The influence of macromolecular chains onto reactivity of the grafted functional group has been investigated through reduction of 6-bromohexene using tin hydride soluble polymer supports. Kinetic investigations clearly indicate a retarding effect of the polymer structure on the substrate diffusion. Correlations of molecular weight and degree of functionalization with reactivity of the functional lateral groups are discussed. In dilute regime, an increasing of internal density of the polymer coil leads to a diminution of the rate constant k(H). Thus, the higher density of the coil limits the substrates diffusion, which favors the radical cyclization and so formation of the cyclic product. At the opposite, in concentrated regime formation of the acyclic product, hex-1-ene is favored despite the higher viscosity of such medium that should limit the diffusion. (c) 2006 Wiley Periodicals, Inc.