Cationic equilibrium ring‐opening polymerization of bicyclic monomers and its application to chemical recycling

Spiro orthoesters give poly(cyclic orthoester)s by single ring‐opening polymerization in the presence of acid catalysts, and this process undergoes the equilibrium polymerization. We have applied the function of equilibrium polymerization to chemical recycling of polymeric materials. Crosslinked poly(cyclic orthoester)s, prepared by radical additions of poly(cyclic orthoester)s possessing exomethylene groups and dithiols, efficiently decrosslinked to bifunctional spiro orthoesters in the presence of CF 3 CO 2 H in CH 2 Cl 2 . The dithiol‐linked bifunctional spiro orthoester monomers, prepared by the radical additions of spiro orthoester possessing exomethylene group and dithiols, afforded the corresponding crosslinked polymers in the presence of CF 3 CO 2 H as a catalyst in bulk. The decrosslinking of the obtained crosslinked polymer proceeded quantitatively to obtain the corresponding bifunctional monomer at room temperature in CH 2 Cl 2 . Further, an acid‐catalyzed reversible crosslinking‐decrosslinking of a polymer having a spiro orthoester group in the side chain was carried out. The copolymer obtained by the radical copolymerization of 2‐methylene‐1,4,6‐trioxaspiro[4.6]undecane with acrylonitrile was treated with CF 3 CO 2 H at −10 °C in CH 2 Cl 2 to afford the crosslinked polymer quantitatively. The crosslinked polymer was then treated with CF 3 CO 2 H at room temperature at a low concentration in CH 2 Cl 2 to recover the original polymer.