Synthesis of Sulfonated Polyimides

1 Sulfonated Polyimides by Postsulfonation No research work about the postsulfonalion of a naphthalenic structure has yet been reported and only few examples of the postsulfonation of a phthahc polyimide are mentioned in the htcrature [25]. Both mentioned articles are concerned with the sulfonation of the polyimide synthesized from bis[4-(3-aminophenoxy)phenyl]sulfone and PMDA, in the presence of either chlorosulfonic acid (CISO3H) or sulfur trioxide-triethyl phosphate (2SO3 TEP) (Fig. 3.1). Because of the very low solubility of the polyimide precursor, the postsulfonation is performed under heterogeneous conditions. 

Another major problem related to the heterogeneous nature of the reaction is the fairly difficult control of the extent of the sulfonic groups grafted on the polymer backbone. More interesting is the direct polymerization of a sulfonated monomer. Indeed, in that case, the final lEC is fixed by the ratio of the sulfonated and nonsulfonated comonomers. Moreover, the introduction of SO3H groups is much better controlled. 

2 Sulfonated Polyimides by Direct Polymerization of a Sulfonated Monomer As reported by Genies et al. [27] from a study on model compounds. 

From NTDA and BDS A monomers, a wide range of sPIs have been synthesized by changing the nonsulfonated diamine comonomer [13,17,34—36], including aliphatic diamines [14,37,38]. Different properties (solubility, water uptake, conductivity, and hydrolytic stability) can be fine-tuned by carefully choosing the structure of the nonsulfonated diamines. On the one hand, flexible nonsulfonated diamines increase the solubility of the final polymer as well as its hydrolytic stability on the other hand, bulky diamines increase the interchain space, which induces a higher conductivity at high humidity rates as well as a higher hydrolytic stability. 

Based on the different above-mentioned synthetic pathways, it is possible to design a great variety of sulfonated diamines. In this respect, the synthesis of various isomers 

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Figure 23. Sulfonated diamines for direct synthesis of sulfonated polyimides.

Geng L, He Y, Liu D, Dai X, Lii C (2012) Facile in situ template synthesis of sulfonated polyimide/mesoporous silica hybrid proton exchange membrane for direct methanol fuel cells. Micropor Mesopor Mat 148 8-14... 

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