Anionic copolymerization of a mixture of 2-(1-adamantyl)-1,3-butadiene (1) and isoprene was carried out with sec-BuLi in cyclohexane at 40 degrees C. The resulting random copolymers possessed the predicted compositions and molecular weights based on the molar ratios between comonomers and initiator and the narrow molecular weight distributions. The both repeating units of poly(1) and polyisoprene contained 1,4-rich microstructures. The resulting copolymer having 1,4-polydiene units was completely converted into a novel saturated terpolymer, poly(ethylene-ran-propylene-ran-1-vinyladamantane) (P(E-ran-P-ran-VAd) by the hydrogenation with p-toluenesulfonhydrazide. The T(g) values of hydrogenated polymers could be changed from -66 degrees C to 122 degrees C by the feed molar ratio of comonomers. A novel well-defined saturated ABA triblock copolymer possessing all alternating polymer segments, P(E-alt-VAd)-b-P(E-alt-P)-b-P(E-alt-VAd), was similarly synthesized by the sequential copolymerization of 1 and isoprene and the following hydrogenation. The microphase separation behaviors of this new thermoplastic elastomer carrying bulky adamantyl groups in the hard end segments were analyzed by dynamic mechanical analysis and transmission electron microscopy. (C) 2009 Elsevier Ltd. All rights reserved.