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Molecular shape is an essential parameter that regulates the self-organization and recognition process, which has not yet been well appreciated and exploited in block polymers due to the lack of precise and efficient modulation methods. This work (i) develops a robust approach to break the intrinsic symmetry of linear polymers by introducing geometric features into otherwise homo­geneous chains and (ii) quantitatively highlights the critical contribution of molecular geometry/architecture to the self-assembly behaviors. Iteratively connecting homologous monomers of different side chains according to pre-designed sequences generates discrete polymers with exact chemical structure, uniform chain length, and programmable side-chain gradient along the backbone, which transcribes into diverse shapes. The precise chemistry eliminates all the defects and heterogeneities, providing a delicate platform for fundamental inquiries into the role of molecular geometry. A rich collection of unconventional complex phases, including Frank–Kasper A15 and σ phases, as well as a dodecagonal quasicrystal phase, were captured in these rigorous single-component systems. The self-assembly behaviors are strikingly sensitive to subtle variations of geometry, such that simply migrating a few methylene units among the side chains would generate substantial differences in lattice size or phase stability, or even trigger a phase transition toward distinct structures. The phenomena can be rationalized with a geometric argument that nonuniform side chain distribution leads to conformational mismatch between two immiscible blocks, resulting in varied interfacial curvatures and distinct lattice symmetries. The profound contribution demonstrates that molecular geometry is an effective and robust parameter for structural engineering.

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Stereocomplexation critically depends on the chain length and stoichiometry of constituent enantiomeric chains. Quantitative understanding of their independent contribution, however, has long been compromised by inherent molecular weight distribution. In this work, we prepared a library of discrete oligo L-lactide and oligo D-lactide and systematically explored the stereocomplexation behaviors. The relative chain length and mole ratio of the two complementary oligomers can be precisely regulated with predesigned recipes. When the two enantiomers have exactly the same chain length (x 1 = x 2 , where x is the number of repeat units), they co-crystallize into highly uniform stereocomplexes with extended chain conformation. On the other hand, when the two components are not of equivalent size, the excess segments of the longer ones could stay amorphous on the basal surfaces of the lamellar crystal (if x 1 < x 2 ≤ 2x 1 ) or complex with other short enantiomers (if x 2 > 2x 1 ), depending on the chain length difference and stoichiometry. This study could enhance our fundamental understanding of stereocomplexation, providing promising opportunities for rational structure engineering.