Preparation And Properties Of Fluorinated Polyether Ether Ketone Modified Polyimide Coatings

With the development of aerospace,electronics and other high-tech nuclear energy,some motors have to work at higher temperatures than 200 ? over a long period of time.In addition,the temperature and humidity of the working environment change a lot,so requiring coil wire enamels with high moist resistance and heat resistance to make sure that the insulation of electrical products could be ensured in hot and humid conditions.Polyimide(PI)is the highest rank of insulating varnish among organic heat-resistant wire enamels,but PI shows poor wet and heat resistance,poor mechanical properties,which limits its application in air navigation.In this thesis,fluorine-containing poly(ether ether ketone)(FPEEK)was introduced into PI chains to improve their heat and humidity mechanical properties.First,polyamide acid(PAA)was synthesized by using pyromellitic dianhydride and 4,4-diaminodiphenyl as starting materials,then PI insulating coating was obtained by imidization of PAA film on the tinplate.The effects of feeding ratio,loading sequence,reaction temperature and reaction time on the synthesis reaction of PAA are mainly analyzed.The effects of heating rate and temperature retention time on PAA fever were studied.The structures and mechanical properties of Polymer were characterized by Fourier transform infrared spectroscopy,X-ray diffractometer,thermogravimetric analyzer and universal testing machine.The influences of different monomer ratio on the molecular weight and mechanical properties of PI and film performance of PI were studied.The study shows that with the increase of molecular weight of PI,the mechanical properties of paint film gradually improved.The highest molecular weight of PI was 3.84×104 g·mol-1 when the molar ratio of pyromellitic dianhydride and 4,4-diaminodiphenyl ether was close to 1.02:1.The temperature of initial decomposition,tensile strength,young's modulus and breaking elongation are optimal and reach 550 ?,84.21MPa,0.86GPa and 15.51%,respectively.The heat and humidity resistance,adhesion,flexibility and impact resistance of PI insulating coatings were grade 3,2,0.5 mm and 50 cm,respectively.The effects of different ratios of hexafluoro-bisphenol A and 4,4'-difluorinated benzophenone on the hydroxyl FPEEK molecular weight were investigated.Tluorine-containing poly(FPEEK)was introduced into PI and got PI-co-FPEEK and PI-co-FPEEK coating.The influences of FPEEK content and molecular weight on structures and mechanical properties of PI-co-FPEEK and PI-co-FPEEK coating were investigated.With the increase of FPEEK content,the thermal stability of PI-co-FPEEK decreased a little bit,keeped 500?.But the adhesion,wet and heat resistance of PI-co-FPEEK coatings increased.With the increases of FPEEK molecular weight,the thermal stability of PI-co-FPEEK decreased,but mechanical properties were deteriorated due to the low molecular weight of copolymers.When the molecular weight of FPEEK was 3011 g·mol-1 and the FPEEK content was 5mol%,the heat and humidity resistance,adhesion,flexibility and impact resistance of PI-co-FPEEK coatings could reach the grade 1,1,4mm and 35cm,respectively.Its initial decomposition temperature,tensile strength,young's modulus and breaking elongation are 520?,81.32MPa,0.79GPa and 13.34%,respectively.