Controllable Confinement Nano-Reinforced Organic–inorganic Cyanate Ester Resins with Optimal Modulus and Dielectric Properties Trade-Offs

Nano-reinforced resins are widely used in the aerospace field, but the improvement of the mechanical properties of nano-modified resins is always low or they are even decreased due to the unsatisfactory dispersion and interfacial properties of nano-fillers. A monofunctional polyhedral oligomeric silsesquioxane (POSS) after recrystallization is introduced into a cyanate ester (CE) by pre-reacting with epoxy to form an organic–inorganic hybrid crosslinking network for performance enhancement. The size of POSS aggregates in the CE decreased after recrystallization and pre-reaction, improving the dispersion into the crosslinking network. The effects of the microstructure and reaction route of the POSS on the crosslinking network are evaluated across the synthesis of pendant and telechelic POSS moieties. Results reveal that only when the size of the monofunctional POSS aggregates and the POSS–polymer configuration match the crosslinking network, can POSS simultaneously introduce free volume due to the nanocore while restricting the chain mobility. Through the comprehensive utilization of the physicochemical properties of POSS for the confinement of POSS in the resin, the CE modified with pendant POSS moieties exhibits a superior modulus (4033 MPa), higher glass transition temperature (271.2 °C), and improved dielectric properties at 3 wt% loading of POSS. This effective strategy is proposed to regulate the interactions between inorganic nano-fillers and organic crosslinking networks, which provides guidance to achieve a simultaneous enhancement in thermosetting resin stiffness and dielectric properties.