Active in Sleep: Iron Guanidine Catalyst Performs ROP on Dormant Side of ATRP

Abstract

Copolymers are the answer to property limitations of homopolymers. In order to use the full variety of monomers available, catalysts active in more than one polymerization mechanism are currently investigated. Iron guanidine catalysts have shown to be extraordinarily active in ROP of lactide and herein prove their versatility by also promoting ATRP of styrene. The presented iron complex is the first polymerizing lactide and styrene simultaneously to a defined block copolymer in a convenient one-pot synthesis. Both mechanisms work hand in hand with ROP using the dominantly present Fe^II species on the dormant side of the ATRP equilibrium. This orthogonal copolymerization by a benign iron catalyst opens up new pathways to biocompatible polymerization procedures broadening the scope of ATRP applications.

Keywords: ATRP; ROP; copolymerization; iron; orthogonal catalysis.

Figure 1

Molecular structure of 1 in the solid state determined by single crystal X‐ray diffraction. Bond lengths: Fe1–Br1 2.393(1) Å, Fe1–Br2 2.406(1) Å, Fe1–N1 2.041(1) Å, Fe1–O1 2.042(2) Å; angles: N1‐Fe1‐O1 86.4(1)°, Br1‐Fe1‐Br2 122.1(1)°. Further bond lengths and angles are listed in Table S2 in comparison with the analogous chloride complex.

Figure 2

Polymerization of styrene. M/I/Cat ratio 100:1:1, 110 °C, 800 rpm, under solvent‐free conditions. Top: semilogarithmic plot of the conversion p vs. time (duplicate measurement, error bars partially invisible due to too small variations. The values are displayed in Table S3). Bottom: theoretical molar masses (black line), experimentally found molar masses (black squares), and dispersities Đ (red circles) in the course of the polymerization.

Figure 3

Simultaneous copolymerization of lactide and styrene. Top: reactRaman spectra of the polymerization. Bottom: semilogarithmic plot of integrated monomer bands (see also Figure S7).

Scheme 1

Proposed mechanism for combined ROP and ATRP.