Gas-Responsive Polymers

Gas-Responsive and Gas-Releasing Polymer Assemblies

In order to explore the unique physiological roles of gas signaling molecules and gasotransmitters in vivo, chemists have engineered a variety of gas-responsive polymers that can monitor their changes in cellular milieu, and gas-releasing polymers that can orchestrate the release of gases. These have advanced their potential applications in the field of bio-imaging, nanodelivery, and theranostics. Since these polymers are of different chain structures and properties, the morphology of their assemblies will manifest distinct transitions after responding to gas or releasing gas. In this review, we summarize the fundamental design rationale of gas-responsive and gas-releasing polymers in structure and their controlled transition in self-assembled morphology and function, as well as present some perspectives in this prosperous field. Emerging challenges faced for the future research are also discussed.

Covalent adaptable polymer networks with CO2-facilitated recyclability

Cross-linked polymers with covalent adaptable networks (CANs) can be reprocessed under external stimuli owing to the exchangeability of dynamic covalent bonds. Optimization of reprocessing conditions is critical since increasing the reprocessing temperature costs more energy and even deteriorates the materials, while reducing the reprocessing temperature via molecular design usually narrows the service temperature range. Exploiting CO2 gas as an external trigger for lowering the reprocessing barrier shows great promise in low sample contamination and environmental friendliness. Herein, we develop a type of CANs incorporated with ionic clusters that achieve CO2-facilitated recyclability without sacrificing performance. The presence of CO2 can facilitate the rearrangement of ionic clusters, thus promoting the exchange of dynamic bonds. The effective stress relaxation and network rearrangement enable the system with rapid recycling under CO2 while retaining excellent mechanical performance in working conditions. This work opens avenues to design recyclable polymer materials with tunable dynamics and responsive recyclability.

CO2-Responsive Water-Soluble Conjugated Polymers as a Multifunctional Fluorescent Probe for Bioimaging Applications

We describe important progress in the synthesis and development of gas-responsive water-soluble conjugated polymers (WSCPs) with potential as multifunctional fluorescent materials for biomedical imaging and probes. A water-soluble WSCP (I-PT) composed of a hydrophobic fluorescent polythiophene backbone and a hydrophilic imidazole side chain was successfully prepared through a facile and efficient two-step synthetic route. Owing to the repulsive force between the hydrophilic and hydrophobic segments and the highly sensitive carbon dioxide (CO2)- and nitrogen (N2)-responsive imidazole groups in its structure, I-PT can spontaneously self-assemble into spherical-like nanoparticles in an aqueous environment, and thus exhibits unique light absorption and fluorescence properties as well as rapid responsiveness to CO2 and N2. In addition, its structure, optical absorption/fluorescence behavior, and surface potential can be quickly turned on and off through alternating cycles of CO2 and N2 bubbling and exhibit controllable cyclic switching stability, thereby allowing effective manipulation of its hierarchical structure and chemical-physical characteristics. More importantly, a series of in vitro cell experiments confirmed that, compared to the significant cytotoxicity of pristine and N2-treated I-PT nanoparticles, CO2-treated I-PT nanoparticles exhibit extremely low cytotoxicity in normal and cancer cells and undergo greatly accelerated cellular uptake, resulting in a significant increase in the intensity and stability of their fluorescence signal in the intracellular environment. Overall, this newly discovered CO2/N2-responsive system provides new insights to effectively enhance the biocompatibility, cellular internalization, and intracellular fluorescence characteristics of WSCPs and holds great potential for biomedical imaging/sensing applications.

Recent Progress in Gas Sensors Based on P3HT Polymer Field-Effect Transistors

In recent decades, the rapid development of the global economy has led to a substantial increase in energy consumption, subsequently resulting in the emission of a significant quantity of toxic gases into the environment. So far, gas sensors based on polymer field-effect transistors (PFETs), a highly practical and cost-efficient strategy, have garnered considerable attention, primarily attributed to their inherent advantages of offering a plethora of material choices, robust flexibility, and cost-effectiveness. Notably, the development of functional organic semiconductors (OSCs), such as poly(3-hexylthiophene-2,5-diyl) (P3HT), has been the subject of extensive scholarly investigation in recent years due to its widespread availability and remarkable sensing characteristics. This paper provides an exhaustive overview encompassing the production, functionalization strategies, and practical applications of gas sensors incorporating P3HT as the OSC layer. The exceptional sensing attributes and wide-ranging utility of P3HT position it as a promising candidate for improving PFET-based gas sensors.

