Volume 53 Issue 1, January 2021

A variety of catalysts including zinc, cobalt and chromium complexes were reviewed for the copolymerization of epoxides and CO₂ with cyclic anhydrides and/or cyclic esters to synthesize CO₂-based poly(ester-co-carbonate)s. The structure and structure-performance relationship of the as-prepared copolymers were discussed in detailed.

The use of iron catalysts in CO₂/epoxide chemistry has been less explored compared with zinc, cobalt, and chromium catalysts. This review highlights recent examples including iron complexes that deoxygenate epoxides in situ and geometry-dependent selectivity towards either polycarbonate or cyclic carbonate production. Reaction conditions (temperature, CO₂ pressure, and amount of nucleophilic cocatalyst) and catalyst structure are all critical in accessing efficient catalysis for polycarbonate formation.

Biodegradable plastics are gaining attention as one of the solutions to marine plastic wastes, which are increasing every year. Among them, polyhydroxyalkanoate (PHA) and polycaprolactone (PCL) are known to exhibit particularly good marine biodegradability. In this review, to understand their excellent marine biodegradability, the biosynthesis of PHA and cutin, a natural analog of PCL, and the biodegradation of PHA and PCL in the carbon cycle in marine ecosystems are described.

Polyhydroxyalkanoates (PHAs) are biobased and biodegradable materials. The artificial PHAs, such as lactate-based polymers, synthesized by engineered platforms expand the range of physical properties. The artificial polymers with superior properties are produced mainly from CO₂-derived biomass using microbial platform with engineered enzymes. The oligomers can be secreted from cells and derivatized into high-molecular-weight polymers through assembling with other segments. The review summaries recent advances in the biosynthesis and biodegradation of artificial PHAs and oligomers.

To shift from a petroleum-dependent society to a sustainable society using eco-friendly materials, polysaccharides from natural products are important candidates as alternative materials. We have researched one of the cyanobacterial polysaccharides, “sacran,” which is extracted from Aphanothece sacrum. In this review, the unique characteristics, structures, and preparation of sacran LC gels are introduced. These matters are discussed especially from the perspectives of polymer science, colloidal science, gel science, etc. We hope that sacran will be used in a variety of fields, such as tissue engineering, pharmacodynamics, and biomedical materials, with possible contributions to the development of a sustainable material society.

Carbon dioxide capture and storage (CCS) technology has become important due to the threat of global warming and climate change. Furthermore, the development of carbon dioxide capture and utilization (CCU) technology, which reuses the captured CO₂, has been prioritized in recent years to accelerate the deployment of “CCUS.” Amine-based CO₂ capture is a key process for realizing a carbon neutral society.

Our recent studies on the cellulose nanofibrils (CNFs)/polymer nanocomposites prepared via Pickering emulsion templating are reviewed. CNF-stabilized monomer-in-water emulsions were used as starting materials to design the composite structures. In the first part of this review, we summarize the preparation of transparent films. The second part describes the approaches to prepare a composite microparticles having CNF shells.

Direct CO₂ capture from the air (DAC), is inevitable to reduce the concentration of CO₂ in the atmosphere. Recent reports of ultrahigh CO₂ permeances in gas separation membranes indicate a potential of new technology for DAC (m-DAC). In this paper, we use chemical process simulation to discuss the potential of m-DAC considering the state-of-the-art performance of organic polymer membranes. Based on the analysis, we propose the target properties for separation membranes required for m-DAC with competitive energy expenses as well as the direction of future membrane development for DAC.

A highly random terpolymer of CO₂, styrene oxide (SO), and propylene oxide (PO) was realized by using a tetraphenylporphyrinatocobalt(III) chloride ((TPP)CoCl)/4-dimethylamino pyridine (DMAP) catalyst system. In contrast, gradient terpolymers were formed in the cases of CO₂, cyclohexylethylene oxide (CyEO), tert-butylethylene oxide (^tBuEO) or 1-adamantylethylene oxide (AdEO), and PO. The glass transition temperatures (T_gs) of these terpolymers are tunable between that of the copolymer of CO₂ with PO (34 °C) and that of the copolymers of CO₂ with the corresponding epoxide with bulky side groups.

Piperazine and its derivatives were incorporated into a thin film of poly(vinyl alcohol), and the CO₂ separation performance of the resulting amin-containing membranes was investigated. The gas transport properties were dependent on the chemical structure of the amines. In particular, 3-(1-piperazinyl)-1,2-propanediol (PzPD)-containing polymeric membranes gave excellent CO₂ separation properties over H₂ and CH₄ under humidity. CO₂ interacted with the secondary amino group on the Pz ring to form a carbamate, which was readily hydrolyzed to produce bicarbonate ions. CO₂ migrates through the membrane in the form of bicarbonate ions.

