The development of robust methodologies to control the solid-state structure of polymeric materials by appropriate design of the macromolecular architecture has a crucial impact on the mechanical properties of these materials(1,2). Here, we demonstrate the feasibility of controlling chain folding of polymers by steric interactions only, in contrast to previous attempts aimed at engineering polymer crystallization through hydrogen bonding(3,4). In a linear synthetic macromolecule similar to polyethylene, we encoded structural instructions that are translated during a crystallization process to generate a unique, semi-crystalline morphology with structure-controlled crystal thickness of similar to5 nm that remains constant over a wide temperature range. The molecular code consists of a linear backbone alternating crystallizable, long alkyl sequences of monodisperse sizes separated by short spacers containing side-chains and acting as stops and fold-controlling units. This simple strategy could be used to produce advanced polymeric materials with fine control of the crystalline and amorphous regions.