In this paper we describe the synthesis and characterization of modified polyurethaneurea-polyether (PEUU) multiblock copolymers, designed to elicit lower permeability to water vapor and gases. The approach was to create polyisobutylene (PIB) segments, which were linked to the PEUU copolymer as combs. Macromonomers of PIE were synthesized, containing two hydroxyl sites on the initiating ends of the molecules for subsequent condensation polymerization. By using a polymerization scheme that offered no termination and no chain transfer, the PIE macromonomer would be assured of having two (and only two) hydroxyl groups. Characterization of the macromonomers and their precursors was performed by GPC, H-1 NMR, and FTIR. Using these products, amphiphilic copolymers, with a polyurethaneurea-polyether multiblock backbone and polyisobutylene combs, were synthesized by a condensation reaction. PIE incorporation varied between about 2 and 30%, with comb lengths ranging from similar to 3000 to 29 000 g/mol. Characterization of this new multiblock multicomb copolymer was performed by GPC, FTIR, solid state C-13 NMR, and Soxhlet extraction techniques.