The effect of the ionic liquid content in tough inorganic/organic double-network (DN) ion gel membrane on the CO₂ permeability was investigated. By optimizing the composition of the inorganic and organic networks, the mechanical strength of the DN ion gel was significantly increased, and the DN ion gel membrane with more than 95 wt% of an ionic liquid was successfully prepared. With the increase in the ionic liquid content, the CO₂ permeability of the DN ion gel membrane exponentially increased up to ~67% of the theoretical maximum CO₂ permeability.

Plasticized poly(ethylene carbonate) (PEC)/LiPF₆ electrolytes were prepared and evaluated their ion-conductive and dielectric relaxation behavior using broadband electric spectroscopy (BES). The BES results indicated that the plasticizer accelerates segmental motion of PEC and improve the dc conductivity, and the plasticizing effect of ionic liquid (EMImTFSI) on the PEC electrolyte is larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was revealed that the degree of decoupling and the value of fragility increase by the addition of plasticizer, and these plasticizers weaken interactions between PEC chains and Li ions in the electrolyte.

Amine-containing microgel particles (GPs), which capture CO₂ at a low temperature and desorb it upon a mild heating, are attractive materials for capturing CO₂. In this paper, the effect of pK_a of ammonium ions in the GPs on the amount of CO₂ desorption upon heating was investigated at various CO₂ concentrations by experiments and thermodynamic predictions. A guideline for designing thermoresponsive amine absorbents for various applications including direct air capture and carbon recycling in closed spaces, such as space stations and submarines, is provided.

Polyhydroxyalkanoate (PHA) is a biopolyester similar to some commodity plastics. The production cost of PHA is high partly due to the cost of feedstock. Spent bleaching clay (SBC) is a byproduct of the palm oil refining process. Adsorbed residual oil in SBC was successfully utilized by Cupriavidus necator Re2058/pCB113 in shaken flask culture for PHA production. Both the SBC and the resulting PHA were characterized by SEM, rheometer, TGA, DSC, GC and ¹H-NMR to demonstrate the production of a PHA copolymer containing 3-hydroxyhexanoate.

Inspired by the natural spinning process, we developed an aqueous spinning system with a citrate/polyethylene glycol buffer for highly extensible silk fibers. This system enabled tuning of the induction of crystallization through the buffer conditions.

Bacteria possibly capable of polyhydroxyalkanoate synthesis from lignin were investigated by genomics and chemistry of biomaterials. Aquitalea sp and Ralstonia pickettii isolated from a blackwater lake rich humic substances, showed great potential to be developed for this purpose. Canonical lignin degradation pathways, such as protocatechuate 4,5-dioxygenase-dependent pathway, CoA-dependent non-β-oxidation pathway of ferulic acid and β-ketoadipate pathway were mapped in their genomes. In addition, traces of P(3HB) were found when using vanillic and gallic acids as sole carbon source, which indicates that the downstream β-ketoadipate pathway is functional.

Aliphatic polycarbonate (APC) macromolecular chain-transfer agents (macro-CTAs) with an allyl end group were successfully synthesized by cobalt-catalyzed epoxide/carbon dioxide copolymerization in the presence of allyl alcohol as a chain-transfer agent. The ring-opening metathesis polymerization of cycloalkene monomers using the obtained APC macro-CTAs yielded the corresponding APC-block-polycycloalkene copolymers.

Ralstonia eutropha is a hydrogen-oxidizing chemolithotrophic bacterium that can synthesize poly[(R)-3-hydroxybutyrate] [P(3HB)], which can be used as a biodegradable plastic. Various genes for carbonic anhydrase involved in CO₂ fixation are present in the genome of R. eutropha. In this study, we investigated the gene dosage effect of the β-carbonic anhydrase (can) gene on P(3HB) accumulation in R. eutropha under autotrophic and mixotrophic conditions.

The synthesis of 100% ¹³C-labelled poly(propylene carbonate) from the completely alternating copolymerization of propylene oxide (rac-PO and R(+)PO) and ¹³CO₂ is reported. The prepared copolymers were shown to be regioselective with predominately head-to-tail (HT) connectivity. The infrared absorption of the polycarbonate in the \(v_{{\mathrm{co}}_{\mathrm{3}}}\) region is red-shifted by 45 cm⁻¹ from the polymer prepared from ¹²CO₂. This shift in frequency allows for the observation of v_NO modes of incorporated dinitrosyl metal complexes.