Preparation And Properties Of Low Dielectic Constant Polyarylene Ether Nitrile And Its Composites

With the development of the wireless communication industry,especially 5G communication system,attention has been focused on the research of high-speed and high-frequency transmission.Theoritically,the signal propagation speed is inversely proportional to the dielectric constant of the material,and the signal propagation loss rate is proportional to the dielectric constant and dielectric loss of the material.Therefore,high performance low dielectric constant materials with low dielectric loss are immennetly requested for application in wireless communication industry.The reported low-dielectric materials to replace Si O₂ mainly include inorganic materials,organic/inorganic hybrid materials and organic materials.Compared with inorganic dielectric materials,organic polymer materials commonly possess a low dielectric constant due to lower material density and lower single bond polarization.In addition,organic polymer materials show obvious advantages in chemical and geometric structure design.The dielectric constant of the fully dense polymer can be reduced to below 3.0 by decreasing the dipole intensity or the dipole number per unit volume or a combination of the two.The most common methods are to use chemical bonds with low polarizability or increase the free volume by reducing the density of the dielectric.Polyarylene ether nitrile(PEN)has attracted much attention due to its excellent heat resistance,corrosion resistance,and mechanical properties,which can be used in aerospace,mechanical industry,rail transit,microelectronics industry,etc.It is one of the possible candidate polymers for the next generation of high performance interlayer dielectrics.Conventional PEN shows a dielectric constant about 4.0,so the work of this paper mainly focuses on the design and preparation of low dielectric constant PEN and its composites with excellent comprehensive properties.Firstly,a series of fluorinated polyarylene ether nitrile random copolymers with different ratos of trifluoromethyl were synthesized from bisphenol A,bisphenol AF and2,6-dichlorobenzonitrile by nucleophilic substitution reaction.The results of IR and ¹H NMR confirme that the synthesized PEN copolymer is successfully synthesized.The performance tests show that the copolymer exhibite excellent thermal stability,with T_5%above 500 ?.Comparing the properties of PEN copolymers,it can be seen that adding symmetrical-CF₃ into the main chain of PEN can reduce its dielectric constant,improve its heat resistance and hydrophobicity.Secondly,PEN/BADCy blends were prepared by solution casting method with BPAF100 as matrix resin in order to alleviate the serious thermal problems caused by different thermal expansion coefficients between polymer and metal.By using different prepolymerization time and final curing temperature,the morphology of the blends can be controlled from phase separation to quasi-continuous phase morphology,and the properties of the blend can be adjusted finally.The results show that the T_g of the blends cured at 230 ? is 40 ? higher than that of the blend cured at 200 ?.The blends have better dielectric-frequency stability after adding cyanate ester resin.The coefficient of thermal expansion(CTE)of the PEN/BADCy blend prepolymerized for 3 h and final cured at 220 ? is 53.67×10^-6 K^-1,which is 18%lower than that of pure PEN.Finally,in order to reduce the dielectric constant of the polymer more effectively,PEN/C₆₀nanocomposites were prepared by introducing C₆₀ through a pure physical method of cosolvent evaporation.The SEM results show that when the content of C₆₀ is less than 3 wt%,C₆₀ is uniformly dispersed in the PEN matrix in the form of monodisperse clusters with a diameter about 500 nm.When the mass fraction of C₆₀reaches 4 wt%,excessive C₆₀causees a large amount of aggregation and uneven dispersion of C₆₀.When the content of C₆₀ reaches 3 wt%,the performance of the composite film is the best.The T_g is 184 ?,the dielectric constant and dielectric loss are 2.65 and 5×10^-3 at 1 MHz,respectively.The thermal decomposition kinetics calculation shows that PEN/C₆₀composites with 3 wt%C₆₀ has an expected service life for 3.3 years reaching 5%weight loss at 300°C in nitrogen.The 180° peeling strength of 3 wt%PEN/C₆₀ composite film with copper foil without any adhesive is 6.91 N·cm^-1.