Recent advances in permeable polymersomes: fabrication, responsiveness, and applications

Polymersomes are vesicular nanostructures enclosed by a bilayer-membrane self-assembled from amphiphilic block copolymers, which exhibit higher stability compared with their biological analogues (e.g. liposomes). Due to their versatility, polymersomes have found various applications in different research fields such as drug delivery, nanomedicine, biological nanoreactors, and artificial cells. However, polymersomes prepared with high molecular weight components typically display low permeability to molecules and ions. It hence remains a major challenge to balance the opposing features of robustness and permeability of polymersomes. In this review, we focus on the design and strategies for fabricating permeable polymersomes, including polymersomes with intrinsic permeability, the formation of nanopores in the membrane bilayers by protein insertion, and the construction of stimuli-responsive polymersomes. Then, we highlight the applications of permeable polymersomes in the fields of biomimetic nanoreactors, artificial cells and organelles, and nanomedicine, to underline the challenges in the development of polymersomes as soft matter with biomedical utilities.

CO2-responsive gels

CO₂-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO₂. The use of CO₂ as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO₂-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO₂-responsive polymers, the study of CO₂-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO₂ such as swelling or a transformed morphology. In the past 15 years, CO₂-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO₂-triggered aggregation and their capacity for reversible CO₂ absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO₂ sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO₂-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO₂-induced self-assembled gels (including poly(ionic liquid) gels).

Scalable and switchable CO2-responsive membranes with high wettability for separation of various oil/water systems

Smart membranes with responsive wettability show promise for controllably separating oil/water mixtures, including immiscible oil-water mixtures and surfactant-stabilized oil/water emulsions. However, the membranes are challenged by unsatisfactory external stimuli, inadequate wettability responsiveness, difficulty in scalability and poor self-cleaning performance. Here, we develop a capillary force-driven confinement self-assembling strategy to construct a scalable and stable CO2-responsive membrane for the smart separation of various oil/water systems. In this process, the CO2-responsive copolymer can homogeneously adhere to the membrane surface by manipulating the capillary force, generating a membrane with a large area up to 3600 cm2 and excellent switching wettability between high hydrophobicity/underwater superoleophilicity and superhydrophilicity/underwater superoleophobicity under CO2/N2 stimulation. The membrane can be applied to various oil/water systems, including immiscible mixtures, surfactant-stabilized emulsions, multiphase emulsions and pollutant-containing emulsions, demonstrating high separation efficiency (>99.9%), recyclability, and self-cleaning performance. Due to robust separation properties coupled with the excellent scalability, the membrane shows great implications for smart liquid separation.

Breathable Lignin Nanoparticles as Reversible Gas Swellable Nanoreactors

The design of stimuli-responsive lignin nanoparticles (LNPs) for advanced applications has hitherto been limited to the preparation of lignin-grafted polymers in which usually the lignin content is low (<25 wt.%) and its role is debatable. Here, the preparation of O₂ -responsive LNPs exceeding 75 wt.% in lignin content is shown. Softwood Kraft lignin (SKL) is coprecipitated with a modified SKL fluorinated oleic acid ester (SKL-OlF) to form colloidal stable hybrid LNPs (hy-LNPs). The hy-LNPs with a SKL-OlF content ranging from 10 to 50 wt.% demonstrated a reversible swelling behavior upon O₂ /N₂ bubbling, increasing their size - ≈35% by volume - and changing their morphology from spherical to core-shell. Exposition of hy-LNPs to O₂ bubbling promotes a polarity change on lignin-fluorinated oleic chains, and consequently their migration from the inner part to the surface of the particle, which not only increases the particle size but also endows hy-LNPs with enhanced stability under harsh conditions (pH < 2.5) by the hydration barrier effect. Furthermore, it is also demonstrated that these new stimuli-responsive particles as gas tunable nanoreactors for the synthesis of gold nanoparticles. Combining a straightforward preparation with their enhanced stability and responsiveness to O₂ gas these new LNPs pave the way for the next generation of smart lignin-based nanomaterials.

