Tacticity control approached by electric-field assisted free radical polymerization – the case of sterically hindered monomers

Abstract

We investigate the effect of a high electric field on the free-radical polymerization (FRP) of an acrylate monomer with a large steric hindrance that comes from the isobornyl pendant group. In the presence of static (DC) fields reaching 140 kV cm⁻¹, the polymer product shows reduced dispersity and a remarkable increase in the molecular weight compared to the zero-field reference. Electric-field assisted polymerization of isobornyl acrylate was carried out at 343 K in the presence of 2,2′-azobis(2-methylpropionitrile) (AIBN) as a radical initiator. Surprisingly, pronounced changes were found in the stereochemistry of the obtained polymer. There is an increasing trend for the isotactic triad content with increasing field magnitude. Depending on the reaction conditions, the isotactic triad content (methine carbon region) could be increased from ∼16% (0 kV cm⁻¹) up to 36% (140 kV cm⁻¹). By analyzing the temperature dependence of the isotactic to syndiotactic diad ratio, we found that high electric fields increase the contribution of the entropic factor almost three-fold. Our finding provides new opportunities for a simple and versatile stereochemistry control at a level inaccessible so far for conventional radical polymerization.