Updating radical ring-opening polymerisation of cyclic ketene acetals from synthesis to degradation

Abstract

Radical ring-opening polymerisation (RROP) of cyclic ketene acetals (CKAs) has gained momentum as it yields polyesters as biodegradable polymers from a radical polymerisation. In order to advance the polymerisation, some of its major limitations were addressed in the research presented, focussing on the four mainly used CKAs in modern research on RROP. Monomer synthesis has been updated towards a cobalt/TMSCl-based system that was performed reliably on several monomers at room temperature. Calculations using the density functional theory (DFT) revealed that the ring-opening step is energetically hampered in comparison to a ring-retaining reaction, which explained the challenges faced to promote the ring-opening reaction. Higher molecular weights up to four times the values reached by thermally initiated polymerisation were obtained by exploiting UV light and ultrasound as alternative methods to facilitate the polymerisation. The reaction procedure also influenced thermal properties of the polymers, which in turn affected the enzymatic degradation of nanoparticles based on those polymers. Altogether, the present study offers a holistic update to enhance the RROP of CKAs.