Unraveling Structure–Reactivity and Structure–Property Relationships for the Amidation of Methyl Ester-Functionalized Poly(2-Oxazoline)s

Abstract

Poly(2-alkyl-2-oxazoline)s (PAOx) featuring methyl ester side chains have received increasing interest in recent years, as they readily undergo various post-polymerization modification reactions, such as amidation, thereby enabling straightforward structural diversification from a single reactive precursor. Furthermore, ester functional PAOx can be generated with various spacer lengths between the ester functional group and the polymer backbone, allowing straightforward tuning of the solution and thermal properties. In this work, we subjected different methyl ester-bearing PAOx to full amidation reactions with various primary and secondary amines to establish the structure–reactivity and structure–property relationships. Kinetic investigations of the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed amidation reactions revealed that the reactivity correlates with the nucleophilicity of the amines and inversely correlates with the spacer length between the polymer backbone and the ester functionality (PC₂MestOx > PC₃MestOx > PC₄MestOx). These results highlight the importance of macromolecular parameters in the TBD-catalyzed amidation of polymers with pendant ester groups involving intramolecular activation. Finally, we explored the thermal solution and bulk properties of a 30-membered library of amidated polymer products to derive structure–property relationships, which can serve as guidelines for the design and synthesis of functional PAOx (bio)materials.