Selectively amino- or phosphino-functionalized block copolymers, and their preparation, for use as anion exchange membrane materials. The selectively functionalized block copolymers have at least two end blocks A each of which are substantially free of amino- or phosphino-functional groups, and have at least one interior block D which comprises at least one amino- or phosphino-functionalized polymer unit of formula (I) wherein Z is nitrogen or phosphorous; R1 is hydrogen or alkyl; R2 is hydrogen or is tertiary alkyl; R each independently, is hydrogen or is alkyl optionally substituted by a moiety -(A1-NRa)xRb; or two R groups, together with the Z to which they are bonded, form an optionally substituted ring; x is 1, 2 or 3; A1 is straight chain alkylene optionally substituted by one or more methyl and/or ethyl groups; and Ra and Rb, each independently, is hydrogen or alkyl; or a corresponding onium salt.