Method for recovering aromatic polyethers

Method for recovering an aromatic polyether as a solid product from a solution thereof in an organic solvent by precipitating with a fluorohydrocarbon which may also contain chlorine or bromine and which boils at -30.degree. C. to +100.degree. C.

The present invention relates to a method for recovering an aromatic 
polyether as a solid from a solution thereof in an organic solvent. 
Aromatic polyethers are polymeric compounds in which the structural 
elements of the polymer chains are inter alia constructed of oxygen atoms 
bivalently coupled to arylene units, with these aromatic ether groups 
constituting parts of the main chain. Aromatic polyethers of this type are 
widely known and are to some extent employed as industrial materials. 
Especially worthy of mention are the polymer obtained by the oxidative 
coupling of 2,6-dimethylphenol, called "PPO", and polyether sulfones such 
as those marketed under the brand names "Polyethersulfon 200 P" and "Udel" 
for instance. Aromatic polyether ketones are known for example from 
European patent application No.0 001 879 and can be obtained by the 
polycondensation of 4,4'-difluorobenzophenone with hydroquinone or 
4,4'-dihydroxy-diphenyl ether or 2,2-bis-(4-hydroxyphenyl) propane, known 
as bisphenol A. Polyethers that still have phosphorus in the structural 
elements of the polymer chain are described in U.S. Pat. No. 4,492,805 and 
are manufactured by the polycondensation of bifunctional starting 
compounds like arylenediols with di-(halophenyl)-phenyl phosphines or the 
corresponding phosphine oxides. The polycondensation is preponderantly 
carried out in solution, with N-methyl pyrrolidone, for example, being an 
appropriate solvent for manufacturing the phosphorus-containing 
polyarylene ethers. To obtain higher molecular weights, solvents that can 
dissolve both the monomeric starting materials and the corresponding 
polycondensate are employed as reaction media. Solvents that usually 
fulfill these demands are not only such polar, high-boiling, substances as 
dimethyl formamide, dimethyl acetamide, N-methyl pyrrolidone, diphenyl 
sulfone, and sulfolane, but also the relatively low-boiling methylene 
chloride. Using media of this type is a great advantage in manufacturing 
polymers because they reduce the viscosity of the reaction mixtures and 
increase their polarity, which is necessary to obtain a high conversion 
and hence increase the molecular weight. 
The technically interesting range of molecular weights for the aromatic 
polyethers employed for further processing into serviceable pieces is 
above 10000. Thus, polymers with molecular weights of 100,000, for 
instance, are obtained from 2,6-dimethylphenol, and the 
phosphorus-containing polyarylene ethers taught in U.S. Pat. No. 4,492,805 
are said to have molecular weights of at least 10000 and preferably 15000 
to 500,000. 
Although the polymer can be obtained from the reaction mixture in the form 
of a solid product by distilling off the solvent, the polymer is usually 
precipitated by mixing the reaction batch with a liquid. Thus, B. 
Vollmert, Grundriss der Makromolekularen Chemie, E. Vollmert-Verlag, 
Karlsruhe, 1980, Vol. II, page 31, describes precipitating PPO from a 
viscous synthesis solution with methyl alcohol, and U.S. Pat. No. 
4,492,805 describes precipitating phosphorus-containing polyethers with 
mixtures of methyl alcohol and water from the solutions obtained when 
synthesizing them. 
The liquids employed up to now to precipitate aromatic polyethers have 
various drawbacks. For example, the evaporation enthalpies are high: 
1101.39 kJ/kg for methyl alcohol and 2257.22 kJ/kg for water at their 
boiling points. The high evaporation energy makes the requisite 
distillation mixture of reaction medium and precipitant very expensive. 
Furthermore, since precipitation with the conventional liquids is not very 
selective, it does not lead to the desired purity and fractionation of the 
precipitated product. Oligomers, for instance, which are polycondensates 
with molecular weights of less than 10,000 and which have a deleterious 
effect on the properties of the polymers, are not completely separated. 
