Tandem Metathesis Polymerization For Block Copolymer With Unique Self-Assembled Nano-structures And Excellent Dielectric Properties

Materials with high dielectric performance are ideal for fabricating thin film capacitors. As the development of microelectronics, polymers and polymer composites have attracted a great deal of attention due to their good flexibility, lower cost, and better mechanical properties.Poly(N-3,5-bisfluorophenyl-norbornen-pyrrolidine)-block-poly(4-pentafluorophenyl formate-1,6-heptadiyne) (PFNPn-b-PFHDm) was synthesized by a tandem ring-opening metathesis polymerization (ROMP) and metathesis cyclopolymerization (MCP) using the third Grubbs’catalysts (Ru-Ⅲ). The solvation difference of the blocks induced an in-siru self-assembly, leading to a verifying morphology of micelle and hollow sphere in chloroform and tetrahydrofuran solution, which were established using DLS and TEM. High dielectric constant of 22 at 100 Hz-1 MHz and high energy density of 0.9 J/cm3 were achieved for PFNP75-b-PFHD25 from the solid film state. Due to the characteristic core-shell nanostructure, no obvious percolation phenomenon was found in copolymers and the dielectric loss of copolymers is all below 0.05.Continuously, we focus on modifying the π-π interaction with expanding the scope of π-conjugation by replacing the difluoro-phenyl with 3,5-bis(trifluoromethyl)biphenyl to the synthesis of block copolymer with PNBE-block-PA backbone. Distinguishingly, a transformational packing mode with dense π-π stacking was observed. Further investigation unveiled the surprising nanotubular structure with a certain helical sense despite that both copolymer and environment were achiral. This superhelix tubular structure was obtained through a hierarchical self-assembly process, providing large conductive-insulative interfacial area, leading to the excellent dielectric properties. XRD tests implied the interplanar distance of stacked PFHD segments was only 3.45 A, which is benefit for electronic migration. The dielectric permittivity of PTNP75-b-PFHD50 was reached to 29 with a relatively low dielectric loss no more than 0.05. Meanwhile, the stored energy density also increased to 1.9 J/cm3.