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

Abstract

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.

Efficient and well-controlled ring opening polymerization of biobased ethylene brassylate by α-diimine FeCl3 catalysts via a coordination–insertion mechanism

“…1,5,7-triazabicyclo[4.4.0]dec-5-ene, TBD) can achieve acceptable high molecular weights, but high catalyst loading is still required. [18][19][20][21] Metal based catalysts have been the workhorses for ROP of ring-strained smaller-sized cyclic esters during the past few decades; [22][23][24][25][26] they also hold great potential for ROP of macrolactone monomers because their metal centers are highly oxophilic, which reveals greater probability for trapping lactone monomers and subsequently initiating ring opening polymerization. [27][28][29][30][31] Because of this reason, catalysts based on main-group metals Bi 4,32-34 and Na 35 have been recently evaluated for the ROP of EB, and acceptable yields as well as high molecular weights of PEB products were achieved (Scheme 1(2)).…”