Preparation And Properties Of Thermoplastic Soluble Polyimide Resins Containing Non-coplanar Structure

Polyimide material exhibits excellent resistance to high and low temperature properties,mechanical properties,dielectric insulation properties,UV radiation resistance and chemical corrosion resistance due to its unique aromatic heterocyclic rigid structure.The top position of the material performance pyramid is widely used in aerospace,machinery,electronics,electrical,nuclear industry and other fields.At the same time,due to the high rigidity of the molecular chain and the strong interaction between the chains,the polyimide material is usually insoluble and infusible,which makes it difficult to process.This topic starts from the free volume theory and uses a twisted non-coplanar structure.A dianhydride monomer 2,3,3',4'-biphenyltetracarboxylic dianhydride(a-BPDA),designed and prepared a series of copolymerized polyimide resin materials with both thermoplastic and soluble characteristics.Structural and performance relationships were characterized and analyzed.First,a-BPDA and two diamines 4,4'-diaminodiphenyl ether(ODA)and 1,3-bis(4'-aminophenoxy)benzene(TPER)were copolymerized by controlling the diamine.A series of polyimide resins were prepared and their solubility,thermal properties and rheological behavior were investigated.The results show that the prepared copolymerized polyimide has good solubility and is soluble in strong polar solvents such as DMAc,NMP and DMF;its thermal properties are excellent,the glass transition temperature is above 256?,and the 5%weight loss temperature is higher.550 ?;rheological test results show that the prepared polyimide resin has good melt flowability and the lowest melt viscosity can reach 601 Pa·s.The polyimide resin was prepared into a molded plate by a hot press forming process and its mechanical properties were tested.The results showed that the tensile strength was higher than 79.5 MPa and the notched impact strength was higher than 11.5KJ/m2.In order to maintain the comprehensive performance of polyimide and improve its melt stability,TPER was replaced by 4,4'-oxydiphthalic anhydride(ODPA)for copolymerization,by controlling the distribution of a-BPDA and ODPA.A series of polyimide resins were prepared and their solubility,thermal properties and rheological behavior were investigated.The results show that the prepared copolymerized polyimide resin has good solubility and can be dissolved in strong polar solvents such as DMAc;the glass transition temperature is higher than 251?,and thermal decomposition does not occur below 500?;rheological test results It shows that the polyimide resin has excellent melt fluidity and melt stability.As the temperature increases,the melt viscosity of the resin first decreases and then stabilizes;at a constant temperature of 1 h,the melt viscosity can be maintained at 10,000 Pa.Below s,it basically satisfies the general hot pressing,extrusion and injection molding processes.The polyimide molded plate obtained after hot pressing has excellent mechanical properties,and the tensile strength and bending strength are higher than 85.9 MPa and 77.6 MPa,respectively.