ATRP of N‐Hydroxyethyl Acrylamide in the Presence of Lewis Acids: Control of Tacticity, Molecular Weight, and Architecture

Abstract

Good control of tacticity, molecular weight, and architecture is attained via atom transfer radical polymerization (ATRP) of N‐hydroxyethyl acrylamide (HEAA), in a one‐pot process in the presence of Y(OTf)3. The effect of temperature, ratio of [Y(OTf)3]/[HEAA], and ATRP procedure on the tacticity and degree of control over the polymerization is investigated in detail. Under optimal conditions, using photo ATRP and 15% Y(OTf)3, the content of meso dyads (m) can be increased from 42% to 80% in a homopolymer with a dispersity D = 1.22. Well‐defined stereoblock copolymers, atactic‐ b ‐isotactic poly(HEAA), with D = 1.27, are obtained by adding Y(OTf)3 at a specific conversion, initially started without Y(OTf)3.

100th Anniversary of Macromolecular Science Viewpoint: The Past, Present, and Future of Stereocontrolled Vinyl Polymerization

“…These methodologies enabled the preparation of isotactic (≤86% m) poly(acrylamide)s with controlled molecular weights, as well as more advanced materials such as atacticblock-isotactic stereoblock copolymers. 188,193,207 In addition, Boyer and co-workers recently reported the preparation of isotactic-enriched (≤84% m) poly(DMA) and atactic-bisotactic stereoblock poly(DMA) under photoinduced electron transfer (PET)-RAFT conditions in the presence of Y-(OTf) 3 . 189 While these examples illustrate great progress in the development of SRP, successful methodologies thus far have nearly exclusively focused on acrylate-and acrylamidebased monomers, with degrees of stereocontrol that are highly dependent on a number of complex variables, including the strength of Lewis acid−base interactions, stability of a chelate formed in situ, and various environmental variables (e.g., solvent identity, reaction dielectric, and temperature) that favor the desired transition state.…”

“…Progress toward understanding stereocontrolled radical polymerization (SRP) has been limited due to inherent difficulties stemming from the high reactivity, lack of intermolecular interactions, and planar sp 2 structure of propagating radical chain ends . Despite these inherent challenges, four approaches have demonstrated significant promise for engendering stereocontrol during radical polymerization: (i) Lewis acid activation of monomers, − (ii) polymerization in the presence of fluoroalcohols, − (iii) using monomers with chiral auxiliaries or sterically hindered substituents, − and (iv) polymerization in a confined environment …”

“…Initial studies by Okamoto et al showed that the free radical polymerization of some acrylamides and methacrylates in the presence of metal triflates resulted in materials with up to 92% m . ,,, Matyjaszewski and co-workers later expanded SRP to controlled polymerization methods, including atom transfer radical polymerization (ATRP), reversible addition–fragmentation chain-transfer polymerization (RAFT), and nitroxide-mediated polymerization (NMP). These methodologies enabled the preparation of isotactic (≤86% m ) poly­(acrylamide)­s with controlled molecular weights, as well as more advanced materials such as atactic- block -isotactic stereoblock copolymers. ,, In addition, Boyer and co-workers recently reported the preparation of isotactic-enriched (≤84% m ) poly­(DMA) and atactic- b -isotactic stereoblock poly­(DMA) under photoinduced electron transfer (PET)-RAFT conditions in the presence of Y­(OTf) 3 . While these examples illustrate great progress in the development of SRP, successful methodologies thus far have nearly exclusively focused on acrylate- and acrylamide-based monomers, with degrees of stereocontrol that are highly dependent on a number of complex variables, including the strength of Lewis acid–base interactions, stability of a chelate formed in situ , and various environmental variables (e.g., solvent identity, reaction dielectric, and temperature) that favor the desired transition state.…”

“…Sun et al recently expanded on the findings of Okamoto et al to develop a stereoselective photo-ATRP of N -hydroxyethyl acrylamide (HEA) in the presence of catalytic Yb­(OTf) 3 or Y­(OTf) 3 (Figure A). , The degree of stereoselectivity could be tuned between 42 and 80% m by modulating the Lewis acid stoichiometry during polymerization, with the highest isotacticity (i.e., 80% m ) obtained at 15 mol % Lewis acid. Further increasing the Lewis acid loading proved to be detrimental to reaction kinetics, which the authors hypothesized was due to transfer of some Me 6 TREN ligand from the Cu ATRP catalyst to the Lewis acid (i.e., Y­(OTf) 3 ).…”

Toward Green Atom Transfer Radical Polymerization: Current Status and Future Challenges

“…Somewhat efficient approaches focus on the addition of Lewis acid and/or chiral ligands, which however decrease the atom efficiency when used in high amounts. Well‐defined homopolymers of N , N ‐dimethylacrylamide (DMAA) [ 53 ] and N ‐hydroxyethyl acrylamide (HEAA) [ 54 ] with 80–85% proportion of meso dyads were prepared by ATRP in the presence of yttrium(III) trifluoromethanesulfonate, Y(OTf) 3 . In addition, one‐pot synthesis of atactic‐ b ‐isotactic PDMAA‐ b ‐PHEAA stereoblock copolymers was achieved for the first time by adding Y(OTf) 3 at a specific conversion.…”