Polynaphthimidazoles Prepared from Naphthalene Dicarboxylic Acid and Their Properties

Abstract

Phosphorus pentoxide/methanesulphonic acid (PPMA) was used as both solvent and condensing agent for the preparation of polynaphthimidazoles (PNIs) through direct polycondensation. The reactions of 2,6-naphthalene dicarboxylic acid and dimethyl 2,6-naphthalene dicarboxylate with tetramine monomer were studied with varying concentration of monomer, reaction temperature and reaction time in order to obtain high-molecular-weight polymer with high conversion. The properties, including solvent resistance, thermal properties and film casting, of synthesized polymers were also investigated. It was found that, using PPMA as both solvent and condensing agent, PNIs can be prepared successfully with high molecular weight by direct polycondensation of 2,6-naphthalene dicarboxylic acid or its derivatives with tetramine. The PNIs had inherent viscosities in the range 0.94-2.38 dl/g (in conc. H 2 SO 4 at 30°C) ; however, polymers synthesized from isophthalic and terephthalic acids with tetramine had inherent viscosities of only 0.56 dl/g and 0.48 dl/g, respectively, with low conversions under similar reaction conditions. The glass transition temperature of the PNI 1 was 403°C. Thermal analysis indicates that these PNIs have excellent thermal stability, and the 10 wt% loss temperatures were recorded in the range 588-648°C in nitrogen gas, 533-580°C in air. The chemical stability and mechanical properties of films are also outstanding.