Guanidine as inexpensive dual function ligand and reducing agent for ATRP of methacrylates

Abstract

N,N,N′,N′-Tetramethyl guanidine (TMG), an inexpensive and commercially available organic base, is used for the first time as ligand without any chemical modification for the supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) of methyl methacrylate (MMA) in the presence of Cu⁰ wire and CuBr₂. The successful use of TMG as ligand was only possible after the adaptation of the polymerization procedure in order to prevent interactions between TMG and initiator. PMMA-Br was synthesized with molecular weight up to 100 000 and low dispersity (M_w/M_n < 1.3), using only 100 ppm of CuBr₂. The high chain-end functionality of the polymer was confirmed by successful self-chain extension and by the preparation of a well-defined PMMA-b-PBMA-Br (BMA: butyl methacrylate) block copolymer (M_w/M_n = 1.06). In addition, glycidyl methacrylate (GMA), ethyl methacrylate (EMA), butyl methacrylate (BMA) and 2-(diisopropylamino)ethyl methacrylate (DPA) were also successfully polymerized in a controlled manner. Polymerization of MMA in the absence of Cu⁰ led to well-controlled polymerizations, proving the efficient dual function of TMG as ligand and reducing agent. Model experiments carried out in the absence of zero valent metals revealed that the reaction is ruled by the activators regenerated by electron transfer (ARGET) ATRP mechanism. This manuscript demonstrates the possibility of using an inexpensive ligand to afford polymethacrylates with well-defined structure, which is particularly relevant knowing that the ligand cost is still a serious hurdle considering the implementation of ATRP at large scale production.