Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From sulfur-containing reactant
Reexamination Certificate
2003-01-13
2004-09-14
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From sulfur-containing reactant
C528S391000, C528S486000, C528S487000, C528S503000
Reexamination Certificate
active
06790931
ABSTRACT:
The present invention relates to a process for preparing sulfonated aromatic polymers, in particular sulfonated aromatic polyether ketones and sulfonated aromatic polyether sulfones, and also to the use of the products of the process for membrane production.
Aromatic sulfonated polymers are used in many applications, for example in the form of membranes, these being used in fuel cells, high-performance capacitors, and dialysis devices.
Fuel cells are electrochemical energy converters which have particularly high efficiency. Among the various types of fuel cells, polymer electrolyte fuel cells have high power density and low weight to power ratio.
For further development of fuel cell technology, in particular for its use on a larger scale, the production costs of the materials used have to be reduced, but this must not lead to any need to accept performance which is inferior to that of the materials used to date.
Polyether sulfones (hereinafter also termed “PES”) are commercially available products and have high resistance to heat, chemicals, and mechanical effects. A typical example of polyether sulfones is given in the figure below.
The sulfonation of PES is of great interest for producing polymers which can be used in separation processes using membrane methods.
The prior art has disclosed various sulfonation processes for PES, for example in EP-A-0,008,894; EP-A-0,112,724; U.S. Pat. No. 4,508,852; U.S. Pat. No. 3,709,841 and DE-A-3,814,760.
However, these previously disclosed sulfonation processes have many disadvantages. For example, the use of strong sulfonating agents, such as oleum or chlorosulfonic acid, at temperatures above 25° C. risks degrading polymer chains. To avoid polymer degradation, therefore, the reaction temperature would have to be kept low. This in turn usually leads to a low degree of sulfonation, and also to long reaction times. Sulfonation by previously disclosed processes in organic solvents has also been found to proceed heterogeneously. This generally gives a sulfonated product with inhomogeneous structure.
U.S. Pat. No. 4,508,852 describes other sulfonation processes for PES. In one of the processes, dichlorosulfonic acid is used as both solvent and sulfonating agent. The temperature during the reaction is initially set at room temperature for 2 h and then to 82° C. for 30 min. A second process uses 1,1,2,2-tetrachloroethane as solvent and chlorosulfonic acid as sulfonating agent. The sulfonation is carried out at 150° C. under a superatmospheric pressure generated by nitrogen. The third process suspends PES in 1,2-dichloroethane. The suspension becomes clear after addition of chlorosulfonic acid. However, the sulfonated PES precipitates during the course of the reaction. Sulfonation by the process therefore proceeds heterogeneously.
These three known processes likewise have many disadvantages. For example, it is impossible to avoid side-reactions and therefore by-products (chlorosulfonated products) by using chlorosulfonic acid. The process is moreover difficult to control, since the high reaction temperature permits only a relatively short reaction time. The sulfonated PES moreover has low viscosity, which may be attributable to polymer chain degradation.
EP-A-0,008,894 and other references (cf. LÜHui-Juan; SHEN Lian-Chun; WANG Cai-Xia; JIANG Da-Zhen; CHEMICAL JOURNAL of CHINESE UNIVERSITIES; No. 5 Vol. 19; 05.1998; pp. 833-835) state that no sulfonation of PES occurs in concentrated sulfuric acid. Sulfonation of PES in chlorosulfonic acid takes more than 20 h at room temperature. The resultant product is water-soluble. The sulfonation of PES can likewise be carried out in concentrated sulfuric acid by using oleum as sulfonating agent “overnight”, the sulfonated PES being water-soluble. This may be attributable to the excessive degree of sulfonation and/or to polymer degradation. According to this prior art, controllable sulfonation is not possible using chlorosulfonic acid or oleum.
The same conclusion is found in EP-A-0,112,724. This prior art describes novel sulfonation processes.