The object of the present invention is to provide a method for isolating or 
recovering aromatic polyethers from solutions by precipitating them with 
precipitants which cannot only be easily and cost-effectively recovered, 
during further processing, from the reaction medium or by reprecipitation 
from the used solvent, but which will contribute to fractionating the 
reaction product. 
It has been discovered that this object can, surprisingly, be attained by 
separating aromatic polyethers from solutions thereof by precipitating 
them with specific fluorohydrocarbons. Solvents for polyethers are 
organic, polar, aprotic compounds which are liquid in the anticipated 
operating range from -30.degree. C. to 120.degree. C. such as 
dichloromethane, N-methylpyrrolidone, dimethylsulfoxide, 
dimethylformamide, tetrahydrofuran, and tetramethylsulfone. 
Using fluorohydrocarbons having 1 to 4 carbon atoms, possibly having 
chlorine atoms and/or bromine atoms, and having no or no more than 4 
hydrogen atoms in the molecule, as precipitants for the isolation of 
polyethers will attain the object of the invention with respect to the 
demands for both a low evaporation enthalpy and for separation of the 
oligomers. The heats of evaporation of the fluorinated hydrocarbons 
employed to carry out the invention, which compounds may be saturated or 
unsaturated, are in the range of 150 .+-.30 kJ/kg at the boiling point of 
the compounds. In terms of a comparable mass of methyl alcohol, this means 
that only about 1/6 to 1/9 as much evaporation energy is consumed in 
processing the reaction medium or the mixture of solvent and precipitant 
by the method in accordance with the invention as would be consumed with 
methyl alcohol as a precipitant. In comparison with water, which can be 
employed as part of the precipitant at the state of the art, the energy of 
evaporation is even lower --about 1/12 to 1/18 --for the same mass. 
It has also been discovered that the new method will precipitate only the 
high molecular weight constituents of the reaction product, with the 
oligomers remaining in solution. The oligomers are then subjected to 
additional polycondensation once the precipitant has been separated with 
the polar solvent. The particular advantage of the new method, 
specifically purifying the polymers by separating the oligomeric 
constituents out while the polyether is being recovered, is evident from 
the properties of the precipitated product. Whereas the reaction product 
precipitated with methyl alcohol and/or water is usually sticky due to its 
content of relatively low molecular weight polycondensation products and 
must be subjected to further purification, the polymer when precipitated 
with fluoro-chloro-bromo-hydrocarbons has also been discovered to be not 
sticky, but powdery to flocculant. In this form the polymer can easily be 
separated, by filtration for instance, from the liquid phase and washed 
and dried if necessary, and will be in a convenient condition for further 
processing. 
Employing highly halogenated chloro-fluoro-hydro carbons in accordance with 
the invention to obtain the polymers by precipitation entails still 
another advantage. These substances, unlike methyl alcohol and such other 
precipitants such as hydrocarbons, are noncombustible and are 
distinguished by their high physiological compatibility. 
The method of the invention can be carried out with fluorinated aliphatic 
compounds, preferably alkanes, having 1 to 4 carbon atoms, having possible 
chlorine atoms and bromine atoms, and with no to no more than 4 hydrogen 
atoms in the molecule. Thus, the compounds include fluorocarbons, 
fluorohydrocarbons, and chlorofluoroalkanes which all may additionally 
contain bromine. Such compounds are well known in the art and are 
discussed under "Organic Fluorocompounds" in Ullmann's Enzyklopedie der 
Technischen Chemie ("Encyclopedia of Technical Chemistry", 4th Edition, 
Vol. 11, pages 635-639. 
