A series of alkene-functional polymers were synthesized by controlled polymerization techniques in order to investigate and compare the efficiency and orthogonality of both photochemically and thermally initiated thiol−ene click coupling reactions. The copolymers were designed to have single or multiple alkene-functional groups along the backbone, and to evaluate the robustness of these procedures, functionalization reactions with a library of mercaptans were studied. In comparing the photoinitiated reaction to its thermal counterpart, the thiol−ene photocoupling was found to proceed with higher efficiency, require shorter reaction times for complete conversion, and displayed a higher tolerance to various backbones and functional groups. To examine the orthogonality of the thiol−ene click reaction, an asymmetric telechelic polymer based on PS was designed with alkene functionality at one end and an azide at the other. The thermally initiated thiol−ene coupling was found to be completely orthogonal with the traditional azide/alkyne click reaction allowing the individual chain ends to be quantitatively functionalized without the need for protection/deprotection strategies. From these studies, the demonstrated efficiency and orthogonality of thiol−ene chemistry shows it to be a practical addition to the family of click reactions that are suitable for polymer functionalization.
Campos, L. M., Killops, K. L., Sakai, R., Paulusse, J. M. J., Damiron, D., Drockenmuller, E., ... Hawker, C. J. (2008). Development of Thermal and Photochemical Strategies for Thiol−Ene Click Polymer Functionalization. Macromolecules, 41(19), 7063-7070. https://doi.org/10.1021/ma801630n