Synergistic enhancement of toughness and flame retardation for cyanate ester composites through hyperbranched polyborosiloxane

Excellent flame resistance is supposed to be taken into consideration for electronic packaging materials due to the spontaneous combustion of short circuits, except for good mechanical and dielectric properties. Herein, a hyperbranched polyborosiloxane (HPSiB) flame retardant was synthesized via a simple one-pot transesterification as a multifunctional additive for cyanate ester (CE) resin. The HPSiB with many active terminals features good compatibility with the resin matrix, while catalyzing the curing reaction that conducts at a lower temperature. With as little as 2 wt% HPSiB incorporated, the HPSiB/bisphenol A cyanate ester (BADCy) resin achieves a UL-94 V0 rating and 32.4% LOI value, and its peak heat release and total smoke production are simultaneously reduced. Its flexural strength and impact strength were significantly enhanced by 30.0% and 85.4%. Besides, the minimum values of dielectric constant and loss can reach 2.77 and 0.0024 at 10 GHz, which are, respectively, reduced by 7.9% and 88.5%. The integration of unique hyperbranched Si-O-B backbone of HPSiB with CE crosslinked network was responsible for the enhanced overall performance. This work paves a facile strategy to develop multifunctional flame retardant as a promising candidate for the high-performance electronic packaging materials. Highlights: A novel hyperbranched polyborosiloxane flame retardant was synthesized. HPSiB shows good compatibility and catalyzes the curing reaction of CE resin. HPSiB/CE resin with significantly enhanced flame retardancy was obtained. Simultaneously high toughness and low dielectric loss were achieved. Hyperbranched structure containing Si-O-B chains led to the great enhancement.