A block copolymer, adapted to self-assemble to form an ordered pattern on a substrate, has first and second blocks with a terminal moiety covalently bonded to the end of the first block. The molecular weight of the terminal moiety is 20% or less than that of the block copolymer and the terminal moiety has a low chemical affinity for the first block. The terminal moiety can assist the accurate positional placement of the domains of the ordered array and lead to improved critical dimension uniformity and/or reduced line edge roughness. The polymer may be useful in combination with a graphoepitaxy template, where the terminal moiety is chosen to associate with a sidewall of the template. This may reduce undesired aggregation of polymer domains at a sidewall and/or assist in domain placement accuracy.