Depolymerization and Reuse of Polycarbonates: Emerging Classes, Mechanisms and Challenges

ABSTRACT

The efficient recycling of plastics and polymers is a focal point within the development of circular chemistry. In this realm, the development of new types of recyclable‐by‐design polymers plays a crucial role in answering a growing need for plastic formulations that can build on this intrinsic feature while using renewable resources. Within the large and diverse family of engineering polymers, polycarbonates (PCs) play an essential role as modular components for many consumer products. Challenges related to a more sustainable production of PCs and their end‐of‐life disposal have created incentives towards a more responsible use and reuse of these macromolecules. This review focuses on key aspects that should guide future PC development, with both a mechanistic understanding of controlled degradation and identifying efficient depolymerization approaches being the major outcomes. In addition, emerging classes of polycarbonates, such as heteroatom‐containing ones are highlighted and discussed.

This review collects the latest developments in the area of chemical and catalytic polycarbonate recycling strategies and includes the controlled degradation of similar types of macromolecules. Apart from the main strategies for deconstruction, the key mechanistic features of these depolymerization processes are also discussed together with the observed chemo‐selectivities towards either the virgin monomers or small molecule synthons useful in the context of upcycling.

1. Introduction

Plastics are essential to life and their implication in our societies is illustrated by their ubiquitous utilization in many of our day‐to‐day activities. Many plastics improve the quality of life, exemplified by food packaging solutions, offering lightweight alternative materials with lower energy requirements in travelling, and being essential to electronics and medical devices [1]. However, this bright side of plastic usage has become overshadowed by a lack of appropriate end‐of‐life disposal strategies, resulting in the accumulation of plastic waste in our ecosystems all over the world, and an increasing fear of microplastic pollution and related health issues [2]. In order to address these current challenges, a circular approach to polymer production and recycling is warranted, allowing for a more easy recovery of the initial atom‐input [3, 4]. Crucial in this respect is the selective transformation of the end‐of‐life‐based polymer waste into either the original monomers [3, 4] or synthetically useful and versatile small molecules [5]. Depending on the type of polymer, there are various strategies of polymer recycling with chemical degradation [6] under catalytic conditions, which are particularly attractive as they may allow for controlling parameters such as chemo‐selectivity and offering a less‐energy‐intensive route toward unzipping the macromolecular chains. In this regard, a detailed understanding of the catalyst performance and the polymer degradation manifolds they can induce is vital to the design of more sustainable polymers [7]. Knowledge of the key reactivity patterns that control the selective breakdown of the polymeric chain is essential to the overall recycling process and can offer future polymer alternatives with a higher degree of sustainability.

Polycarbonates (PCs) are a special class of macromolecules that find applications in many consumer goods, ranging from their presence in electronics, automotive components, optical data storage devices, and construction materials due to their excellent mechanical strength, thermal resistance, and optical properties [8, 9, 10]. However, the growing consumption of PCs has led to significant post‐consumer waste streams, calling for more sustainable end‐of‐life solutions. These polymers, and their related waste, are characterized by a relatively high oxygen content, and the carbonate group can be regarded as the most abundant reactive center. At the same time, often the polycarbonate chains are hydroxyl‐terminated, offering ways to activate these end‐groups towards back‐biting processes, and controlled backbone degradation. The synthetic chemistry of PCs has been the subject of many studies [11, 12, 13, 14] offering a great deal of variation of the macromolecular structure through monomer design and polymerization techniques, including step‐growth polymerization (SGP) [15], ring‐opening polymerization (ROP) [8, 16], and ring‐opening copolymerization (ROCOP) [10, 13]. More recently, several biobased PCs have been reported utilizing renewable feedstock [17, 18], thereby extending the scope of carbonate‐derived macromolecules and showing that catalysis is of vital importance to access intrinsically more benign PC alternatives. Alongside these latest developments, the field has witnessed an increasing attention for (catalytic) processes that can transform these PCs back into their virgin monomers or closely related small molecules that can be upcycled to new monomers or valuable synthons [19].

Given the importance of these recent achievements, this review provides a comprehensive summary of the critical steps taken forward in the area in terms of atom‐recycling strategies, key mechanistic findings and design elements, emerging classes of PCs, and identification of knowledge gaps and future opportunities.

