Preparation And Radiation Properties Of Helical Polyacetylene Based Nanocomposite

With the continuous improvement of the detection system on the battlefield,the research on stealth technology is promoted towards wide frequency band,all-round and multi-function.The energy conversion forms of the infrared band radiation in the absorbing medium are mainly valence band transition,lattice vibration or chemical bond vibration,and may cause the radiation wave to be shifted away from the infrared atmospheric window,so that the effective infrared emission of the target surface is reduced;Microwave absorption refers to the use of electrical and magnetic losses to significantly absorb and attenuate the microwave energy projected onto the target surface and convert it into thermal energy or dissipate it due to interference to reduce the echo energy.Due to the variability of the absorbing mechanism,how to achieve effective compatibility of electromagnetic waves under wide-spectrum and multi-band conditions is a difficult and hot topic in the research of absorbing materials.In this paper,bromine-based helical polyacetylene is the main component,and it was combined with the prepared g-C₃N₄-based nano-alloy material to obtain organic-inorganic nanocomposites.The structure of the polyalkyne molecule was determined by characterization of FT-IR,¹H-NMR,UV-vis,CD and[α]_D.The Br atom content was adjusted and the infrared emissivity of the polymer was determined.The mechanism of intramolecular hydrogen bonding caused by internal atomic vibration on the reduction of infrared emissivity was studied.The organic-inorganic composites were prepared by combining brominated helical polyacetylene with hollow tubular carbon nitride coated with NiCo-alloy nanosheets.The structure-activity relationship between microstructure and properties of composites was studied.The conclusions reached are as follows:1.Preparation,characterization and infrared radiation properties of brominated polyacetyleneThe bromine atom-based N-propargyl amide monomer M1 and the chiral monomer M2 were polymerized under the coordination polymerization of a ruthenium metal catalyst and formed the helical polyacetylene copolymer（polyM1-M2）which have a moderate molecular weight and a uniform distribution.By adjusting the proportion of monomers,different bromine content polymers were obtained and the relationship between specific optical rotation and infrared emissivity was compared.It was found that the infrared emissivity and the specific optical rotation showed a downward trend with the increase of Br content.We attribute it to the fact that halogen atoms are more susceptible to polarization than alkane chains,and the polarity of the molecules increases the attraction between the molecules（positive and negative charge attraction）.We simulated the unit structure of the copolymer,demonstrating that the Br atom was exposed to the outside of the polyacetylene backbone,and the C-Br bond with a small bond strength resulted in high frequency vibrations,ie,vibrations at relatively short wavelengths.Therefore,as the Br content increases,the intramolecular vibration increases and a large amount of reflection is generated instead of absorption,which in turn causes the infrared emissivity of the copolymer to decrease.2.Hollow Ni-Co layered double hydroxides-derived NiCo-alloy@T-g-C3N4microtubule with high-performance microwave absorptionThe g-C₃N₄ was used as the C carrier,and the NiCo-LDH nanosheet was wrapped on the outside.After hydrothermal reaction and calcination,the hollow tubular alloy g-C₃N₄ composite（NC@TCN）was obtained.Adjusting the ratio of metal Ni and Co can change the microwave absorption capacity of NC@TCN composite.When the ratio of the composite metal in the paraffin matrix is 1:1,the filler content is 20 wt%,and the thickness is 2.5 mm,the optimum reflection loss RL_min value of the composite can reach-36.7 dB at a frequency of 10.8 GHz.In addition,an effective adjustable bandwidth of 4.9 GHz（8.7-13.6 GHz）can be achieved by varying the thickness of the absorber coating.When the ratio of Ni to Co is adjusted to 1:1,the infrared emissivity is 0.729.Due to the high porosity,multi-layer heterostructure,interfacial polarization,dielectric resonance and other factors of NC@TCN,the absorbing ability of NC@TCN is improved.3.Composite of bromine-containing helical polyacetylene and NC@TCN microtubes and their radiation propertiesA novel multi-stage heterogeneous PA/NiCo-alloy@T-g-C₃N₄ composite was successfully prepared by a simple and feasible solution blending method.The polyacetylene（PA）changes from a regular network structure to a uniform spherical particle,and the degree of dispersion increases.The introduction of PA does not destroy the crystal structure and surface morphology of the tubular carbon nitride material,and the composite has the optical activity of the polyalkyne molecule,and the infrared emissivity can be reduced to 0.537.Due to the introduction of polyacetylene particles,the synergistic effect between the components is greatly improved,and the NiCo alloy nanosheets are more stably wrapped on the surface of the tubular g-C₃N₄ and are not easily oxidized.The PA/NiCo-alloy@T-g-C₃N₄composite has a filling capacity of only 20 wt%in paraffin and a maximum absorption band of 7.2 GHz and a RL_min of-44.5 dB at a thickness of 2.0 mm.