• A novel copolymer PDVB-co-PACl is synthesized and grafted onto AlN, significantly improving its hydrolysis resistance and interfacial compatibility with PMHS matrix.
• Optimal grafting (molecular weight 5100 g mol−1, density 0.8 wt%) yields composites with thermal conductivity of 1.14 W m−1 K−1, a 420% enhancement over pure PMHS.
• The functionalized AlN/PMHS composites retain 99.1% of their thermal conductivity after 80 h in 90 °C water, demonstrating exceptional hydrothermal aging resistance.
• This work provides a promising strategy for developing highly thermally conductive and durable polysiloxane composites for thermal interface applications.