2. Depolymerization Methods

In the last two decades, advances in catalysis have allowed to produce PCs from CO₂ via versatile ring‐opening copolymerization (ROCOP) with epoxides [10, 13, 20] or through ring‐opening polymerization (ROP) of cyclic carbonates (CCs) [8, 16, 21]. In this context, two process design aspects have become a focal point: the use of renewable feedstocks as sustainable alternatives to petroleum‐based ones, shown in Scheme 1a, b, and PCs that would allow for efficient depolymerization to close the lifecycle of the PC involved, thereby reducing its environmental impact. This section provides an overview of the frequently used initial chemical degradation pathways (Scheme 1c) and the more recent catalytic avenues, including emerging enzymatic and photoinduced degradation strategies.

SCHEME 1.

Conventional and modern PC synthesis. (a) Phosgene/DPC‐based routes and fossil BPA analogues. (b) Alternative routes towards PCs via ROP and ROCOP. (c) Well‐developed depolymerization methods for BPA‐PC.

2.1. Thermal and Solvolytic Depolymerization

Conventional BPA‐PC (BPA = bisphenol A) degradation approaches rely on high‐temperature thermolysis or non‐catalyzed solvolysis (Scheme 1c), and both methods require harsh conditions and are consequently poorly selective. Pyrolysis of BPA‐PC (>400°C, inert atmosphere) triggers random scission of the carbonate and isopropylidene units, thereby releasing light gases (CO₂, CO, CH₄, and H₂) and phenolic fragments [22]. It is clear that such energy‐intensive conditions are ill‐suited for the selective recovery of virgin monomers or other types of small molecules.

Solvolysis, in contrast, cleaves carbonate bonds under typically milder (temperature) conditions by nucleophilic attack. Noncatalyzed hydrolysis, however, is limited by the poor nucleophilic character of water and the rigid, hydrophobic BPA‐PC matrix and thus requires very high temperatures (250‐300°C) and high‐pressure conditions with concomitant BPA degradation and as a result overall low chemo‐selectivity [23].

Alcoholysis and glycolysis are more attractive yielding dialkyl and glycol carbonates, respectively, which both are reusable as reagents or solvents. Often these processes need temperatures >100°C, excess reagents, co‐solvents, can only be operated at low polymer loadings and show incomplete conversion with oligomer/heterocyclic byproducts [24]. These requirements are particularly relevant for organobase catalysis, since polycarbonate hydrolysis first generates a carbonic acid intermediate that can attenuate the performance of a base catalyst. Alcoholysis, on the other hand, avoids acidic products and can therefore proceed under milder conditions [25].

Aminolysis of BPA‐PC produces BPA and carbamate and/or urea derivatives under milder reaction conditions, but complicates BPA purification [26]. A notable exception is represented by biobased poly(isosorbide carbonate), which fully depolymerizes in aqueous NH₃ at 90°C to give isosorbide and urea [27], highlighting the greater solvolytic susceptibility of aliphatic PCs. In general, harsh conditions, modest selectivity, and the necessity for corrosion‐resistant reactors limit the suitability of these methods for circular recycling.

Catalytic depolymerization usually enables milder and more selective BPA‐PC depolymerization [28, 29]. Base‐catalyzed (Na₂CO₃, NaOH) hydrolysis can result in complete depolymerization but requires a large excess of water and base, with a risk of BPA degradation [30]. The utilization of ionic liquids (ILs) allows for increasing the polymer loading and BPA yield, yet relies on expensive and potentially toxic media [31, 32]. Rare‐earth metal triflates such as La(OTf)₃ are recyclable and deliver high BPA yields (∼97%) at lower temperatures, high catalyst loadings, and long reaction times [33].

Heterogeneous alkaline‐earth oxides (e.g., CaO‐based materials and Mg/Al‐layered double oxides) promote methanolysis of BPA‐PC to furnish a nearly quantitative yield of BPA and DMC at 60–120°C with easy catalyst recovery [34, 35]. Metal acetates also catalyze glycolysis and convert BPA‐PC into BPA‐based diols suitable for reuse in PC or polyurethane synthesis, thus coupling depolymerization with upcycling [36]. Organic N‐based (super)bases [DBU = 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; TBD = 1,5,7‐triazabicyclo[4.4.0]‐dec‐5‐ene; DABCO = 1,4‐diazabicyclo[2.2.2]octane; DMAP = 4‐(dimethylamino)pyridine] and DBU‐based ILs efficiently catalyze alcoholysis and hydrolysis of BPA‐PC at ≤ 100°C with near quantitative BPA recovery [29, 37, 38], and Lewis acids such as [Ph₃C][B(C₆F₅)₄] enable metal‐free methanolysis [39].

