Radical Ring-Opening Polymerization Monomers for the Development of Degradable Polymers

In recent years, biodegradable and degradable polymers have been increasingly developed, particularly in relation to biomedical applications and strategies aimed at achieving a circular society. Among various approaches, radical ring-opening polymerization (rROP) monomers, which enable the incorporation of degradable units into vinyl polymers, have attracted increasing attention. Cyclic ketene acetals (CKAs) and thionolactones are representative rROP monomers, allowing introduction of ester and thioester linkages, respectively, into vinyl polymers.
The most widely investigated CKA monomer is 2-methylene-1,3-dioxepane (1).^1,2) Although a ring-retaining reaction can compete in rROP of CKAs, monomer 1 is known to exhibit high ring-opening efficiency due to its relatively large ring size.³⁾ Representative thionolactone monomers include dibenzo[c,e]oxepine-5(7H)-thione (2) and oxepane-2-thione (3). It has been reported that 2 is suitable for copolymerization with monomers such as acrylates, acrylamides, and acrylonitriles,^4,5) whereas 3 is suitable for copolymerization with vinyl esters.⁶⁾

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