Regarding the synthesis of polymers bearing in-chain carbonate esters (groups in which the two hydrogens of carbonic acid (H₂CO₃) are replaced with carbon substituents), two approcaches are introduced: one is a polymerization that uses CO₂ directly as a monomer, and the other is a polymerization reaction that uses monomers derived from CO₂. The reactions are described in relation to their mechanisms.

Glass transition temperature, melting temperature, viscosity and tensile strength are reduced by plasticizing with high pressure carbon dioxide. By plasticizing polymers with high pressure carbon dioxide, the phase separated structure of polymer blends, the dispersed structure of composites, and the crystallization rate and crystalline structure can be controlled. In addition, porous structures having various sizes and shapes can be formed by foaming and stretching of carbon dioxide-plasticized polymers, and by drying in a polymer/solvent system using high-pressure carbon dioxide. These structural controls are used to create functional materials such as electronic materials and medical materials.

We are focusing on CO₂ sorption and separation technology at low temperature and high pressure using PDMS rubber as a low-cost recovery method. This method has lower capital investment cost and consumes less energy than AGR (acid gas removal) process and membrane separation methods. Our method is particularly advantageous for emission sources with high pressure and high CO₂ concentration. Therefore, it is expected to be applied to CH₄/CO₂ separation in natural gas fields containing high concentrations of CO₂, H₂/CO₂ separation after water gas shift reactions, etc.

Direct air capture (DAC) of CO₂ has become essential to reduce atmospheric CO₂ levels. Previously, DAC technologies has limited sorbent based CO₂ capture process. However, recent investigations are revealing that gas separation membranes with ultrahigh CO₂ permeances also have a large potential new DAC technology. In order to realize membrane-based DAC (m-DAC), membrane thinning is a straightfoward way to enphance CO₂ permeances. This paper fucuses on the the development and utlization of free-standing and nonometer thick membranes for DAC and shows current stage to enhance the membrane performances of CO₂ capture directly from the air. Finally, m-DAC's potential is discussed.

Recent progress in our elastomers that respond to CO₂ gas has been reviewed. Our group developed two kinds of CO₂-responsive elastomers that chnages their mechanical properties with CO₂ gas. One is CO₂-plastic elastomer in which polydimethylsiloxoane (PDMS) is physically crosslinked via aggregations of ionic groups attached along the main chain. This elastomer is significantly plasticized via the exposure of CO₂ gas because the physical crosslinking is weakened with CO₂. The CO₂-plasticization enhances the self-healing behavior of this elastomer. In addition, the adhesion of this elastomer switchably increases under CO₂ gas flow. The other one is CO₂-toughening elastomer. This elastomer is chemically crosslinked PDMS containg amine groups. The amine groups react with CO₂ molecules and form ammonium carbamates. In the PDMS matrix, the ammonium carbamates form nanodomains which behave like viscoelastic nanofillers that dissipate a large amount of energy during deformation. As a result, the fracture of the elastomer is inhibited and the elastomer is significantly toughned.

Polyurethanes are important polymers used in foams, adhesives, paints, structural materials, etc, but their synthesis involves environmental loads. As greener non-isocyanate and non-phosgene pathways, CO₂-based syntheses have been applied to polyurethanes. Five-membered cyclic carbonates, prepared from epoxides and CO₂, react with amines to give urethanes with hydroxy moieties, and this reaction is applied to two synthetic routes, polyhydroxyurethane (PHU) synthesis and transurethanization polycondensation.PHUs are prepared by polyaddition of bis-five-membered cyclic carbonates and diamines. The presence of primary and secondary hydroxy groups in the side chains set PHUs apart from industrial polyurethanes. However, the hydroxy groups can be converted to various functional groups, opening up broader potential applications.Transurethanization polycondensation of bishydroxyurethanes prepared with aliphatic diamines and ethylene carbonate yields polyurethanes with structures similar to industrial polyurethanes. Polyurethanes with various structures are produced, but the harsh conditions and limited molecular weights are the current challenges to be solved.

Aliphatic and aromatic amine derivatives have been investigated as absorbents to capture waste CO₂ in industrial processes for many years. The formed carbamic acids release CO₂ and are recovered reversibly. Here we design various diamine derivatives to stabilize carbamates as a zwitterion group, and develop a unique polymer coating with wettability switching by CO₂ capture. The diamine with optimized spacer length enhanced the stability of the CO₂ adduct, and the CO₂-responsive diamine polymer was incorporated into epoxy thermosets. The obtained coating exhibited super-hydrophilicity (contact angle of an air bubble in water ～170°) by bubbling CO₂. Surprisingly, the hydrophilicity switching was also achieved by simple immersion for a few hours in water with low conc. CO₂ (400 ppm). Our approach will provide new insights of low conc. CO₂ utilization in polymer materials. Polyimide synthesis based on diamine-CO₂ adduct was also described.

As a high school student, the author studied the gel composed of boric acid and poly(vinyl alcohol). Although the presentation was met with strict comments due to the immaturity, the author enjoyed the research. Such experience currently engages the author to make progress in the study of boron-based polymer synthesis.

Two-dimensional (2D) materials have attracted much interest in recent years. This review focuses on both layered materials and nanosheets with 2D anisotropic structures. The chemical interactions in the lateral and vertical directions play important roles for the flexibility of the layered structures enabling the dynamic functions as polymer materials. A variety of dynamic properties can be extracted from the flexibility control. Section 1 summaries the background and structural characteristics of these 2D materials. Section 2 shows the layered materials exhibiting the dynamic functions including our recent works. Section 3 introduces exfoliated nanosheets from layered materials and their applications. Section 4 focuses on the designed new 2D materials in recent works. Whereas classical 2D materials were rigid and static in previous works, the more flexible and dynamic structures are achieved in recent works. Such 2D materials can be regarded as a new family of polymer materials.