Process for sulfonating of polymers containing dicarboxylic acid cyclic imide units

A process for producing sulfonated polymers containing styrene moieties and cyclic imide moieties comprises reacting a styrene/maleic anhydride copolymer with a primary amine to produce a polyimide and then subjecting the polyimide to sulfonation wherein both the imidization step and the sulfonation step are conducted in a solvent inert to both reaction steps, such as nitrobenzene.

Having described the materials and methods of this invention, the following 
non-limiting examples serve to further demonstrate and illustrate the 
invention. 
EXAMPLE I 
Styrene-maleic anhydride copolymer SMA.RTM. 1000 (40 grams) was dissolved 
in a solvent system containing 333 grams of nitrobenzene and 143 grams 
xylene. The solution was heated to 115.degree. C. under a blanket of dry 
nitrogen, and treated with 16 grams of neat aniline. The temperature was 
increased until a mixture of water and xylene refluxed and reflux was 
maintained for 4 hours. The water/xylene azeotrope was distilled into a 
Dean-Stark trap during this period. At this point the Dean-Stark trap was 
drained and allowed to refill. This procedure was continued with 
increasing temperature until xylene no longer distilled from the flask (1 
hr., 179.degree. C). The mixture was cooled to room temperature and a 15 
gram aliquot was removed. This was added to 30 grams of ether to 
precipitate the terpolymer. The terpolymer was characterized by combustion 
analysis and filtration and the terpolymer composition was determined to 
be: 
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Monomer Mole % Weight % 
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Styrene 50 37 
N--phenylmaleimide 
29 35 
N--phenyl-maleamic acid 
15 21 
Cumene 6 6 
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This corresponds to approximately 65 mole % conversion of SMA anhydride 
units to imide units. 
Half of the remaining 351 grams of terpolymer solution, was added to a 
solution of 15 grams of sulfur trioxide in 500 grams of nitrobenzene. The 
sulfonic acid of the terpolymer slowly crystallized from solution as the 
sulfonation proceeded. The rate of which the two solutions were mixed was 
adjusted to maintain a reaction temperature of 30.degree. C. Upon 
completing the addition step, the slurry was heated to 65.degree. C. for 1 
hour. A 10% aqueous solution of sodium hydroxide was added until a pH of 
7.5 was reached and the mixture was heated at 65.degree. C. for 40 min. to 
extract the sulfonated polymer as its sodium salt. The aqueous extract was 
recovered and stripped to dryness. The terpolymer sulfonate was crushed to 
a fine powder and dried under vacuum to constant weight. An analysis of 
the product indicated a total sulfur content of 9.1 weight percent and a 
free sulfate content of 11.8 weight percent. 
EXAMPLE II 
A solution of 40 grams of SMA.RTM.-1000 styrene-maleic anhydride copolymer 
was prepared in 476 grams of nitrobenzene and warmed to 70.degree. C. 
under a blanket of dry nitrogen. The mixture was treated with 16 grams of 
aniline and then vacuum was applied to the reaction vessel (90 mm.) before 
gradually increasing the temperature. At 130.degree. C., refluxing the 
solvent was observed and these conditions were maintained for 4 hours. A 
16.3 gram aliquot of nitrobenzene and 2.94 grams of water were recovered 
during this process. The reaction mixture was cooled to room temperature 
and a 50 gram aliquot was removed and precipitated with ether. The solid 
polymer was dried (16 hr. at 100.degree. C./20mm) and subjected to 
combustion analysis and filtration. The nitrogen content was found to be 
4.3 weight percent and the carboxylic acid level was determined to be 1.86 
meq/g. This indicated that approximately 39.5 mole percent of the 
anhydride sites were converted to imide, with the remainder present as 
amide acid. 
A 230 gram portion of the nitrobenzene solution described above, was added 
to a solution of 14.5 grams of sulfur trioxide in 469 grams of 
nitrobenzene. The rate of polyimide solution addition was adjusted to 
maintain a reaction temperature of 30.degree. C. The sulfonated product 
slowly crystallized from solution as the reaction proceeded. Upon 
completing the addition, the mixture was warmed to 65.degree. C. for 45 
minutes. The product was extracted by the addition of 140 grams of 10 
weight percent aqueous caustic and mixing for 45 minutes. The aqueous 
phase was recovered and spray dried providing a tan powder. The sulfur 
content of the dry product was 11 weight percent and the sulfate level was 
21 weight percent.