An original design strategy for the
preparation of thermosetting
resins with both super-high-frequency low dielectric constant (k) and low dielectric loss (f) as well
as high glass transition temperature (T
g) values is presented. The key to this design strategy is incorporating
a bulky group and reactive furan ring to increase the free volume
and the cross-linking density, respectively. The formed multistructural
networks (relatively dense near furan rings and relatively loose near
bulky groups) are beneficial not only for lowering k values but also for maintaining high T
gs of main-chain benzoxazine copolymers. More importantly, the optimized
copolymers possess low f values (≤0.008) under
5 and 10 GHz, satisfying the requirement of super-high-frequency communications.
The correlations between the free volume and thermal and dielectric
properties are also discussed to understand the synergistic mechanism.
The work opens a new route for the structural design and preparation
of super-high-frequency low dielectric functional polymeric materials.
Poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as a kind of low dielectric polymer has been applied in telecommunications. However, developing PPO based thermosetting resins with good comprehensive properties is highly challenging. Herein, an interpenetrating polymer network (IPN) design strategy for the preparation of methacrylate‐terminated oligo(2,6‐dimethyl‐1,4‐phenylene oxide) (SA9000) based thermosetting resins is presented. Two series of prepolymers are prepared by blending bisphenol A/furfurylamine benzoxazine (B‐f) or bisphenol A/aniline benzoxazine (B‐a) with SA9000. Then the IPN films are fabricated by the programmed temperature rising method with simultaneous polymerization reactions of both SA9000 and benzoxazines. Owing to the intermolecular interactions between SA9000 and benzoxazines, the polymerization peak temperatures of all prepolymers are lower than those of SA9000 and benzoxazines. In comparison with B‐a based films, B‐f/SA9000 films display better miscibility and higher thermal resistances over the entire composition range, due to the strengthened hydrogen bonding and higher cross‐linking density resulting from the presence of furan ring of B‐f. Specifically, B‐f/SA9000 films possess the advantages of low dielectric constants (2.296–2.475) and low‐loss grade dielectric losses (0.00550–0.00683) at 10 GHz. The current work provides a simple and effective path for the fabrication of high‐performance thermosetting PPO resins based on benzoxazine chemistry and IPN structure design.
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