Recently, Dove and coworkers further demonstrated orthogonal, multistage depolymerization of mixed PLA/PET/BPA‐PC using MgCl₂ and imidazole, recovering each monomer in high yield from a single waste stream [40]. Analogous catalytic solvolysis routes have been extended to ROCOP‐derived PCs. Grinstaff et al. reported hydrolysable PCs fabricated from alkyl glycidate and glycidyl ester epoxides, which undergo pH‐controlled hydrolysis to glyceric acid or glycerol, and CO₂ [41]. Enthaler and co‐workers showed that Zn(OAc)₂ and NaOAc catalyzed methanolysis converts poly(propylene carbonate), PPC, into 1,2‐propanediol and DMC [42]. These latter two examples illustrate how judiciously designed catalytic solvolysis can unlock closed‐loop, value‐added recycling pathways for both BPA‐ and CO₂‐based PCs.

In general, the results discussed in this section suggest that for a successful catalytic alcoholysis to occur, both the presence of a suitable and soluble base (cf., pK _b) and a Lewis acid (cf., oxophilicity) are favorable catalyst components that can activate end‐ and/or carbonate groups. It should be noted that the presence of trace amounts of water may be crucial to generate in situ the necessary nucleophiles for carbonate cleavage.

Apart from solvolysis methods, PCs can be conveniently hydrogenated under attractive process conditions. Ru/Fe pincer complexes hydrogenate BPA‐PC into BPA and methanol, and they can also convert CO₂‐derived PCs (such as PPC) into methanol and vicinal diols that can be upgraded to fuel‐range hydrocarbons [43, 44].

2.2. Catalytic Depolymerization of Aliphatic and Alicyclic Polycarbonates

Darensbourg's seminal studies established that classical aliphatic PCs such as PPC undergo base‐initiated end‐group backbiting to deliver five‐membered cyclic carbonates (CCs). Cyclic groups, such as those present in cyclopentene or cyclohexene oxide, suppress depolymerization, whereas resonance‐stabilized chain end groups enhance polymer unzipping. Coordination to Cr^III(salen) (see Scheme 2a) deactivates the anionic chain end and hence slows down depolymerization [45]. PPC's strong tendency to depolymerize towards propylene carbonate was exploited by Byers, who, for this purpose used ZnCl₂/PEG600 based reactive‐distillation setup [46] while the Fieser group utilized pyridine(diimine)cobalt catalysts (Scheme 2b) to achieve the degradation of PPC [47].

SCHEME 2.

Representative catalysts for the depolymerization of polycarbonates. Panels (a–f) illustrate selected metal‐ and organo‐catalysts and indicate the main polymer substrate(s) investigated in each case. PCPC = poly(cyclopentene carbonate), PCHC = poly(cyclohexene carbonate), PPC = poly(propylene carbonate), PLC = poly(limonene carbonate).

For PCs derived from more constrained alicyclic epoxides (cyclopentene/cyclohexene/cycloheptene oxides, N‐aryl epoxy‐pyrrolidines, indene oxide, and limonene oxide), both the ring strain and choice of catalyst determine the fate of the depolymerization process toward either epoxides (and CO₂) or trans‐configured cyclic carbonates. Poly(indene carbonate) is a special case, whose photochemically induced depolymerization predominantly provides cis‐indene carbonate as a product [48]. For the depolymerization of poly(cyclopentene carbonate), PCPC, weak bases such as DBU are inactive, while strongly basic NaHMDS only induces slow, non‐selective depolymerization, leading to a mixture of epoxide and the cis‐cyclic carbonate [49]. This latter scenario is consistent with the computationally studied chemo‐preference under strongly basic conditions [50]. These results are in contrast to those attained in the presence of binary catalyst Cr^III(salen)/Y‐N₃ (Y = (nBu)₄N or PPN; PPN = bis(triphenylphosphine)iminium) mediated pyrolysis [51], and with the outcome of bifunctional organoboron/KOH catalysis (Scheme 2c) [52]. In both cases, the depolymerization process of PCPC leads to quantitative epoxide recovery.

