Disclosed herein is a functionalized block copolymer comprising (a) at least one end block D comprising on average at least one amino- or phosphino-functionalized polymer unit of formula (I) and one or more additional blocks selected from the group consisting of (b) one or more A blocks substantially free of amino- or phosphino- functional groups and having a number average molecular weight of from about 1,000 to about 60,000, and has a high service temperature, and (c) one or more B blocks, wherein each block B is essentially non-functionalized, has a number average molecular weight of from about 1,000 to about 1,000,000, and has a glass transition temperature of at most about 20° C., and (d) mixtures of one or more A blocks and one or more B blocks; wherein Z is nitrogen or phosphorus; R1 is hydrogen or alkyl; R2 is hydrogen or is tertiary alkyl; R each independently, is alkyl or phenyl optionally substituted by a moiety -(A1-NRa)xRb or -(A1-ORa)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.