Synthesis And Characterization Of A Series Of Organosoluble Polynaphthalimides

Polyimides,because of their good thermal stability and mechanical and dielectric properties,have been found wide applications in aerospace and microelectronic industries.Most of the commercial available aromatic polyimides are based on phthalimide unit which owns a five-membered imide ring.But the phthalic polyimides always have poor hydrolysis stability,which limits their applications in a moist environment,such as proton exchange membrane for fuel cells.Recently,more and more interest has been focused on polynaphthalimides(PNIs) due to the six-membered imide ring containing better thermal and chemical stabilities.Especially the sulfonated PNIs are expected as promising materials for proton-exchange membrane materials of fuel cells.Unlike polyphthalimides,PNIs are commonly synthesized by one-step polycondensation method without poly(amid acid)(PAA) step,and therefore solubility of PNIs in organic solvents is the most important factor of their processability.However almost of the research works about organosoluble PNIs stressed the design of diamine monomer and little attention was paid on the design of dianhydride monomer.In this study,PPOBNDA containing two ether linkages and a phenyl substituent,which would improve the PNIs' solubility,was synthesized by nucleophilic substitution.Then,a series of PNIs based on PPOBNDA were synthesized via one-step process with high-temperature condensation,whose solubility,thermal properties,chemical stability and mechanical properties were also investigated.All the polymers dissolved easily in CHCl₃,NMP and m-cresol。All PNIs also exhibited high glass transition temperatures(Tg),which are all over 270℃, and good 10%weight loss temperatures(T₁₀),which are all over 510℃.The PNI films exhibited good tensile properties,which had the strength at yield more than 120 MPa,and initial moduli more than 2.7 GPa.Polynaphthalimides derived from six-membered imide ring exhibit much better hydrolysis stability than polyphthalimides which are based on five-membered imide ring structure especially in base solution.