A CO2-Responsive Imidazole-Functionalized Fluorescent Material Mediates Cancer Chemotherapy

We present a breakthrough in the synthesis and development of functional gas-responsive materials as highly potent anticancer agents suitable for applications in cancer treatment. Herein, we successfully synthesised a stimuli-responsive multifunctional material (I-R6G) consisting of a carbon dioxide (CO₂)-sensitive imidazole moiety and spirolactam-containing conjugated rhodamine 6G (R6G) molecule. The resulting I-R6G is highly hydrophobic and non- or weakly fluorescent. Simple CO₂ bubbling treatment induces hydrophobic I-R6G to completely dissolve in water and subsequently form self-assembled nanoparticles, which exhibit unique optical absorption and fluorescence behaviours in water and extremely low haemolytic ability against sheep red blood cells. Reversibility testing indicated that I-R6G undergoes reversible CO₂/nitrogen (N₂)-dependent stimulation in water, as its structural and physical properties can be reversibly and stably switched by alternating cycles of CO₂ and N₂ bubbling. Importantly, in vitro cellular assays clearly demonstrated that the CO₂-protonated imidazole moiety promotes rapid internalisation of CO₂-treated I-R6G into cancer cells, which subsequently induces massive levels of necrotic cell death. In contrast, CO₂-treated I-R6G was not internalised and did not affect the viability of normal cells. Therefore, this newly created system may provide an innovative and efficient route to remarkably improve the selectivity, safety and efficacy of cancer treatment.

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.

Smart surfaces with reversibly switchable wettability: Concepts, synthesis and applications

As a growing hot research topic, manufacturing smart switchable surfaces has attracted much attention in the past a few years. The state-of-the-art study on reversibly switchable wettability of smart surfaces has been presented in this systematic review. External stimuli are brought about to render the alteration in chemical conformation and surface morphology to drive the wettability switch. Here, starting from the fundamental theories related to the surfaces wetting principles, highlights on different triggers for switchable wettability, such as pH, light, ions, temperature, electric field, gas, mechanical force, and multi-stimuli are discussed. Different applications that have various wettability requirement are targeted, including oil-water separation, droplets manipulation, patterning, liquid transport, and so on. This review aims to provide a deep insight into responsive interfacial science and offer guidance for smart surface engineering. It ends with a summary of current challenges, future opportunities, and potential solutions on smart switch of wettability on superwetting surfaces.

CO2-Responsive Water-Soluble Conjugated Polymers for In Vitro and In Vivo Biological Imaging

Water-soluble conjugated polymers (WCPs) composed of a hydrophobic polythiophene main chain with hydrophilic tertiary amine side-chains can directly self-assemble into sphere-like nano-objects in an aqueous solution due to phase separation between the hydrophilic and hydrophobic segments of the polymeric structure. Due to the presence of gas-responsive tertiary amine moieties in the spherical structure, the resulting polymers rapidly and reversibly tune their structural features, surface charge, and fluorescence performance in response to alternating carbon dioxide (CO₂) and nitrogen (N₂) bubbling, which leads to significantly enhanced fluorescence and surface charge switching properties and a stable cycle of on and off switching response. In vitro studies confirmed that the CO₂-treated polymers exhibited extremely low cytotoxicity and enhanced cellular uptake ability in normal and tumor cells, and thus possess significantly improved fluorescence stability, distribution, and endocytic uptake efficiency within cellular organisms compared to the pristine polymer. More importantly, in vivo assays demonstrated that the CO₂-treated polymers displayed excellent biocompatibility and high fluorescence enhancement in living zebrafish, whereas the fluorescence intensity and stability of zebrafish incubated with the pristine polymer decreased linearly over time. Thus, these CO₂ and N₂-responsive WCPs could potentially be applied as multifunctional fluorescent probes for in vivo biological imaging.

