A simple but efficient strategy has been developed for the synthesis of novel di-, tri-, multi-, and star-block copolymers comprising poly(ethylene glycol) (PEG) and polyisobutylene (PIB) blocks. The synthesis principle involves the coupling of appropriately terminally functionalized PEG and PIE sequences, specifically the hydrosilation of mono-, di-, and tetra-allyl-telechelic PEGs (PEG-allyl, allyl-PEG-allyl, and Ct-PEG-allyl)(4) by mono- and di-Si(CH3)(2)H telechelic PIBs (PIB-SiH and HiS-PIB-SiH). Representative block copolymers, for example, PEG-PIB, PIB-PEG-PIB, (-PIB-PEG-)(n), and Ct-PEG-PIE), have been assembled and their structures determined by H-1 and C-13 NMR spectroscopy. The bulk and surface morphology of select triblocks have been investigated by DSC and AFM and the findings interpreted in terms of phase-separated PEG and PIE microdomains. The swelling behavior in water of various block copolymers also has been studied. Block copolymers containing 50-70 wt % PIE produce hydrogels, the integrity of which is maintained by physical crosslinks by PIE segments.