Emerging Applications of CO₂‐Based Polyurethanes: Bridging Material Sustainability and High‐Performance Engineering

Abstract

Carbon dioxide‐derived polyols (CO₂‐polyols), synthesized via the copolymerization of CO₂ with epoxides, have emerged as a compelling sustainable alternative to petroleum‐based polyols for polyurethane (PU) manufacturing, offering the dual benefit of sequestering waste CO₂ and reducing reliance on fossil feedstocks. However, the carbonate linkages embedded within the CO₂‐polyol backbone impart a chain rigidity that alters intermolecular interactions and physico‐mechanical behavior relative to conventional polyols, creating uncertainty over how CO₂ incorporation translates into end‐use performance and slowing industrial adoption despite clear environmental incentives. This review maps the diverse application frontiers of CO₂‐polyol‐derived PUs. Specifically, we highlight their critical roles in adhesives, coatings, thermal stimuli‐ responsive shape‐memory materials, waterborne PUs with enhanced hydrolytic and oxidative resistance, lithium‐ion battery binders, and polyurethane foams. Across these systems, we describe how tuning the carbonate unit content and polyol functionality allows the rigidity, crosslink density, and thermal transitions of the resulting PUs to be precisely engineered, often matching or exceeding the performance of conventional counterparts while retaining a favorable sustainability profile. Collectively, this review provides a practical design framework to accelerate the transition of CO₂‐polyol‐based PUs from laboratory‐scale demonstrations to industrially viable, sustainable materials.

This review provides a comprehensive overview of high‐performance polyurethanes using CO₂‐derived polyols. Emphasizing formulation strategies and structure–property relationships, it highlights advanced applications in adhesives, coatings, shape‐memory materials, hydrolytically robust waterborne polyurethanes, lithium‐ion battery binders, and polyurethane foams, effectively bridging material sustainability with high‐performance engineering.

1. Introduction

As innovative and sustainable materials, CO₂‐polymers offer a compelling solution to both environmental and industrial challenges [1, 2, 3, 4, 5]. By incorporating CO₂ into their backbone via carbon capture and utilization (CCU), these materials provide dual benefits: sequestering significant volumes of CO₂ and reducing the polymer industry’s reliance on fossil fuel feedstocks [6, 7]. Among CO₂‐based polymers, polycarbonate synthesized from CO₂ and epoxides holds immense commercial promise, having been commercialized since 2016 by major global manufacturers, including Covestro, Saudi Aramco, and several enterprises in China [8, 9, 10, 11, 12]. Although their versatile applications, ranging from coatings and adhesives to polyol precursors for polyurethane synthesis, have driven extensive research into developing efficient, economical catalytic systems suitable for industrial‐scale production, the global mass production and adoption of CO₂‐derived products remain relatively slow [13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28].

Through industrially viable catalytic platforms, CO₂‐polyols with tunable carbonate content and hydroxyl terminal groups have emerged as key building blocks for sustainable polyurethanes (PUs). Analogous to assembling LEGO blocks, versatile synthetic strategies utilizing structurally diverse CO₂ polyols allow for the tailored design of a wide range of PUs that are indispensable to the global chemical industries. Given the vast commercial market for PUs in foams, coatings, elastomers, adhesives, and biomedical materials, substituting conventional polyols with CO₂‐polyols serves as a powerful driver to transition the PU industry toward sustainability [29, 30, 31, 32, 33].

However, despite sharing structural similarities with conventional polyols such as possessing a hydroxy group, CO₂‐polyols exhibit inherent chain rigidity imparted by their backbone carbonate functionality. This rigidity alters the intermolecular interactions within the polymer matrix, resulting in distinct physical and mechanical properties compared to those of conventional commercial PUs. Consequently, these performance discrepancies remain a primary bottleneck, causing industry hesitation in adopting CO₂ polyols despite the clear environmental benefits of CO₂ utilization. To establish clear structure‐property relationships, this review provides a comprehensive overview of CO₂‐polyol‐based PUs, systematically categorizing recent advancements by their target applications and CO₂‐induced property enhancements. Specifically, we sequentially examine their implementation in adhesives, coatings, and shape‐memory materials and discuss how CO₂ incorporation enhances the desired property. In addition, examples of PUs derived from CO₂‐polyols exhibit improved hydrolysis/oxidation resistance in waterborne PUs (WPUs). Finally, we explored these sustainable PUs’ cutting‐edge roles in lithium‐ion battery (LIB) binders and polyurethane foams (PUFs).

2. Synthesis of PUs Derived From CO₂‐Polyols

PUs are synthesized from polyols involving hydroxyl terminals and polyisocyanates under various reaction conditions tailored to their specific applications. Utilizing these primary components, two major synthetic protocols are generally employed (Figure 1a). Thermoplastic PUs (TPUs) are synthesized from polyol and polyisocyanates with an average functionality ≤2.1 (mostly diols and diisocyanates) via a two‐step synthetic pathway (Figure 1a) [29]. In this approach, the reaction of diols with an excess of diisocyanates initially yields isocyanate‐terminated prepolymers. The subsequent addition of a chain extender, such as 1,4‐butanediol, completes the TPU synthesis, resulting in a copolymer composed of soft segments (derived from the diols) and hard segments (comprising isocyanates and chain extenders). In contrast, thermoset PUs featuring three‐dimensional (3D) networks are synthesized from multifunctional monomers with an average functionality >2.1, e.g., triols and tetraols. The synthetic routes for PU foams (PUFs) often involve a one‐pot process combining isocyanates, polyols, and water. Water readily reacts with isocyanates to generate amines and CO₂ gas; the in situ generation of CO₂ during polymerization induces a foam‐like structure. Simultaneously, the reaction of the generated amines with isocyanates yields urea linkages, while the hydroxyl groups of the polyols react with isocyanates to afford urethane linkages. Therefore, PUFs involve both urea and urethane linkages in the polymer chains.

