Influence of Type of Initiation on Thiol–Ene “Click” Chemistry

Abstract

Thermally and photochemically initiated thiol–ene click reactions using thiol‐ and allyl‐ end functionalized linear polystyrenes with various enes (allyl bromide, methyl acrylate, and methyl methacrylate) and thiol (3‐mercaptopropionic acid) have been investigated. Allyl‐ and thiol‐end‐capped polystyrenes with controlled molecular weight and low polydispersity were prepared by atom transfer radical polymerization (ATRP) of styrene using functional initiator and end group modification approaches, respectively. Thiol–ene reactions can be initiated by both cleavage type photoinitiators such as (2,4,6‐trimethylbenzoyl)diphenylphosphine oxide (TMDPO) and 2,2‐dimethoxy‐2‐phenyl acetophenone (DMPA) and H‐abstraction type photoinitiators such as benzophenone (BP), thioxanthone (TX), camphorquinone (CQ), and classical thermal initiator, 2,2′‐azobis(isobutyronitrile) (AIBN) at 80 °C. The kinetics of the reactions was monitored online with a real time ATR‐FTIR monitoring system and the conversions were determined by 1 H NMR spectroscopy. A comparison of click efficiencies of the studied initiator systems was performed. Compare to the thermal initiators and H‐abstraction type photoinitiators, cleavage type photoinitiators were found to induce thiol–ene click reactions with higher efficiency. magnified image