The main objective of this work focused on the chemical modification of polyamide 12 (PA12) properties through the reaction with a hydride-terminated polydimethylsiloxane (PDMS-SiH). The investigated PA12/PDMS-SiH blend was compatibilized by ruthenium derivative catalyzed hydrosilylation reaction in molten state. This original route enhanced interfacial adhesion and avoid PDMS-SiH leaching phenomenon between the two immiscible phases. More specifically, the size of PDMS-SiH domains in the blend decreased from around 4 m to 800 nm and from 30 to 1 m after compatibilization with 10 and 20 wt % PDMS-SiH, respectively. For the best compatibilized PA12/PDMS-SiH blend, the introduction of PDMS lowered the surface free energy and the PA12-based blend turned from hydrophilic to hydrophobic behavior, as evidenced by the water contact angle measurements. Gas permeability and CO2/H-2 and CO2/He gas selectivity were also improved with the increase in PDMS content. Besides, the mechanical properties were enhanced with 13% increase in Young's modulus after in situ compatibilization with 15 wt % PDMS-SiH. Thermal stability was also improved after compatibilization as the initial degradation temperature of reactive blends obviously increased compared with nonreactive ones. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 978-988