Iron(III) Triflate as a Green Catalyst for Janus Polymerization to Prepare Block Polyesters

Iron-based compounds are promising but challenging catalysts for the ring-opening polymerization of cyclic esters and ethers due to their nontoxicity, inexpensiveness, and adequate supply. Herein, iron(III) triflate [Fe(OTf)3], a commercially available catalyst, is successfully applied to catalyze the copolymerization of ε-caprolactone (CL) with tetrahydrofuran (THF) which is confirmed to be Janus polymerization, where cationic ring-opening polymerization (CROP) and anionic ring-opening polymerization (AROP) propagate at the two ends, respectively, in one single growing chain. CROP of THF with CL produces an amorphous P(THF-co-CL) block, while AROP of CL generates a semicrystalline homo-PCL one. As a result, P(THF-co-CL)-b-PCL block polymers are obtained in one step. It is the first time post-transition metal catalysts have activated Janus polymerization instead of rare earth ones, facilitating the potential application of the products as biomaterials.