Preparation And Dielectric Regulation Of Polyimides Containing High Dipolar Pendant Groups

Polymer dielectrics with high dielectric constant and low dielectric loss are essential in pulse power devices and advanced electronic applications.Although most polymer materials have low dielectric constant,significant progress in improving the dielectric constant has been made by constructing polymer composite dielectrics.However,due to the high content of nanofillers,dielectric mismatch and interface incompatibility between nanofillers and matrix,polymer composite dielectrics inevitably generate significant dielectric loss.Intrinsic polymers have unique advantages in the development of high dielectric materials due to accurate molecular design.Five types of polarization mechanisms are involved in polymer dielectrics,such as electron polarization,atomic polarization,ion polarization,dipole polarization,and interface polarization.Among them,electronic polarization and atomic polarization are difficult to increase the dielectric constant through structural modification,while ion polarization and interface polarization bring high loss.Dipole polarization has been considered as a promising candidate for polymer dielectrics to increase the dielectric constant and decrease dielectric loss.Incorporating high dipolar groups into the polymer skeleton and utilizing the rotation and orientation of dipolar groups increase the dielectric constant while maintaining low dielectric loss through weak coupling interactions,especially by introducing dipolar pendant groups.Therefore,the development of intrinsic dipolar polymers containing pendant groups is of great research significance for achieving high dielectric and low loss characteristics.In practical applications,these materials are expected to play a key role in high-performance electronic devices and promote the progress of advanced electronic technology.In this paper,numerous novel intrinsic dipolar polyimide dielectrics containing high dipolar pendant groups have been constructed through dipolar glass polymer strategy.By incorporating different dipolar pendant groups,such as sulfonyl,carbamate,and urea groups,into the structure of polymer dielectrics,the influence of different dipolar groups on the dielectric properties of intrinsic dipolar polyimide dielectrics was systematically elucidated.Simultaneously,introducing bulky substituents and twisted structures,such as phenyl and fluorene groups,increases the rotational space of dipolar groups and improves the dielectric properties of intrinsic dipolar polymers.And combining the theoretical simulation,the high dielectric performance of dipolar polyimide dielectrics was further studied.Finally,the potential applications in dielectric capacitors and organic thin film transistors have been further investigated for dipolar polyimide dielectrics with high dielectric constant and low loss.The main research contents are as follows:1.A novel diamine monomer（BSBPA）containing sulfonyl pendant groups was synthesized,then polymerized with dianhydride monomers containing different bridge linkages（ODPA,6FDA,DSDA,BPDA,and BTDA）to prepare a series of dipolar polyimides containing sulfonyl pendant groups.The collaborative control of the sulfonyl pendant groups and the main chain spatial structure enhances the orientation polarization of the polymers,resulting in high dielectric constant of the dipolar polyimides over a wide frequency range.OD-BS achieved a dielectric constant value higher than 5.35 at room temperature and 1 k Hz,higher than the dielectric constant value of OD-DM without side chain polyimide（3.28）,but accompanied by high dielectric loss at high frequencies.The low activation energy obtained by linear fitting of theγrelaxation peak with temperature confirms that sulfone-containing dipolar polyimides present excellent dielectric properties over a wide temperature range,which contributes to achieving excellent energy storage performance.2.The achievement of high dielectric constant inevitably accompanies high dielectric loss,while the small-sized dipolar groups are beneficial for frictionless rotation and can effectively suppress dielectric loss.A novel diamine monomer（BCBPA）containing carbamate pendant groups was prepared and polymerized with ODPA,6FDA,and DSDA dianhydride to prepare soluble dipolar polyimides containing carbamate pendant groups.The small-sized carbamate groups enable dipolar polyimides to exhibit stable dielectric constant and dielectric loss below 0.009 at a wide temperature and frequency.Meanwhile,the lower activation energy also confirms the excellent dielectric properties of dipolar polyimides containing carbamate pendant groups at different temperatures.However,the improvement of dielectric constant is limited by the carbamate group with moderate dipole moment.3.The