Triggering Depolymerization: Progress and Opportunities for Self-Immolative Polymers

Abstract

Polymers that depolymerize end-to-end upon cleavage of their backbones or end-caps, often termed “self-immolative” polymers (SIPs), have garnered significant interest in recent years. They can be distinguished from other degradable and stimuli-responsive polymers by their ability to provide amplified responses to stimuli, as a single bond cleavage event is translated into the release of many small molecules through a cascade of reactions. Here, the synthesis and properties of the major classes of SIPs including poly­(benzyl carbamate)­s, poly­(benzyl carbonate)­s, poly­(benzyl ether)­s polyphthalaldehydes, polyglyoxylates, polyglyoxylamides, and poly­(olefin sulfone)­s are presented. In addition, their advantages and limitations as well as their recent applications in areas including sensors, drug delivery, micro- and nanopatterning, transient devices and composites, coatings, antibacterial, and recyclable plastics are described. Finally, the challenges associated with the development of new SIP backbones and their translation into commercial products are discussed.

Sugar‐Based Polymers from d‐Xylose: Living Cascade Polymerization, Tunable Degradation, and Small Molecule Release

“…With this specific reactivity in mind, we designed a furfuryl carbonate degradation product (an analogue to D3 ) which would enable the release of covalently bound molecular cargo, after the acidic degradation of the polymer. Polymers that release cargo upon degradation (Figure 6 A) are relevant to various applications including sensing, self‐healing, and drug delivery [16, 53–56] . We designed two new monomers, M5 and M6 (see Figure S6 in the SI for synthetic details), such that their polymers ( P5 and P6 ) would generate D5 and D6 , which would subsequently release p ‐nitrophenol (PNP) as a model cargo molecule (Figure 6 B), which could be easily monitored by UV‐vis and NMR analysis.…”

Flexible Cyclic‐Poly(phthalaldehyde)/Poly(ε‐caprolactone) Blend Fibers with Fast Daylight‐Triggered Transience

“…[ 1 ] The applications for transient materials are widespread, including triggerable capsules for controlled drug release, [ 2–4 ] lithography, [ 5 ] electronic devices, [ 1,6 ] biocompatible devices, [ 7–10 ] and self‐healing materials. [ 11,12 ] Polymers such as poly (lactic acid), [ 13 ] poly (lactic‐co‐glycolic acid), [ 13 ] polyvinyl alcohol, [ 14 ] poly(benzyl carbamate)s, [ 15,16 ] and poly(olefin sulfone)s [ 16,17 ] have been proposed as candidates for transient materials, whereby transience is accomplished with dissolving solvents [ 1,13–15,18 ] or thermal heating. [ 16,17,19–21 ] Poly(phthalaldehyde) (PPHA) is gaining attention as a stimuli‐responsive material, especially since the photo‐trigger in the form of UV‐absorbing photo‐acid generators (PAGs) are incorporated within PPHA.…”

“…[ 11,12 ] Polymers such as poly (lactic acid), [ 13 ] poly (lactic‐co‐glycolic acid), [ 13 ] polyvinyl alcohol, [ 14 ] poly(benzyl carbamate)s, [ 15,16 ] and poly(olefin sulfone)s [ 16,17 ] have been proposed as candidates for transient materials, whereby transience is accomplished with dissolving solvents [ 1,13–15,18 ] or thermal heating. [ 16,17,19–21 ] Poly(phthalaldehyde) (PPHA) is gaining attention as a stimuli‐responsive material, especially since the photo‐trigger in the form of UV‐absorbing photo‐acid generators (PAGs) are incorporated within PPHA. [ 22 ] In the 1960s, linear‐PPHA was first synthesized through the cationic polymerization of o‐phthalaldehyde, having two end caps to prevent unzipping.…”

“…(2) Its high glass transition temperature ( T g > 75 °C) and brittleness at room temperature are shortcomings of using cPPHA plastics. [ 22,29,30 ] To improve its flexibility, plasticizers like ionic‐liquids and ether‐esters were added to cPPHA films at high concentrations, [ 16,26,31 ] nevertheless, these plasticizers will eventually leach out leaving the cPPHA film brittle over time; [ 30 ] In addition, synthesizing new cPPHA copolymers has also been put forward to address these limitations. [ 29 ] (3) The UV‐responsive transience of cPPHA, which can vary from minutes to hours, depends on the formulation of photo‐triggers for specific wavelengths of UV light.…”

Functionalized and Degradable Polyphthalaldehyde Derivatives

“…Low-ceiling temperature (Tc) polymers are a class of metastable materials that are readily triggered to depolymerize back to monomers at temperatures above their Tc (Scheme 1). 1,2 Such materials have the potential to address a grand challenge in sustainability by facilitating recycling through repeated depolymerization/repolymerization cycles, extending their useful lifetimes. 3,4 Depolymerizable polymers also have important applications in areas such as lithography, 5 triggered release, 6 and transient electronics.…”