Photoinduced Side-Chain Functionalization, Grafting, Cross-Linking, and Chain Extension by Thiol-Epoxide Click Reaction Using Photo Base Generator

In this work, photoinduced thiol-epoxy click reaction for side-chain functionalization, chain-extension, grafting, and cross-linking of polymers prepared by atom transfer radical polymerization by using 1,5-diazabicyclo[5.4.0]undec-5-ene thioxanthone acetate (Tx-DBU) as a photo base generator (PBG) is described. Irradiation of Tx-DBU at 365 nm leads to the generation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in neutral form as a super base. DBU is capable of abstracting protons from thiols and thus formed thiolates are excellent nucleophiles that exhibit high affinity toward electrophiles such as epoxide rings. Appropriately selected thiols are successfully used for the desired reactions. The precursors and resulting polymers are characterized using ¹H-NMR, Fourier transform infrared, gel permeation chromatography, and differential scanning calorimetry measurements. This study shows that the use PBGs can further be extended to the synthesis of various complex macromolecular structures by the described post modification processes.