Polyglyoxylates: A Versatile Class of Triggerable Self-Immolative Polymers from Readily Accessible Monomers

Self-Immolative Polymers Derived from Renewable Resources via Thiol-Ene Chemistry

The development of polymers from renewable resources is a promising approach to reduce reliance on petrochemicals. In addition, depolymerization is attracting significant attention for the breakdown of polymers at their end-of-life or to achieve specific stimuli-responsive functions. However, the design of polymers incorporating both of these features remains a challenge. Herein, we report a new class of self-immolative polymers based on lignin-derived aldehydes via a simple thiol-ene polymerization. These self-immolative polymers undergo cascade degradation in response to specific stimuli through alternating 1,6-elimination and cyclization reactions. The two methoxy substituents on the syringaldehyde monomer accelerated the desired depolymerization reaction, while enhancing stability against undesired backbone hydrolysis. Moreover, diverse responsive end-caps could be introduced through post-polymerization functionalization from a single polymer precursor.

Efficient Encapsulation of β-Lapachone into Self-Immolative Polymer Nanoparticles for Cyclic Amplification of Intracellular Reactive Oxygen Species Stress

The selective upregulation of intracellular oxidative stress in cancer cells presents a promising approach for effective cancer treatment. In this study, we report the integration of enzyme catalytic amplification and chemical amplification reactions in β-lapachone (Lap)-loaded micellar nanoparticles (NPs), which are self-assembled from reactive oxygen species (ROS)-responsive self-immolative polymers (SIPs). This integration enables cyclic amplification of intracellular oxidative stress in cancer cells. Specifically, we have developed ROS-responsive SIPs with phenylboronic ester triggering motifs and hexafluoroisopropanol moieties in the side chains, significantly enhancing Lap loading efficiency (98%) and loading capacity (33%) through multiple noncovalent interactions. Upon ROS activation in tumor cells, the Lap-loaded micellar NPs disassemble, releasing Lap and generating additional ROS via enzyme catalytic amplification. This process elevates intracellular oxidative stress and triggers polymer depolymerization in a positive feedback loop. Furthermore, the degradation of SIPs via chemical amplification produces azaquinone methide intermediates, which consume intracellular thiol-related substrates, disrupt intracellular redox hemostasis, further intensify oxidative stress, and promote cancer cell apoptosis. This work introduces a strategy to enhance intracellular oxidative stress by combining enzymatic and chemical amplification reactions, providing a potential pathway for the development of highly efficient anticancer agents.

Self-immolative Polymer Hydrogels via In Situ Gelation

Hydrogels are of interest for a wide range of applications. The ability to control when the hydrogel degrades can provide beneficial properties such as controlled degradation in the environment or the stimulated release of drugs or cells. Self-immolative polymers are a class of degradable polymers that undergo complete end-to-end depolymerization upon the application of a stimulus. They have been explored for hydrogel development, but the ability to prepare and selectively degrade self-immolative hydrogels under neutral aqueous conditions has so far been limited. We describe here the preparation of water-soluble polyglyoxylamides with cross-linkable pendent azides and their cross-linking to form hydrogels with 4-arm poly(ethylene glycol)s having unstrained and strained alkynes using copper-assisted and strain-promoted azide-alkyne click chemistry respectively. The influence of pendent azide density and solution polymer content on the resulting hydrogels was evaluated. A polyglyoxylamide with a 70 : 30 ratio of pendent hydroxyl:azide successfully provided hydrogels with compressive moduli ranging from 1.3-6.3 kPa under copper-free conditions at 10-20 % (w/w) of polymer in phosphate-buffered saline. Selective depolymerization and degradation of the hydrogels upon irradiation with light was demonstrated, resulting in reductions in the compressive moduli and the release of depolymerization products that were detected by NMR spectroscopy.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Click to Self-immolation: A "Click" Functionalization Strategy towards Triggerable Self-Immolative Homopolymers and Block Copolymers

Self-immolative polymers (SIPs) are a class of degradable macromolecules that undergo stimuli-triggered head-to-tail depolymerization. However, a general approach to readily end-functionalize SIP precursors for programmed degradation remains elusive, restricting access to complex, functional SIP-based materials. Here we present a "click to self-immolation" strategy based on aroyl azide-capped SIP precursors, enabling the facile construction of diverse SIPs with different trigger units through a Curtius rearrangement and alcohol/thiol-isocyanate "click" reaction. This strategy is also applied to polymer-polymer coupling to access fully depolymerizable block copolymer amphiphiles, even combining different SIP backbones. Our results demonstrate that the depolymerization can be actuated efficiently under physiologically-relevant conditions by the removal of the trigger units and ensuing self-immolation of the p-aminobenzyl carbonate linkage, indicating promise for controlled release applications involving nanoparticles and hydrogels.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Self-Immolative Polymer Nanoparticles with Precise and Controllable pH-Dependent Degradation