urea group with high dipole moment and compact size simultaneously is a promising building block to explore high dielectric and low loss materials.A novel diamine monomer（BUBPA）containing urea pendant groups was synthesized and polymerized with ODPA,6FDA,and DSDA dianhydride monomers to prepare soluble dipolar polyimides containing urea pendant groups.The incorporation of high polar urea pendant groups with compact size endows dipolar polyimides with stable high dielectric constant and reasonable low dielectric loss over different frequencies and wide temperature ranges,revealing its superiority in improving the dielectric properties of intrinsic dipolar polymers.The dielectric constant of OD-BU at room temperature and 1 k Hz is 6.14,and the low dielectric loss is 0.0097.The low activation energy obtained by linear fitting ofγrelaxation and temperature ensures excellent dielectric properties of dipolar polyimides containing urea pendant groups in the measured temperature and frequency range,which can be used as high-temperature energy storage materials.In addition,the dipole mobility reflects the limited contribution of dipole polarization to the dielectric constant in polyimide,only 7.5%.4.Increasing the free volume in polymers can effectively improve dipole mobility and further improve dielectric properties.Based on the dipolar polyimide containing urea pendant groups,a series of urea-containing dipolar copolyimides with bulky phenyl groups were prepared by introducing bulky substituents through copolymerization.Compared to dipolar polyimides,the introduction of bulky phenyl group can expand the polymer chain segments,providing a frictionless free rotation space for the dipoles,further increasing the dielectric constant and decreasing the dielectric loss of the dipolar copolyimides.The dielectric constant and dielectric loss of PE-BU are 6.47 and 0.0081,respectively.Meanwhile,the introduction of bulky phenyl group reduces the energy barrier in dipole polymers,endowing them with excellent dielectric properties.Theoretical permittivity simulations further demonstrate that the introduction of bulky phenyl groups can increase the dipole mobility in polymers（10.5%）.The introduction of bulky phenyl structure into dipolar polyimides containing sulfonyl pendant groups confirms its universality in improving dielectric properties.Finally,the urea-containing dipolar polyimides with bulky phenyl groups have been applied to the gate dielectric layer of organic thin film transistors to explore its potential for improving field effect mobility under low voltage operation.The device achieved a high field effect mobility of 4.31 cm² V^-1 s^-1 at-5 V low operating voltage.5.Twisted structures can regulate free volume,thereby improving dielectric properties.Based on the dipolar polyimide containing urea pendant groups,a variety of urea-containing dipolar polyimides with twisted fluorene groups were constructed using copolymerization.Compared with dipolar polyimides,the incorporation of twisted fluorene group enables dipolar copolyimides to achieve frictionless rotation,reduces the activation energy in dipolar polymers,further improving the dielectric constant and reducing dielectric loss.The dielectric constant and dielectric loss of BP-BU_0.7 are 6.37 and 0.0083,respectively.Theoretical permittivity simulation shows that the introduction of twisted fluorene groups increases the dipole migration rate（9.6%）in dipolar copolyimides.The twisted fluorene group was introduced into the dipolar polyimide containing sulfonyl pendant groups,validating its universality.Meanwhile,the addition of free rotation space in intrinsic dipolar polymers to regulate dielectric properties is also supported.Finally,the potential applications of urea-containing dipolar copolyimides with twisted fluorene groups as gate dielectrics have been explored in low-voltage operating organic thin film transistors.The device can achieve excellent performance such as high field effect mobility of 4.09 cm² V^-1 s^-1 at low operating voltage of-5 V.This paper focuses on the introduction of high dipolar groups into the polyimide side chain,such as sulfonyl,carbamate,and urea groups,and utilizes the orientation polarization and dipole-dipole interactions of pendant dipoles to achieve precise regulation of dielectric constant and dielectric loss.Bulky substituents and twisted structures are used to increase free rotation space,achieving frictionless rotation of dipoles and further breaking through the barrier between high dielectric constant and low dielectric loss.This provides a new approach for the design and development of intrinsic high dielectric and low loss dipolar glass polymer dielectric materials,and further explores their potential applications in dielectric capacitors and organic thin film transistors...