The
new main-chain benzoxazine copolymer oligomers with bulky hydrocarbon
end groups are first designed and synthesized. In particular, the
aliphatic diamine based copolymers owning low dielectric constants
(<3) and ultralow dielectric losses (<0.005) under high frequencies,
is suitable for applications in the field of high-frequency communications.
Therefore, this work not only provides a facile and effective protocol
to simultaneously obtain excellent high-frequency dielectric properties,
and improved processing and thermal properties of benzoxazine resins,
but also widens the scope of the design and synthesis of functional
and high-performance thermosetting polymers.
The effects of the reaction solvent on the preparation, polymerization kinetics, and high-frequency dielectric properties of aliphatic main-chain benzoxazine copolymers were investigated.
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.
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