FIGURE 1.

synthetic strategies for CO₂‐polyol‐based polyurethanes (PUs). (a) general synthetic routes to PUs via a two‐step prepolymer/chain‐extension process and PUFs via a one‐pot reaction involving in situ CO₂ generation from isocyanate–water reactions. (b) strategies for modulating CO₂ content in CO₂‐polyols: an in‐situ approach regulating CO₂ feed during polyol preparation and an ex‐situ approach blending CO₂‐polyols with conventional non‐CO₂ polyols (e.g., PTMEG and PEG). (c) representative aliphatic and aromatic isocyanates (MHI, HDI, IPDI, MDI, 2,4‐/2,6‐TDI) used in PU synthesis.

As polyols, conventionally, polyesters and polyethers featuring terminal hydroxyl groups have been employed. Recently, CO₂‐derived polycarbonates possessing terminal hydroxyl groups (CO₂‐polyols) have emerged as highly attractive sustainable alternatives due to their environmental benefits and carbon‐capturing potential. The precise carbonate linkage content within these CO₂‐polyols varies significantly depending on the specific synthetic protocols and commercial suppliers (Figure 1b). For instance, the Converge polyol series (originally developed by Novomer and later acquired by Aramco) contains approximately 40–50 wt% of CO₂, corresponding to a nearly perfectly alternating copolymer of CO₂ and epoxides [34]. In contrast, Covestro’s Cardyon polyols exhibit a lower CO₂ content of up to 20 wt%, featuring a macromolecular architecture that consists of both ether and carbonate segments within the backbone [35]. These poly(ether‐carbonate) polyols with low‐to‐moderate CO₂ fractions are typically synthesized by double‐metal‐cyanide (DMC)‐catalyzed reactions. To systematically elucidate the distinct impact of these backbone carbonate units on the final macroscopic properties of PUs, researchers frequently conduct comparative assessments of CO₂‐polyol‐derived with modulated contents of CO₂ or the comparison with no CO₂‐incorporated PUs. Fine‐tuning the CO₂ loading within the resulting PUs is generally approached via two distinct methodologies (Figure 1b); either an in‐situ approach that involves the meticulous regulation of CO₂ feeding parameters during the polyol polymerization itself or an ex‐situ formulation strategy that systematically varies the stoichiometric ratio between the CO₂‐polyol and traditional non‐CO₂ polyols such as polyethylene glycol (PEG), poly(tetrahydrofuran) diol (PTMEG), or polyadipate of 1,4‐butanediol. Isocyanates consist of aliphatic or aromatic backbones bearing diisocyanate groups, as illustrated in Figure 1c. Commonly used aliphatic isocyanates are methylene bis(cyclohexyl isocyanate) (MHI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). The isocyanates possessing aromatic backbones are methylene diphenyl diisocyanate (MDI) and 2,4‐ and 2,6‐toluene diisocyanate (TDI). In the following sections discussing applications of PUs, the synthesis of most PUs follows these synthetic protocols. In the case of reactive PUs, slightly different approaches have been employed, which are illustrated in the corresponding section.

3. CO₂‐Polyol‐Based PUs for High‐Performance Adhesives and Coating Applications

3.1. PUs for Adhesives

Orgilés‐Calpena et al. investigated the synthesis and performance of PUs tailored for footwear adhesive applications by blending CO₂‐polyol (Converge) and a conventional polyester polyol (polyadipate of 1,4‐butanediol, Hoopol F580) [36]. By varying the CO₂‐polyol content from 0 to 90 wt% relative to the total polyol fraction, the physical properties of the soft segments in the resulting PUs could be systematically modulated. Prepolymers were prepared using CO₂‐content‐regulated polyols with MDI and subsequently chain‐extended with 1,4‐butanediol (Figure 2a). The adhesion properties of these CO₂‐containing PUs were evaluated by T‐peel strength tests using leather/PU adhesives/styrene‐butadiene rubber (SBR) joints (according to the standard EN 1392:2007). The prepared TPU solutions were applied between the leather and the SBR joint, and their T‐peel strengths were evaluated after solvent evaporation. Remarkably, across the entire blending range (10–90 wt%), all CO₂‐polyol‐based PU adhesives satisfied the technical benchmarks required for footwear joints. However, the specific CO₂‐polyol content and bonding duration profoundly influenced both the peel strength and the resulting failure mechanism. Shortly after bonding (30 min), all formulation exhibited 100% adhesive failure (100%A) at the SBR surface, with the 70 wt% CO₂‐polyol sample (PU70CO2) achieving the highest initial peel strength of approximately 12 N/mm (Figure 2b). Extending the bonding duration to 72 h improves the peel strength, shifting the failure mode toward cohesive failure (C) within the SBR substrate, which indicates that the interfacial bonding strength of PU exceeded the mechanical strength of the rubber itself. Crucially, the PU formulation containing 50 wt% of CO₂‐polyol (PU50CO2) demonstrated the optimal synergistic effect, yielding the highest peel strength (~16.5 N/mm) along with a complete 100% cohesive failure of the SBR rubber (100%C) (Figure 2b). The PU without CO₂ incorporation displayed a mixed adhesive/cohesive failure mode after the 72 h bonding, indicating that CO₂‐polyols can replace conventional polyols without compromising standard technical requirements. More importantly, optimizing the CO₂‐polyol incorporation ratio can enhance both the immediate and long‐term adhesion performance.

FIGURE 2.

