Anionic polymerization of methacrylates under sterically confined environment in a spherical beads-shaped networked. polystyrene (NwPS) matrix is described. The initiator used herein is a samarium (Sm) (III) enolate, which was formed by treatment of 2-bromoisobutylate immobilized in the side chain of NwPS with Sm (II) iodide. By using this NwPS-bound initiator, polymerization of a series of methacrylates (=solid-supported polymerization) was studied to find its two aspects: (1) In the early stages, the rate constant for each methacrylate was comparable to that for its conventional solution-phase polymerization using a Sm (III) enolate, suggesting that methacrylate can be efficiently supplied to the propagating end by its free permeation without any interference by the networked structure of the matrix. (2) After the early stages, the rate constant decreased remarkably, implying that permeation of methacrylate was sterically interfered by the formed poly(methacrylate) that filled the confined space in NwPS, as supported by a SEM image of the resulting beads, of which pores were filled with the formed polymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1510-1521, 2009