Structural Design And Synthesis Of N,S-containing Heterocyclic Polymers With Controlled Infrared Optical Properties

The military detection technology mainly includes visible-light,near-infrared light,mid-far-infrared and microwave detectors.Traditional stealth materials are incapable of meeting informational and diversify battlefield field with the rapid development of military science and technology.Thus,multi-band stealth,lightweight and low-cost processing camouflage materials are an important research area at present.Infrared camouflage requires excellent near-infrared absorption properties and low mid-far-infrared emissivity.For the present,most infrared stealth materials are metals and inorganic semiconductors.These materials suffer from poor compatibility with resin matrix and high processing costs.Metals could exhibit ultra low mid-far-infrared emissivity.However,the compatibility of infrared emittance and microwave stealth is an insurmountable issue for metal materials.With the advantages of "flexible,light,thin" and processibility,conjugated polymer as a new type of semiconductor material has achieved rapid development in optoelectronics research field such as solar cells,organic thin film transistors,organic light-emitting diodes,etc.It has reported that conjugated polymers can be used as near-infrared,mid-far-infrared and microwave stealth materials.However,most are still in their preliminary stage.The stealth mechanism of conjugated polymer materials is not consummate.Based on above considerations,three different polymer systems are synthesized:a)donor-acceptor polymers containing phthalazionone(acceptor)and thiophene(donor)structures,b)poly(aryl ether)s containing nickel bis(dithiolene)moiety.c)bimetal coordination polymer coating containing dithiene and Schiff base moieties.The relationship between polymer structures,near-infrared light absorption,mid-far-infrared and microwave stealth properties has been studied.Main works and results of this thesis are summarized as following:(1)Donor-acceptor polymers containing phthalazionone(acceptor)and thiophene(donor)structures:three di-N-H monomers DT1(thiophene as donor and phthalazionone as acceptor),DT2(bithiophene as donor and phthalazionone as acceptor)and DT3(terthiophene as as donor and phthalazionone as acceptor)were synthesized.With the increasing donor-acceptor effect and electron delocalization of phthalazionone and thiophene structures,the maximum absorption wavelength is gradually red shifting:DT1(349 nm)<DT2(377 nm)<DT3(398 nm),the maximum emission wavelength gradually redshifts:DT1(420 nm)<DT2(477 nm)<DT3(498 nm),the band gap gradually decreases:DT1(3.08 eV)>DT2(2.40 eV)>DT3(2.28 eV).Twenty-one donor-acceptor polymers containing phthalazionone(acceptor)and thiophene(donor)structures were synthesized by di-N-H monomers and di-halide monomer via aromatic nucleophilic substitution polymerization and copper-catalyzed Ullmann C-N polymerization.Corresponding polymerization conditions and polymer structures were investigated.The thermal stability,macromolecular chain configuration,UV-Vis-NIR absorption and emission spectra,band gap and aggregation states in thin film states of polymers were studied.With increasing of D-A conjugation effect and electron delocalization in the polymer chain,the maximum absorption wavelength is gradually red shifting from 350 nm to 651 nm,the maximum emission wavelength gradually redshifts from 465 nm to 716 nm,the band gap gradually decreases from 3.09 eV to 1.39 eV.(2)Poly(aryl ether)s containing nickel bis(dithiolene)moiety:high molecular weight poly(aryl ether)s(Mn=16.7 kg/mol,PDI=2.50)were synthesized via aromatic nucleophilic substitution polymerization with 4,4'-difluorobenzil and 4,4'-(9-Fluorenylidene)diphenol.By transforming benzil groups into nickel bis(dithiolene)groups via ligand-exchange post-polymerization modification,poly(aryl ether)s containing nickel bis(dithiolene)moiety were successfully synthesized.The involved ligand-exchange reaction in the post polymerization modification reduced the cross-linking and branching side reactions.Content of nickel bis(dithiolene)segments is high up to 46 mol%(higher than the highest reported value 20 mol%in soluble high molecular polymers up to data).The polymer structures,thermal properties,NIR absorption and electrochemical properties were investigated.The maximum absorption wavelength of poly(aryl ether)s containing nickel bis(dithiolene)moiety with dodecanoxy side chain and di(dodecyl)amino side chain are 967 nm and 1200 nm in N-methyl pyrrolidone solution.Also,their band gaps are 1.06 eV and 0.81 eV,respectively.Aging resistance experiments demonstrate that incorporating the nickel bis(dithiolene)moiety into polymer backbone via chemical linking is superior to physical blending for stabilitizing the nickel bis(dithiolene)structures(excellent NIR absorption stability at 70 ? for 144 h).Stealth performance experiments show:the polymer film(thickness=36 ?m)can reduced the maximal detection range of near-infrared radar and rangefinder by 6%and 11%.The infrared emissivity(2-22 ?m)can decrease to 0.70±0.02,Meanwhile,the polymer coating exhibits compatible microwave radar stealth properties at 10-18 GHz.(3)Bimetal coordination conjugated polymer coating containing dithiolene and Schiff base moieties:in order to reduce mid-far-infrared emissivity with maintaining the near-infrared absorption properties of polymer systems,the bimetal coordination conjugated polymer coatings are fabricated via baking of organic linkers(oligomer containing nickel bis(dithiolene)moiety,3,3'-diaminobenzidine,metal salts)in the presence of co-reagents(dimethylacetamide and acetic acid).The fabrication processes were investigated.The structures were confirmed by FT-IR,XPS and ICP.The results indicate that the metal(Cu,La,Sm and Lu)coordination effect with conjugated polymer mainchains are formed,as well as nickled-bis(dithiolene)structures.Stealth performance experiments show:the maximum absorption wavelength of bimetal coordination polymer coatings is 930-1100 nm.The polymer coating(thickness=ca.40 ?m)can reduce the maximal detection range of near-infrared radar and rangefinder by 5%and 10%.The infrared emissivity(2-22 ?m)of nickel/samarium-containing coating can decrease to 0.47±0.03.Meanwhile,benefiting from the dielectric loss in high frequencies of bimetallic complex structure and magnetic loss in low frequencies of copper complex structure,the nickel/copper-containing polymer coating exhibits compatible microwave radar stealth properties at 1-18 GHz.