Synthesis and adhesive performance of CO₂‐polyol‐based PU adhesives for footwear applications. (a) synthetic scheme for PU prepolymers derived from CO₂‐polyol blends, MDI, and 1,4‐butanediol. (b) T‐peel strength of leather/PU/SBR joints as a function of CO₂‐polyol content (0, 50 and 70 wt%) and bonding time (30 min vs. 72 h), with corresponding failure modes (adhesive (A) versus cohesive failure (C)).

The same research group reported reactive polyurethane hot melt adhesives (HMPURs) synthesized from polyol mixtures combining a CO₂‐polyol (Converge) and a conventional polyadipate of 1,4‐butanediol (Hoopol, F‐580), with the CO₂‐polyol content ranging from 0 to 90 wt% relative to the total polyol fraction [37]. As illustrated in Figure 3a, HMPURs are low‐melting‐point solid prepolymers featuring reactive terminal isocyanate groups, which are applied to substrate surfaces in a molten liquid state. The adhesion and curing mechanism of HMPURs involves a dual pathway: initial physical crosslinking driven by the crystallization of the polyol segments during cooling, followed by chemical crosslinking via the reaction of terminal isocyanates with ambient and substrate moisture. Given the critical role of moisture in developing bond strength during the curing step, T‐peel tests on leather/HMPUR adhesives/SBR joints were conducted after aging for 3 days at 70 °C and 95% relative humidity in accordance with the EN 15062:2006 standard (Figure 3b). All CO₂‐polyol‐containing HMPUR formulations exhibited a mixed failure mode, characterized by partial adhesive failure at the SBR surface (A2) and cohesive failure within the SBR substrate (C). In contrast, the control HMPUR prepared without CO₂‐polyols displayed a distinct mixed mode featuring adhesive failure at the leather surface (A1) and cohesive failure within the SBR. Notably, HMPURs incorporating 30, 70, and 90 wt% of CO₂‐polyols demonstrated significantly higher peel strengths compared to the CO₂‐free control, enhancing the ultimate mechanical performance of reactive hot‐melt systems by CO₂‐derived soft segment reinforcement.

FIGURE 3.

Reactive hot‐melt polyurethane adhesives (HMPURs) derived from CO₂‐polyol (Converge)/Hoopol F‐580 blends. (a) Synthetic scheme for isocyanate‐terminated HMPUR. (b) T‐peel strength of leather/HMPUR/SBR joints as a function of CO₂‐polyol content (0–90 wt%) after moisture‐curing aging.

A similar HMPUR series was recently reported for adhesive applications across the footwear, wood, and furniture industries (Figure 4) [38]. These HMPURs were synthesized via a prepolymer method by reacting MDI with a polyol mixture consisting of polyadipate of 1,4‐butanediol (Hoopol, F‐580), polypropylene glycol (PPG), and CO₂ polyols (from Covestro) (Figure 4a). The ratios of PPG and CO₂‐polyol were varied; for instance, the formulation designated as PU‐25%C2 incorporated 25 wt% of CO₂‐polyol (M _w = 1000 g/mol) paired with 75 wt% of PPG. To evaluate their performance, T‐peel tests on leather/HMPUR adhesives/SBR joints were conducted in accordance with the EN 15307:2015 standard (Figure 4b). Compared to the CO₂‐free control (PU‐0%C2, Figure 4b), which exhibited cohesive failure within the SBR substrate, the substitution of PPG with the CO₂‐polyol generally led to a slight decrease in peel strength. Nevertheless, the resulting adhesion values remained well within acceptable thresholds for the footwear manufacturing. Furthermore, when evaluated for wood and furniture applications, the HMPUR variants with 25% to 50% CO₂‐polyol substitution demonstrated optimal performance. These formulations successfully satisfied the stringent technical standards of the wood and furniture sectors, highlighting the potential of CO₂‐based polyols to deliver both robust mechanical performance and environmental benefits.

FIGURE 4.

HMPUR adhesives formulated from MDI, polyadipate 1,4‐butanediol, polypropylene glycol (PPG), and CO₂‐polyol blends. (a) Synthetic scheme of HMPUR. (b) T‐peel strength of leather/HMPUR/SBR joints as a function of CO₂‐polyol fraction (0–75 wt%) relative to the total polyol content.

Another series of reactive hot‐melt polyurethane adhesives (RHMPAs) was synthesized using MDI and various polyol combinations (Figure 5) [39]. A formulation prepared with an equimolar mixture of CO₂‐polyol (Converge) and poly(tetramethylene glycol) (PTMEG) was designated as PPC‐RHMPA. For comparison, control systems were prepared by partially or completely replacing the CO₂‐polyol with polyhexamethylene adipate glycol (PHA), yielding PPC/PHA‐RHMPA and PHA‐RHMPA, respectively. The adhesive performance of these polymers was evaluated through lap shear strength tests on representative metal and plastic substrates (overlap area: 25 mm × 12.5 mm) and compared against a commercial benchmark, LOCTITE 3542. On bisphenol A‐based polycarbonate (PC) substrates, all synthesized RHMPAs exhibited adhesive failure with higher lap shear strengths than the commercial benchmark; however, no distinct enhancement from CO₂‐polyol incorporation was observed. In contrast, the CO₂‐incorporated RHMPA demonstrated superior bonding strength on poly(methyl methacrylate) (PMMA) with a substrate failure, even though the absolute lap shear strength of PPC‐RHMPA was comparable to that of LOCTITE 3542. On metallic surfaces, such as aluminum and steel, the adhesion‐promoting effect of CO₂ incorporation was less pronounced, suggesting that the performance benefits of CO₂‐derived soft segments in RHMPAs are highly dependent on the chemical nature of the substrate interface.

FIGURE 5.

