Process for preparing sulphurous polymers

Details Process for preparing sulphurous polymers Process for preparing sulphurous polymers

1999-05-24

2001-03-13

Hampton-Hightower, P. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From sulfur-containing reactant

C528S125000, C528S126000, C528S128000, C528S220000, C528S222000, C528S226000, C528S387000

Reexamination Certificate

active

06201098

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a process for the preparation of linear or branched sulfur-containing polymers such as polyarylene sulfides, in particular polyphenylene sulfide (PPS).
U.S. Pat. No. 4,910,294 describes a process for the preparation of PPS. The monomers used are dihalogenated, aromatic hydrocarbons, in particular dichlorobenzene (DCB), and sodium sulfide, which are reacted in a highboiling, dipolar aprotic solvent such as N-methylpyrrolidone (NMP). The sodium chloride which forms as a byproduct is removed from the polymer after the polymerization reaction has finished either, as described in EP 220 490, by filtering the reaction solution whilst it is still hot at elevated temperature under pressure, or by dissolving in water. According to the prior art, the molar mass of the end product of the polycondensation reaction is attained before the sodium chloride is removed.
A disadvantage of this preparation process is, however, that the space-time yield of the reactors is unsatisfactory because a relatively long reaction time is required.
The object is therefore to overcome this disadvantage.
SUMMARY OF THE INVENTION
Surprisingly, we found that removal of the salt before the polymerization reaction has finished shortens the reaction time overall and leads to higher molar masses. Presumably, the sulfide content in the solid salt residue from the polymerization of a polyarylene sulfide leads to a significant decrease in the molar mass of the highly polymerized arylene sulfide, or hinders a rapid increase in the molar mass.
The invention therefore provides a process for the preparation of sulfur-containing polymers from at least one aromatic dihalo compound and at least one sulfide in a solvent by
a) partially reacting the aromatic dihalo compound and the sulfide,
b) removing the salt formed, which is practically insoluble in the reaction medium, and
c) further polymerizing the reaction mixture, substantially freed from the salt is further polymerized.
It has thus been possible to considerably improve the space-time yield during the preparation of sulfur-containing polymers, in particular polyarylene sulfides from aromatic dihalo compounds and alkali metal sulfides, because the salt which forms as a byproduct is removed before the polycondensation reaction has finished and the reaction mixture, substantially freed from the salt and still not completely polymerized, is more readily susceptible to further polymerization.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the invention makes it possible to obtain sulfur-containing polymers, in particular polyarylene sulfides, over a wide molar mass range (e.g., Mw=10,000-200,000 g/mol) in good space-time yield under very mild reaction conditions and with very little contamination from byproducts.
Sulfur-containing polymers are polymers which contain arylene sulfide units. The arylene moieties of the arylene sulfide units contain monocyclic or polycyclic aromatic compounds or coupled aromatic compounds. The aromatic compounds can also contain hetero atoms. Such aromatic compounds, which can be substituted or unsubstituted, are, for example, benzene, pyridine, biphenyl, naphthalene and phenanthrene. Substituents include C1-C6-alkyl, C1-C6-alkoxy, carboxyl, amino and sulfo groups. Coupled aromatic compounds are, for example, biphenyl or aromatic compounds linked by ether bridges (arylene ethers).
Preferred sulfur-containing polymers are polyarylene sulfides, in particular polyphenylene sulfide.
The aromatic dihalo compounds used for the preparation of the polyarylene compounds are, for example, dihalogenated aromatic hydrocarbons, including dihalobenzenes such as o-, m- and p-dichlorobenzene, substituted dihalobenzenes such as 2,5-dichlorotoluene, 3,5-dichlorobenzoic acid, 2,5-dichlorobenzenesulfonic acid or 3,5-dichlorobenzenesulfonic acid and their salts. Dihalonaphthalenes such as 1,4-dibromonaphthalene or dihalodiphenyl ethers such as 4,4′-dichlorodiphenyl ether can, however, also be used. Mixtures of different arylene dihalides can also be used. Small quantities (0.2 to 5 mol %, based on the dihaloaromatic compound) of polyhalogenated aromatic hydrocarbons can also be used in order to obtain branched or crosslinked sulfur-containing polymers.
Suitable sulfides for the preparation of the polymers are inorganic and organic sulfides. Inorganic sulfides are sulfides of the alkali metals and alkaline-earth metals, such as lithium sulfide, potassium sulfide, calcium sulfide and, preferably, sodium sulfide. The corresponding hydrosulfides or hydrogen sulfide can also be used, optionally in conjunction with alkali metal hydroxides.
Suitable organic sulfides are salt-like sulfides with organic cations. Organic sulfides which can be used for the present invention are also those organic sulfur compounds which release sulfide or hydrosulfide anions under the reaction conditions, such as thioacetamide, carbon disulfide or thio-N-methylpyrrolidone. The sulfides can also contain water of crystallization.
Dihaloaromatic compounds and sulfide are generally also referred to as monomers.
Suitable solvents for the preparation of the polymer are dipolar aprotic solvents of the amide type such as dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylcaprolactam or N-alkylated pyrrolidones such as N-methylpyrrolidone (NMP) or mixtures thereof. NMP is particularly preferred.
To prepare the sulfur-containing polymer by the process according to the invention, the aromatic dihalo compound is reacted in step a) with the sulfide in a solvent to about 40 to 98% (based on the aromatic dihalo compound). At this point in time, the reaction mixture a) contains the low molecular weight polymer, substantially undissolved salt (e.g., sodium chloride), unconverted monomers and the solvent. The precipitated salt formed during the reaction is removed from the reaction mixture in step b), for example by hot filtration. Filtration is advantageously carried out at a temperature at which the sulfur-containing polymer is in the liquid or dissolved state in the reaction mixture. The reaction mixture, substantially freed from the precipitated salt, is then further polymerized in step c), if necessary under pressure. The polymer is finally isolated from the reaction mixture by known methods.
The reaction conditions for step a) can be varied within wide limits. For example, the reaction temperatures can be 180° C. to 280° C., preferably 220 to 260° C. The reaction times can be 10 minutes to 20 hours, preferably 30 minutes to 3 hours. Temperature programs can also be used advantageously, for example 30 minutes at 225° C. and then 1 hour at 245° C.
The average molar mass, expressed as the weight-average Mw, is in the range from 1000 to 30,000 g/mol, preferably 2000 to 20,000 g/mol and in particular 3000 to 15,000 g/mol after step a).
At the end of step a), the salt is substantially in the form of a crystalline precipitate in the reaction mixture and is removed by suitable methods.
The salt is removed from the reaction mixture when the reaction conversion, based on the aromatic dihalo compound, is from 40 to 98%, preferably 50 to 96% and in particular 60 to 94%.
The salt can be removed by simple pressure filtration at a temperature at which the polymer is in the liquid or dissolved state in the reaction mixture. These temperatures are usually 100 to 300° C. Instead of pressure filtration, other methods for removing solids from liquids can, however, also be used, for example centrifugation or decantation.
It is usual that the reaction under step a) releases chemically bound water of hydration. For the filtration in step b) it can be advantageous to remove some or all of the water of reaction. If desired, the contents of the reactor can, before being worked up, be rendered neutral or slightly acidic by the addition of acids. Suitable acids are, for example, acetic acid, hydrochloric acid or carbon dioxide.
The filtration residue is advantageously washed with solvent in order to remove adhering mother liquor residues. The

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