Structure And Properties Of Low-Dielectric Composites Modified Based On Cage Polyhedral Oligomeric Silsesquioxanes

With the rapid development of communication and information technology,high-performance insulating materials with low dielectric constant(?)and dielectric loss(tan?)have become a research hotspot.Because the dielectric properties of materials are closely related to the propagation of electrical signals,the lower the dielectric constant,the faster the propagation of electrical signals;the lower the dielectric loss,the lower the propagation loss rate of electrical signals.Cage polyhedral oligomeric silsesquioxanes(POSS)have excellent dielectric properties,heat resistance,mechanical properties and compatibility,and can be dispersed in polymer matrix by copolymerization,chemical grafting or blending in order to improve the comprehensive performance of the material and effectively reduce the dielectric constant,it has received extensive attention in the electronic communication industry.In this paper,epoxy-based POSS(EOVS)was synthesized from octavinyl POSS(OVS),and the dielectric properties of EOVS on epoxy resin(E51)and epoxy/cyanate resin(E51/BADCy)composites were investigated respectively heat resistance,thermomechanical properties,moisture resistance and toughness.In the E51/EOVS composite system,SEM and EDS results showed that when the EOVS content was less than 15 wt%,it could be uniformly dispersed in the composite.The DMA results demonstrated that the storage modulus of E51/EOVS composites is greatly improved after adding EOVS,from 2842.3 MPa of pure resin to 4660.0 MPa,which is the joint contribution of rigid particles and crosslinking density.Due to the introduction of nanopores,the dielectric constant of the E51/EOVS composite was reduced from 4.21 to 2.51(MHz).It can be seen from the TGA that with the increase of EOVS,the thermal stability of the composite increased.When the addition of EOVS was20 wt%,the T_d10 increases by 9?,and the carbon residue rate reached 26.63%,which is attributed to the inorganic framework of EOVS and crosslinking density.At the same time,due to the hydrophobicity of the Si-O-Si inorganic framework,the E51/EOVS composite had good moisture resistance,and the surface contact angle increased from 84°to 97°.In the E51/BADCy/EOVS composite system,first,the free volume of the network system was compared by positron annihilation lifetime spectroscopy(PALS)to explore the effect of free volume on the dielectric constant.The introduction of EOVS fillers and cyanate esters could increase the free volume of epoxy resin,in favor of reducing the dielectric constant.Secondly,Fourier transform infrared spectroscopy(FT-IR)and electron paramagnetic resonance spectroscopy(EPR)were used to determine the dipole types in the E51/BADCy/EOVS ternary system,and to deeply analyze the effect of microstructure on dielectric loss.The results showed that when the EOVS loading was15%and the mass ratio of epoxy resin and cyanate resin was 1:1,ultra-low dielectric composites(?=2.0,1MHz)were prepared.Elemental energy spectroscopy(EDS)and X-ray diffraction(XRD)displayed that EOVS had good dispersion in the E51/BADCy copolymer.Impact test and scanning electron microscope(SEM)showed that the addition of EOVS could significantly improve the toughness of the composites.With the 10 wt%content of EOVS,the impact strength of E51/BADCy/EOVS composites could be increased by 59%compared with E51/BADCy,and the toughening mechanism of rigid particles was explored.According to thermogravimetric analysis(TGA),the composite with EOVS content of 20 wt%had high thermal stability,and the carbon residue rate at800°C was 33.3%.The immersion experimental data displayed that the water absorption of the composites decreased significantly after the introduction of EOVS.With the increase of EOVS content,the contact angle of the material increased from 75.5°to103.4°,from hydrophilic material to hydrophobic material,and the moisture resistance was greatly improved.