A methacrylate-functionalized, cyclic poly(tetrahydrofuran), poly(THF) (1m), has been synthesized and copolymerized through a free-radical mechanism involving methyl methacrylate (MMA) and using 2,2 ' -azobisisobutyronitrile as the initiator in benzene at 65 degreesC. A copolymer product with cyclic poly(THF) branches was produced initially, with gelation taking place at a later stage of the reaction. In contrast, no gelation was observed either in the quantitative-conversion copolymerization of a related methacrylate-functionalized, open-chain poly(THF) with MMA or in the quantitative homopolymerization of MMA in the presence of a methacrylate-free, cyclic poly(THF). These results demonstrate that the propagating polymer segment threaded the large but constrained cyclic polymer branches covalently attached to the polymer backbone, to produce a novel polymer network architecture having both covalent and physical linkages.