Surface-Initiated Photoinduced Iron-Catalyzed Atom Transfer Radical Polymerization with ppm Concentration of FeBr3 under Visible Light.

Monika Słowikowska,Kamila Chajec,Adam Michalski,Karol Wolski,Szczepan Zapotoczny

doi:10.3390/ma13225139

Abstract

Reversible deactivation radical polymerizations with reduced amount of organometallic catalyst are currently a field of interest of many applications. One of the very promising techniques is photoinduced atom transfer radical polymerization (photo-ATRP) that is mainly studied for copper catalysts in the solution. Recently, advantageous iron-catalyzed photo-ATRP (photo-Fe-ATRP) compatible with high demanding biological applications was presented. In response to that, we developed surface-initiated photo-Fe-ATRP (SI-photo-Fe-ATRP) that was used for facile synthesis of poly(methyl methacrylate) brushes with the presence of only 200 ppm of FeBr3/tetrabutylammonium bromide catalyst (FeBr3/TBABr) under visible light irradiation (wavelength: 450 nm). The kinetics of both SI-photo-Fe-ATRP and photo-Fe-ATRP in solution were compared and followed by 1H NMR, atomic force microscopy (AFM) and gel permeation chromatography (GPC). Brush grafting densities were determined using two methodologies. The influence of the sacrificial initiator on the kinetics of brush growth was studied. It was found that SI-photo-Fe-ATRP could be effectively controlled even without any sacrificial initiators thanks to in situ production of ATRP initiator in solution as a result of reaction between the monomer and Br radicals generated in photoreduction of FeBr3/TBABr. The optimized and simplified reaction setup allowed synthesis of very thick (up to 110 nm) PMMA brushes at room temperature, under visible light with only 200 ppm of iron-based catalyst. The same reaction conditions, but with the presence of sacrificial initiator, enabled formation of much thinner layers (18 nm).

Highlights

The reversibly deactivation radical polymerizations (RDRP) such as atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), reversible addition−fragmentation chain transfer (RAFT), and photoiniferter-mediated polymerization (PIMP) are the first choice methods for synthesis of various functional polymeric materials with advanced architectures such as molecular brushes [1,2], star-like polymers [3,4], polymer brushes [5,6,7,8], etc
Semilogarithmic kinetics plots as well as the evolution of masses of grafted macromolecules with monomer conversion indicate on controlled characteristics molar masses of grafted macromolecules with monomer conversion indicate on controlled of SI-photo-Fe-ATRP
The comparison of the kinetics of SI-photo-Fe-ATRP and photo-Fe-ATRP revealed obtaining of smaller molar masses of grafted chains at low monomer conversions, while higher for high conversions compared to polymers generated in the solution

Summary

Introduction

The reversibly deactivation radical polymerizations (RDRP) such as atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), reversible addition−fragmentation chain transfer (RAFT), and photoiniferter-mediated polymerization (PIMP) are the first choice methods for synthesis of various functional polymeric materials with advanced architectures such as molecular brushes [1,2], star-like polymers [3,4], polymer brushes [5,6,7,8], etc. ATRP requires the use of substantial amounts of catalyst to maintain the control over the reactive. ATRP requires the use of substantial amounts of catalyst to maintain the control over the reactive radicals. Most of biological and electronic applications are highly restricted to the presence radicals. Most of biological and electronic applications are highly restricted to the presence of impurities coming from transition metals. Significant scientific efforts have been of impurities coming from transition metals. Significant scientific efforts have been devoted devoted to development of new ATRP techniques, in which concentration of transition metal to development of new ATRP techniques, in which concentration of transition metal complex is greatly complex is greatly limited, due to regeneration of activator by the use of: radical chemical reducing limited, due to regeneration of activator by the use of: radical chemical reducing agent in initiators for agent in initiators for continuous activator regeneration (ICAR) ATRP [10], chemical reductants in continuous activator regeneration (ICAR) ATRP [10], chemical reductants in activators regenerated by activators regenerated by electron transfer (ARGET) ATRP [11], zero-valent metals in supplemental electron transfer (ARGET) ATRP [11], zero-valent metals in supplemental activator and reducing agent activator and reducing agent (SARA) ATRP [12], electrochemical reactions in electrochemically (SARA) ATRP [12], electrochemical reactions in electrochemically mediated ATRP (eATRP) [13], light in mediated ATRP (eATRP) [13], light in both metal-free [14] and photoinduced ATRP (photo-ATRP)

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Discussion

Conclusion