Synthesis of Poly(ionic liquid)s by Atom Transfer Radical Polymerization with ppm of Cu Catalyst

Abstract

Well-defined poly(ionic liquid)s (PILs) were synthesized by activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The ionic liquid monomer 1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (VBBI+Tf2N–) was directly polymerized with tris(2-pyridylmethyl)amine (TPMA) ligand and ppm level of copper catalyst. The addition of reducing agent tin(II) 2-ethylhexanoate (SnII(EH)2) to continuously regenerate the catalyst in the ARGET ATRP enabled the synthesis of PILs with a significantly lower concentration of catalysts than required for a normal ATRP. PILs with well-controlled molecular weight and relatively low dispersity (Mw/Mn < 1.3) were obtained. ATRP chain extension of the resulting PILs with polystyrene revealed that the chain-end functionality of the PILs was significantly improved by slow feeding of the reducing agent during the polymerization. Simple and effective methods were developed to remove the residual halide ions from the ionic liquid monomer by ion exchange with LiTf2N or precipitation with AgTf2N, which allowed ARGET ATRP of the purified ionic liquid monomer to occur with as low as 20 ppm copper catalyst. Additionally, ARGET ATRP was used for the preparation of PIL block copolymers, including AB diblock and ABA triblock with PIL segment(s) as the middle or side blocks, using ionic liquid monomer or mono/difunctional PIL macroinitiators.