Preparation And Properties Of Semi-crystalline Decafluorobiphenyl Poly(Aryl Ether Ketone)

Poly(aryl ether ketone)s(PAEKs)is a kind of semi-crystalline special engineering plastics,which have excellent comprehensive properties such as high temperature resistance,solvent corrosion resistance,radiation resistance,wear resistance,self-lubrication,high electrical insulation,strong and tough,flexible processing.Since the success of the development of PAEK,it has been widely used in the fields of aerospace,automotive,electronic and electrical,medical equipment and other fields.In order to meet the further needs of industrial production of high-performance materials,the researches on the synthesis and modification of novel PAEKs have been widely concerned by researchers.The direct and effective method to improve the properties and functionalized modification of PAEK is the modification of the molecular structure.Because the fluorine atom has the highest electronegativity,smallest van der Waals radius,low polarizability,and the C-F bond has high bond energy,fluorinated polymers generally show weather resistance and chemical stability,good electrical insulation,as well as low friction coefficient,low surface free energy,low dielectric constant and other excellent properties.Accordingly,the introduction of fluorine into the PAEKs can effectively improve the solubility,water absorption,optical properties and dielectric properties,which would make it a promising material for microelectronics devices,optical waveguide equipment,gas separation membrane and proten wxchange membrane,etc.In addition to the molecular structure,the aggregated structure of polymer also plays an important role in the properties of polymer.The aggregated structures of polymer are mainly crystalline,amorphous and oriented,the most important of these is the crystalline state.The excellent comprehensive properties of poly(ether ketone)series polymers are mainly depend on their semi-crystalline aggregated structure.The crystallization properties have an important influence on their thermal properties,mechanical properties,weather resistance and wear resistance.However,most fluorinated poly(ether ketone)s reported in the literature are amorphous or functionalized materials,sacrificing the semi-crystalline properties of poly(ether ketone)s,which is undoubtedly detrimental to their application as structural materials.In this paper,considering that the intrinsic factors of polymer crystallization are structure and the regularity of molecular chain.The higher symmetry of molecular chain,the better crystallization ability of polymer.A semi-crystalline poly(aryl ether ketone)(SC-FPAEK)with decafluorobiphenyl structure was prepared by nucleophilic substitution condensation reaction of 4,4'-dihydroxybenzophenone and decafluorobiphenyl with high fluorine content and symmetry molecular structure.The molecular structure and crystal structure were characterized by IR,XRD and polarizing microscopy(POM).Similar to the commercial poly(ether ether ketone)(PEEK),SC-FPAEK resin had the semi-crystalline structure and exhibited similar solvent resistance properties.SC-FPAEK was insoluble in most conventional organic solvents,only soluble in concentrated sulfuric acid,so the molecular weight of SC-FPAEK was determined in concentrated sulfuric acid in this paper.Due to the high crystallinity of SC-FPAEK,the precipitation problem during the polymerization process seriously limited the chain growth of the polymer.The molecular weight of the SC-FPAEKs obtained were not very high,and the maximum intrinsic viscosity was 0.32 d L/g.The DSC test results showed that the glass transition temperature(T_g)of SC-FPAEK increased with the increase of molecular weight.The T_gof the SC-FPAEK-H with the highest molecular weight reached 154?and its melting point T_mwas 295?.Through XRD test,the crystal diffraction peak of SC-FPAEK can be observed.The crystallinity of different molecular weights ranged from 40 to 45%through Jade fitting.The results showed that the SC-FPAEKs had good crystallization ability.Moreover,the crystal morphology and specific growth process of small molecular weight were observed by polarizing microscope(POM).Meanwhile,in this paper,the non-isothermal crystallization behavior of SC-FPAEK-L at different melting temperatures was studied.The results performs that