Novel poly(pyridine imide) with pendent naphthalene groups: Synthesis and thermal, optical, electrochemical, electrochromic, and protonation characterization

A new diamine containing a pyridine heterocyclic group and a naphthalene substituent, 4‐(2‐naphthyl)‐2,6‐bis(4‐aminophenyl) pyridine (NBAPP), was synthesized with the Chichibabin reaction and used in the preparation of poly(pyridine imide) by direct polycondensation with 4,4′‐hexafluoroisopropylidenediphathalic anhydride in N‐methyl‐2‐pyrrolidinone (NMP). The poly(pyridine imide) derived from diamine NBAPP with naphthalene substituents was highly organosoluble: it was soluble in tetrahydrofuran, NMP, N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide, and γ‐butyrolactone at room temperature and in pyridine, dimethyl sulfoxide, and cyclohexanone upon heating at 70 °C. The poly(pyridine imide) was converted into lightly colored, optically transparent, flexible, and tough polyimide films via casting onto glass from a DMAc solution. This polymer exhibited good thermal stability (temperature of 10% weight loss = 527 °C) in air and high dielectric constants (as high as 4.20 at 1 kHz). The polyimide films had a tensile strength of 102 MPa and a tensile modulus of 1.8 GPa. As for the optical properties, the polymer exhibited UV–vis absorption bands in the region of 223–450 nm and possessed strong green‐yellow fluorescence (500 nm) after being protonated with acid.