Synthesis and Properties of Novel Polyimides Bearing Sulfonated Benzimidazole Pendant Groups


A new diamine monomer containing benzimidazole-5-sulfonic acid has been synthesised. It has been reacted, alone or mixed with diaminodiphenyl ether, with naphthalenic dianhydride to attain polynaphthalimides in which the sulfonic acid functionality is borne by pendant benzimidazole groups. The presence of sulfonic and benzimidazole groups greatly affected the physical properties of the polyimides as the novel polymers were found to be soluble in polar organic solvents and exhibited a lower thermal resistance than their non-sulfonated counterparts. The polymer films exhibited good mechanical properties with tensile strength in the range 100-120 MPa and with moduli in the range 2.2-3.1 GPa. Sulfonic and benzimidazole groups significantly enhanced the hydrophilicity of the copolyimides, which showed water uptake up to 39%.
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