Stereospecific radical polymerization of optically active (S)-N-(2-hydroxy-1-phenylethyl) methacrylamide catalyzed by Lewis acids

• Stereospecific radical polymerization of optically active (S)-HPEMA was realized.
• A catalytic amount of the Lewis acid is enough to control the stereoregularity.
• Solvents strongly influence the effect of Lewis acids on the tacticity of the polymer.
• The polymerization in n-BuOH in the presence of La(OTf)3 shows the highest isotacticity.
• The mechanism of stereocontrol was analyzed based on Lewis acid-monomer interaction.

The effects of Lewis acids, namely, rare earth metal trifluoromethanesulfonates, on the radical polymerization of (S)-N-(2-hydroxy-1-phenylethyl) methacrylamide were examined under various conditions. In the absence of Lewis acids, syndiotactic-rich polymers (r = 84%) were obtained, whereas in the presence of a catalytic amount of Lewis acids, the polymerization proceeded in an isotactic-specific manner (m up to 64%). Polymerization solvents strongly influenced the effect of the Lewis acids. The polymerization in n-butyl alcohol showed the highest isotactic selectivity, whereas the polymerization in DMSO showed no isotacticity-enhancing effect. Further increases in the Lewis acid concentration and the polymerization temperature did not produce clear effects on the tacticity of the polymers. The interaction between the monomer and Lewis acids was investigated, and the plausible mechanism of stereocontrol in the radical polymerization of (S)-HPEMA was analyzed based on the Lewis acid-monomer interaction.

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