Cyclo-depolymerizations of polycarbonates in solution: Use of the macrocyclic oligomers obtained in entropically-driven ring-opening polymerizations and copolymerizations to give carbonate-carbonate and carbonate-carboxylate ester copolymers

We report cyclo-depolymerizations of solutions of poly(bisphenol-A carbonate) and two poly(alkylene carbonate)s to give, in each case, mixtures of macrocyclic oligomers (MCOs). The aromatic carbonate was less reactive than the aliphatic carbonates. Using various catalysts small-scale entropically-driven ring-opening polymerizations (ED-ROPs) of the MCOs reformed the original polymers. Tetra-n-butylammonium tetraphenylborate was the most generally useful catalyst of those investigated. At 230 °C in the absence of added catalyst the aliphatic carbonate-containing MCOs underwent thermal ED-ROPs. In order to probe the possibility of extending the use of ED-ROP for copolymer synthesis, copolymerizations of the carbonate-containing MCOs, both with each other and with carboxylate ester-containing MCOs were investigated. These afforded a range of copolymers in high yields, several of which were shown by 13C NMR spectroscopy to have the repeat units in random sequences. This approach to the synthesis of copolymers containing carbonate linkages has the potential to be used for the synthesis of polymer libraries.