(225a) Point and Click Synthesis: Spatiotemporal Control over Polymer Network Formation and Modification

The introduction of the click chemistry concept has created a shift in how new polymers are designed and synthesized.  Click reactions are modular reactions that exhibit high selectivity and quantitative yields, owing to their extraordinarily high thermodynamic driving force.  While many of these reactions have been known about for decades, the reduction of all organic chemical reactions to a select group of “good reactions” provides a versatile functional group palette for designing new polymers while reducing their synthetic complexity.  Within this exemplary set of efficient chemical reactions, there are a few reactions that additionally possess the attribute of spatiotemporal control afforded by light initiation: so-called photo-click reactions. 

In this talk, approaches to implement new photo-enabled click reactions for polymerization and polymer modification will be discussed.  Beyond the archetypal photoinitiated thiol-ene and thiol-yne reactions, photo-enabled click reactions will be presented that are initiated via the photochemical production of a catalyst: namely, the base-catalyzed thiol-Michael and copper-catalyzed alkyne-azide cycloaddition (CuAAC) reactions.  We have demonstrated both formation and spatially specific modification of polymer networks with each of these reactions utilizing moderate intensities of long wavelength UV (365 nm) and visible light (400-500 nm).  These fundamental studies of reaction kinetics and temporal evolution of network properties have paved the way for use of these light-mediated approaches in a number of applications, from hydrogels to dental materials.  Further, these two new photo-click reactions increase the number functional groups and monomers for polymer design that possess both orthogonal reactivity and spatiotemporal reaction control.  This talk will address relevant synthesis strategies and limitations, as well as polymerization kinetics and network formation properties that can be achieved using photoclick reactions.