Emerging Trends in the Chemistry of End-to-End Depolymerization

Abstract

Over the past couple of decades, polymers that depolymerize end-to-end upon cleavage of their backbone or activation of a terminal functional group, sometimes referred to as "self-immolative" polymers, have been attracting increasing attention. They are of growing interest in the context of enhancing polymer degradability but also in polymer recycling as they allow monomers to be regenerated in a controlled manner under mild conditions. Furthermore, they are highly promising for applications as smart materials due to their ability to provide an amplified response to a specific signal, as a single sensing event is translated into the generation of many small molecules through a cascade of reactions. From a chemistry perspective, end-to-end depolymerization relies on the principles of self-immolative linkers and polymer ceiling temperature (T c ). In this article, we will introduce the key chemical concepts and foundations of the field and then provide our perspective on recent exciting developments. For example, over the past few years, new depolymerizable backbones, including polyacetals, polydisulfides, polyesters, polythioesters, and polyalkenamers, have been developed, while modern approaches to depolymerize conventional backbones such as polymethacrylates have also been introduced. Progress has also been made on the topological evolution of depolymerizable systems, including the introduction of fully depolymerizable block copolymers, hyperbranched polymers, and polymer networks. Furthermore, precision sequence-defined oligomers have been synthesized and studied for data storage and encryption. Finally, our perspectives on future opportunities and challenges in the field will be discussed.

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

“…The reader is referred to other recent reviews for other polymer classes and further challenges of the recycling process. 24–27 While chemical recycling via pyrolysis, where the polymer is exposed to high temperatures (typically T > 300 °C) under the exclusion of oxygen to produce monomer and other small molecules, has been described and reviewed for a vast range of addition polymers, 28–33 reports of depolymerization at lower temperatures and with monomer as the product are much more recent. Recent exciting work has sought to overcome this challenge by utilizing addition polymers predominantly made by reversible-deactivation radical polymerization (RDRP) methods.…”

Design of depolymerizable polymers toward a circular economy

“…With the latest growing interests in depolymerizable polymers for the purpose of recycling, the two fields certainly merge with a common principle of controlling the monomer–polymer equilibrium. 158 Some of the polymers we have discussed so far depolymerize in an end-to-end fashion, such as the polymethacrylates, but at higher temperatures.…”

Recent Advances in Stimuli-Responsive Self-Immolative Polymers for Drug Delivery and Molecular Imaging

“…Over the past two decades, researchers have made significant efforts in the chemical structure and stimuli-responsive end-cap moieties of SIPs. Various architectures of SIPs with different self-immolation mechanisms and degradation characteristics have been developed . Here, we provide a brief overview and primarily focus on the latest updates in recent years.…”