A propylene polymer is coupled with an olefinic interpolymer by a process comprising contacting under reactive processing conditions at least: A. 10 wt % of at least one propylene polymer; B. 10 wt % of at least one olefinic interpolymer; C. 35 wt % of at least one metal hydrate; and D. A coupling amount of a coupling agent, each weight percent based on the combined weight of the propylene polymer, olefinic interpolymer and metal hydrate. Wire and cable insulation sheaths made from compositions comprising the coupled polymer exhibit desirable heat resistance.