Synthesis,Characterization And Application Of Soluble Poly (Amide-Imide)

Poly（amide-imide）（PAI）is a class of high-performance polymers,which contains imide rings and amide groups in the main chain.PAI has been widely used in aerospace,electronic devices and other fields due to its unique properties such as excellent mechanical property,high heat resistance and good chemical stability.However,the solubility of PAI is poor,which limits its application of the simple and easy solution methods.In order to develop PAI with excellent comprehensive properties,two types of PAIs（semi-aromatic PAI and full-aromatic PAI）were synthesized by introducing flexible group,fluorine-containing group and non-coplanar structure into the main chain,and the prepared PAIs were used in electromagnetic shielding and flame retardant fields.The main research contents and results are as follows:（1）Firstly,an imide monomer with alkyl chain was synthesized by the imidization reaction between 4,4’-oxydiphthalic anhydride（ODPA）and aminobutyric acid（GABA）.Then,three semi-aromatic PAIs with different structure（PAI-DP,PAI-DCP,PAI-DFP）were synthesized by Yamazaki phosphonylation.The effect of diamine monomer structure on the properties of PAI films was discussed.It is found that the semi-aromatic PAI exhibited good solubility,which could be dissolved in some common organic solvents such as N,N-dimethylacetamide（DMAc）and N-methylpyrrolidone（NMP）;In addition,PAI films showed excellent thermal properties,the glass transition temperatures（T_g）and the initial thermal decomposition temperature(T_5%)were respectively higher than185 ^oC and 405 ^oC,the linear thermal expansion coefficient（CTE）coverred from-4 to-1 ppm/^oC;Furthermore,the prepared PAI films had good mechanical property and low dielectric constant,their tensile strengths were 63-75 MPa,and dielectric constants were lower than 3.3F/m;Optical transmittance test showed that the introduction of trifluoromethyl groups significantly decreased the formation of charge transfer complexes,and the transmittance of PAI-DFP film at 500 nm was as high as 89%.（2）The prepared PAI-DFP film and silver nanowires（Ag NWs）were respectively used as substrate and conductive filler to fabricate transparent electromagnetic shielding films through layer-by-layer casting method.PAI/Ag NWs/PAI composite films showed a shielding effectiveness（SE）of 35 d B and simultaneously possessed an optical transmittance of beyond 80%.More encouragingly,the composite films remained more than 92%EMI SE with random deformations（>5000times）.Furthermore,even after high temperature treatment and soaking in acid-base solutions,the EMI SE of the electromagnetic shielding film only slightly decreased.Therefore,the electromagnetic shielding film based on semi-aromatic PAI not only exhibited good electromagnetic shielding efficiency and optical transmittance,but also showed excellent stability.（3）In order to further improve the thermal stability and mechanical property of PAI,three full-aromatic PAIs（TMA-DP-DP,TMA-DP-DCP,TMA-DP-DFP）were synthesized.Firstly,a diacid monomer（TMA-DP）was synthesize by the imidization reaction between trimellitic anhydride（TMA）and m-tolidine（DP）.Then,the full-aromatic PAIs were synthesized by Yamazaki phosphonylation reaction.The effect of diamine monomer structure on the properties of PAI film was investigated.It is found that the full-aromatic PAI resins also exhibited good solubility,which can be dissolved in some common solvents such as DMAc and NMP;On the other hand,tensile strength of the full-aromatic PAI films was further increased to 95 MPa,which was much higher than that of the semi-aromatic PAI films.In addition,the full-aromatic PAI films showed excellt thermal properties,their T_g and T_5%were respectively higher than275 and 480 ^oC,and the carbon residue rate（CR）at 750 ^oC was as high as72.5%.In other words,the prepared full-aromatic PAI not only showed good mechanical properties,but also exhibited high thermal stability,suggesting that they can be used as carbon-forming agent for polymer material.（4）TMA-DP-DFP and hexaphenoxycyclotriphosphazene（HPCP）were respectively used as carbon-forming agent and flame retardant to fabricate epoxy resin（EP）blend materials,and the effect of formulations and process on the flame retardant behavior and combustion behavior of EP blends were discussed.It is found that the EP blends just passed UL94 V-1 when 4 wt%TMA-DP-DFP or 4 wt%HPCP was separately added into EP resin,while the EP blends passed UL 94 V-0 when 1 wt%TMA-DP-DFP and 3 wt%HPCP were added into EP resin,suggesting that TMA-DP-DFP and HPCP played a synergistic role in flame retardant epoxy resin.The combustion behavior of EP blends showed that HPCP released incombustible gas while the generated phosphate promoted the formation of dense carbon layer.On the other hand,TMA-DP-DFP generated a large number of graphitized carbon layers and nitrogen.The synergistic effect between HPCP and TMA-DP-DFP promoted the formation of continuous and dense carbon layer,and achieved good flame retardant effect.