A pentamethylcyclotrisiloxane moiety was introduced into cyclic polystyrene (cPSt) and cyclic PDMS (cPDMS) to obtain noncovalent cross-linking agents, D-3-cPSt and D-3-cPDMS, respectively. Anionic ring-opening polymerization of octamethylcyclotetrasiloxane (D-4) in nitrobenzene was carried out in the presence of D-3-cPSt to obtain a cloudy white PDMS gel as a precipitation. On the other hand, bulk copolymerization of D-3-cPDMS with D-4 proceeded in a homogeneous state to give a colorless transparent PDMS gel in high yield. The formation of mechanically linked PDMS with movable cross-linking was indicated by control experiment. (c) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5882-5890, 2009