Design And Properties Of Styrene-based Low Dielectric Fluorine-containing Silicone Materials At High Frequency

With the development of 5G communication technology,more and more sophisticated devices need higher signal transmission rate and lower signal delay.Dielectric materials with low dielectric constant（low-D_k）and low dielectric loss（low-D_f）have important application prospects in the process of component design and manufacturing required by 5G communication applications.Traditional intrinsic dielectric materials（such as Epoxy resin）can no longer meet the dielectric performance requirements in 5G communication,so it is urgent to have D_k below 2.5 under high frequency conditions.In this thesis,the research progress of low dielectric materials in recent years is summarized,and on this basis,several new fluorine-containing organic low dielectric materials are designed and synthesized by efficient and convenient methods.Organic low dielectric materials have obvious advantages in structural adjustability,stability and processability.The introduction of fluorine atoms with strong electron-withdrawing effect to inhibit the deformation and polarization of charge can effectively reduce the dielectric constant and dielectric loss of polymers.Polysiloxane with high and low temperature resistance,low surface tension,good transparency and adhesion is used as the main chain structure of molecules,and the selected styrene group has high reactivity and can be crosslinked without catalyst or curing agent,including two polymers with trifluoromethyl phenyl as side group and perfluoro fatty chain as side group.（1）Four monomers with different side groups were synthesized by Piers-Rubinsztajn reaction.Under high frequency conditions,the cured resin with larger free volume of trifluoromethyl phenyl and bis-trifluoromethyl phenyl had lower dielectric constant（D_k=2.45）and dielectric loss（D_f=0.002）compared with the cured resin with vinyl and methyl side groups.The highly crosslinked network structure makes these thermosetting polymers show high thermal stability.The weight loss temperature(T_5d)of 5%is over 440℃,and the carbon residue rate can still reach over 40%at the high temperature of 1000℃.All the cured resins have excellent surface hydrophobicity（water absorption is as low as 0.14%）,and they can still maintain stable dielectric properties after soaking in boiling water for 72 h.（2）Saturated perfluoroaliphatic chains have lower polarization than unsaturated benzene rings,which is more conducive to reducing the dielectric constant of materials,and the increase of fluorine-containing groups will further improve the hydrophobic properties of materials.Therefore,we introduced long alkyl chains with different lengths and fluorine content into silicone monomer.Compared with the cured resin containing trifluoromethyl,it was found that the cured resin with perfluoroalkyl chain had a lower dielectric constant,and the dielectric constant decreased to 2.34 with the increase of fluorine content.The perfluoroalkyl chain itself has super-high hydrophobic characteristics,and through the water absorption test,we found that the water absorption of the material decreased to 0.08%.Besides,they also have ideal thermal stability(T_5d>430℃)and high transmittance.