The dielectric constant of the halogenated alkanes employed as precipitants 
is less than 7 (measured in the liquid at 25.degree. , cf. Ullmann, op 
cit. 3rd Edition., 2/1, pp. 460-63). Appropriate compounds, for example, 
are 1,1,2-trichloro-l,2,2-trifluoroethane,1,2-dichlorotetrafluoroethane, 
1,2-dibromotetrafluoroethane, 2-chloro-1,1,1-trifluoro-2-bromoethane, and 
octafluorocyclobutane, as well as such unsaturated halogen hydrocarbons as 
1,1-dichloro-difluoroethylene and 1-chloro-2,2-difluoroethylene. 
Mixtures of the fluorinated hydrocarbons can also be used in the method. 
Practical fluorinated hydrocarbons have boiling points in the range of 
-30.degree. C. to +100.degree. C. 
The polyether is precipitated from its solution at a temperature that 
depends on the boiling point of the particular fluorinated hydrocarbon 
employed. The general range is from 0.degree. C. to 120.degree. C. The 
relatively low boiling points of the precipitant often makes it necessary 
to carry out the precipitation in a pressurized vessel (a closed agitated 
tank, for example) and to introduce the precipitant in the form of a gas. 
It is practical to prevent agglomeration by continuously adding the 
precipitant with stirring. In an opposite procedure, the polymer solution 
can, when necessary, be introduced into the fluorinated hydrocarbon. 
The concentration of aromatic polyether in the solution being treated can 
vary widely, from about 1 to about 50 percent by weight, and depends in 
particular on the molecular weight of the polymer, which in turn dictates 
the viscosity of the solution and hence how easy it is to handle. About 10 
to 150 parts of precipitant per part of dissolved polyether are employed 
to precipitate the polymer. The amount of precipitant also depends on the 
specific dissolving power of the solvent for the polymer and on the 
intended degree of fractionation. The polyether, which precipitates out in 
a powdered or flocculant form, can be separated from the liquid medium by 
filtration or by screen centrifuging, for example, washed in a practical 
way with the same precipitant if necessary, and dried. 
The halogenated precipitant can easily be distilled from the polar solvent 
or reaction medium at relatively low energy consumption and recovered. 
Oligomeric condensation constituents will remain dissolved in the 
distillation residue and can be subjected to additional polycondensation.

A better understanding of the present invention and of its many advantages 
will be had by referring to the following specific examples, given by way 
of illustration. 
EXAMPLE 1 
342.5 g (1.5 moles) of bisphenol A, 327.0 g (1.5 moles) of 
4,4'-difluorobenzophenone, 220.0 g (1.6 moles) of potassium carbonate, 
2270 g of N-methylpyrrolidone, and 750 g of chlorobenzene were heated to 
boiling in a 6-liter four-necked flask equipped with a stirrer, a dropping 
funnel, a Claisen apparatus, and a Liebig condenser. A mixture of 
chlorobenzene and water was distilled off as far as possible. Another 750 
g of chlorobenzene was dropped into the reaction mixture and concurrently 
distilled off. The reaction mixture was maintained at 160.degree. C. for 
15 hours, after which the condensation was discontinued by pumping methyl 
chloride in at the same temperature. 100 ml of N-methylpyrrolidone were 
then added to the reaction flask and its contents suctioned through a 
coarse glass filter. The filter residue was rewashed with 70 ml of 
N-methylpyrrolidone. 
To precipitate the polyether, 5 g of the filtrate (containing approximately 
1 g of the polycondensate) were employed. 100 ml of 
1,1,2-trichloro-1,2,2-trifluoroethane were stirred as strongly as possible 
with a vane stirrer in a 250 ml Witt jar at room temperature and the 
polycondensate solution was slowly dropped in over about 15 minutes. 
Agitation was continued for about another 15 minutes and the flocculant 
polyether precipitate was then suctioned off and rewashed with 20 ml of 
1,1,2-trichloro1,2,2-trifluoroethane. Drying yielded 0.75 g of 
polycondensate. 