Salt-Enhanced CO2-Responsiveness of Microgels

Here, we report a distinct mechanism for harnessing CO₂-responsiveness through enhancing CO₂ capture ability. The finding is demonstrated on the microgels that are composed of oligo(ethylene glycol) and sulfonate moieties. Laser light scattering studies on dilute aqueous dispersion of these microgels indicated a low CO₂-responsivity, which can be significantly enhanced by adding NaCl and other salts. This salt-enhanced CO₂-responsiveness of microgels can be elucidated by the antipolyelectrolyte behavior and its superposition of forming cross-links physically with CO₂ as an intermediate. Further results of the filtration experiments on microgel translocation through pores suggest the feasibility of the explanation. The finding is also supported by the CO₂ capture-release experiments on the dispersion, which can reversibly absorb and desorb CO₂.

A CO2-gated anodic aluminum oxide based nanocomposite membrane for de-emulsification

A carbon-dioxide-responsive organic-inorganic nanocomposite membrane based on a through-hole anodic aluminum oxide (AAO) template was constructed. The composite was prepared via a surface-initiated reversible addition-fragmentation chain-transfer (SI-RAFT) polymerization strategy to achieve the grafting of poly(methyl methacrylate-co-2-(diethylamino)ethyl methacrylate) brushes on the AAO membrane. The grafted polymer chain length could be controlled based on the feed ratio between the free chain transfer agent (CTA) and reactive monomer, e.g., methyl methacrylate and 2-(diethylamino)ethyl methacrylate, resulting in a membrane that features adjustable water permeability. Importantly, the membrane pore size and surface wettability could be switched from hydrophobic to hydrophilic upon the introduction of carbon dioxide and nitrogen gases. This allowed for the nanocomposite membrane to be utilized for controlled water flux and oil/water emulsion separation. The simple fabrication methodology as well as sustainable gaseous stimulus will be useful for the construction of future smart membranes.

Dual Biochemically Breakable Drug Carriers from Programmed Telechelic Homopolymers

Well-defined hydrophilic telechelic dibromo poly(triethylene glycol monomethyl ether acrylate)s were prepared by single-electron transfer living radical polymerization employing a hydrophobic difunctional initiator containing acetal and disulfide linkages. Although the resulting homopolymers have low hydrophobic contents (<8.5 wt % of the entire structure), they are able to self-assemble in water into nanoscale micellelike particles via chain folding. Acetal and disulfide linkages were demonstrated to be "keystone" units for their dual stimuli-responsive behavior under biochemically relevant conditions. Their site-selective middle-chain cleavage under both acidic pH and reductive conditions splits the homopolymer into two equal-sized fragments and results in the breakdown of the nanoassemblies. The drug loading/delivery potential of these nanoparticles was investigated using curcumine combining in vitro drug release, cytotoxicity, and cellular uptake studies with human cancer cell lines (HT-29 and HeLa). Importantly, this strategy may be extended to prepare innovative nanoplatforms based on hydrophilic homopolymers or random copolymers for intelligent drug delivery.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Two-Way CO2-Responsive Polymer Particles with Controllable Amphiphilic Properties

Multiple stimuli-responsive amphiphilic block copolymers of poly(methacrylic acid) (PMAA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) were used as emulsifiers to prepare two-way CO2 stimuli-responsive poly(methyl methacrylate) (PMMA) latex particles via aqueous emulsion polymerization. The polymerization at pH 2 and 50 °C produced mainly PDMAEMA-surfaced PMMA latex particles, whereas the polymerization at pH 12 and 50 °C produced mainly PMAA-surfaced particles. Both types of latex particles appeared to precipitate at higher pH values from the emulsifier of a longer PDMAEMA block length. The direction from precipitation to dispersion for PDMAEMA-surfaced particles or from dispersion to precipitation for PMAA-surfaced particles in response to CO2 bubbling of the pH 12 dispersion of particles depended on the PDMAEMA block length. Together, this study reveals that-by tuning the PDMAEMA block length in PMAA-b-PDMAEMA used as an emulsifier and polymerization at pH 2 or 12-PMMA latex particles can exhibit two-way CO2 responsiveness between dispersion and precipitation. Thus, due to their simple preparation and unique dual pH and CO2 responsiveness, these newly developed PMAA-b-PDMAEMA emulsifiers provide a highly efficient approach for the development of smart PMMA latex nanoparticles with desirable multifunctional properties.

