Abstract
Catalysts are essential for mediating a controlled polymerization in atom transfer radical polymerization (ATRP). Copper-based catalysts are widely explored in ATRP and are highly efficient, leading to well-controlled polymerization of a variety of functional monomers. In addition to copper, iron-based complexes offer new opportunities in ATRP catalysis to develop environmentally friendly, less toxic, inexpensive, and abundant catalytic systems. Despite the high efficiency of iron catalysts in controlling polymerization of various monomers including methacrylates and styrene, ATRP of acrylate-based monomers by iron catalysts still remains a challenge. In this paper, we review the fundamentals and recent advances of iron-catalyzed ATRP focusing on development of ligands, catalyst design, and techniques used for iron catalysis in ATRP.
Highlights
Reversible deactivation radical polymerization (RDRP) techniques have provided access to advanced polymers with precise control over molecular weight, dispersity, composition, and structure
Atom transfer radical polymerization (ATRP) employs, primarily, Cu-based catalysts to control the growth of polymer chains via a reversible redox process that involves transfer of halogen atoms to activate dormant species generating initiating radicals and to deactivate propagating chains [1,2,3,4]
Iron complexes form an important class of atom transfer radical polymerization (ATRP) catalysts that provide efficient and well-controlled polymerization of various functional monomers
Summary
Reversible deactivation radical polymerization (RDRP) techniques have provided access to advanced polymers with precise control over molecular weight, dispersity, composition, and structure. Typical approaches to control the growth of polymer chains in radical polymerizations include reversible deactivation of propagating radicals or using degenerative transfer processes to exchange radicals with dormant species in the presence of chain transfer agents. Atom transfer radical polymerization (ATRP) employs, primarily, Cu-based catalysts to control the growth of polymer chains via a reversible redox process that involves transfer of halogen atoms to activate dormant species generating initiating radicals and to deactivate propagating chains [1,2,3,4]. ATRP catalysis involves generation of radicals via activation of halogen chain ends by L/CuI activator and reversible deactivation of propagating radicals by a halogen atom transfer from L/CuII -X deactivator (X = Br or Cl). In iron-catalyzed ATRP, L/FeII species activate dormant halogen chain ends, whereas L/FeIII -X deactivate propagating radicals via a reversible halogen atom transfer process. Different ATRP initiating systems based on developing activator regeneration techniques and challenges and opportunities offered by iron complexes in ATRP are discussed
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