the melt crystallization peak obtained in the subsequent cooling process were also different at different melting temperatures.In a temperature range above the melting point,the crystal nucleus did not completely disappear,which would significantly increase the subsequent crystallization rate.Meanwhile,the non-isothermal crystallization kinetics of SC-FPAEK-L was analyzed by at different melting temperatures.The crystallization rate constant and Avrami index under different melting conditions were obtained.Finally,the contact angle and surface energy of SC-FPAEK sample prepared by hot pressing were studied.The results indicated that the sample show a high water contact angle of 104°and a low surface energy of 24.58 m J/m²due to the introduction of fluorine.Blend modification of polymers is one of the important ways to produce high performance polymers.In this paper,the synthetic SC-FPAEK resin was alloyed to modify the commercial poly(ether ether ketone)(PEEK).And a series of SC-FPAEK/PEEK blend systems with different proportions were prepared.The DSC test results showed that SC-FPAEK/PEEK showed a single T_g,when SC-FPAEK content lower than 20 wt%.The numerical value was basically consistent with the calculated value of Fox equation.And SEM results showed that the blend sample quenching section flat and smooth with uniform morphology.The obvious groove or holes were not observed,so it suggested that SC-FPAEK/PEEK is fully compatible system when SC-FPAEK content lower than 20 wt%.The results of DSC test showed that when the SC-FPAEK content was higher(>20 wt%),the SC-FPAEK/PEEK blend system showed two T_gcorresponding to PEEK and SC-FPAEK.T_gcorresponding to pure PEEK component decreased to 142?,and T_gcorresponding to SC-FPAEK component increased to 131?.And the SEM results also showed that the two phases with obvious"island"structure.This indicated that SC-FPAEK/PEEK was a partially compatible system when the SC-FPAEK content was higher than 20 wt%.In this paper,the mechanical properties of SC-FPAEK/PEEK blend systems with good compatibility of 2 wt%,5 wt%,7 wt%,10 wt%,15 wt%and 20 wt%were evaluated.And the results showed that the blends with low SC-FPAEK content of 2-7 wt%showed excellent mechanical properties,especially the toughness of PEEK was improved remarkably.When the content of SC-FPAEK is 5 wt%,the tensile strength and elongation at break of SC-FPAEK/PEEK alloy reach the maximum value,which ware 114.4 MPa and 146%,respectively.Compared with pure PEEK,the tensile strength and elongation at break of SC-FPAEK/PEEK alloy were increased by10%and 110%respectively.Therefore,the strength and toughness of PEEK had been greatly improved simultaneously,which have important guiding significance for PEEK modification and application research of reinforcing and toughening study.In addition,because the fluorine element migrates towards the surface.Therefore,the water contact angle and surface energy of the SC-FPAEK/PEEK blend system before and after heat treatment were tested.The results showed that the blend samples showed similar contact angle values to PEEK before annealed treatment,and blend samples of water contact angle greatly increased after annealed.For example,When SC-FPAEK content was 5wt%,the water contact angle of FPAEK/PEEK increased from 83°of PEEK to 102°.And the surface energy by 42 m J/m²dropped to 35.8m J/m².EDS was used to characterize the fluoride content of 5%SC-FPAEK/95%PEEK suface before and after annealed,the results showed the mass ratio of fluorine element increased from 2.5 wt%to 6.7 wt%,which proved that the fluoride migration to the polymer surface during the annealed.The surface migration behavior of fluorine atoms provided an important theoretical basis for improving the friction and wear properties of poly(ether ether ketone)resin.The tribological properties of SC-FPAEK/PEEK alloys with excellent mechanical properties were tested by injection molding friction samples.The results showd that SC-FPAEK/PEEK alloys exhibited excellent friction reducing and wear resistant effects.The friction coefficient and wear rate of PEEK were 0.376 and 2.60×10^-6mm³/Nm,respectively,while the those of 5%SC-FPAEK/95%PEEK were 0.32and 0.772×10^-6mm³/Nm respectively.This had important guiding significance for the development and application of high performance polymer friction resistant materials.