To produce a blend exhibiting excellent heat-resistance over a long period and having excellent thermal aging performance and compressing set resistance by compounding an acrylonitrile/butadiene copolymer bonded with an antioxidant with a polyvinyl chloride having an ultra-high molecular weight.

The objective resin has a heat-resistance of 135°C and contains (A) 75-25wt.% of a polyacrylonitrile/butadiene containing 28-33wt.% of acrylonitrile and stabilized by a bonded antioxidant and (B) 25-75wt.% of a polyvinyl chloride having an intrinsic viscosity of >1.5 in cyclohexane at 30°C. The component A can be produced usually by dissolving a monomer bonded with an antioxidant such as N-(4-anilinophenyl)methacrylamide in a small amount of acrylonitrile, pouring the solution into a polymerization solution of acrylonitrile and butadiene with a pump and polymerizing the monomers.