Multistimuli-Responsive Emulsifiers Based on Two-Way Amphiphilic Diblock Polymers

Diblock copolymers of poly(tert-butyl methacrylate) (PtBuMA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) of four different block lengths were prepared by sequential two-step reversible addition-fragmentation chain transfer radical polymerization, followed by hydrolysis of the PtBuMA blocks to obtain poly(methacrylic acid)-b-PDMAEMA (PMAA-b-PDMAEMA). The effect of the PDMAEMA block length on the multistimuli-responsive amphiphilic features of both types of diblock copolymers was investigated as CO2-switchable emulsifiers for emulsification/demulsification of n-octane (an oil) in water in response to CO2/N2 bubbling. The amphiphilicity of PtBuMA-b-PDMAEMA was switched on, and the amphiphilicity of PMAA-b-PDMAEMA was switched off by CO2 bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAA-b-PDMAEMA conferred more sensitive CO2-responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N2 bubbling. This newly developed diblock copolymer system could potentially serve as a "multifunctional surfactant" for CO2-switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.

Nitric Oxide (NO)-Releasing Macromolecules: Rational Design and Biomedical Applications

Nitric oxide (NO) has been recognized as a ubiquitous gaseous transmitter and the therapeutic potential has nowadays received increasing interest. However, NO cannot be easily directly administered due to its high reactivity in air and high concentration-dependent physiological roles. As such, a plethora of NO donors have been developed that can reversibly store and release NO under specific conditions. To enhance the stability and modulate the NO release profiles, small molecule-based NO donors were covalently linked to polymeric scaffolds, rendering them with multifunctional integration, prolonged release durations, and optimized therapeutic outcomes. In this minireview, we highlight the recent achievements of NO-releasing macromolecules in terms of chemical design and biomedical applications. We hope that more efforts could be devoted to this emerging yet promising field.

Using green emitting pH-responsive nanogels to report environmental changes within hydrogels: a nanoprobe for versatile sensing

Remotely reporting the local environment within hydrogels using inexpensive laboratory techniques has excellent potential to improve our understanding of the nanometer-scale changes that cause macroscopic swelling or deswelling. Whilst photoluminescence (PL) spectroscopy is a popular method for such studies this approach commonly requires bespoke and time-consuming synthesis to attach fluorophores which may leave toxic residues. A promising and more versatile alternative is to use a pre-formed nanogel probe that contains a donor/acceptor pair and then "dope" that into the gel during gel assembly. Here, we introduce green-emitting methacrylic acid-based nanogel probe particles and use them to report the local environment within four different gels as well as stem cells. As the swelling of the nanogel probe changes within the gels the non-radiative energy transfer efficiency is strongly altered. This efficiency change is sensitively reported using the PL ratiometric intensity from the donor and acceptor. We demonstrate that our new nanoprobes can reversibly report gel swelling changes due to five different environmental stimuli. The latter are divalent cations, gel degradation, pH changes, temperature changes and tensile strain. In the latter case, the nanoprobe rendered a nanocomposite gel mechanochromic. The results not only provide new structural insights for hierarchical natural and synthetic gels, but also demonstrate that our new green-fluorescing nanoprobes provide a viable alternative to custom fluorophore labelling for reporting the internal gel environment and its changes.

A polyelectrolyte-containing copolymer with a gas-switchable lower critical solution temperature-type phase transition

A polyelectrolyte-containing copolymer with a CO₂/N₂-switchable cloud point, resulting from the gas-induced alternation of hydrophilicity, was prepared.

Dual CO2/temperature-responsive diblock copolymers confer controlled reversible emulsion behavior

Dual-stimuli responsive diblock copolymers possessing unique temperature-sensitive and CO₂/N₂-switching ability were successfully developed to promote efficient manipulation of reversible emulsification processes.

