Silane-grafted polyolefin composition comprising a brominated, flame retardant additive is prepared by a process comprising the step of contacting within a reaction-extrusion zone operated at grafting conditions: A. A polyolefin, B. A hydrolysable unsaturated silane, C. A free radical generator, and D. Halogenated polyaryl alkane, e.g., decabromodiphenyl ethane, such that at least a portion of the hydrolysable unsaturated silane is grafted to the polyolefin. The silane-grafted polyolefin is crosslinked after extrusion from the zone, typically as a wire and cable coating, upon exposure to moisture.