Novel stars of many polyisobutylene(PIB) arms radiating from a core of condensed methylcyclosiloxanes are described. The synthesis involves hydrosilation of allyl-terminated PIB prearms by small methylcyclosiloxanes (e.g., D-4(H), DBH) and competitive moisture-mediated core-core coupling. The effect of conditions (e.g., time, temperature, stoichiometry, nature and molecular weight of prearms, and size of methylcyclosiloxane) on synthesis was investigated. The processes can be controlled and well-defined 21-28 arm stars have been perpared. Microstructures were characterized by various techniques. The intrinsic viscosities of stars are much lower than those of linear PIBs of the same molecular weight over the 30-100 degrees C range. Branching coefficients depend on the number of arms. Hydrodynamic volumes of stars and combs (polysiloxane backbone carrying PIB branches) are similar, indicating that both assume radial conformations. The stars are resistant to strong acids and bases indicating that resistant PIE coronas protect acid- and base-vulnerable cores. The temperature resistance of stars is similar to that of PIB.