In the case of poly(cyclohexene carbonate), PCHC, the use of Cr^III(salen)/PPNN₃, homo‐ and hetero‐dinuclear Mg(II)/Co(II)‐based macrocyclic complexes (Scheme 2d) [53, 54, 55] and dinuclear Zn(II) species [BDI‐ZnMe·xH₂O)₂, Scheme 2e) [56] regenerate the epoxide product in high selectivity. In contrast, Cr^III(salen)/nBu₄NN₃ [57], Zn(OAc)₂, TBD, and KHMDS (HMDS = bis(trimethylsilyl)amide) divert the reaction to trans‐cyclohexene carbonate [53]. For other aliphatic PCs such as poly(3,3‐dimethyltrimethylenecarbonate) (PDTC), Williams and co‐workers showed that depolymerization to their respective cyclic carbonates using simple divalent Zn‐, Co‐, or Mg‐ethylhexanoates (with the Zn‐based complex being the fastest) proceeds best at intermediate Lewis acidity, with polymer carbonyl activation and alkoxide nucleophilic lability being optimally balanced [7].

Lanthanide bis(trimethylsilyl)amides (Ln[N(TMS)₂]₃, Scheme 2f) allow for solvent‐free, chemo‐divergent depolymerization of PCHC to either cyclohexene oxide and CO₂, or trans‐cyclohexene carbonate, depending on the type of Ln metal ion and the applied vacuum [58]. Silyl amides such as NaHMDS accommodate the depolymerization of hydroxyl‐terminated poly(cyclohexadiene carbonate) (PCHDC) towards the trans‐configured cyclic carbonate product [59]. Poly(cycloheptene carbonate), treated with Cr^III(salen)/nBu₄NN₃ [60], also affords trans‐fused bicyclic carbonates, which are viable ROP monomers [16].

Organocatalysts offer a complementary, metal‐free platform for the depolymerization of PC [25]. Koning reported that TBD depolymerizes poly(limonene carbonate), PLC, at 110°C to give limonene oxide in quantitative yield via an end‐group‐initiated decarboxylative degradation pathway [61]. Later on, Kleij and co‐workers demonstrated that temperature‐controlled, mechanistically divergent PLC depolymerization takes place, where both end‐group‐based backbiting and main‐chain scission pathways work in concert to afford both trans‐limonene carbonate (maximum yield: 60%) and/or limonene oxide (maximum yield >95%). The trans‐carbonate is of high interest as it allows to regenerate PLC through ROP, and as such it delivers a potentially closed‐loop recycling of this PC, avoiding the requisite for high‐pressure equipment [62].

TBD also depolymerizes PCs derived from fatty‐acid epoxides to cyclic carbonate [63] and biohybrid terpene‐based PCs to terpene epoxide mixtures with >95% epoxide selectivity [64]. In contrast, sterically more demanding macromolecular carbonate‐drug‐conjugates only undergo partial cleavage [65]. More recently, Zhang and co‐workers reported a “polymer A to polymer B” upcycling of PPC into sulfur‐containing polymers. First, base‐catalyzed (KOtBu, DBU) depolymerization of PPC to propylene carbonate takes place. The latter then undergoes decarboxylation, giving propylene oxide that reacts with carbonyl sulfide (COS) to provide a cyclic (thio)carbonate. A second decarboxylation then finally affords poly‐thioethers with a tunable (72%–100%) sulfur content [66].

CO₂‐sourced PCs obtained by the ROP of cyclic carbonates can also undergo efficient depolymerization. The Coates group showed that iso‐tactic PCHC cleanly hydrolyzes into an enantio‐pure trans‐diol, which can be converted into trans‐cyclic cyclohexene carbonate [67], with the latter being polymerizable towards PCHC. Binary Cr^III(salen)/nBu₄NN₃ induces backbiting‐based depolymerization of poly(5‐methyl‐5‐benzyloxymethyl‐1,3‐dioxan‐2‐one) to its six‐membered cyclic carbonate [68], which in turn can deliver the PC by ROP. Finally, treatment of the seven‐membered bicyclic carbonate monomer with a ytterbium‐alkyl based catalyst at rt yields a polycarbonate with very high molecular weight (M _n´s > 500 kg/mol). Catalytic depolymerization of the latter by KOMe at rt affords unusual larger‐ring, cyclic dimeric carbonates (around 80% yield), which can be repolymerized by anionic ROP using KOMe at 150°C, potentially closing the polymer‐monomer loop [69]. Mechanistic aspects of various selected catalytic systems described here are discussed in detail in Section 3.

