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Sulfur-centered radicals are important intermediates in radical-based polymerization processes, such as thiol-ene, thiol-yne, and certain free-radical polymerizations. They are also important in the repair mechanism of certain classes of self-healing materials. This chapter outlines these applications, with a special emphasis on their mechanistic aspects, as clarified by computational chemistry. Based on a review of the literature, we outline structure-reactivity considerations in reagent design for these processes, explain why sulfur-centered radical addition reactions are so reactive despite their thermodynamic unfavorability, and clarify the mechanism by which dithiuram-based self-healing polymers undergo reshuffling.

Herein we highlight recent studies and active areas of interest in the ongoing challenge to model photochemical processes in a wide variety of molecules. We also discuss recent significant methodological improvements and developments that may aid future investigations. Studies using the wide range of techniques available in modern electronic structure software packages have been included, with their successes and shortcomings forming part of the discussion. This study should therefore aid in the design of future computational studies.

The regulation of stereochemistry in radical polymerization has thus far proved enormously challenging, being the subject of more than 50 years of intense and innovative research. The relatively recent development of living radical polymerization has revitalized interest in stereocontrol, as the lack of tacticity control is now the greatest obstacle to the synthesis of precisely controlled macromolecules by highly versatile and efficient radical-based processes. Lewis acids (LAs) have been employed in an attempt to overcome the relatively poor stereoselectivity of unmediated radical polymerization, although the level of stereocontrol achieved is highly variable and condition dependent. We examine the use of LAs in radical polymerization from a mechanistic perspective, considering the underlying mechanism of tacticity determination and the likely requirements for effective stereocontrol. Concurrently, we examine the use of LAs in synthetic radical transformations, where they can facilitate very high levels of diastereocontrol but similar variability and condition dependencies are also noted. This chapter outlines and assesses some of the key factors likely to underlie the success or failure LA-mediated isotactic control in radical polymerization.