Through mimicking the synthesis of hereditary-information-containing nucleic acids, scientists are committed to synthesizing sequence-defined macromolecules. Herein, a protecting-group-free, metal-free, and atom-economical chemistry combining hydroxyl-yne and thiol-ene click reactions was developed to efficiently synthesize sequence-defined oligo-(monothioacetals) (overall yield of 54% for an 11-step synthesis) from readily available starting compounds and monomers under ambient conditions. The sequences of linear oligo(monothioacetals) could be easily decoded via a tandem ESI-MS/MS technique, making them new kinds of digital macromolecules with a high data storage density (0.013 bit/Da). Moreover, star oligo(monothioacetals) could also be facilely generated through divergent and convergent strategies and their combination. An unprecedented sequence-defined miktoarm star oligo(monothioacetal) was obtained, which could serve as a new nonlinear digital macromolecule to achieve 2D information matrix encoding and hold great potential to be applied for information encryption, anticouterfeiting, secret communication, etc. Thus, this work provides a powerful stepwise iterative approach to facilely access sequence-defined linear and topological oligo(monothioacetals) for high-density data storage.