SynopsisPoly(2,6-dimethyl-l,4-phenylene oxide) has been crosslinked in the presence of large poly(dimethylsiloxane) cyclics (92 repeating units). Approximately 26% by weight of the cyclics were threaded and permanently captured by the polymer network forming a topological isomeric structure referred to as a polymeric catenane. Nonentrapped cyclics were extracted with chloroform. Chemical analyses and micrographs showed evidence for crosslinking and cyclic entrapment, while physical testing demonstrated distinct differences in physical properties such as the glass transition temperature, ultimate mechanical properties, and dynamic viscoelastic response between the crosslinked control samples, and those containing cyclic poly(dimethylsi1oxane). EXPERIMENTAL MaterialsPoly(2,6-dirnethyl-l,Cphenylene oxide), polymer I, was supplied by the General Electric Company. A sharp fraction of cyclic poly(dimethylsi1oxane) [(CH,),SiO), (PDMS)] was obtained from a ring-chain equilibrate using