Reactive hot‐melt polyurethane adhesives (RHMPAs) based on CO₂‐polyol/PTMEG or PHA blends. (a) Synthetic scheme for PPC‐RHMPA, PPC/PHA‐RHMPA, and PHA‐RHMPA. (b) Lap shear strength of the RHMPA formulations on polycarbonate (PC), PMMA, aluminum, and steel substrates, benchmarked against a commercial adhesive (LOCTITE 3542).

Sustainable waterborne PU adhesives derived from a binary bio‐ and CO₂‐based polyol system have been developed [40]. Designated as lignin‐based waterborne polyurethane adhesives (LWPUs), these sustainable systems were synthesized by combining CO₂‐polyol (from Guangdong Dazhi Environmental Protection Co., Ltd.) with low‐molecular‐weight lignin (Figure 6). The CO₂‐polyol reacted with isophorone diisocyanate (IPDI) in the presence of a dibutyltin dilaurate (DBTDL) catalyst, followed by the incorporation of 2,2‐dimethylol propionic acid (DMPA) and a specific lignin fraction bearing both hydroxyl and carboxylic acid groups (AOH). To impart water dispersibility, N‐(2‐aminoethyl)‐2‐aminopropyl sulfonic acid (AAS) was introduced into the reaction mixture to provide hydrophilic ionic groups along the LWPU backbone. Beyond the ecological advantages of incorporating these sustainable feedstocks, the resulting LWPUs displayed outstanding high‐performance lap shear strengths, reaching 14.7 MPa on wood, 10.6 MPa on steel, and 9.0 MPa on aluminum substrates. These mechanical adhesion profiles were systematically evaluated using double‐layer lap joint specimens in accordance with the Chinese National Standard GB/T 33333‐2016. This remarkable performance is attributed to the structural reinforcement provided by the lignin segments, which facilitate the formation of a dense network and abundant hydrogen bonding within the LWPU matrix.

FIGURE 6.

Sustainable lignin/CO₂‐polyol‐based waterborne PU adhesives (LWPUs).

3.2. PUs for Coatings

Due to their inherent flexibility and robust substrate adhesion, polyurethane acrylates (PUAs) have been widely utilized in ultraviolet (UV)‐curable strippable coatings. Integrating CO₂ into the PUA backbone via CO₂‐polyols offers a highly sustainable pathway for the strippable coating sector. To synthesize these eco‐friendly PUAs, a CO₂‐polyol (from Jiangsu Jinlong Co., Ltd) was reacted with isocyanates (IPDI or methylene bis(cyclohexyl isocyanate) (MHI or HMDI)), followed by capping with 2‐hydroxyethyl acrylate (HEA) to yield acrylate‐functionalized PUAs (designated as PPC2000‐IPDI‐HEA and PPC2000‐HMDI‐HEA, respectively) as illustrated in Figure 7 [41]. These PUAs (70 wt%) were then blended with isobornyl acrylate (IBOA, 30 wt%) and photo‐polymerized under UVA irradiation using various photo‐initiators (1173, 184, or TPO). The performance of the resulting strippable coatings was evaluated through 180° peel tests (according to the GB/T 2792‐1998 standard) and surface decontamination efficiency measurements across diverse substrates, including glass, steel plate, concrete, and paint plate. The formulation composed of PPC2000‐IPDI‐HEA, IBOA, and the 1173 photo‐initiator exhibited the highest 180° peel strength (2.6 N/cm, 0.26 N/mm) on steel plates, which is higher than that of PPC2000‐HMDI‐HEA‐derived materials (2.4 N/cm, 0.24 N/mm). This adhesion performance underscores the critical role of the IPDI structure, which induces a higher cross‐linking density than that of HMDI within the PUA matrix. Because strippable coatings function as temporary protective agents that physically entrap and remove contaminants upon peeling, the decontamination rate serves as a key quantitative barometer of their practical performance. Notably, the PPC2000‐IPDI‐HEA/IBOA matrix system with the photo‐initiator 1173 achieved the highest decontamination rate on painted surfaces (higher than 90%), while lower efficiencies were observed on other substrates. This substrate‐specific performance is attributed to the superior wetting behavior and optimized interfacial adhesion of this CO₂‐polyol‐based PUA formulation on the painted surfaces.

FIGURE 7.

Eco‐friendly UV‐curable polyurethane acrylate (PUA) strippable coatings derived from CO₂‐polyol. Synthetic scheme for PPC2000‐IPDI‐HEA and PPC2000‐HMDI‐HEA acrylate‐capped prepolymers and their UV‐photopolymerization with isobornyl acrylate (IBOA) and 180° peel strength of the coatings on steel substrates as a function of isocyanate type and photo‐initiator (184, 1173, TPO).

The eco‐friendly PU wood coatings designed to enhance the durability and longevity of wooden furniture have been synthesized using CO₂‐polyols [42]. The carbonate and ether linkages within these CO₂‐based polyols are well‐known to provide good hydrolysis and aging resistance. To further optimize coating performance, soybean oil‐based polyols (P‐ESO) synthesized through the reaction of epoxidized soybean oil with 1,3‐propylene glycol (Figure 8a) were incorporated alongside the CO₂‐polyols (from Poly Material Technology in Hangzhou) during PU synthesis to yield modified PU coatings designated as SPUs (Figure 8b). The PUs without P‐ESO were synthesized as a control (Figure 8b). The resulting coating properties were evaluated in terms of gloss, pencil hardness, and adhesion strength in accordance with the GB/T 4893.8‐2013 standard for furniture surface paint films. The strategic introduction of P‐ESO significantly improved the overall performance of the coatings. In the 60° gloss test, SPU achieved a value of 91.2, higher than that of control PU (87.4). Furthermore, the pencil hardness improved from HB for the control PU to 2H for the SPU, indicating a highly durable and scratch‐resistant surface. Interfacial adhesion strength also increased from 2.72 MPa (PU) to 3.66 MPa (SPU). These comprehensive improvements in coating properties are directly driven by the high cross‐linking density afforded by the multi‐hydroxy groups of P‐ESO. This dense polymer network not only enhances surface smoothness to promote better gloss but also constructs a highly rigid framework that elevates pencil hardness and strengthens interfacial chemical anchoring on the wood substrate.

