2024 AIChE Annual Meeting
Quantifying Radical Production from UV-Irradiation of a Trithiocarbonate-Containing RAFT Agent
In the past few years, advancements have established reversible addition-fragmentation chain transfer (RAFT) polymerization as a favorable approach for the synthesis of polymers with a diverse range of applications such as drug delivery and smart materials. Trithiocarbonate (TTC) groups, widely used in RAFT polymerizations, are susceptible to light, heat, and force due to their labile carbon-sulfur bonds, resulting in radical formation via homolytic cleavage. Conducting these polymerizations in aqueous solution provides a cost-effective, biologically safe, and environmentally friendly alternative to traditional organic solvents. In this work, we quantify radical production generated from the photolytic covalent bond scission of a TTC-containing RAFT agent in water. The method relies on the Fenton reaction which, when activated in the presence of the colorimetric indicator xylenol orange (XO), leads to an observable color change from yellow-to-brown, quantified using UV-Vis spectroscopy. Specifically, aqueous solutions of a TTC-containing RAFT agent were irradiated at its peak absorbance of 310 nm, and resulting color changes were measured as a function of concentration. For each concentration, the color changes were quantified by comparing the ratio of the peak absorbances at 580 nm to 440 nm, corresponding to complexed XO and unbound XO, respectively. Using known concentrations of radical generators, a calibration curve relating the extent of color change to the radical concentration was developed. This spectroscopic analysis enables the quantification of radicals produced from the stimuli-induced cleavage of TTC-containing polymer solutions and hydrogels, contributing to the use and further understanding of TTC-containing RAFT agents, and can be adapted for use with other radical generators.