Polymer nanoparticles have generated significant interest as delivery systems for therapeutic cargo. Self-immolative polymers (SIPs) are an interesting category of materials for delivery applications, as the characteristic property of end-to-end depolymerization allows for the disintegration of the delivery system, facilitating a more effective release of the cargo and clearance from the body after use. In this work, nanoparticles based on a pH-responsive polymer poly(ethylene glycol)-b-(2-diisopropyl)amino ethyl methacrylate) and a self-immolative polymer poly[N,N-(diisopropylamino)ethyl glyoxylamide-r-N,N-(dibutylamino)ethyl glyoxylamide] (P(DPAEGAm-r-DBAEGAm)) were developed. Four particles were synthesized based on P(DPAEGAm-r-DBAEGAm) polymers with varied diisopropylamino to dibutylamino ratios of 4:1, 2:1, 2:3, and 0:1, termed 4:1, 2:1, 2:3, and 0:1 PGAm particles. The pH of particle disassembly was tuned from pH 7.0 to pH 5.0 by adjusting the ratio of diisopropylamino to dibutylamino substituents on the pendant tertiary amine. The P(DPAEGAm-r-DBAEGAm) polymers were observed to depolymerize (60-80%) below the particle disassembly pH after ∼2 h, compared to <10% at pH 7.4 and maintained reasonable stability at pH 7.4 (20-50% depolymerization) after 1 week. While all particles exhibited the ability to load a peptide cargo, only the 4:1 PGAm particles had higher endosomal escape efficiency (∼4%) compared to the 2:3 or 0:1 PGAm particles (<1%). The 4:1 PGAm particle is a promising candidate for further optimization as an intracellular drug delivery system with rapid and precisely controlled degradation.

Self-Immolative Hydrogels with Stimulus-Mediated On-Off Degradation

Hydrogels are of interest for a wide range of applications from sensors to drug delivery and tissue engineering. Self-immolative polymers, which depolymerize from end-to-end following a single backbone or end-cap cleavage, offer advantages such as amplification of the stimulus-mediated cleavage event through a cascade degradation process. It is also possible to change the active stimulus by changing only a single end-cap or linker unit. However, there are very few examples of self-immolative polymer hydrogels, and the reported examples exhibited relatively poor stability in their nontriggered state or slow degradation after triggering. Described here is the preparation of hydrogels composed of self-immolative poly(ethyl glyoxylate) (PEtG) and poly(ethylene glycol) (PEG). Hydrogels formed from 2 kg/mol 4-arm PEG and 1.2 kg/mol PEtG with a light-responsive linker end-cap had high gel content (90%), an equilibrium water content of 89%, and a compressive modulus of 26 kPa. The hydrogel degradation could be turned on and off repeatedly through alternating cycles of irradiation and dark storage. Similar cycles could also be used to control the release of the anti-inflammatory drug celecoxib. These results demonstrate the potential for self-immolative hydrogels to afford a high degree of control over responses to stimuli in the context of smart materials for a variety of applications.

Mechanisms of Degradation for Polydisulfides: Main Chain Scission, Self-Immolation, Or Chain Transfer Depolymerization

Organic polydisulfides hold immense potential for the design of recyclable materials. Of these, polymers based on lipoic acid are attractive, as they are based on a natural, renewable resource. Herein, we demonstrate that reductive degradation of lipoic acid polydisulfides is a rapid process whereby the quantity of added initiator relative to the polymer content defines the mechanism of polymer degradation, through the main chain scission, self-immolation, or "chain transfer" depolymerization. The latter mechanism is defined as the one during which a thiol group released through the decomposition of one polydisulfide chain initiates depolymerization of the neighbor macromolecule. The chain transfer mechanism afforded the highest yields of recovery of the monomer in its pristine form, and just one molecule of the reducing agent to initiate polymer degradation afforded recovery of over 50% of the monomer. These data are important to facilitate the development of polymer recycling and monomer reuse schemes.

