Despite nearly 60 years of research, controlling the stereochemistry of free-radical polymerization remains elusive for most common monomers. Typically, Lewis acids are used to coordinate with the terminal and penultimate side chains of the growing polymer radical, and thereby constrain their relative orientation in the transition structure. Unfortunately, the control achieved usually is modest at best. Our theoretical studies suggest a key problem is the selectivity of Lewis acid binding. Even when terminal-penultimate binding is optimized, this mode deactivates the propagating radical, and terminal-monomer binding, which catalyses propagation, dominates the propagation step. In that light, use of ionic auxiliary monomers such as (meth)acrylic acid salts, which contain a metal ion at every side chain, could potentially address this problem. Indeed, one of the highest levels of isotactic control achieved to date is in the polymerization of calcium methacrylate (80% meso diads). In an attempt to improve upon this, we have been examining the polymerization of other methacrylic and acrylic acid salts in the presence of various ligands. We have also been developing improved experimental approaches to converting the auxiliaries, post-polymerization. This presentation will outline our latest results, and discuss future prospects for stereocontrolled radical polymerization.

Ionic auxiliaries for stereocontrolled radical polymerization

254th National Meeting (2017)

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