A Mechanistic Study on the Hydrolysis of Cyclic Ketene Acetal (CKA) and Proof of Concept of Polymerization in Water

Abstract

AbstractThe present work systematically investigates the hydrolysis mechanism of cyclic ketene acetal (CKA) monomers in detail and explores polymerization in water under organic solvent‐free and surfactant‐free conditions. To understand the effect of CKA structure on hydrolysis, the ring size of the monomers is varied from 5–8‐membered rings systematically and hydrolysis experiments are performed. In all cases, hydrolysis yields monoacetylated diol products. Deuterium and 17O‐isotopic labeled experiments are carried out for 5‐ and 7‐membered‐(2‐methylene‐1,3‐dioxepane, MDO) CKAs to understand the reaction pathway. The experimental analysis from the reaction of CKA with water revealed that the increasing hydrophobicity from 5–8‐membered rings and the pH of the reaction medium play important roles in the order of reactivity. Density functional theory (DFT) and experimental studies demonstrated that basic reaction conditions have some control over the hydrolysis rate of CKA. Despite this progress, achieving controlled polymerization of CKA in water while suppressing hydrolysis remains challenge. Only up to 3 mol% CKA incorporation is attained in polyacrylate and polyacrylamide backbone via radical ring‐opening polymerization (rROP) of MDO and 8‐membered CKAs with 2‐hydroxyethyl acrylate (HEA) and acrylamide (AAm) in water. The results serve a proof of concept for advancing aqueous copolymerizations using CKA monomers.