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The main-chain benzoxazine copolymers (MCBCs) based on bisphenols, diamines, and capping monophenols have been increasingly explored in the field of high-frequency communication. However, the optimization of chemical structures and high-frequency low dielectric properties has still not been investigated. Herein, the key to structural design is incorporating low polar and bulky groups into monophenols, enlarging the chain lengths of aliphatic diamines, and introducing bulky bridging groups into bisphenols to decrease the oxazine ring concentrations of oligomers. The strategy is effective to decrease the oriental polarization, leading to the reduction of the dielectric constants (k) and dissipation factor (f) values of MCBCs. Besides, both the k and f values of MCBCs can be regulated by polymerization conditions owing to the strong hydrogen bonding formed during polymerization, which is also beneficial to reduce the oriental polarization. In view of the synergistic effect of the optimized chemical structure and polymerization conditions, the fabricated MCBCs show excellent dielectric properties (k < 2.4, f < 0.005) at 10 GHz. Therefore, the optimization strategies for both structural design and polymerization conditions are favorable to obtain high-frequency low dielectric benzoxazine resins, which possibly could be extended to other low dielectric resins.
Zeng et al. (Thu,) studied this question.