The association behavior of telechelic hydrogen-bonded poly(ether ketone) (PEK) and polyisobutylene (PIB) polymers and the formation of a new class of pseudo-block copolymers is reported. The attachment of complementing hydrogen bonds (thymine/2,6-diaminotriazine and cytosine/2,6-diaminotriazine) onto the respective PIB and PEK polymers leads to a dramatic increase in the miscibility between the normally immiscible PEK and PIB polymers. The structure formation in the liquid state was studied by dynamic NMR spectroscopy as well as in the solid state via solid-state NMR-spectroscopy, DSC, and TEM methods. The polymers form a nanophase structure with a periodicity of 70 mm with the microphase separation occurring specifically within the donor-acceptor pair with the higher binding constant (thymine/2,6-diaminotriazine) and not within the weaker bonded cytosine/2,6-diaminotriazine pair. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 162-172, 2004.