FIGURE 8.

CO₂‐polyol/soybean oil‐based PU wood coatings (SPUs). (a) synthesis of epoxidized soybean oil‐derived polyol (P‐ESO) from ESO and 1,3‐propylene glycol. (b) synthetic scheme for SPU coatings incorporating CO₂‐polyol, P‐ESO, and IPDI and for the control PU coatings incorporating CO₂‐polyol and IPDI.

4. Thermal Stimuli‐Responsive CO₂‐Polyol‐Derived PUs

For the development of shape‐memory polyurethanes (SMPs), an architecture‐controlled synthetic approach was deployed using an amorphous CO₂‐based hydroxyl‐telechelic three‐armed oligo(carbonate‐ether) triol (Triol) with a tailored molecular weight (M _n) and carbonate unit (CU) content (Figure 9) [43]. Triol was synthesized from CO₂, propylene oxide (PO), and trimesic acid in the presence of the Zn‐Co‐DMC catalyst, with CU values ranging from 20% to 50% [44]. This triol was reacted with polyethylene glycol (PEG) and 1,6‐hexamethylene diisocyanate (HDI) to construct the SMP networks (Figure 9). These thermally induced SMPs, which alter their macrostructure in response to thermal stimuli, consist of a fixed phase and a reversible phase. Within this framework, the cross‐linked triol acts as the fixed phase responsible for maintaining the permanent shape via covalent networks, whereas the PEG segments serve as the reversible phase (molecular switch) that locks the temporary shape below the transition temperature (T _trans), governed by the melting temperature (T _m). Because adjusting the quantitative ratio between Triol and PEG directly alters the thermal transitions of the resulting PU, the shape‐memory behavior can be modulated. For instance, as the Triol content increases from 40% to 60%, the shape fixity ratio (R _f) decreases from 100% to 65%. This trend indicates that a higher fraction of triol disrupts the crystalline domains of PEG required to lock the temporary shape. Conversely, an efficient shape recovery ratio (R _r) is maintained regardless of the triol content. The covalent crosslinks provided by triol store substantial elastic strain energy during deformation, which serves as the driving force returning to the original shape. Crucially, increasing the CU content within the triol architecture shortens the shape recovery time. This result is attributed to the enhanced structural rigidity introduced by the higher concentration of carbonate segments within the fixed phase. Consequently, these CO₂‐based PU networks offer a highly tunable platform where both the shape‐fixing capability and recovery speed can be engineered by varying the triol content and its internal carbonate‐to‐ether linkages.

FIGURE 9.

CO₂‐based shape‐memory polyurethane (SMP) networks. Synthetic scheme for the CO₂/propylene oxide/trimesic acid‐derived three‐armed oligo(carbonate‐ether) triol (Triol) and its reaction with PEG and HDI to form crosslinked SMP networks composed of a rigid Triol‐based fixed phase and a crystalline PEG‐based reversible phase.

The shape‐memory performance was systematically investigated using PUs synthesized by varying the ratio between a rigid CO₂‐polyol (Converge Polyol 212‐20) and a flexible poly(tetrahydrofuran) diol (PTMEG), as illustrated in Figure 10 [45]. In contrast to the aforementioned networks derived from a low‐CU Triol and crystalline PEG (Figure 9), this system pairs a CO₂‐polyol possessing a high CU content with highly flexible PTMEG chains. The incorporation of the CO₂‐polyol yielded significantly enhanced shape‐memory properties compared to the pure PTMEG‐based control during thermomechanical cycling tests. Specifically, the CO₂‐based PU (TPU‐N‐1) achieved an outstanding R _f of 95% (second and third cycles) and an R _r of 100%, whereas the pure PU (TPU‐P‐5) exhibited a lower R _f of 75% (second and third cycles) and an R _r of 97%. This superior performance is directly attributed to the short, rigid carbonate linkages within the CO₂‐polyol backbone, where the strong dipole–dipole interactions among carbonate groups enhance the stiffness of the soft segments. This increased rigidity restricts overall chain flexibility and reinforces the network architecture, thereby facilitating shape recovery. When CO₂‐polyol and PTMEG were used at molar ratios of 1:1, 1:2, and 1:3 (TPU‐NP‐2, TPU‐NP‐3, and TPU‐NP‐4), the R _f values progressively declined from 95% to 36% (the third cycle) as the fraction of flexible PTMEG increased. This decrease in R _f occurs because a higher content of highly flexible PTMEG soft segments requires significantly lower temperatures to undergo segmental vitrification. Consequently, under standard testing conditions, the matrix becomes less capable of effectively freezing the polymer chains to lock in the temporary macrostructure.

FIGURE 10.

Shape‐memory PUs derived from CO₂‐polyol/PTMEG blends. Synthetic scheme for TPU formation via MHI‐based prepolymers and chain extension, and a summary table of shape fixity (R _f) and shape recovery (R _r) values across different CO₂‐polyol:PTMEG molar ratios and thermal cycling conditions.

