Synthesis and properties of soluble sulfonated polybenzimidazoles Shengbo Qing, Wei Huang, Deyue Yan * College of Chemistry and Chemical Technology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, PeopleÕs Republic of China Received 13 January 2005; received in revised form 28 June 2005; accepted 28 July 2005 Available online 12 September 2005 Abstract A new sulfonated aromatic diacid, 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid (DSNDA), was prepared from 2,6-naphthalenedicarboxylic acid by direct sulfonation. The chemical structure of the sulfonated monomer was charac- terized by FTIR, 1 H NMR, 13 C NMR and MS. A series of sulfonated polybenzimidazoles (sPBI-NF) were successfully synthesized from DSNDA, 2,2-bis(4-carboxyphenyl)hexafluoropropane and 3,3 0 -diaminobenzidine in poly(phosphoric acid). All the sulfonated samples having high-molecular-weights (M n , 74,100–109,500) were soluble in some polar apro- tic solvents such as DMF, DMSO and DMAc, and they could be easily formed into tough and flexible films via solution casting. The films presented good thermal stabilities (T 5% > 453 °C), high storage moduli and glass-transition temper- atures (T g > 220 °C), as well as tensile strengths of about 95 MPa and swelling degrees lower than 12%. The conduc- tivity values of sPBI-NF60H measured at the temperature range from 30 to 90 °C vary from 5.7 · 10 À4 to 2.7 · 10 À3 S/cm at 100% relative humidity. Ó 2005 Elsevier B.V. All rights reserved. Keywords: High performance polymers; Mechanical properties; 2,6-Naphthalenedicarboxylic acid; Sulfonated polybenzimidazole; Thermal properties 1. Introduction It is well known that polybenzimidazole (PBI) is an excellent high performance resin, which pos- sesses good thermoplastic toughness, thermal and chemical stabilities [1]. A main application of PBI is spun into fiber, which has been commercial- ized by Hoechst Celanese. In recent years, other potential applications of PBI have been developed in despite of its difficult processibility. For exam- ple, PBI has been employed to be a promising sup- port for metal catalysis [2–5] and a modifier of polyimide and epoxy resin [6–10]. In addition, 1381-5148/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2005.07.020 * Corresponding author. Tel.: +86 021 54742665; fax: +86 021 54741297. E-mail addresses: qsbhhy@sjtu.edu.cn (S. Qing), dyyan@ sjtu.edu.cn (D. Yan). Reactive & Functional Polymers 66 (2006) 219–227 REACTIVE & FUNCTIONAL POLYMERS www.elsevier.com/locate/react