The ABA-type triblock copolymers consisting of poly(2-adamantyl vinyl ether) [poly(2-AdVE)] as outer hard segments and poly(6-acetoxyhexyl vinyl ether) [poly(AcHVE)], poly(6-hydroxyhexyl vinyl ether) [poly(HHVE)], or poly(2-(2-methoxyethoxy)ethyl vinyl ether) [poly(MOEOVE)] as inner soft segments were synthesized by sequential living cationic polymerization. Despite the presence of polar functional groups such as ester, hydroxyl, and oxyethylene units in their soft segments, the block copolymers formed elastomeric films. The thermal and mechanical properties and morphology of the block copolymers showed that the two polymer segments of these triblock copolymers were segregated into microphase-separated structure. Effect of the functional groups in the soft segments on gas permeability was investigated as one of the characteristics of the new functional thermoplastic elastomers composed solely of poly(vinyl ether) backbones. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1114-1124