The process describes suspends PES in dichloromethane and treats it with sulfonating agents, e.g. SO
3
or chlorosulfonic acid, for a period of 4 hours at a temperature of from 0 to 5° C.
U.S. Pat. No. 4,413,106 carries out the same sulfonation of PES using oleum. However, the sulfonation is carried out heterogeneously, and this may be the cause of structural inhomogeneity of the sulfonated PES.
DE-A-38 14 760 describes the sulfonation of PES in pure sulfuric acid using 65% strength oleum. The PES sulfonated within a short time (3 hours) and at a low temperature has a low degree of sulfonation (22%) and a reduced viscosity. Carrying out the reaction within a period of 22 hours at 25° C. gives a 39% degree of sulfonation of the PES. If the temperature is 40° C. the PES is degraded. However, no satisfactory result is obtained using the previously disclosed process when the temperature is below 5° C.
An article by LüHui-Juan et al. in Chemical Journal of Chinese Universities; No. 5 Vol. 19; 05.1998; pp. 833-835 describes the kinetics of sulfonation reactions. From this it is apparent that the sulfonation rate in concentrated sulfuric acid when using chlorosulfonic acid is very low within the first 10 hours. In contrast, the sulfonation rate in dichloromethane is very high even at the start of the reaction.
There continues to be a requirement for processes which can be carried out cost-effectively for the sulfonation of aromatic polymers. A particular issue is whether sulfonation can be carried out within a short period and at a low temperature, without polymer chain degradation. Sulfonation should also be controllable and the degree of sulfonation should be variable.
WO-A-96/29,359 and WO-A-96/29,360 describe polymer electrolytes made from sulfonated aromatic polyether ketones and the production of membranes from these materials.
EP-A-0 152 161 describes polyether ketones (hereinafter termed “PEK”) mainly composed of the repeat units —O—Ar—CO—Ar— (Ar=divalent aromatic radical), and shaped structures produced from these.
J. Polym. Sci.: Vol. 23, 2205-2222, 1985 describes sulfonated, strictly alternating polyether ketones with the repeat unit —O—Ar—CO—Ar—. Here, the polyether ketone synthesis uses electrophilic attack rather than nucleophilic attack as described in EP-A-0 152 161. The polymers were sulfonated by sulfur trioxide using triethyl phosphate in dichloroethane. Another sulfonation method used in this reference is chlorosulfonation using chlorosulfonic acid. However, molecular weight degradation is again observed with this method, depending on the degree of sulfonation. Amidation of the acid chloride follows.
Starting from this prior art, the object on which the present invention is based is therefore to provide a simple and cost-effective process which sulforiates aromatic polymers and which minimizes degradation of the polymer during sulfonation, and which can be carried out in a homogeneous phase, and which maximizes product homogeneity.
The present invention provides a process for preparing sulfonated aromatic polymers, encompassing:
a) dissolving the aromatic polymer in a substantially anhydrous acid selected from the group consisting of concentrated sulfuric acid, chlorosulfonic acid, and oleum,
b) adding an organic solvent which is inert under the conditions of the reaction,
c) adding a carboxylic anhydride,
d) adding a sulfonating agent, and
e) carrying out the sulfonation at a temperature below 25° C. and for a time sufficient to achieve the desired degree of sulfonation.
The sequence of steps b) to d) of the process may be as desired. These steps may also be undertaken simultaneously.
The aromatic polymer used in step a) may be any polymer whose main polymer chain has sulfonatable aromatic groups and which is soluble in the solvents used in step a). Examples of these are aromatic polyamides, aromatic polyimides, aromatic polyether ketones (in the widest sense, i.e. polymers having ether bridges and ketone bridges in the main polymer chain), aro
Cui Wei
Frank Georg
Soczka-Guth Thomas
Celanese Ventures GmbH
Robert H. Hammer III, P.C.
Truong Duc
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