With the popularization of 4G communication technologies and the continuous development of 5G communication technologies, higher-frequency communication technologies (6G, 7G...10G) will be the future development trend, and the demand for corresponding high-frequency low-dielectric materials is also growing. The high-frequency low-dielectric material needs to satisfy low dielectric constant and dielectric loss under high-frequency conditions. In addition, the material itself should meet application conditions such as low water absorption, high heat resistance, mechanical properties, and excellent processability. Fluoropolymers have good low dielectric properties at high frequencies, such as polytetrafluoroethylene (PTFE), but due to their molecular inertness, their processing performance is poor and they need to be etched on their surface. Increase the adhesion with the copper foil for further application. Therefore, it is of great significance to develop easily processed and high-performance fluorine-containing low dielectric materials.
Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai Institute of Organic Chemistry, Key Laboratory of Functional Synthesis and Assemblies of Organic Chemistry, Fang Qiang's Research Group conducted a systematic study in this area, using the heat-cyclable nature of trifluorovinyl ether to develop a thermally crosslinkable composition. Fluoropolymers, and in the near future made a series of research results. By designing a multi-functional (>3) macromonomer strategy, the chain growth of the polymer proceeds in a plurality of directions, effectively avoiding the defect that the trifluorovinyl ether monomer is difficult to form a high molecular weight polymer. This strategy can not only improve the processability of fluoropolymers, but also obtain good insulation, heat resistance, and transparency. In the synthesis method of trifluorovinyl ether, the use of a strong alkaline and weak nucleophilic lithium 2,6-dimethyl hydrazine (LTMP) for the elimination reaction of tetrafluoroethyl ether is simple and convenient. Tetra-substituted trifluorovinyl ethers of tetraphenylmethane (TPM-TFVE) were prepared in high yield. The molecule has a tetrahedral skeleton, and a fluoropolymer having a microporous structure can be obtained by thermal crosslinking. The polymer exhibits excellent dielectric properties, its dielectric constant is less than 2.29 below 10 MHz, and its dielectric constant and dielectric loss at high frequency of 5 GHz are 2.36 and 1.29×10-3, respectively, superior to conventional ones. Commercial Low Dielectric Materials (Macromolecules 2016, 49, 7314).
Silsesquioxanes (POSS) are nanomaterials with unique cage structures that are often incorporated as additives into polymers to improve their mechanical and dielectric properties. However, the study of functionalization of fluorine by POSS is less, mainly due to the lack of an effective method of direct fluorination. After exploration, the research group adopted a highly efficient platinum-catalyzed hydrosilylation reaction, in which a one-step reaction was to introduce fluorine-containing groups into the POSS to achieve fluoroalkylation and functionalization of POSS. This method makes both insoluble and refractory POSS both soluble and meltable, and the novel organic-inorganic hybrid material sheets and films obtained by thermal polymerization exhibit high transparency and excellent dielectric properties under high frequency conditions ( The dielectric constant at 2.5GHz is 2.51 and the dielectric loss is 3.1x10-3. Even in wet environments, this hybrid material maintains stable dielectric properties, creating conditions for the potential use of this material in high-frequency communications (ACS Applied Materials & Interfaces 2017, 9, 12782).
The research group found that Si-OH groups are generated during the hydrolytic condensation of organosiloxanes, and the flexible -Si-CH2-CH2- segments are also generated during the hydrosilylation reaction. The presence of these groups and segments is The dielectric properties and thermal stability of polysiloxanes at high frequencies have an adverse effect. In order to solve this problem, the research group carried out the fluorine functionalization of the basic industrial raw material tetraethylorthosilicate (TEOS) through one-step Piers-Rubinsztajn reaction. The in-situ formed fluorine-containing organosiloxane macromonomer can be formed after thermal polymerization. A transparent film exhibiting a dielectric constant of 2.50 and a dielectric loss of 4.0*10<-3 > at an ultra-high frequency of 10 GHz, while an ordinary unporous silica film and a polyorganosiloxane are introduced. The electrical constant is usually greater than 3.0 (Macromolecules 2017, 50, 9394).
The research work was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Chinese Academy of Sciences' strategic pilot technology project (Class B).
Figure 1. Synthesis of tetrafunctional trifluorovinyl ether monomers and polymers.
Figure 2. Preparation of organic-inorganic hybrid fluorine-containing POSS.
Figure 3. Preparation of fluoroorganosiloxane macromonomers and polymers based on TEOS.
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