The 5th generation mobile communication technology (5G) requires materials with high reliability, high dimensional stabilities, and low dielectric constant (D k) and low loss factor (D f). However, achieving both high dimensional stabilities and low dielectric is difficult. In this work, we propose a strategy to improve dimensional stabilities of printed circuit board (PCB) substrates without reducing their dielectric properties by introducing crosslinking agents with trifluoromethyl groups and allyl groups to polymers. Polyphenylene oxide (PPO) was selected as the representative research object, and a series of cured PPO-Allyl-F with varying contents of trifluoromethyl and allyl side chains were designed and synthesized. The molecular structures of the thermosetting PPO were characterized using 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. The isothermal curing kinetics of the thermosetting PPO were monitored with in situ FTIR. The thermal stability, mechanical properties, glass transition temperature (T g), coefficient of thermal expansion (CTE), and dielectric properties of the cured PPO-Allyl-F materials were investigated in detail. The results show that the obtained thermosetting PPO with improved dimensional stabilities and low dielectrics has great potential for the application in high-frequency electronic circuits. This work provides a new approach for developing high-performance polymers that can address the contradiction between dielectric properties and dimensional stability.

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Soft, stretchable, tough, and adhesive elastomers are developed based on the metal‐ionic crosslinked double network structure, where the metal ion coordination of sulfonated poly(phenylene oxide) (SPPO) is used for the first network and the soft chemical crosslinked poly(ethyl acrylate) (PEA) is used for the second network. The influence of SPPO content on the tensile, cyclic tensile, adhesive, and rheological behavior of the elastomers is systematically investigated. It is observed that the elastomers are immensely soft and stretchable with tunable modulus from 0.038 to 0.086 MPa, fracture strain of ≈1400%, fracture stress in the range 0.20–1.2 MPa, work of extension of 0.72–5.6 MJ m−3, fast self‐recovery of 5 s after experiencing 200% strain, and robust adhesive behavior on glass substrates with interface debonding energy ≈35.2 J m−2. The mechanical behavior of the double‐network elastomers at the macroscopic scale is related to the dynamic breaking and reforming of the metal‐ion coordination at the molecular scale in the first network. This study provides a facile approach for the synthesis of elastomers with multidimensional mechanical behavior and broadens the applications of the elastomers in the field of flexible electronic devices, soft robotics, among others.

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