Nitro-Containing Self-Immolative Systems for Biological Applications

Since its introduction in 1981, the chemistry of self-immolative systems has received increasing attention in different application areas, such as analytical chemistry, medicinal chemistry, and materials science. This strategy is based on a stimulation that triggers a cascade of disassembling reactions leading to the release of smaller molecules. The particular reactivity of the nitro group, due to its powerful electron-withdrawing nature, has been exploited in the field of self-immolative chemistry. In this context, the present review describes the major role of the nitro group in self-immolative processes depending on its position.

Self-immolative Amphiphilic Diblock Copolymers with Individually Triggerable Blocks

Self-immolative polymers are a growing class of degradable polymers that undergo end-to-end depolymerization after the stimuli-responsive cleavage of an end-cap or backbone unit. Their incorporation into amphiphilic block copolymers can lead to functions such as the disintegration of copolymer nanoassemblies when depolymerization is triggered. However, diblock copolymers have not yet been developed where both blocks are self-immolative. Described here is the synthesis, self-assembly, and triggered depolymerization of self-immolative block copolymers with individually triggerable hydrophilic and hydrophobic blocks. Neutral and cationic hydrophilic polyglyxoylamides (PGAm) with acid-responsive end caps were synthesized and coupled to an ultraviolet (UV) light-triggerable poly(ethyl glyoxylate) (PEtG) hydrophobic block. The resulting block copolymers self-assembled to form nanoparticles in aqueous solution, and their depolymerization in response to acid and UV light was studied by techniques including light scattering, NMR spectroscopy, and electron microscopy. Acid led to selective depolymerization of the PGAm blocks, leading to aggregation, while UV light led to selective depolymerization of the PEtG block, leading to disassembly. This self-immolative block copolymer system provides an enhanced level of control over smart copolymer assemblies and their degradation.

Electrocatalytic Depolymerization of Self-Immolative Poly(Dithiothreitol) Derivatives

We report the use of electrogenerated anthraquinone radical anion (AQ•-) to trigger fast catalytic depolymerization of polymers derived from poly(dithiothreitol) (pDTT)-a self-immolative polymer (SIP) with a backbone of dithiothreitols connected with disulfide bonds and end-capped via disulfide bonds to pyridyl groups. The pDTT derivatives studied include polymers with simple thiohexyl end-caps or modified with AQ or methyl groups by Steglich esterification. All polymers were shown to be depolymerized using catalytic amounts of electrons delivered by AQ•-. For pDTT, as little as 0.2 electrons per polymer chain was needed to achieve complete depolymerization. We hypothesize that the reaction proceeds with AQ•- as an electron carrier (either molecularly or as a pendant group), which transfers an electron to a disulfide bond in the polymer in a dissociative manner, generating a thiyl radical and a thiolate. The rapid and catalytic depolymerization is driven by thiyl radicals attacking other disulfide bonds internally or between pDTT chains in a chain reaction. Electrochemical triggering works as a general method for initiating depolymerization of pDTT derivatives and may likely also be used for depolymerization of other disulfide polymers.

Degradable polyprodrugs: design and therapeutic efficiency

Prodrugs are developed to increase the therapeutic properties of drugs and reduce their side effects. Polyprodrugs emerged as highly efficient prodrugs produced by the polymerization of one or several drug monomers. Polyprodrugs can be gradually degraded to release therapeutic agents. The complete degradation of polyprodrugs is an important factor to guarantee the successful disposal of the drug delivery system from the body. The degradation of polyprodrugs and release rate of the drugs can be controlled by the type of covalent bonds linking the monomer drug units in the polymer structure. Therefore, various types of polyprodrugs have been developed based on polyesters, polyanhydrides, polycarbonates, polyurethanes, polyamides, polyketals, polymetallodrugs, polyphosphazenes, and polyimines. Furthermore, the presence of stimuli-responsive groups, such as redox-responsive linkages (disulfide, boronate ester, metal-complex, and oxalate), pH-responsive linkages (ester, imine, hydrazone, acetal, orthoester, P-O and P-N), light-responsive (metal-complex, o-nitrophenyl groups) and enzyme-responsive linkages (ester, peptides) allow for a selective degradation of the polymer backbone in targeted tumors. We envision that new strategies providing a more efficient synergistic therapy will be developed by combining polyprodrugs with gene delivery segments and targeting moieties.

