Polyimides Based on Naphthalene-1,4,5,8-Tetracarboxylic Acid Dianhydride

3 Polyimides Based on Naphthalene-1,4,5,8-Tetracarboxylic Acid Dianhydride 

Another class of polyimides that are characterised by a higher chain flexibility, when compared to PPI, are based on naphthalene-l,4,5,8-tetracarboxylic acid dianhydride (DNTA). These polymers are of considerable interest due to their high heat resistance and thermal stability and due to easy accessibility of the starting monomers. DNTA is a widely available dianhydride showing the highest electrophilic reactivity among bisfnaphthalene-tetracarboxylic anhydrides [18, 19]. 

Although some authors [20] state that poly(naphthalenecarboximides) (PNI) can be synthesised by the classical two-stage method, this approach seems to be ineffective in the synthesis of these polymers. 

Earlier investigations into the single-stage synthesis of PNI [21-29] revealed that the reaction of DNTA with m- and p-phenylenediamines, benzidine, 4,4 -diaminodiphenyloxide, etc., yields only low-viscous products (rii = 0.05-0.15 dl/g), which precipitate from the reaction solution at early stages of the process because of their insolubility in organic solvents. 

When the polycondensation process was carried out in organic solvents (nitrobenzene, NMP, and m-cresol) at 180-210 C and an effective catalyst (benzoic acid) was used, PNI having high viscosity characteristics and exhibiting film-forming properties were synthesised [3-36]. 

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