Telechelic poly(ether ketone)s (PEKs) and polyisobutylenes (PIBs) were combined to form PIB-PEK-PIB triblock copolymers and (PIB-PEK)(n) multiblock copolymers via the formation of urea linkages. Monovalent and bivalent amino telechelic PIBs were prepared quantitatively from allyl telechelic PIBs by a newly developed reaction sequence featuring nucleophilic reaction steps. Telechelic PEK-NCO polymers were prepared from the corresponding amino telechelic PEKs via a reaction with diphosgene. The highly reactive PEK-NCO and PIB-NH2 telechelics formed PEK-PIB block copolymers only quantitatively when appropriately reactive primary amino groups were present on the amino telechelic PIBs. The obtained block copolymers were microphase-separated and featured mostly lamellar structures, as determined by small-angle X-ray scattering (SAXS). Temperature-dependent SAXS measurements revealed ordered polymers in the melt up to 210degreesC. (C) 2004 Wiley Periodicals, Inc.