Synthesis and properties of phenolphthalein-based thermoplastic poly(ether nitrile imide)s via aromatic nucleophilic substitution polymerization

Aromatic nucleophilic substitution polymerization was used to synthesize five poly(ether nitrile imide)s (PENIs) that include benzonitrile and bulky cardo groups from a mixture of phenolphthalein (PP), 4,4'-bis(4-fluorophthalimide) diphenyl ether (4,4'-BFPI), and 2,6-difluorobenzonitrile (DFBN). The structure and properties relationship of PENIs with different ratios of DFBN and 4,4'-BFPI was explored. It was found that the glass transition temperature (Tg) of PENIs decreased from 280 to 260(o)C, while the temperature of 5% thermal weight loss (T-5%) in N2 increased from 429 to 453(o)C as the benzonitrile content in PENI increased. The produced PENI films had good mechanical characteristics, including tensile strengths of 103-112 MPa, elongations at break of 5.6%-8.2%, and tensile moduli of 2.9-3.4 GPa. Furthermore, the solubility and melt processability were also improved with the introduction of the benzonitrile group. Compared with poly(ether ketone imide)s (PEKIs) and poly(ether sulfone imide)s (PESIs), PENIs with benzonitrile displayed higher T-g, tensile modules, and lower complex viscosity.