Preparation And Properties Of Cross-linked Polyetherimide /Oolyetheretherketone Polymer Blends

Dielectric materials are the foundation of modern electronics industry.They are mainly used for insulation coating,electronic packaging,energy storage/conversion,etc.,and are widely used in aerospace,defense and military industry,electrical and electronic,and automotive industries.Compared with ceramic materials,polymers as dielectric material have higher breakdown field strength and lower dielectric loss（the key properties of most dielectric materials）,and have the characteristics of light weight,easy processing and good flexibility,so polymers have attracted more and more attention.However,most polymers have low working temperature,limited by their own thermal properties.Then they cannot meet the requirements for high-temperature environments such as new energy,aerospace,defense and military industry,and deep-sea and deep exploration.The development of high-temperature,high-performance polymer-based dielectric materials is still a challenge,that meet the needs of electronics industry applications.Polyetheretherketone（PEEK）has excellent mechanical and thermodynamic properties due to its benzene ring structure and crystallization ability.It is one of the most promising high-temperature polymer dielectric materials.However,the motion of molecular segments in the amorphous region at high temperature and high field will lead to the relaxation of polymer segments,and this relaxation will reduce the dielectric properties of PEEK.In this paper,from the perspective of molecular design,self-crosslinking polyetherimide（c-PEI）containing phenylethynyl group was prepared,and PEEK-based polymer blends was prepared by blending modifying.A cross-linked network of polyetherimide was constructed,taking advantage of the good compatibility between polyetherimide and polyetheretherketone.Then the relaxation of molecular segments in the amorphous region of polyetheretherketone under high temperature and high electric field is restricted,improving the dielectric stability of PEEK.The main research contents and important results obtained are as follows:1.The self-crosslinkable polyetherimide（c-PEI）terminated by phenylacetylene group was prepared by polycondensation reaction and simple end-capping technology.By adjusting the molecular weight（crosslinking group content）of c-PEI,the cross-linking temperature has been matched with the processing temperature of PEEK.And a series of c-PEI/PEEK polymer blends are prepared by mechanical blending,extrusion granulation and thermoforming formation.Then the balance of processability and other properties is achieved through the control of the degree of crosslinking.Compared with commercial polyetherimide（s-PEI）/PEEK polymer blends,the c-PEI/PEEK polymer blends have more excellent thermal properties,mechanical properties,electrical properties,due to the construction of the cross-linked network suppressing the relaxation phenomenon caused by the movement of molecular segments in the amorphous region.In addition,the small amount of c-PEI added can reduce the influence on the crystallization behavior of PEEK,which is beneficial to maintain the excellent properties of PEEK itself.The dielectric loss of 20 wt%c-PEI 10/PEEK is only 0.0019 at 160 ^oC and 1 k Hz,which is smaller than 0.0134 for PEEK and 0.0075for 20 wt%s-PEI/PEEK.2.Against the problem that the construction of the cross-linking system leads to the decrease of the dielectric constant of the c-PEI/PEEK blends,this study further modified the c-PEI/PEEK blends with nano-alumina（Al₂O₃）,by adding a trace amount of nano-alumina to the c-PEI/PEEK blends.Then the dielectric constant of c-PEI/PEEK blends are increased,while ensuring other comprehensive properties（especially dielectric stability）,by using the nano-effect to increase the space for the polarization rotation of the dipole under the electric field.Among them,0.5 wt%of nano-alumina modified cross-linked polyetherimide/polyetheretherketone polymer blends（0.5 wt%Al₂O₃@20 wt%c-PEI 10/PEEK）has the highest dielectric constant（4.11）and lower dielectric loss（0.0041）at 160 ^oC,1k Hz.In summary,the blend modification of cross-linked polyetherimide to polyetheretherketone can significantly improve the thermal,mechanical and electrical properties,on the premise of maintaining the crystallization behavior of polyetheretherketone.The addition of trace nanoparticles can improve the dielectric constant of the blends while ensuring other properties.Under the synergistic effect of the two modification methods,the dielectric properties of polyetheretherketone at high temperature are greatly improved,so that the polyetheretherketone blends have great application potential in the field of high temperature dielectric materials.