Recent Developments In APT-Based Polymerization Reactions: The Iodo-Ene Reaction

The thiol-ene ‘click’ reaction has been described as the only radical-mediated, step-growth polymerization mechanism;¹ however, our recent account of radical-mediated thiol-yne polymerizations belies this premise.²  Rather, thiol-ene reactions constitute only one category of a greater class of radical-mediated, step-growth polymerizations, designated here as “Alternating Propagation-chain Transfer” (APT) polymerizations.  In this presentation, we will discuss photoinitiated APT polymerizations, which afford several distinct and advantageous attributes, such as low shrinkage and shrinkage stress, delayed gelation, low extractable content, and the formation of homogeneous polymer networks with very narrow glass transition regions.  Additionally, we will introduce a new radical-mediated APT polymerization: the iodo-ene polymerization.  While possessing all the advantages of thiol-ene APT polymerizations, the iodo-ene reaction utilizes iodinated perfluoroalkane comonomers, assuring the covalent incorporation of both iodine and fluorine in high concentrations throughout the polymer matrix.  This imparts the iodo-ene polymer product with intrinsic radiopacity, an inert, low energy surface, and chemical stability, which are desirable in a number of biomedical applications.  Moreover, this material has the capacity for facile nucleophilic substitution for surface passivation while the bulk of the material remains iodinated but inert.

1. H. Lu, J. A. Carioscia, J. W. Stansbury, C. N. Bowman, Dent. Mater. 21, 1129 (Dec, 2005).

2. B. D. Fairbanks, T. F. Scott, C. J. Kloxin, K. S. Anseth, C. N. Bowman,  Macromolecules 42, 211 (Jan, 2009).