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

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 B₂-type dinucleophiles has a preferential reaction pathway between the functionality A' of the asymmetric AA' monomer with B₂. 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.