Mao et al. evaluated the impact of CO₂‐polyols on the SMP performance by comparing a series of PUs synthesized from diverse polyols (Figure 11a). Specifically, they contrasted poly(carbonate‐ether) (PEC) polyols containing different CU fractions (40 wt% of CO₂ (212‐10) and 30 wt% of CO₂ (HMA‐1)), with conventional polycarbonatediol (PCDL) and 1,4‐butylene adipate (PBA) (Figure 11b). The results demonstrated that both the CO₂ content and the intrinsic flexibility of the polyol backbone dictate the resulting thermal and shape‐memory profiles (Figure 11c) [46]. Owing to the structural rigidity of the carbonate linkages, the T _{g values} of the PCE‐based PUs were significantly higher than those of the PCDL‐ and PBA‐derived controls. Within the PCE series, a higher CO₂ content correlates with an elevated T _g; the PU utilizing the 40 wt% CO₂ polyol (PCE‐CO₂‐40) exhibited a T _g of 55 °C, whereas the 30 wt% variant (PCE‐CO₂‐30) showed a T _g of 48 °C. Because the shape‐memory behavior is thermally triggered at the T _g, the operational window, including the fixing and recovery temperatures, is governed by the rigidity of polymers. Consequently, CO₂‐rich PCE‐type PUs are suited for high‐temperature shape‐memory applications, while the more flexible PCDL and PBA‐derived PUs operate at low temperatures. In thermomechanical cycling tests, all formulations demonstrated good R _f values, confirming efficient chain immobilization at their respective fixing temperatures. The R _r values improved from the first to the third cycle, where cyclic deformation drives the microstructural reorganization and alignment of the polymer networks.

FIGURE 11.

Comparison of shape‐memory PUs derived from poly(carbonate‐ether) (PCE) polyols with varying CO₂ content (PCE‐CO₂‐40, PCE‐CO₂‐30) versus conventional polycarbonate diol (PCDL) and polyadipate (PBA) polyols. (a) Synthetic scheme for the corresponding PU networks. (b) Molecular architecture of soft‐segment polyols. (c) Glass transition temperature (T _g), fixing/recovery temperatures, and cyclic shape fixity/recovery ratios (R _f, R _r) for each PU formulation.

5. Enhanced Hydrolysis/Oxidation Resistance in CO₂‐Polyol‐Derived WPUs

Waterborne PUs (WPUs) are increasingly preferred in industrial applications due to their ability to form stable aqueous dispersions with negligible volatile organic compound (VOCs) emissions. However, conventional WPUs based on oligoesterols, while mechanically robust, are highly susceptible to hydrolytic degradation, whereas those derived from oligoetherols exhibit excellent hydrolysis resistance but suffer from inferior mechanical properties and oxidation stability. To bridge this performance gap, WPUs incorporating CO₂ polyols have been developed [47]. These polyols synergistically leverage carbonate units to improve mechanical strength and oxidation resistance and ether units to enhance hydrolysis resistance within a single backbone. To evaluate this approach, three distinct WPU systems were synthesized using CO₂‐polyol, polybutylene adipate glycol (PBA), and poly(propylene glycol) (PPG) as soft segments (Figure 12a). The mechanical profile of CO₂‐WPU (66% of CU) revealed a tensile strength of 52.2 MPa, outperforming the PPG‐WPU control (20.3 MPa), though lower than that of PBA‐WPU (68.2 MPa) (Figure 12b). The elongation at break of CO₂‐WPU (410%) was lower than that of both counterparts, reflecting the inherent rigidity contributed by the carbonate linkages. The superior durability of CO₂‐WPU was evidenced by accelerated aging tests. In hydrolytic stability assessments (immersion in 0.25% NaOH for 300 min), both CO₂‐WPU and PPG‐WPU maintained 100% tensile strength retention, whereas PBA‐WPU suffered a 50% loss. Furthermore, in oxidative stability tests (immersion in 6% H₂O₂ for 46 h), CO₂‐WPU demonstrated the highest resistance, retaining 72.2% of its initial strength. Further investigation into the impact of CU% revealed that reducing CU% led to a simultaneous decrease in tensile strength and an increase in elongation at break (Figure 12c). This trend confirms that the carbonate units act as a rigidifying structural motif, directly dictating the mechanical modulus and deformation behavior of the resulting WPU matrix.

FIGURE 12.

Waterborne PUs (WPUs) incorporating CO₂‐polyol, PBA, or PPG soft segments. (a) Synthetic scheme for WPUs via DMPA‐modified prepolymers and TEA/water‐based neutralization and molecular architecture of CO₂‐polyol, PBA, and PPG. (b) Tabulated tensile strength, elongation at break, and retention of tensile strength after NaOH (hydrolytic) and H₂O₂ (oxidative) aging tests. (c) Effect of carbonate‐unit (CU) content on the mechanical properties of CO₂‐WPUs.

To overcome the viscosity‐induced dispersion limitations that often challenge the development of completely organic solvent‐free processes for WPUs, an elevated‐temperature dispersing (ETD) strategy has been introduced [48]. Prepolymers utilizing either a CO₂‐polyol (30% of CU) or a conventional PBA polyol were prepared by blending with DMPA, followed by a step‐growth reaction with IPDI (Figure 13). After neutralizing the carboxylic acid groups with TEA, the prepolymer mixtures were subjected to ETD conditions to generate a stable aqueous emulsion. Subsequent chain extension using ethylene diamine (EDA) afforded high‐molecular‐weight CO₂‐WPU and PBA‐WPU, respectively. Mechanically, the resulting CO₂‐WPU exhibited a robust tensile strength of 49 MPa, which was slightly lower than that of the ester‐based PBA‐WPU control (67 MPa). However, CO₂‐WPU demonstrated exceptional hydrolytic stability when evaluated in an alkaline medium. Upon exposure to a 0.5% NaOH solution for 8 h, CO₂‐WPU achieved 100% tensile strength retention, whereas PBA‐WPU suffered a complete loss of mechanical strength due to ester cleavage. This finding underscores that the ETD strategy, combined with CO₂‐derived soft segments, provides a highly viable, eco‐friendly pathway to fabricate high‐performance, organic solvent‐free PUs with long‐term durability.

