Regulating Dielectric And Energy Storage Properties Of Linear Polystyrene Via Using Cyanoyl Liquid Crystalline Polymers

Dielectric polymer materials are in line with the current electronic industry’s demand for lightweight,flexible and stable materials due to their low density,good flexibility,high breakdown strength（Eb）and self-healing properties.However,dielectric polymer materials with low energy density（U_e）can hardly meet the miniaturization of energy storage electronic devices.Currently,polymer-based organic dielectric composite materials and chemically modified dielectric polymers are two effective strategies to improve the Ue of polymers.Linear polystyrene（PS）has the characteristics of excellent processability,low cost,good film-forming properties,low dielectric loss（tanδ）,and high charge-discharge efficiency,which is beneficial to large-scale industrial production.Liquid crystal polymers have the advantages of self-assembly order,electric field stimuli responsiveness,designability of molecular and phase structures,and tunability of dielectric properties,which are ideal functional organic fillers and chemical modifiers.Aiming at the low dielectric constant（ε_r）and U_e of PS,this paper systematically researched the influence of polar cyano liquid crystal polymers as physical modifiers and chemical modifiers on the dielectric and energy storage properties of PS,and obtained the preparation process of dielectric PS with high performance.The detailed research contents are as follows:（1）Research on the properties of cyano-containing mesogen-jacketed liquid crystal polymer chemically modified PS:cyano-containing mesogen-jacketed liquid crystal homopolymers poly[bis（4-cyanophenyl）2-vinylterephthalate]（PBCN）and block copolymer polystyrene-block-poly[bis（4-cyanophenyl）2-vinylterephthalate]（PS-b-PBCN）were synthesized by molecular design.The results show that PBCN forms columnar nematic phase,the glass transition temperature is 156℃,ε_r is up to 14,and the band gap is about 3.44 eV.The PS-based organic dielectric composite films filled with PBCN and PS-b-PBCN were prepared by solution casting method,respectively.The experimental results show that theε_r and breakdown strength（E_b）of the dielectric composite films increase gradually with the increase of the mass fraction of PBCN or PS-b-PBCN organic fillers.Among them,the highestε_r（5.8）and low tanδ（0.018）are obtained in the 30 wt%PS₁₅₈-b-PBCN₇₈/PS dielectric film at 10³ Hz due to the good compatibility of PS-b-PBCN with PS.In addition,the maximum discharge energy density of 2.16 J/cm³ and the efficiency of 90%are acheieved in 30 wt%PS₁₅₈-b-PBCN₇₈/PS at 295 MV/m,which is attributed to the ability of PBCN to immobilize free electrons and restrict the long-distance transport of charges.（2）Research on the properties of cyano side-chain type liquid crystal polymer chemically modified PS:the polystyrene random copolymer P（St-co-CBMA）and the polystyrene block copolymer PS-b-PCBMA were synthesized by free radical polymerization and reversible addition-fragmentation chain transfer（RAFT）methods,respectively.Among them,the cyano side chain type liquid crystal polymer poly[11-（（4’-cyano-[1,1’-biphenyl]-4-yl）oxy）undecyl methacrylate]（PCBMA）has the advantages of highε_r,low band gap width and good film formation.The corresponding dielectric polymer films were prepared by solution casting method.The experimental results show that theε_r of 5.2 at 10³ Hz,and a high discharge energy density of 8.94J/cm³ and an efficiency of 87.4%are obtained at 476 MV/m in the random copolymer film P（St-co-CBMA）with 92 mol%CBMA due to the strong orientation polarization ability,the electron trap effect between cyano mesogens and the good film-forming ability of the polymer.