Chemoselective Polymerization of Fully Biorenewableα-Methylene-γ-Butyrolactone Using Organophosphazene/Urea Binary Catalysts Toward Sustainable Polyesters

Despite the great potential of biorenewableα-methylene-γ-butyrolactone(MBL)to produce functional,recyclable polyester,the ring-opening polymerization(ROP)of MBL remains a challenge due to the competing polymerization of the highly reactive exocyclic double bond and low-strained five-membered ring.In this contribution,we present the first organocatalytic chemoselective ROP of MBL to exclusively produce functional unsaturated polyester by utilizing a phosphazene base/urea binary catalyst.We show that delicate chemoselectivity can be realized by controlling the temperature and using selected urea catalysts.The obtained polyester can be completely recycled back to its monomer by chemolysis under mild conditions.Experimental and theoretical calculations provide mechanistic insights and indicate that the ROP pathway is kinetically favored by using urea with stronger acidity at low temperatures.