Cyclocarbonylation of Allenyl Glyoxylate Strategy to Build the Tricyclic Core of Cyclocalopin A

An approach for the construction of the tricyclic framework of naturally occurring cyclocalopin A is described. The establishment of the crucial intermediate α-methylene bis-γ,δ-lactone involves a [2 + 2 + 1]-cyclocarbonylation of newly introduced allenyl glyoxylate via direct methods using Mo(CO)₆ or sequential reaction pathways. The sequential reaction route involved a stannylative cyclization by Pd(0) catalyst, bromination of an vinyl stannane moiety, and final cyclocarbonylation by palladium catalysis to provide the bis-γ,δ-lactone. The feasibility of forming the spiro-system by an exo-selective [4 + 2]-cycloaddition was accomplished.

Self-immolative Polyplexes for DNA Delivery

Nucleic acids have immense potential for the treatment and prevention of a wide range of diseases, but delivery vehicles are needed to assist with their entry into cells. Polycations can...

Discrete, self-immolative N-substituted oligourethanes and their use as molecular tags

The depolymerization of N-substituted oligourethanes via an intramolecular cyclization event was studied in-depth, while the applicability of these macromolecules as anti-counterfeiting tags was demonstrated by labeling a polyurethane material.

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

Self-Immolative Polymers: An Emerging Class of Degradable Materials with Distinct Disassembly Profiles

Self-immolative polymers are an emerging class of macromolecules with distinct disassembly profiles that set them apart from other general degradable materials. These polymers are programmed to disassemble spontaneously from head to tail, through a domino-like fragmentation, upon response to extremal stimuli. In the time since we first reported this unique type of molecule, several groups around the world have developed new, creative molecular structures that perform analogously to our pioneering polymers. Self-immolative polymers are now widely recognized as an important class of stimuli-responsive materials for a wide range of applications such as signal amplification, biosensing, drug delivery, and materials science. The quinone-methide elimination was shown to be an effective tool to achieve rapid domino-like fragmentation of polymeric molecules. Thus, numerous applications of self-immolative polymers are based on this disassembly chemistry. Although several other fragmentation reactions achieved the function requested for sequential disassembly, we predominantly focused in this Perspective on examples of self-immolative polymers that disassemble through the quinone-methide elimination. Selected examples of self-immolative polymers that disassembled through other chemistries are briefly described. The growing demand for stimuli-responsive degradable materials with novel molecular backbones and enhanced properties guarantees the future interest of the scientific community in this unique class of polymers.

Metathesis Cascade-Triggered Depolymerization of Enyne Self-Immolative Polymers*

A novel class of enyne self-immolative polymers (SIPs) capable of metathesis cascade-triggered depolymerization is reported. Studies on model compounds established 1,6-enyne structures for efficient metathesis cascade reactions. SIPs incorporating the optimized 1,6-enyne motif were prepared via both polycondensation and iterative exponential growth approaches. These SIPs demonstrated excellent stability in strong acid, base, nucleophiles, or at elevated temperatures, and can undergo efficient and complete depolymerization once triggered by a metathesis catalyst. Further studies revealed that introducing a terminal alkene to the chain end of the enyne SIPs improved the depolymerization efficiency, and established their potential as stimuli-responsive materials.

The Chemical Recycling of Polyesters for a Circular Plastics Economy: Challenges and Emerging Opportunities

Whilst plastics have played an instrumental role in human development, growing environmental concerns have led to increasing public scrutiny and demands for outright bans. This has stimulated considerable research into renewable alternatives, and more recently, the development of alternative waste management strategies. Herein, the aim was to highlight recent developments in the catalytic chemical recycling of two commercial polyesters, namely poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET). The concept of chemical recycling is first introduced, and associated opportunities/challenges are discussed within the context of the governing depolymerisation thermodynamics. Chemical recycling methods for PLA and PET are then discussed, with a particular focus on upcycling and the use of metal-based catalysts. Finally, the attention shifts to the emergence of new materials with the potential to modernise the plastics economy. Emerging opportunities and challenges are discussed within the context of industrial feasibility.

Acid-Responsive Poly(glyoxylate) Self-Immolative Star Polymers

Self-immolative polymers have significant potential for applications such as drug or gene delivery. However, to realize this potential, such materials need to be customized to respond to specific variations in biological conditions. In this work, we investigated the design of new star-shaped self-immolative poly(ethyl glyoxylate)s (PEtGs) and their incorporation into responsive nanoparticles. PEtGs are a subclass of stimulus-responsive self-immolative polymers, which can be combined with different stimuli-responsive functionalities. Two different tetrathiol initiators were used for the polymerization in combination with a variety of potential pH-responsive end-caps, yielding a library of star PEtG polymers which were responsive to pH. Characterization of the depolymerization behavior of the polymers showed that the depolymerization rate was controlled by the end caps rather than the architecture of the polymer. A selection of the star polymers were modified with amines to allow introduction of charge-shifting properties. It was shown that pH-responsive nanoparticles could be prepared from these modified polymers and they demonstrated pH-dependent particle disruption. The pH responsiveness of these particles was studied by dynamic light scattering and ¹H nuclear magnetic resonance spectroscopy.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

