Synthesis And Performance Study Of High Hydrolytic Resistance Polynaphthalimide Contained Six-Membered Ring Structure

Polyimide(PI)is a high molecular polymer with an imide ring structure,and is currently one of the engineering materials with the best comprehensive performance.However,most PI contains a five-membered imide ring structure with poor hydrolysis resistance,and its application in alkaline or humid environments is limited.Polynaphthaleneimide(PNI)is a type of PI derivative polymer with hexavalent naphthalene anhydride imide formed by the polymerization of dianhydrides and diamines of naphthalene anhydride structure.From the perspective of molecular structure,the six-membered naphthalene anhydride imide ring structure has more stable properties than five-membered polyimides,especially in terms of hydrolysis resistance.Therefore,preparation of PNI with hydrolysis resistance based on the six-membered naphthalene anhydride imide ring structure has attracted attention.However,the insolubility of PNI and the low activity of naphthalene anhydride bring many difficulties to synthesis and processing.Therefore,higher requirements are put forward for PNI processing methods.In this thesis,a series of PNI fiber membranes and films were prepared by design,synthesis and processing methods,and their properties were studied,and the hydrolysis resistance of PNI was explained through its mechanical properties.The specific content of the paper mainly includes the following two parts:1.Polynaphthalimide fiber: Polynaphthalene amic acid solution is prepared with1,4,5,8-naphthalenetetracarboxylic dianhydride(NTDA)and 4,4'-diaminodiphenyl ether(ODA)as raw materials(6-PAA).(1): 5-PAA is added to 6-PAA as a template,and 6-PAA composite nanofibers are prepared by electrostatic spinning;after heat treatment,6-PNI/5-PI composite nanofibers are obtained.(2): Add PVP as a template and tackifier to 6-PAA,and prepare 6-PNI/PVP composite nanofibers by electrospinning and heat treatment.The influence of the blending template ratio on the hydrolysis resistance of composite nanofibers was investigated.The results show that the 6-PNI/5-PI-10 composite fiber tape has better hydrolysis resistance when treated at370?,and the tensile strength after immersing in lye,acid and salt solution for 24 hours retains 54.32%,74.89% and 93.23%,the 5% weight loss temperature of the fiber is 539?.At the same temperature,the 24-hour hydrolysis resistance test results of the6-PNI/PVP-10 composite fiber tape were 43.77%,72.31% and 85.511% respectively;further heating the 6-PNI/PVP-10 fiber to 450°C,you can get 6-PNI-450°C fiber tape.The tensile strength of the 6-PNI-450°C fiber tape after being immersed in lye,acid and salt for 24 hours retains 58.72%,79.03% and 93.88%,respectively.It maintains good mechanical properties and can be used.value.2.Polynaphthaleneimide film:(1): co-BD-PNI film(NTDA/BAPP/DAB),using different proportions of 2,2-Bis[4-(4-aminophenoxy)phenyl]propane(BAPP),3,3',4,4'-tetraaminobiphenyl(DAB)and dianhydride NTDA are prepared by polycondensation.(2): co-HD-PNI film(NTDA/HFBAPP/DAB),using different ratios of 2,2-Bis[4-(4-aminophenoxy)phenyl]-hexafluoropropanane(HFBAPP),DAB and NTDA is prepared by polycondensation.(3): co-DD-PNI film(NTDA/DMB/DAB),2,2?-dimethyl-4,4?-benzidine diamine(DMB),DAB and NTDA are prepared by polycondensation.The results show that when the molar mass ratio of HFBAPP to DAB is 9.2:0.8,the tensile strength is 74.22 MPa,the modulus is 2.81 GPa,and the elongation at break is 4.05%.The tensile strength retained 79.14%,90.61% and 97.77% after 24 hours immersion in lye,acid and salt solution,respectively.After 24 hours of lye soaking for other films,the retention rate of the tensile strength of the film is also above 65%,and it has excellent hydrolysis resistance.