FIGURE 13.

Organic solvent‐free CO₂‐WPU synthesis via an elevated‐temperature dispersing (ETD) strategy. Synthetic scheme including CO₂‐polyol‐ and PBA‐based prepolymers, DMPA/IPDI reaction, TEA neutralization, ETD‐based emulsification, and ethylenediamine (EDA) chain extension.

A similar comparative study expanded this evaluation to ultraviolet (UV)‐curable WPUs, which were synthesized by end‐capping the PU chains with acrylate functional groups (pentaerythritol triacrylate (PETA) and 2‐hydroxyethyl acrylate (HEA)) (Figure 14) [49]. Specifically, the hydrolytic stability of a CO₂‐polyol‐derived UV‐WPU (CO₂‐UV‐WPU) was contrasted against a conventional PBA‐based analog (PBA‐UV‐WPU). Upon immersion in a 1.5% NaOH solution for 15 h, CO₂‐UV‐WPU demonstrated enhanced durability, retaining 88% of its initial tensile strength. In contrast, ester‐based PBA‐UV‐WPU suffered a complete loss of mechanical strength due to severe hydrolytic degradation. These results further reinforce that employing CO₂‐polyol as soft segments effectively suppresses ester bond cleavage, thereby significantly enhancing the long‐term hydrolytic resistance of UV‐curable WPU systems.

FIGURE 14.

UV‐curable waterborne PUs (UV‐WPUs) end‐capped with acrylate functional groups. Synthetic scheme illustrating prepolymer formation from CO₂‐polyol or PBA polyol, DMPA incorporation, acrylate end‐capping with PETA/HEA, and TEA‐based neutralization to yield CO₂‐UV‐WPU and PBA‐UV‐WPU.

In contrast to the extensively studied anionic WPUs decorated with carboxylate anions (as illustrated in the preceding figures), cationic WPUs (CWPUs) typically suffer from inherent performance trade‐offs, most notably poor water resistance due to the high density of hydrophilic cationic groups. To overcome these limitations, an engineered synthetic strategy for UV‐curable CWPUs was introduced (Figure 15) [50]. This approach synergistically combines three key structural motifs: (1) 3‐dimethylaminopropane‐1,2‐diol (DMAD) as a terminal hydrophilic group to facilitate efficient aqueous dispersion, (2) 3‐allyloxy‐1,2‐propanediol (AOPD) as a functional chain extender to enable rapid UV cross‐linking, and (3) a CO₂‐polyol to inherently enhance the water resistance by the carbonate group. Remarkably, the resulting UV‐cured CWPU film derived from CO₂‐polyol (CO₂‐UV‐CWPU) demonstrated durability, retaining 95.7% of its initial tensile strength even after immersion in 6.0 wt% H₂O₂ solution for 336 h. This superior hydrolytic stability significantly outperformed that of PBA‐ or PPG‐based analogs (PBA‐UV‐CWPU or PPG‐UV‐CWPU), which exhibited lower tensile strength retention values of 88.4% and 85.1%, respectively. These findings highlight the efficacy of blending CO₂‐derived segments with tailored cross‐linking agents to mitigate the intrinsic moisture vulnerability of CWPU systems.

FIGURE 15.

Cationic UV‐curable WPUs (CWPUs) incorporating CO₂‐polyol, PBA, or PPG soft segments. Synthetic scheme showing incorporation of the hydrophilic terminal group DMAD and UV‐cross‐linkable chain extender AOPD, yielding CO₂‐UV‐CWPU, PBA‐UV‐CWPU, and PPG‐UV‐CWPU.

6. CO₂‐Polyol‐Based PUs for LIB Binders

In the pursuit of high‐performance lithium‐ion batteries (LIBs), the development of polymeric binders with robust mechanical integrity and strong interfacial adhesion is critical. While CO₂‐polyol‐based PUs are promising candidates for such applications owing to their abundant polar carbonyl groups and extensive hydrogen‐bonding networks that can facilitate substrate anchoring, their utilization as battery binders remains largely underexplored. Addressing this issue, Meng and coworkers deployed a series of bifunctional catalysts integrating ammonium salts and boron centers to synthesize a diverse library of CO₂‐polyols, systematically tailoring the choice of epoxides, chain‐transfer agents, and CU contents [51]. For binder applications, they selected a CO₂‐polyol derived from propylene oxide (PO) possessing a high CU fraction of 75 mol%. By reacting this polyol with MHI and BDO, they fabricated a PU featuring 20 wt% hard‐segment content (refer to Figure 1a for the general synthetic method). When implemented in energy storage cells, LiFePO₄ cathodes prepared with this CO₂‐derived PU binder demonstrated a capacity retention of 81% over 800 cycles, significantly outperforming conventional commercial poly(vinylidene fluoride) (PVDF). This breakthrough highlights a highly viable, high‐value, sustainable avenue for CO₂‐utilizing polymers in advanced electrochemical energy storage systems.

7. Sustainable Foams: CO₂‐Polyol‐Derived Polyurethane Foams (PUFs)

PUFs represent a cornerstone material in automotive manufacturing. Depending on their specific application, such as seating cushions or instrumental panels, PUFs are formulated into distinct categories, primarily encompassing flexible and rigid foams. Driven by the industrial imperative to source renewable feedstocks for these high‐volume sectors, CO₂‐polyol‐derived PUFs have garnered significant attention. Beyond the obvious ecological advantages of carbon capture and utilization, these sustainable foam matrices frequently exhibit enhanced mechanical and thermal profiles.