Amine-Catalyzed Chain Polymerization of Ethyl Glyoxylate from Alcohol and Thiol Initiators

Polyacetals have significant potential as degradable polymers, but aldehyde polymerizations are generally difficult to control. Here we show that polymerization of ethyl glyoxylate can be initiated from alcohols or thiols by activation with triethylamine to afford poly(ethyl glyoxylate) with controllable molecular weights and relatively low dispersities (Đ = 1.3-1.4), as evidenced by MALDI-TOF mass spectrometry. Stabilization against depolymerization by chain-capping with benzyl chloroformate was found to proceed without side reactions observed from chain-capping with tolyl isocyanate. The use of the stronger base DBU leads to competing side reactions that limit polymer molecular weight.

Post-polymerization ‘click’ end-capping of polyglyoxylate self-immolative polymers

Post-polymerization CuAAC reactions are used to ‘click’ stimuli-cleavable triazole end-caps onto self-immolative poly(ethyl glyoxylate).

100th Anniversary of Macromolecular Science Viewpoint: Toward Catalytic Chemical Recycling of Waste (and Future) Plastics

The current global materials economy has long been inefficient due to unproductive reuse and recycling efforts. Within the wider materials portfolio, plastics have been revolutionary to many industries but they have been treated as disposable commodities leading to their increasing accumulation in the environment as waste. The field of chemistry has had significant bearing in ushering in the current plastics industry and will undoubtedly have a hand in transforming it to become more sustainable. Existing approaches include the development of synthetic biodegradable plastics and turning to renewable raw materials in order to produce plastics similar to our current petrol-based materials or to create new polymers. Additionally, chemists are confronting the environmental crisis by developing alternative recycling methods to deal with the legacy of plastic waste. Important emergent technologies, such as catalytic chemical recycling or upcycling, have the potential to alleviate numerous issues related to our current and future refuse and, in doing so, help pivot our materials economy from linearity to circularity.

Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation

Many plastic packaging materials manufactured today are composites made of distinct polymer layers (i.e., multilayer films). Billions of pounds of these multilayer films are produced annually, but manufacturing inefficiencies result in large, corresponding postindustrial waste streams. Although relatively clean (as opposed to municipal wastes) and of near-constant composition, no commercially practiced technologies exist to fully deconstruct postindustrial multilayer film wastes into pure, recyclable polymers. Here, we demonstrate a unique strategy we call solvent-targeted recovery and precipitation (STRAP) to deconstruct multilayer films into their constituent resins using a series of solvent washes that are guided by thermodynamic calculations of polymer solubility. We show that the STRAP process is able to separate three representative polymers (polyethylene, ethylene vinyl alcohol, and polyethylene terephthalate) from a commercially available multilayer film with nearly 100% material efficiency, affording recyclable resins that are cost-competitive with the corresponding virgin materials.

Covalent Post-Assembly Modification: A Synthetic Multipurpose Tool in Supramolecular Chemistry

The use of covalent post-assembly modification (PAM) in supramolecular chemistry has grown significantly in recent years, to the point where PAM is now a versatile synthesis tool for tuning, modulating, and expanding the functionality of self-assembled complexes and materials. PAM underpins supramolecular template-synthesis strategies, enables modular derivatization of supramolecular assemblies, permits the covalent 'locking' of unstable structures, and can trigger controlled structural transformations between different assembled morphologies. This Review discusses key examples of PAM spanning a range of material classes, including discrete supramolecular complexes, self-assembled soft nanostructures and hierarchically ordered polymeric and framework materials. As such, we hope to highlight how PAM has continued to evolve as a creative and functional addition to the synthetic chemist's toolbox for constructing bespoke self-assembled complexes and materials.

Poly(carboxypyrrole)s That Depolymerize from Head to Tail in the Solid State in Response to Specific Applied Signals

This Article describes the design, synthesis, and analysis of a new class of polymer that is capable of depolymerizing continuously, completely, and cleanly from head to tail when a detection unit on the head of the polymer is exposed to a specific applied signal. The backbone of this polymer consists of 1,3-disubstituted pyrroles and carboxy linkages similar to polyurethanes. Diverse side chains or reactive end-groups can be introduced readily, which provides modular design of polymer structure. The designed depolymerization mechanism proceeds through spontaneous release of carbon dioxide and azafulvene in response to a single triggering reaction with the detection unit. These poly(carboxypyrrole)s depolymerize readily in nonpolar environments, and even in the bulk as solid-state plastics.

