Stereocontrol during the free‐radical polymerization of methacrylamides in the presence of Lewis acids

Abstract

The effects of Lewis acids, that is, rare earth metal trifluoromethanesulfonates, on the free-radical polymerization of N-methylmethacrylamide (MMAM), Nisopropylmethacrylamide (IPMAM), N-tert-butylmethacrylamide (tBMAM), N-phenylmethacrylamide (PMAM), and methacrylamide were examined under various conditions. A catalytic amount of Yb(OSO 2 CF 3 ) 3 significantly affected the stereochemistry during the radical polymerization. Polymerization solvents strongly influenced the effect of the Lewis acids. Methanol was the best solvent for increasing the isotactic specificity during the polymerization of MMAM and IPMAM, whereas tetrahydrofuran was more effective for the tBMAM and PMAM polymerizations.

Novel Initiating System for the Stereocontrolled Radical Polymerization of Acrylamides: Alkyl Bromide/Rare Earth Metal Triflate System

“…The increase in the isotacticity of the polymer is ascribed to the effective complexation of Y(OTf) 3 with the last two pendant amide groups of the propagating radical and the incoming monomer unit which in turn favors the meso-type addition of the Lewis acid-complexed NIPAM monomer. Similar observations have been reported for the polymerization of acrylamides, 15,16,18,19,22 methacrylamides, [16][17][18][19][20][21] and methacrylates 24 in the presence of bulky lanthanide triflate Lewis acids. The increase in the EBIB concentration from 10 mM to 30 mM (entries 3, 5 and 6) while keeping other conditions the same increases the polymer yield, decreases the molecular weight of the polymer, and increases the polydispersities.…”

“…[15][16][17][18][19][20][21][22] The Lewis acids further affected the stereochemistry of the polymers. Especially, for the acrylamides, highly isotactic polymers were obtained with rare-earth metal triflates.…”

Mechanistic Perspectives on Stereocontrol in Lewis Acid-Mediated Radical Polymerization

“…Okamoto and coworkers found that the mild syndiotactic preference of MAM (m ¼ 27%) could be reversed by the presence of Y(OTf) 3 to afford isotactic-rich poly(MAM) (m ¼ 68). 148,149 Good levels of isotactic control were also observed for NMMAM in the presence of Yb(OTf) 3 , while MgBr 2 was found to be ineffective. In the absence of any mediator, poly(NMMAM) with an isotactic content of m ¼ 17% was obtained in CH 3 OH, while addition of Yb(OTf) 3 afforded isotactic-rich polymer (m ¼ 68%).…”

“…These authors investigated the use of various rare earth metal triflates in the polymerizations of an array of acrylamides 146,147 and methacrylamides (Table 1). 148,149 Remarkably, for the radical polymerization of N,N-disubstituted acrylamides, such as DMA (which are polymerizable directly with anionic and coordination processes), the isotactic control afforded by LAs is comparable to that obtained via anionic polymerization under much more demanding conditions. 150,151 For instance, Okamoto and coworkers reported that an isotactic content of m ¼ 88% could be obtained during the radical polymerization of DMA in methanol at 0 C by using 10 mol% Yb(OTf) 3 as a control agent.…”

“…133 Excellent isotactic control was also observed in NIPMAM, with the high syndiotactic preference of the unmediated polymerization (m ¼ 10%) nearly completely reversed by the inclusion of Yb(OTf) 3 (m ¼ 80e82%). 148,149 We should also briefly discuss attempts to control stereochemistry of several more novel monomers with LAs ( Table 2). Endo and coworkers examined the RAFT polymerization of an acrylamide with a chiral L-phenylalanine auxiliary (APAMEAM).…”