PURPOSE: To provide the titled elastomer having excellent bond strength to acrylonitrile resins, consisting of a specified block copolymer elastomer.

CONSTITUTION: 90W45wt% conjugated diene compd. (e.g. butadiene) and 10W 55wt% arom. vinyl compd. (e.g. styrene) are copolymerized in the presence of an organolithium compd. catalyst in a hydrocarbon solvent. If desired, the resulting copolymer is reacted with a bi- or polyfunctional coupling agent (e.g. CCl4) to obtain a block copolymer elastomer having a number-average MW of 10,000W 1,000,000 and the formula (wherein A is an arom. vinyl polymer block; B is a diene polymer block; n is at least 1). Not more than 100pts.wt. resin (e.g. coumarone/indene resin or a petroleum hydrocarbon resin), an org. peroxide, an antioxidant, a filler, etc. are blended with 100pts.wt. said elastomer.