Hemiacetal Ester Side Chains as a Mild Protecting Group for Carboxylic Acids in Polycarbonate Backbones.

Hemiacetal esters are versatile functional groups known for their unique ability to degrade under mild conditions such as exposure to water, alcohols, organic acids, or heat. In this study, hemiacetal esters are introduced as mild, transient protecting groups for carboxylic acids along polycarbonate backbones. A six-membered cyclic carbonate monomer is synthesized by reacting ethyl vinyl ether with a carboxylic acid precursor, demonstrating high efficiency and stability under nucleophilic polymerization conditions. Potential susceptibilities of the hemiacetal esters to transacetalization reactions do not occur under these polymerization conditions. Instead, well-defined homo and PEG-based block copolymers are obtained with narrow molecular weight distributions and preserved hemiacetal ester functionalities. These labile side chain groups enabled facile deprotection, yielding polycarbonates with free carboxylic acids, holding significant potential for applications in drug delivery, sustainable polymers, and advanced functional materials.