Polyphilicity-An Extension of the Concept of Amphiphilicity in Polymers

Recent developments in synthetic pathways as simple reversible-deactivation radical polymerization (RDRP) techniques and quantitative post-polymerization reactions, most notoriously 'click' reactions, leading to segmented copolymers, have broadened the molecular architectures accessible to polymer chemists as a matter of routine. Segments can be blocks, grafted chains, branchings, telechelic end-groups, covalently attached nanoparticles, nanodomains in networks, even sequences of random copolymers, and so on. In this review, we describe the variety of the segmented synthetic copolymers landscape from the point of view of their chemical affinity, or synonymous philicity, in bulk or with their surroundings, such as solvents, permeant gases, and solid surfaces. We focus on recent contributions, current trends, and perspectives regarding polyphilic copolymers, which have, in addition to hydrophilic and lipophilic segments, other philicities, for example, towards solvents, fluorophilic entities, ions, silicones, metals, nanoparticles, and liquid crystalline moieties.

CO2 -Breathing Polymer Assemblies via One-Pot Sequential RAFT Dispersion Polymerization

ABC triblock copolymer assemblies with reversible "breathing" behaviors based on poly[oligo(ethylene glycol) methyl ether methacrylate]-b-poly(benzyl methacrylate)-b-poly[2-(diethylamino)ethyl methacrylate] (POEGMA-b-PBnMA-b-PDEA) are fabricated via one-pot sequential reverisble addition-fragmentation chain transfer dispersion polymerization. Using a POEGMA as the macromolecular chain transfer agent, chain extension with BnMA and DEA is conducted in ethanol, where PBnMA acts as the core-forming block, and the PDEA block endows the solvophilicity and CO₂ -responsiveness. With the increment of the DP of PBnMA, the morphology of the assemblies evolves from spheres to worms, and to vesicles, while it degenerates from conglutinated vesicles to spheres as the DP of PDEA increases. After replacing ethanol with water, the morphologies of these assemblies remain unchanged, while their size decreases due to the collapse of the hydrophobic PDEA chains. Interestingly, due to the protonation and deprotonation of PDEA blocks, both the spheres and vesicles manifest a reversible expansion/shrinkage upon alternative CO₂ /Ar stimulation, exhibiting distinctive breathing feature.

Controlling CO2 -Responsive Behaviors of Polymersomes Self-Assembled by Coumarin-Containing Star Polymer via Regulating Its Crosslinking Pattern

An oligo(ethylene glycol)-based star polymer of N₂ -(OEG-C)₃ with fluorescent coumarin as hydrophobic end groups and dual tertiary amines as the star center is designed and synthesized. Owing to its amphiphilic nature of N₂ -(OEG-C)₃ , it will self-assemble into hollow vesicles with coumarin groups dispersed in the hydrophobic membrane and exhibits CO₂ -responsive behavior due to the protonation of amine centers with CO₂ . More importantly, coumarin moieties can either form non-crosslinking with γ-cyclodextrin via the 2/1 host-guest inclusion, or covalently photodimerized by 365 nm light, offering a tunable crosslinking pattern in the hydrophobic membrane and thus adjusting its CO₂ -stimulated reorganization and disassembly behaviors of these vesicles in aqueous solution.

Facile Fabrication of CO2-Responsive Nanofibers from Photo-Cross-Linked Poly(pentafluorophenyl acrylate) Nanofibers

CO₂-responsive nanofibers were facilely prepared from photo-cross-linked poly(pentafluorophenyl acrylate) (PPFPA) nanofibers via "amine-active ester" chemical modification. Photo-cross-linked PPFPA nanofibers were modified with histamine under mild conditions to generate cross-linked poly(histamine acrylamide) (PHAAA) nanofibers featuring a CO₂ responsiveness. As expected, the prepared cross-linked PHAAA nanofibers can exhibit a CO₂-responsive behavior to induce a reversible transition from hydrophobic to hydrophilic upon alternating addition and removal of CO₂ on the surface of nanofibrous membranes. Based on this finding, we could demonstrate that cross-linked PHAAA nanofibers can be employed for reversible absorption and release of protein using bovine serum albumin (BSA) as a model.