The fabrication of PUFs typically follows a standardized protocol: (1) blending the CO₂‐polyol, catalysts, and surfactants, followed by mixing with isocyanates, (2) initiating free‐rise foaming within an open mold, and (3) subsequent thermal aging (as illustrated in Figure 1a). DeBolt and coworkers investigated flexible PUFs formulated by blending petroleum‐based polyols with CO₂‐polyols (20 wt% CO₂ content) to systematically modulate the sustainable fraction [52]. Irrespective of the CO₂ loading, the resulting PUFs maintained a stable apparent density between 43 and 45 kg/m³, falling within the required threshold for automotive seat cushions (20–95 kg/m³). However, the elevated inherent viscosity of the CO₂‐polyols at higher incorporation levels restricted bubble expansion during blowing, resulting in smaller cell sizes. This morphological shift slightly compromised the overall cushioning quality, as evidenced by an increase in wet compression set values.

While DeBolt’s group relied on physical blending with petroleum polyol to alter the CO₂ content, Hong and coworkers regulated the CO₂ content directly during polyol synthesis. They employed a double‐metal‐cyanide (DMC)‐catalyzed CO₂‐polyol synthesis where adjusting the CO₂ pressure directed the content of CO₂ in CO₂‐polyol and resulting CO₂‐derived flexible PUFs [53, 54]. In comparison to PUF without CO₂ incorporation, PUFs involving CO₂ showed reduced elongation at break and increased modulus values upon increasing carbonate linkages. These mechanical property shifts are driven by reduced segmental flexibility, which stems from the strong dipole–dipole interaction of carbonate groups within the CO₂‐polyol backbone. In addition to the mechanical property, VOC generation was evaluated because minimizing VOC generation such as acetaldehyde (AA) is critical in automobile industries. Increased carbonate linkages in PUFs improved the stability during thermo‐oxidative degradation, resulting in lower AA concentration from CO₂‐derived PUFs than those from no CO₂‐involved PUFs. Compared to the utility of flexible PUFs in seats and cushions, rigid PUFs are commonly used in insulation for construction. In this field, improved mechanical properties can be expected from CO₂‐derived PUFs due to the presence of the rigid carbonate linkages. As presented by Baik’s group, CO₂‐polyols with low molecular weights (1000–2000 g/mol) and high OH values up to 190 mgKOH/g were synthesized using pentaerythritol propoxylate as an initiator and a DMC catalyst [55]. The CO₂‐polyol involving 20 mol% of CO₂ was employed for the synthesis of rigid PUFs, showing enhanced mechanical properties and stable thermal performance.

8. Summary and Outlook

CO₂‐derived polyurethanes (PUs) represent a next‐generation class of engineering materials capable of simultaneously satisfying structural rigidity and chemical durability requirements that are often mutually exclusive in conventional systems. As summarized throughout this review, the incorporation of carbonate linkages into the polyol backbone consistently confers enhanced hydrolytic and oxidative stability, improved mechanical modulus, and tunable thermal transitions across adhesives, coatings, shape‐memory networks, battery binders, and foams. Despite this considerable technical promise, several challenges must be addressed before CO₂‐polyol‐based PUs can be widely adopted at an industrial scale. First, the carbonate content and molecular weight of commercially available CO₂‐polyols remain narrowly distributed, largely dictated by the specific catalytic system and epoxide feedstock employed by each manufacturer; broadening this compositional window through advances in catalyst design would allow more precise tailoring of soft‐segment rigidity to match target applications. Second, the inherently higher viscosity of CO₂‐polyols relative to conventional polyester or polyether polyols complicates processing steps such as foam blowing, waterborne dispersion, and hot‐melt application, and process engineering solutions or viscosity‐modifying co‐polyol blends will be needed to fully translate laboratory‐scale performance into manufacturable products. Third, techno‐economic and life‐cycle assessments comparing CO₂‐polyol‐derived PUs with their petroleum‐based counterparts remain scarce; a rigorous, standardized accounting of both the carbon footprint reduction and the cost implications of CO₂ utilization is essential to convince industry stakeholders of the genuine sustainability benefit beyond the qualitative appeal of carbon capture and utilization.

Looking forward, we anticipate that this review will serve as a practical design guide for matching CO₂‐polyol architecture, including carbonate content and functionality, with the performance demands of specific PU applications. Emerging opportunities include the exploitation of CO₂‐polyols bearing higher functionality (triols, tetraols, and star‐shaped architectures) for densely crosslinked thermosets, the copolymerization of CO₂‐epoxide sequences with bio‐based comonomers to further green the overall feedstock profile, and the extension of CO₂‐polyol chemistry into underexplored application spaces such as solid‐state electrolytes and recyclable or chemically degradable PU networks that align with circular economy principles. Continued collaboration between catalyst chemists, polymer engineers, and end‐use industries will be essential to close the remaining performance and cost gaps, ultimately enabling CO₂‐derived polyurethanes to transition from promising laboratory materials into mainstream sustainable replacements for their fossil‐derived counterparts.

Funding

This study was supported by the Ministry of Education of Korea (RS‐2023‐00285390, RS‐2021‐NR060141) and the Ministry of Science and ICT (RS‐2025‐00533012).

Conflicts of Interest

The authors declare no conflicts of interest.

Biographies

Kihyuk Sung earned his Ph.D. in 2026 from the Department of Energy Systems Research at Ajou University. His doctoral research focused on developing an efficient catalytic system for CO₂ polymerization and the applications of CO₂ polymers.

Hye‐Young Jang has been a Professor in the Department of Energy Systems Research at Ajou University in Korea since 2006. She received her B.S. and M.S. degrees in Chemistry from Seoul National University in 1998 and 2000, respectively, before completing her Ph.D. in Chemistry at the University of Texas at Austin in 2005. Following her doctoral studies, she conducted postdoctoral research at the California Institute of Technology. Prof. Jang’s current research centers on developing sustainable catalytic reactions utilizing renewable resources, including CO₂ polymerization.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.