Atom transfer radical polymerization
Atom transfer radical polymerization (ATRP) is an example of a reversible-deactivation radical polymerization. Like its counterpart, ATRA or atom transfer radical addition, it is a means of forming a carbon-carbon bond through a transition metal catalyst. The polymerization from this method is called Atom transfer radical addition polymerization (ATRAP). As the name implies, the atom transfer step is the key step in the reaction responsible for uniform polymer chain growth. ATRP (or transition metal-mediated living radical polymerization) was independently discovered by Mitsuo Sawamoto and by Jin-Shan Wang and Krzysztof Matyjaszewski in 1995.
Controlled reversible-deactivation radical polymerization in which the deactivation
of the radicals involves reversible atom transfer or reversible group transfer catalyzed usually,
though not exclusively, by transition-metal complexes.
ATRP usually employs a transition metal complex as the catalyst with an alkyl halide as the initiator (R-X). Various transition metal complexes, namely those of Cu, Fe, Ru, Ni, Os, etc., have been employed as catalysts for ATRP. In an ATRP process, the dormant species is activated by the transition metal complex to generate radicals via one electron transfer process. Simultaneously the transition metal is oxidized to higher oxidation state. This reversible process rapidly establishes an equilibrium that is predominately shifted to the side with very low radical concentrations. The number of polymer chains is determined by the number of initiators. Each growing chain has the same probability to propagate with monomers to form living/dormant polymer chains (R-Pn-X). As a result, polymers with similar molecular weights and narrow molecular weight distribution can be prepared.
ATRP reactions are very robust in that they are tolerant of many functional groups like allyl, amino, epoxy, hydroxy and vinyl groups present in either the monomer or the initiator. ATRP methods are also advantageous due to the ease of preparation, commercially available and inexpensive catalysts (copper complexes), pyridine based ligands and initiators (alkyl halides).
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