Design,Synthesis,and Properties Of Side-Chain Dielectric Polymers Modified By Sulfone Groups

With the advantages of easy processing,good flexibility,high power density and fast charge and discharge speed,polymer film capacitor is one of the indispensable key energy storage components in electronic power system.However,the traditional commercial polymer dielectrics can not meet the requirements of high energy density or miniaturization of modern electronic components because of their low dielectric constant.Therefore,how to develop polymer dielectrics with high dielectric constant(),low loss(tan?)and high energy density(U_d)through structural design is a research difficulty that needs to be overcome.Based on the point of view of molecular structure design,this paper regulates the side chain structure of two kinds of side chain dielectric polymers with different main chains,in addition to introducing sulfone functional groups with large dipole moment,respectively,the characteristics of shell liquid crystal polymers and?-?stacking interaction are used to adjust the distribution of dipoles.The effects of side-chain structure on the phase behavior,phase structure,dielectric properties and energy storage of side-chain dielectric polymers were investigated systematically.The specific research contents are as follows:(1)Side-chain polymer dielectrics with polystyrene as the main chain:two kinds of side-chain sulfonyl-containing dipolar polymers based on polyolefin main chains,poly{2,5-bis[(4-(methylsulfonyl)phenyl)oxycarbonyl]styrenes}(PBSO₂)and poly{2,5-bis[(4-(methylsulfonyl)ethyl)oxycarbonyl]styrenes}(PESO₂),were prepared via radical polymerization.The results showed that PBSO₂possessed a high glass transition temperature(T_g?195°C)and formed the columnar nematic phase owing to the rigid side chain structure.A dielectric constant of 20.8(25°C,10³Hz)was obtained for the polymer PBSO₂ due to the highly orientational polarization and the possible interfacial polarization between the amorphous phase and liquid crystalline phase,which is 18%higher than that of PESO₂.However,PBSO₂ exhibited a low breakdown strength(?60 MV/m)because of the low band gap and brittleness of the film.As a result,the maximum U_d for PBSO₂ is only 0.34 J/cm³,while a U_d of 6.2 J/cm³ for PESO₂ was achieved at 270 MV/m.(2)Side-chain polymer dielectrics with polynorbornene as the main chain:Two kind of sulfonyl-containing poly(norbornene)s were synthesized by ring-opening metathesis polymerization(ROMP),which were Poly(2-(4-(methylsulfonyl)butyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-dione)(denoted as PTMD-SO₂)and Poly(2-(4-((4'-(4-(methylsulfonyl)butoxy)-[1,1'-biphenyl]-4-yl)oxy)butyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-dione)(denoted as PBTMD-SO₂).XRD results show that both polymers are amorphous,but the order degree of molecular for PBTMD-SO₂ with biphenyl side groups is greatly increased.The permittivity of PBTMD-SO₂ with the biphenyl side groups was as high as 11.0 at 25°C and 1 k Hz,which was nearly 34%higher than that of PTMD-SO₂ due to the large dipole moment of the sulfonyl groups.In addition,the dielectric loss in the range of 100 Hz-10 MHz decreased from 0.054-0.174 for PTMD-SO₂ to 0.045-0.080 for PBTMD-SO₂.Polarization-electric field loops studies indicated that the discharge energy density of PBTMD-SO₂ reached 1.25 J/cm³ at 150 MV/m,which exceeded the discharge energy density of PTMD-SO₂ at 173 MV/m of 1.08 J/cm³.These results show that the use of the?-?stacking interaction of side chain groups can effectively enhance the orientational polarization of dielectric polymers and thus improve their dielectric properties.