Preparation Of Lead-ion-bonded Polyimide Films

Lead,which is the most frequently used material for radiation shielding,has a strong shielding effect of blocking X and ? rays.However,because of its toxicity and high density,the application range of lead has been greatly restricted.At present,the main research tendency is preparing the organic-inorganic composite materials.In this method,a kind of light-weight and easily-processed composite material were prepared by adding lead or lead salts into the polymer matrix.However,phase segregation will occur due to the dissolution of inorganic lead salts or lead in polymer materials,which cause uniform distribution.of lead,and damaging the radiation shielding effect of composite materials.Polyimide(PI),a polymer material with comprehensive performance,such as outstanding thermal stability,excellent mechanical properties and good radiation resistance,is an ideal choice for composite matrix.In order to solve the problem of agglomeration and precipitation of lead in polymer matrix,in this paper,we bind the lead ions into the side groups of PI,which provides a stable organic framework for lead,with a sandwich structure design,we successfully prepared composite materials with ionic-bonding lead element.The problem of the inhomogeneous distribution of lead in the composite material is solved,and the mechanical properties of the material are improved,the main researches are listed as follows:1.Synthesis of three kinds of bisamine monomers with the binding of lead ions.First,we synthesized 4,4'-diamino-2,2'-biphenyldicarboxylic acid(DDPA),4,4'-diaminodiphenyl ether-2,2'-disulfonicacidacid(ODADS)and 4,4'-diaminobiphenyl-2,2'-disulfonic acid(BDSA),then the corresponding products 4,4'-diamino-2,2'-biphenyldicarboxylic lead acid(DDPA(Pb)),4,4'-diaminodiphenyl ether-2,2'-disulfonic lead acid(ODADS(Pb))and 4,4'-diaminobiphenyl-2,2'-disulfonic lead acid(BDSA(Pb))were prepared by ion exchange method.2.Preparation of different polyimide films with sandwich structure.The synthesized bisamine monomer,4,4'-diaminodiphenyl ether(ODA)and 1,2,4,5-benzenetetracarboxylic anhydride(PMDA)were used as co-monomers to conduct condensation polymerization in N-methyl-2-pyrrolidone(NMP),and a series of polyimide/lead(PI(Pb))composites were prepared by using thermal imine method and coating process.In a sandwich structure,the upper and lower two layers are pure PI layer and the middle layer is PI(Pb)layer.3.Performance testing and related structural characterization.Proton nuclear magnetic resonance spectroscopy(H-NMR),fourier transform infrared spectroscopy(FTIR),elemental analysis(EA),X-ray diffraction(XRD)were applied to characterize the synthesized compounds.The thermal stability and mechanical properties of prepared PI(Pb)composite materials were tested and analyzed.In addition,the 60Co ?-ray radiation test was carried out on pure PI and PI(Pb)to analyze their radiation resistances.Finally,the shielding properties of the materials were studied by using the multi-channel gamma spectroscopy.The results show that:compared with pure PI,the radiation resistance properties of the prepared PI(Pb)get improved dramatically,and its ?-ray shielding effects towards 241Am(59.5 keV),238Pu(79.9 keV),and 238Pu(176.7 keV)sources also get enhanced.Besides,PI(Pb)material has excellent thermal stability and good mechanical flexibility,and its advantages of portability,flexibility,processibility bring it a wide application prospect.