Development of a Universal Alkoxyamine for “Living” Free Radical Polymerizations

TLDR

Nitroxide-based alkoxyamines are essential for achieving living or controlled polymerization of diverse vinyl monomers. The authors designed α‑hydrido alkoxyamines derived from a 2,2,5‑trimethyl‑4‑phenyl‑3‑azahexane‑3‑oxy skeleton that successfully mediate the polymerization of styrene, acrylate, acrylamide, and acrylonitrile monomers. These new alkoxyamines enable precise control of molecular weight from 1,000 to 200,000 Da with polydispersities of 1.05–1.15, allow synthesis of block and random copolymers, and expand the monomer scope beyond TEMPO to rival ATRP systems.

Abstract

Examination of novel alkoxyamines has demonstrated the pivotal role that the nitroxide plays in mediating the "living" or controlled polymerization of a wide range of vinyl monomers. Surveying a variety of different alkoxyamine structures led to α-hydrido derivatives based on a 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy, 1, skeleton which were able to control the polymerization of styrene, acrylate, acrylamide, and acrylonitrile based monomers. For each monomer set, the molecular weight could be controlled from 1000 to 200 000 amu with polydispersities typically 1.05−1.15. Block and random copolymers based on combinations of the above monomers could also be prepared with similar control. In comparison with 2,2,6,6-tetramethylpiperidinoxy (TEMPO), these new systems represent a dramatic increase in the range of monomers that can be polymerized under controlled conditions and overcome many of the limitations associated with nitroxide-mediated "living" free radical procedures. Monomer selection and functional group compatibility now approach those of ATRP-based systems.