Development of thermal and photochemical strategies for thiol-ene click polymer functionalization

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.