Eco-inspired multifunctional cyanate ester-epoxy resin blends for high-thermal, flame-retardant, and hydrophobic applications

The present work deals with the development of new type of cyanate ester-epoxy resin hybrid blends using four different types of cyanate esters derived from bio-based phenolic precursors and fossil-based phenolic precursors through simple synthetic path appropriate for low dielectric constant, thermal, flame-retardant behaviour and hydrophobic applications. The multifunctional cyanate esters (CEs), cardanol and benzaldehyde-based CE (CBC), cardanol and terephthalaldehyde based CE (CTC), imidazole bisphenol-based CE (IMC), and phenol and 4-hydroxybenzaldehyde based CE (HTC) were produced using phenolic derivatives and cyanogen bromide under appropriate experimental conditions. Later, the synthesized CEs were blended with two types of epoxy resins, bio-based cardanol- bisphenol epoxy resin (CBE) and fossil-based bisphenol-F epoxy resin (BFE) and the hybrid blends obtained were cured through thermal polymerization in the absence of any catalysts. The blends are designed to achieve moderate cure behaviour, enhanced thermal stability, high char yield, exceptional flame retardance, lower value of dielectric constant and dielectric loss, higher water contact angle, and low moisture absorption compared to those of individual cyanate esters or epoxy resins. The curing temperature of cyanate ester-epoxy resin blends in the absence of catalyst are ranged between 148 °C and 215 °C. Among them, HTC/BFE blend was found to be the most efficient hybrid system and which holds the maximum value of char yield of 32.8 %. The values of dielectric constant of cyanate ester-epoxy resin blends are observed between 2.9 and 3.6 at 1 MHz. Similarly, the values of dielectric loss are ranged between 0.02 and 0.005 at 1 MHz. The value of water contact angle of cyanate ester-epoxy resin blends is found to be in the range between 142° and 148°. Further, the developed HTC/BFE cyanate ester-epoxy resin hybrid blend possesses the flame-retardant behaviour of V0 rating. The cyanate ester-epoxy resin blends developed in the present work is considered as cutting-edge concept in the field of cyanate ester-epoxy hybrid technology suitable for production of printed circuit board (PCB) with better performance, also used in the form of adhesives, sealants, encapsulants, matrices for microelectronics insulation applications. • Developed of new type of multifunctional cyanate ester-epoxy resin blends using bio-based phenols and fossil-based phenols. • Cyanate ester-epoxy resin blends showed improved thermal stability, achieving a high residual char of 32.8 %. • Developed CE/EP blend exhibited the higher value of water contact angle (145°). • Developed CE/EP blend exhibited the low dielectric constant value of 2.9 with dielectric loss of 0.005. • Developed CE/EP blend exhibited the enhanced flame resistance properties of V0 rating from UL-94.