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., D4 H , D6 H ) 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 °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 PIB coronas protect acid-and base-vulnerable cores. The temperature resistance of stars is similar to that of PIB.

Bioaccumulation and trophic transfer of cyclic volatile methylsiloxanes (cVMS), specifically octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), were evaluated in the pelagic marine food web of Tokyo Bay, Japan. Polychlorinated biphenyl (PCB) congeners that are "legacy" chemicals known to bioaccumulate in aquatic organisms and biomagnify across aquatic food webs were used as a benchmark chemical (CB-180) to calibrate the sampled food web and as a reference chemical (CB-153) to validate the results. Trophic magnification factors (TMFs) were calculated from slopes of ordinary least-squares (OLS) regression models and slopes of bootstrap regression models, which were used as robust alternatives to the OLS models. Various regression models were developed that incorporated benchmarking to control bias associated with experimental design, food web dynamics, and trophic level structure. There was no evidence from any of the regression models to suggest biomagnification of cVMS in Tokyo Bay. Rather, the regression models indicated that trophic dilution of cVMS, not trophic magnification, occurred across the sampled food web. Comparison of results for Tokyo Bay to results from other studies indicated that bioaccumulation of cVMS was not related to type of food web (pelagic vs demersal), environment (marine vs freshwater), species composition, or location. Rather, results suggested that differences between study areas was likely related to food web dynamics and variable conditions of exposure resulting from non-uniform patterns of organism movement across spatial concentration gradients.

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