Construction from Destruction: Hydrogel Formation from Triggered Depolymerization-Based Release of an Enzymatic Catalyst

Biomimetic systems that undergo macroscopic phase transformations by transducing and amplifying external cues are highly desirable for applications such as self-healing. Here, we report self-assembly of polyelectrolyte complexes into a vesicular structure that can accommodate hydrophilic guest molecules, including enzymes. Triggered depolymerization of one of the polyelectrolyte molecules in the complex causes the vesicle to disassemble and release its contents. Such a triggered release of enzymes causes molecular-scale events to be amplified due to the enzyme's catalytic properties. This feature has been utilized to demonstrate construction of hydrogels from the destruction of nanoscopic polymeric vesicles. The design principles developed here are broadly adaptable to other triggerable depolymerization motifs reported in the literature.

Dynamic pH responsivity of triazole-based self-immolative linkers

Gating the release of chemical payloads in response to transient signals is an important feature of ‘smart’ delivery systems. Herein, we report a triazole-based self-immolative linker that can be reversibly paused or slowed and restarted throughout its elimination cascade in response to pH changes in both organic and organic-aqueous solvents. The linker is conveniently prepared using the alkyne–azide cycloaddition reaction, which introduces a 1,4-triazole ring that expresses a pH-sensitive intermediate during its elimination sequence. Using a series of model compounds, we demonstrate that this intermediate can be switched between active and dormant states depending on the presence of acid or base, cleanly gating the release of payload in response to a fluctuating external stimulus.

Triazole-based self-immolative linkers can be reversibly paused and restarted throughout their elimination cascades in response to environmental pH changes.

Base-triggered self-amplifying degradable polyurethanes with the ability to translate local stimulation to continuous long-range degradation

A new type of base-triggered self-amplifying degradable polyurethane is reported that degrades under mild conditions, with the release of increasing amounts of amine product leading to self-amplified degradation. The polymer incorporates a base-sensitive Fmoc-derivative into every repeating unit to enable highly sensitive amine amplified degradation. A sigmoidal degradation curve for the linear polymer was observed consistent with a self-amplifying degradation mechanism. An analogous cross-linked polyurethane gel was prepared and also found to undergo amplified breakdown. In this case, a trace amount of localized base initiates the degradation, which in turn propagates through the material in an amplified manner. The results demonstrate the potential utility of these new generation polyurethanes in enhanced disposability and as stimuli responsive materials.

Room temperature synthesis of block copolymer nano-objects with different morphologies via ultrasound initiated RAFT polymerization-induced self-assembly (sono-RAFT-PISA)

The first room temperature synthesis of diblock copolymer nano-objects with different morphologies using ultrasound (990 kHz) initiated reversible addition-fragmentation chain transfer PISA (sono-RAFT-PISA) in aqueous system.

Construction from destruction using a photo-triggered self-propagating degradable polyurethane as a one-pot epoxy

We report a photo-triggered, base generating, base propagating degradable polyurethane that is triggered by 365 nm UV light irradiation.

Self-immolative polymers in biomedicine

Biomedical use cases for self-immolative polymers.

Development of Fertilizer Coatings from Polyglyoxylate-Polyester Blends Responsive to Root-Driven pH Change

Many current controlled-release fertilizers (CRFs) are coated with nonbiodegradable polymers that can contribute to microplastic pollution. Here, coatings of self-immolative poly(ethyl glyoxylate) (PEtG) capped with a carbamate and blended with polycaprolactone (PCL) or poly(l-lactic acid) (PLA) were evaluated. They were designed to depolymerize and release fertilizers in the vicinity of plant roots, where the pH is lower than that in the surrounding environment. PEtG/PCL coatings exhibited significant temperature and pH effects, requiring 18 days at pH 5 and 30 °C, compared to 77 days at pH 7 and 22 °C, to reach 15% mass loss. Plant roots were also effective in triggering coating degradation. Spray-coating and melt-coating were explored, with the latter being more effective in providing pellets that retained urea prior to polymer degradation. Finally, PEtG/PCL-coated pellets promoted plant growth to a similar degree or better than currently available CRFs.