Structurally well-defined end-functionalized syndiotactic polystyrene (sPS) can be prepared by conducting a simultaneous selective chain transfer reaction during the syndiospecific polymerization of styrene in the presence of vinylsilanes. The production of vinylsilane end-capped sPS involves a unique selective chain transfer pathway via the incorporation of a terminal vinylsilane unit at the polymer chain end by 2,1-insertion. This unusual insertion pattern situates the bulky silyl functional group at a closer beta-position from the active catalyst center, thus deactivating the propagating chain by a steric jam between the vinylsilane end group and the active catalyst. Subsequently, chain releasing by hydrogen addition (in the presence of H-2) or by beta-elimination (in the absence of H-2) can take place, which leads to the production of end-functionalized sPS with precise controls of stereoregularity and of the location of functionality. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1690-1698, 2010