The synthesis and characterization of novel thermoplastic elastomers consisting of multiple polystyrene-b-polyisobutylene (PSt-b-PIB) arms emanating from cyclosiloxane cores is described. The synthesis involved the sequential living cationic block copolymerization of styrene (St) and isobutylene (IB), followed by quantitative allylic end-functionalization of the living PSt-b-PIB+ to produce PSt-b-PIB-CH2- CH=CH2 prearms, and finally Linking by hydrosilation of these prearms with Si-H-containing cyclosiloxanes (e.g., 2,4,6,8,10,12-hexamethylcyclohexasiloxan D-6(H)). Two types of star-blocks, namely primary and higher-order star-blocks, mere prepared : Primary star-blocks containing 3-9 PSt-b-PIB arms were obtained by using various cyclosiloxanes (D-6(H) to D-12(H)) and a dose to exact stoichiometry between the Si-H and allyl groups, [Si-H]/[C=C] similar to 1, in the essential absence of moisture ([H2O] similar to 100 ppm). Higher-order star-blocks consisting of 13-24 PSt-b-PIB arms radiating from complex coupled cyclosiloxanes were prepared by the use of Si-H/allyl ratios significantly larger than unity ([Si-H]/[C=C] = 2-3) in the presence of controlled amounts of moisture ([H2O] similar to 600 ppm). Reaction conditions (temperature, concentration, stoichiometry, solvent nature, catalyst concentration, etc.) for efficient syntheses have been developed. The products were characterized by 200 and 600 MHz H-1-NMR spectroscopy and triple-detector (RI, UV, LLS) GPC. The microstructure of the condensed cores in the higher-order star-blocks was studied by 2D-NMR (HMQC) spectroscopy, and the number of cyclosiloxane rings in the cores (i.e., the content (wt %) of cores in the star-blocks) was determined.