A method was developed for free-radical polymerization in the confines of a hollow latex particle. Hollow particles were prepared via the dynamic swelling method from polystyrene seed and divinylbenzene and had hollows of 500-1000 nm. So that these hollow poly(divinylbenzene) particles could function as submicrometer reactors, the particles were filled with a monomer (N-isopropylacrylamide) via the dispersion of the dried particles in the molten monomer. The monomer that was not contained in the hollows was removed by washing and gentle abrasion. Free-radical polymerization was then initiated by gamma radiolysis in the solid state. Transmission electron microscopy showed that poly(N-isopropylacrylamide) formed in the hollow interior of the particles, which functioned as submicrometer reactors. (C) 2004 Wiley Periodicals, Inc.