EXAMPLE 2 
60 g of the polyether solution of 4,4'-difluorobenzophenone and bisphenol A 
(approximately 12 g of polycondensate) described in Example 1 were dropped 
as described in that Example into 600 ml of 
1,1,2-trichloro-1,2,2-trifluoroethane. Agitation was continued for another 
15 minutes. The precipitate was suctioned off and rewashed with about 200 
ml of the precipitant. The flocculant precipitate was dried to constant 
weight, first at room temperature and then in vacuum at 90.degree. C. The 
yield was 10 g of polycondensate. 
EXAMPLE 3 
5 g of a polyether made from bisphenol A and 4,4'-difluorobenzophenone were 
dissolved in 45 g of dichloromethane. 25 g of this solution were dropped 
at about 20.degree. C. into 500 ml of strongly agitated 
1,1,2-trichloro-1,2,2-trifluoroethane. Agitation was continued for another 
15 minutes. The resulting voluminous, white, flocculant, and non-sticky 
precipitate was suctioned off, rewashed with about 100 ml of the same 
precipitate, and dried to constant weight at 60.degree. C. The yield was 
3.5 g of the original polycondensate. 
EXAMPLE 4 
10 g of a polycondensate of 4,4'-difluoro-triphenylphosphinic oxide and 
bisphenol A were dissolved in 50 ml of N-methylpyrrolidone. The solution 
was dropped slowly into 700 ml of well stirred 
1,1,2-trichloro-1,2,2-trifluoroethane. Stirring was continued for another 
30 minutes. The precipitate was suctioned off and the filter residue 
rewashed with about 100 ml of the same precipitant. The flocculant 
precipitate was dried in vacuum at 100.degree. to constant weight. The 
yield was 7.5 g. A flexible sheet of cast resin was manufactured from the 
polymer. 
The fluorohydrocarbon was recovered from the filtrate by distillation and 
the N-methylpyrrolidone, still containing polycondensate, was transferred 
to a new batch. 
EXAMPLE 5 
2 g of a polycondensate formed from bisphenol A and 
4,4'-dichlorodiphenolsulfone were dissolved in 15 g of dimethylacetamide. 
This solution was added dropwise at about 20.degree. C. with intensive 
stirring to 300 ml of bromochlorodifluoromethane ("Frigen 12Bl") having a 
boiling point of -4.degree. C. present in a 1 liter glass autoclave. The 
autogenous pressure which was established in the reaction vessel was about 
2.5 bars. Subsequently, the mixture was stirred for an additional 15 
minutes and the liquid phase was then removed by filtration through a 
coarse frit into a 1 liter flask having an exhaust connection and cooled 
with acetone/dry ice. The polycondensate which precipitated was washed 
with bromochlorodifluoromethane. After drying a 70.degree. C. in vacuum to 
constant weight, 1.7 g of a flocculant polycondensate were obtained. 
EXAMPLE 6 
5 g of a polycondensate formed between bisphenol A and 
4,4'-difluorobenzophenone were dissolved in 25 g of anhydrous 
tetrahydrofuran. This solution was slowly dropped at 0.degree. C. and with 
good stirring into 3 ml of trichlorofluoromethane ("Frigen 11") having a 
boiling point of 23.degree. C. Subsequently, the mixture was stirred for 
an additional 20 minutes. The white flocculant precipitate which formed 
was recovered from the liquid by filtration into a cooled vessel, was 
washed with about 50 ml of the precipitant, cooled to 0.degree. C., and 
subsequently was dried to constant weight in vacuum at 80.degree. C. 4 g 
of polycondensate were obtained. 
EXAMPLE 7 
A solution of 2 g of a polyether formed between bisphenol A and 
4,4'-difluorobenzophenone in 10 g of 1,3- 
dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone was treated as in Example 
5, with the difference that about 100 ml of a 1:1 mixture (by volume) of 
dichlorotetrafluoroethane ("Frigen 114") having a boiling point of 
3.degree. C. and of trichlorotrifluoroethane ("Frigen 113") having a 
boiling point of 47.degree. C. were used. 1.5 g of polyether were obtained 
.