One-Pot Two-Step (First ROP, Then SET-LRP) Synthesis of Polycaprolactone-Polyacrylate Star Block Copolymers

Abstract

A one-pot, two-step method is applied to the controlled synthesis of polyacrylate-b-(polycaprolactone)2 three-arm AB2-type star block polymers. First, ring-opening polymerization (ROP) of ε-caprolactone is carried out in toluene using either stannous octoate (Sn(Oct)2) or diphenyl phosphate (DPP) as catalyst, and a multifunctional initiator featuring one bromoester and two alcohol groups. Then, single-electron transfer living radical polymerization (SET-LRP) of methyl acrylate and isobornyl acrylate is conducted in the same reaction vessel after sequential addition of its typical reactants, apart from the (PCL)2-Br macroinitiator generated in the first step, in either toluene/toluene + phenol or toluene/dimethyl sulfoxide solvent systems. DPP (the ROP catalyst) from the first step is found to take part in an acid?base reaction with tris[2-(dimethylamino)ethyl]amine (the SET-LRP N-ligand) in the second part, but stoichiometry could be adjusted to avoid interference and keep the controlled nature of the polymerizations. Interestingly, the electrochemically active Sn(Oct)2 ROP catalyst does not interfere with the SET-LRP process. Well-defined poly(methyl acrylate)-b-(polycaprolactone)2 and poly(isobornyl acrylate)-b-(polycaprolactone)2 are thus synthesized through a simple and cost-effective experimental procedure. The technique also applies to the synthesis of linear block copolymers.