Hierarchical self-assembly has been demonstrated with diblock copolymers comprising poly(dimethylsiloxane) (PDMS) and poly(lactide) (PLA) with supramolecular, 4-fold hydrogen-bonding junctions. PDMS with a single ureidoguanosine unit at the end was synthesized by a postpolymerization strategy. PLA with a single 1,7-diamidonaphthyridine was synthesized by ring-opening polymerization from the appropriate functional initiator. Selective association of the end groups to form distinct, noncovalent connections between the respective homopolymers in blends was established by H-1 NMR spectroscopy. The orthogonal self-assembly of the resulting pseudoblock copolymer, driven by immiscibility between the polymer constituents was demonstrated. Bulk polymer blends were prepared that have approximately symmetric composition and a 1:1 end-group stoichiometry. Small angle X-ray scattering combined with differential scanning calorimetry and transmission electron microscopy provide unambiguous evidence for the adoption of a lamellar morphology having long-range order, nanoscopic domain dimensions (20 nm pitch), and a sharp domain interface defined by the supramolecular building blocks.