Synthesis of Diazocine-Containing Poly(arylene ether sulfone)s for Tailored Mechanical and Electrochemical Performance

A series of poly(arylene ether sulfone) copolymers containing the diazocine unit (0, 20, 50, 80, 100 mol %) were synthesized via step-growth polymerization. Copolymer compositions exhibited number-average molecular weights exceeding 30 000 g/mol, and mechanically ductile films were obtained for all compositions. The random copolymers exhibited enhanced thermal stability (T-d10% = 500-550 degrees C) and mechanical properties (tensile stress = 45-65 MPa), and the thermomechanical performance was predictable based on copolymer composition. A secondary transition in the dynamic mechanical analysis appeared at 28 degrees C, which was attributed to segmental motion of the bulky diazocine and biphenyl units. X-ray single crystallography and H-1 NMR spectroscopy as a function of temperature revealed that the diazocine ring existed in the boat-shaped conformation. The effective dipolar couplings of site-specific H-1-C-13 dipolar couplings in the aromatic rings were measured using DIPSHIFT solid state NMR spectroscopy at various temperatures. The experimental data indicated that the bulkier diazocine group experienced slower ring-flip motion than the smaller phenylene group. Cyclic voltammograms of diazocine-containing poly(arylene ether sulfone)s exhibited two reversible reduction peaks at -0.68 and -1.21 V under inert and basic conditions. UV spectra of the diazocine group in the reduced state indicated an extended pi-electron structure, which supported the boat- to planar-conformational change (molecular actuation) via redox reactions.