Tailoring CO₂-Responsive Polymers and Nanohybrids for Green Chemistry and Processes

Abstract

Stimuli-responsive materials are functional materials that can change their physical and chemical properties or perform specific functions in response to external stimuli. The use of these materials in chemical reactions and processes can make the production or operations controllable and repeatable (or recyclable), which may allow green chemistry and technologies with lower consumption of matter and energy. Among various stimuli-responsive materials, CO2-responsive polymer materials are highly attractive because of their unique advantages of using CO2 as a trigger in aspects of responding speed, contamination accumulation, operation scale, cost, and environmental friendliness, in addition to the characteristic capability to precisely regulate the response performance of polymers through manipulating their chain structures. In this review, we discuss the development of CO2-responsive polymers and nanocomposites with designed performance from tailoring the polymer chain structures including functionalities, compositions, and topologies, as well as hybridizing with inorganic nanomaterials. Applications of these materials in fields of catalysis, nanoreactors, switchable surfactant/stabilizers, and separation are also summarized in detail. Our focus is on how the CO2-responsive polymer materials with specific properties can be designed to reduce energy consumption and waste production. We believe that by tailoring the chain structures of CO2-responsive polymer materials, customizing their properties, and hybridizing them with functional nanomaterials, they could be utilized in the fields of catalysis, colloids, separations, and others to enable greener and more energy-efficient processes.

Enhancing oil–solid and oil–water separation in heavy oil recovery by CO2‐responsive surfactants

“…It is commonly involved in our daily life that oil needs to be separated from solid substrates, such as in dishwashing 1 and laundry 2,3 . Oil‐solid separation is also essential to many commercial applications, including drug delivery, 4‐6 cosmetic formulation and pharmaceutical products, 7 wastewater treatment, 8,9 enhanced oil recovery, 10‐13 contaminated soil remediation, 14‐16 and emulsion polymerization 17 . One of the most direct and effective methods to achieve successful separation is by surfactant washing, which consists of washing the oil‐solid mixture by an aqueous surfactant solution.…”

CO2-Responsive Nano-Objects with Assembly-Related Aggregation-Induced Emission and Tunable Morphologies

“…26−28 However, a multistep process and low concentration (about 1 mg/mL) via BCPSA limit the practical application of CO 2responsive polymeric nanoparticles. 16,29,30 Polymerizationinduced self-assembly (PISA) offered an emerging technique to prepare polymeric nanoparticles with various morphologies and high concentration (up to 50% solid content) compared to BCPSA, making the synthesis process simple and significantly increasing the yields. 31−49 PISA realizes the preparation of CO 2 -responsive polymeric nanoparticles during the synthesis of block copolymers.…”

“…Stimulus-responsive polymeric nanomaterials with different morphologies have attracted great attention in life science due to their unique features. − Various stimuli including pH, , light, , temperature, , and enzyme , have been employed to fabricate stimulus-responsive nanomaterials. CO 2 , a mild and green stimulus, has prominent advantages to be employed in designing responsive nanomaterials. − Currently, most of the CO 2 -responsive nanomaterials were produced via block copolymer self-assembly (BCPSA) of amphiphilic copolymers containing CO 2 -sensitive structures such as tertiary amine, − guanidine, or amidine. − However, a multistep process and low concentration (about 1 mg/mL) via BCPSA limit the practical application of CO 2 -responsive polymeric nanoparticles. ,, Polymerization-induced self-assembly (PISA) offered an emerging technique to prepare polymeric nanoparticles with various morphologies and high concentration (up to 50% solid content) compared to BCPSA, making the synthesis process simple and significantly increasing the yields. − PISA realizes the preparation of CO 2 -responsive polymeric nanoparticles during the synthesis of block copolymers. − Tan and co-workers employed the photo-PISA of 2-(diethylamino)­ethyl methacrylate (DEAEMA) and hydroxypropyl methacrylate (HPMA) to prepare CO 2 -stimulated vesicles with good dispersibility. Yuan and co-workers exploited sequential reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) and DEAEMA to obtain CO 2 -breathing triblock copolymer assemblies.…”

Salt-Enhanced CO2-Responsiveness of Microgels

“…The capture and release of carbon dioxide (CO 2 ) is one important step in carbon circle on the earth. Recently, stimuli-responsive polymeric materials that are capable of chemical, conformational, and volume changes in response to CO 2 have attracted great attention. − Besides its importance in CO 2 capture for minimizing greenhouse gas emissions, with CO 2 as a trigger to drive polymer phase transitions, one can manipulate properties of CO 2 -responsive materials for cellular mimicking, photosynthesis, drug delivery, and other applications. − In comparison with responsive materials with temperature, pH, light, or other stimuli as a trigger, CO 2 -responsive materials possess advantages endowed by low-energy consumption and good penetration depth. − …”

“…To synthesize those CO 2 -responsive polymeric materials, the present strategy typically requires the incorporation of functional moieties with CO 2 sensitivity to polymer chains via direct polymerization or post-modification. − The most widely engaged CO 2 -sensitive functional moieties include base groups, like amines, amidines, and guanidines, − and the carboxylic acid group, , which can react with the carbonic acid generated by CO 2 gas in water based on the Brønsted acid–base theory and thus change the solubility of polymers. Following this mechanism, CO 2 -responsiveness is also achieved on cellulose that can donate protons to bases, which facilitate the coupling reaction between CO 2 and the alcohol groups on cellulose in dimethyl sulfoxide .…”