 to 50 mol %, of the dihalogenated aromatic hydrocarbon, based on the stoichiometric amount of sulfide, is metered into the second reaction vessel. This gives a halogen-terminated prepolymer. This prepolymer is isolated and, in a second stage, reacted with a small amount of sulfide to give the high-molecular-weight polymer.
Another embodiment of the present invention is a process for preparing a sulfur-containing high-molecular-weight polymer from at least one halogen-terminated prepolymer prepared as in steps (a) to (c) and from a small amount of sulfide, where
d) less than 10 mol % of sulfide, based
Haubs Michael
Lehrl Markus
Wagener Reinhard
Connolly Bove & Lodge & Hutz LLP
Ticona GmbH
Truong Duc
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