Preparation And Properties Of Crystalline Poly (Aryl Ether Nitrile)

In today's society with the rapid development of polymer materials,crystalline polymer materials occupy the majority.As a special polymer material containing cyano side groups,poly(arylene ether nitrile)(PEN)is widely used in high-precision fields such as defense and military industry,aerospace,information electronics,and biomedicine.Crystalline PEN has excellent high temperature resistance,mechanical strength,corrosion resistance and other properties due to the regular arrangement of its molecular chains.Crystalline polyarylene ether nitrile is easy to precipitate during the synthesis process,and there is a general problem that it is difficult to form a stable synthesis process.Therefore,its excellent performance and the high cost of preparation have become a pair of obvious contradictions.In view of the above problems,in order to solve the problem of difficult synthesis of crystalline PEN,a PEN copolymer(HQ/BPA-PEN)with certain crystallinity was prepared by research on process improvement and raw material ratio,and modified by uniaxial thermal stretching.The PEN composite filled with aramid fiber(AF/PEN)was preparedand and the properties of the composite material were further improved by means of thermal stretching.The main research contents are as follows:1.Bisphenol A and hydroquinone are selected as the diphenol raw materials for the synthesis of PEN,and randomly copolymerized with 2,6-dichlorobenzonitrile to form a PEN material with certain crystallinity.By changing the ratio of bisphenol A to hydroquinone,the contradiction between poor crystallinity and easy precipitation of crystals during synthesis,resulting in low molecular weight was balanced.With the decrease of bisphenol A content,the crystallinity of PEN increased,but the synthesis was more difficult,and it was difficult to obtain high molecular weight PEN.When the bisphenol A content was 15%(HQ/BPA-PEN85),the PEN had a higher molecular weight and still had a certain crystallinity,and its crystallinity was 23.47%.And its tensile strength and elongation at break were 134.18 MPa and 9.54%,respectively.2.Taking HQ/BPA-PEN85 as the research object,after getting films by the casting method,the time and temperature were respectively controlled for isothermal thermal treatment.From DSC test,the crystal perfection degree of PEN gradually increased with the increase of temperature and time,and was more sensitive to temperature.The changes of PEN crystallinity were qualitatively analyzed by optical methods such as fluorescence micro-area test and UV-visible light test.After comprehensive analysis of crystallinity,thermal properties,and other properties,the uniaxial thermal stretching conditions were between 270°C and 280°C,and stable at 280°C for 1 h.The uniaxial thermal stretching was carried out using the applied temperature field and gravity field,and the effect of uniaxial thermal stretching on its properties was researched Through the analysis of thermal,mechanical,dielectric,observed micro-morphology and XRD fitting of crystallinity,the comprehensive performance was the best when the elongation rate was200%.Its crystallinity increased from 14.26%to 34.49%,the thermal decomposition temperature of 5%(T_d5%)was greater than 500°C,the tensile strength increased by 46.6%,the elongation at break increased from 8.16%to 17.64%,and the dielectric constant remained at 3.3 around,the dielectric loss was less than 0.02.3.Using the high strength and one-dimensional properties of the aramid fiber powder to fill the crystalline PEN to prepare the aramid fiber filled PEN composite material(PEN/AF)with different contents of the aramid fiber powder.After filling the aramid fibers,the crystallinity was fitted by XRD curve and the microstructure was observed,and it was found that the crystallinity increased,the measured dielectric constant increased significantly,and the dielectric loss decreased slightly.After analysis of thermal properties and mechanical properties,when the content of aramid fiber powder was 0.3%,it had the highest T_g and T_m,the highest tensile strength,elastic modulus and strongest toughness.Therefore,the composite film with aramid fiber content of 0.3%was selected for unidirectional thermal stretching.Through the test of thermal and mechanical properties of film materials with different stretching ratios,the fitting of XRD to crystallinity and the observation of microscopic morphology,it was found that the film material with 300%stretching ratio(PEN/AF3-300)had the most excellent comprehensive properties,its crystallinity increased from 31.44%to 36.14%,T_mdecreased by about 20°C,and T_d5%increased by about 10°C.In addition,the dielectric constant of the PEN/AF3 film was slightly increased and the dielectric loss decreased from 0.017 to 0.007 by uniaxial thermal stretching.From the XRD curve and the melting peak change of DSC,it can be seen that the crystallinity of PEN/AF3 film increases while the crystallinity gradually tends to be perfect.