Tough epoxy/cyanate ester resins with improved thermal stability, lower dielectric constant and loss based on unique hyperbranched polysiloxane liquid crystalline

Toughening thermally resistant resin without sacrificing outstanding performances of original resin is still a big challenge. Herein, a novel liquid crystalline hyperbranched polysiloxane (LCPSi) with wide transition temperature range and terminal amino groups was facilely synthesized, which was then used to toughen epoxy (EP)/cyanate (CE) ester (the weight ratio of EP to CE is 1:9, coded as eCE). Results show that a small addition of LCPSi can remarkably improve the integrated performances of eCE resin including toughness, stiffness, thermal and dielectric properties. For example, the impact strength and flexural modulus of 1.5LCPSi/eCE resin (with 1.5 wt% LCPSi) are 2.3 and 1.5 times of those of eCE resin, respectively; meanwhile the initial thermal decomposition temperature (Tdi) at which the weight loss of the sample reaches 5 wt% of the former is 18.9°C higher than that of the latter; moreover, both dielectric constant and loss decrease. Those attractive performances demonstrate that LCPSi is a multi‐functional modifier of eCE resin. The origin behind was intensively discussed through the structure–property relationship.