Research And Application Of The Dielectric Properties Of Crosslinkable PMMA/BaTiO₃ Composite Materials

In this paper,two polymer nanocomposites with high dielectric properties of PMAM/BaTiO₃ system are prepared by combining polymethyl methacrylate（PMMA）and barium titanate（BaTiO₃,BT）.In order to improve the dispersibility of BT in PMMA and the interfacial compatibility of the two phases,BT is modified on the surface,and composite materials with core-shell structure are prepared by in-situ polymerization.A thin film with dual crosslinked networks are prepared by thermal crosslinking of the thin films,obtaining flexible thin film capacitors with excellent comprehensive performance.In order to obtain composites with high dielectric constant,the modified BT is doped into the photocrosslinkable polymer matrix with PMMA as the main body,which increased the filling amount of nanoparticles and obtained composites with high dielectric constant.The main work contents are as follows:（1）The surface of BaTiO₃ is modified using polyethylene glycol methacrylate phosphate(C₆H₁₁O₆P),and the C=C bond is introduced as a site for the in-situ polymerization reaction with methyl methacrylate（MMA）monomers.PMMA-BT composite materials are prepared,which can be dissolved in DMF solvent to obtain a colorless and transparent solution.The surface modification,in-situ polymerization,and thermal crosslinked structure of PMMA-BT are confirmed by FTIR,EDS,XRD,and XPS characterization.Under TEM characterization,BT is coated with organic compounds,forming a core shell structure composite material.Under the surface and cross-section SEM characterization,the polymer nanocomposites films have the advantage of being extremely uniform with the thickness of about 700 nm.The dielectric loss of PMMA-BT（13 wt%）thin films is as low as 0.043,the dielectric constant is 9.55,the maximum energy storage density is 8.5 J/cm³,and the dielectric strength was as high as 447V/μm.By adding methylated poly（melamine formaldehyde）solution（PMF）to PMMA-BT,a double-crosslinked network structure PMMA-BT composite is prepared,and the dielectric loss is further reduced to 0.031.The dual crosslinked network structure reduces the polarization of the two-phase interface and the movement of polymer chains at high temperatures,resulting in better thermal stability of the film.（2）In order to obtain high-quality photocrosslinkable polymer matrix,the photocrosslinking of PMMA polymers was achieved by synthesizing poly（methyl methacrylate-co-2-hydroxyethyl methacrylate）[f-P（MMA-co-HEMA）]functionalized with cinnamyl chloride.The functionalization and photocrosslinking of PMMA are confirmed by FTIR,¹H NMR,and UV characterization.When preparing photocrosslinked polymers,using ethyl acetate as a reaction solvent and ether as a washing agent can better promote polymerization.The mixed solvent of DMSO and NMP with high polarity and a dissolution temperature of 90℃are most conducive to the dispersion of photocrosslinked polymers.High quality films with dense and pinhole-free can be obtained by using the treatment method of photocrosslinking followed by thermal annealing.When the crosslinked time is 10 min and the crosslinked degree is 55%,the dielectric constant of the capacitor reaches 4.65,the dielectric loss is as low as 0.04,the dielectric strength is as high as 343 V/μm,and the maximum energy density is 2.4 J/cm³.（3）In order to obtain composite materials with high dielectric constant,a photocrosslinkable functional copolymer f-P（MMA-co-HEMA）/m-BT composite film is prepared using a ball-milling dispersion method and phosphate surface modified BT as the polymer matrix.Under surface and cross-section SEM characterization,BT is uniformly dispersed in the polymer matrix.FTIR confirmed that the C=C group on the surface modified BT disappeared after photocrosslinking,forming a chemical bonding between the two phases in the nanocomposite material.When the BT content reaches 30 wt%,the dielectric constant of the capacitor reaches as high as 51.When the bending angle changes by 120°,the capacitance value changes by 27%,showing good linearity and sensitivity.