Photocatalytic ATRP Depolymerization: Temporal Control at Low ppm of Catalyst Concentration

Abstract

A photocatalytic ATRP depolymerization is introduced that significantly suppresses the reaction temperature from 170 to 100 °C while enabling temporal regulation. In the presence of low-toxicity iron-based catalysts and under visible light irradiation, near-quantitative monomer recovery could be achieved (up to 90%), albeit with minimal temporal control. By employing ppm concentrations of either FeCl2 or FeCl3, the depolymerization during the dark periods could be completely eliminated, thus enabling temporal control and the possibility to modulate the rate by simply turning the light “on” and “off”. Notably, our approach allowed preservation of the end-group fidelity throughout the reaction, could be carried out at high polymer loadings (up to 2M), and was compatible with various polymers and light sources. This methodology provides a facile, environmentally friendly, and temporally regulated route to chemically recycle ATRP-synthesized polymers, thus opening the door for further opportunities.

The thermodynamics and kinetics of depolymerization: what makes vinyl monomer regeneration feasible?

“…When light was used for activation in addition to an iron catalyst in a photothermal system, the temperature could be lowered to 100 °C, and almost perfect temporal control was achieved with low catalyst loadings at 120 °C. 152 Once again, the results for the polymers produced by ATRP show that the depolymerization temperature can be lowered signicantly compared to conditions used for FRP (∼300 °C (ref. 127) vs. 100 °C for polymethacrylates) as the activation energy of the initiation step is decreased by the functional end-groups.…”

Chemical recycling of bromine-terminated polymers synthesized by ATRP

“…49 Impressively, the Matyjaszewski group was able to significantly boost the depolymerization conversions to 70-80%, by performing reactions at 170 °C and utilizing either a copper or iron-based catalyst. [50][51][52] On the photo-thermal front, our group recently reported that photocatalytic ATRP depolymerization could also be successful under blue light irradiation and iron catalysis, 53 also reaching high monomer recovery (up to 90%). It is noted that the depolymerization of the aforementioned ATRP-made materials can take place in up to 2 M concentration with the exception of a recent report that showcases a higher temperature bulk depolymerization.…”

“…It is noted that the depolymerization of the aforementioned ATRP-made materials can take place in up to 2 M concentration with the exception of a recent report that showcases a higher temperature bulk depolymerization. 54 However, current literature reports, including both solution and bulk depolymerization strategies, have focused nearly exclusively on chlorine-terminated polymers, 45,[49][50][51][52][53][54] even though the vast majority of polymers prepared by ATRP have a bromine end-group. Therefore, the development of a single-step method to depolymerize bromine-terminated polymers yielding high conversions would significantly expand the scope of materials compatible with chemical recycling.…”

A Versatile Comonomer Additive for Radically Recyclable Vinyl‐derived Polymers

“…[8][9][10] Current chemical methods for recycling vinyl-derived homopolymers are limited to a few energy-intensive processes, such as heating above a ceiling temperature, [11][12][13][14] pyrolysis, [15] and incineration, [16] which can result in complex product mixtures not suitable for repolymerization. Promising recent studies on catalyzed [17,18] and end-group assisted depolymerization, [19,20] address the highenergy concerns associated with other ceiling temperature schemes, but thus far remain material-specific.…”