Enhancing the Self‐Assembly of Step‐Growth Polymers by Narrowing Their Molar Mass Distribution: A Dynamic Bond‐Mediated Approach

Abstract Step‐growth polymerization (SGP) typically produces polymers with exceptional versatility in terms of applications, but its inherently uncontrolled nature leads to broad molecular weight distributions ( Đ ) and consequently polymers with poor nanostructure control in comparison to chain growth polymers. In this study, we provide a solution to this long‐lasting problem by introducing a new concept, asymmetric dynamic bond mediated polymerization (ADBP). In this case, the polymerization between asymmetric and reversibly deactivated AA’‐type dielectrophiles and B 2 ‐type dinucleophiles has a preferential reaction pathway between the functionality A’ of the asymmetric AA’ monomer with B 2 . We observe that this polymerization allows us to achieve better control of the step‐growth process where in the first stage only well‐defined trimers and dimers are primarily formed up to conversion ( p ) ≤ 0.6, followed by their polymerization stage ( p ≥ 0.6). This leads to polymers with reduced Đ (<1.5), in comparison to traditional SGP, and improved molar mass control. Such technique is further exploited to prepare polyurethanes with Đ = 1.2, which exhibit the ability to form microphase‐separated domains with higher ordering, giving rise to polyurethane thermosets with superior mechanical properties compared to a traditional SGP analog.