Whereas the use of metal‐based depolymerization catalysis is the focal point in this section, many of the discussed metal complexes are often part of systems that favor polymerization. In this respect, it is crucial to emphasize the complete nature of the catalyst system, either being bifunctional or binary. The presence of (sub‐stoichiometric amounts) of a suitable base (or basic ligand in the complex), combined with an elevated reaction temperature can be generally considered to favor depolymerization. Polymerization activity with the same metal complex is usually observed at moderately high temperatures in the presence of equimolar‐or‐lower amounts of a nucleophilic species such as chloride.

2.3. Enzymatic and Photochemical Degradation

Enzymatic and phototriggered routes provide, in essence, low‐impacting chemical approaches for polymer degradation. BPA‐PC is barely biodegradable, and rare strains (e.g., Pseudoxanthomonas sp. NyZ600) and a few purified hydrolases mainly attack through slow surface erosion of bulk BPA‐PC material with <10% weight loss per year [70]. Lipase‐catalyzed degradation of BPA‐PC films proceeds via enzyme adsorption and catalytic carbonate cleavage, releasing BPA and phenolic derivatives. Genetically engineered cutinizes/hydrolases only reach significant conversion in thin films and remain far less active than polyester hydrolases [71, 72].

Aliphatic PCs such as poly(ethylene carbonate), PEC, and poly(trimethylene carbonate), PTMC are more labile, thus displaying pronounced surface erosion and mass loss both in vitro and in vivo. In contrast, PPC is markedly more stable, underscoring strong structure‐degradability correlations [73]. Carbonate bond cleavage affords soluble oligocarbonates and five‐membered cyclic carbonates that further hydrolyze towards diols and CO₂. Candida Antarctica (a lipase) depolymerizes PTMC to trimethylene carbonate (TMC) with a high monomer yield (80%) under optimized conditions [74], while the depolymerization of PEC and PPC primarily results in mixtures of diols and short oligomers. The degradability of aliphatic and CO₂‐based PCs can be tuned by variation in molecular weight, composition, architecture, end‐groups, and crosslinking density. ‘Hydration‐driven degradability’ further suggests that side‐chain polarity (and linker identity) can promote neutral hydrolysis and affect enzyme recognition, and thus degradability and product recovery should be considered at the monomer‐design stage [8, 25]. The enzymatic degradation of PCs such as PCHC and PLC generally exhibits only small mass losses and negligible reduction of their molecular weight, consistent with slow, surface‐confined chain scissions [14].

Photodegradation of PCs using light or photocatalysts is another emerging frontier. BPA‐PC undergoes photo‐oxidative chain scission under prolonged UV irradiation, causing yellowing, embrittlement, micro‐cracking, rapid molecular‐weight loss, and BPA release [75]. Nanosized TiO₂ accelerates these processes in solution under UV or simulated solar light by generating radicals that attack the carbonate backbone, eventually yielding BPA, CO₂, and low‐molecular‐weight products [76]. Both direct photo‐oxidation and TiO₂‐based photocatalysis mainly induce surface oxidation and fragmentation of the PC material rather than giving complete mineralization, with degradation rates depending on the light intensity, temperature, and water chemistry [77]. For PPC, the backbone is relatively UV‐stable; however, photo‐generated acids enable light‐triggered, acid‐catalyzed polymer “unzipping” to give propylene carbonate. This approach is used in transient or sacrificial devices rather than applying it for environmental degradation [78].

To date, enzymatic and photo driven routes remain too slow and unselective for large‐scale closed‐loop recycling of BPA‐PC, but they offer low‐temperature, low‐environmental footprint options to mitigate PC microplastics and degrade more labile aliphatic PCs.

3. Mechanisms of Catalytic Depolymerizations

3.1. General Considerations

BPA‐PC is the most widespread commercially available PC with known variations in the bisphenol fragment (BPA, BPS, BPF; see Scheme 1a). In addition to bisphenol‐derived PCs, two other types of polycarbonates are currently commercially available on a quite large scale, viz. polyisosorbide (PISC, Scheme 3a and b) and polypropylene (PPC) carbonate. Examples of commercially available PISCs are Polysorb [79] and Durabio [80], while PPC has been commercialized, for instance, as QPAC40 [81]. Compared to PISC and PPC, poly(cyclohexene carbonate), PCHC, has only been commercialized to a minor extent [82] as CHO as a relatively expensive monomer for bulk chemical applications. Relatively novel types of (non‐commercial) biobased polycarbonates are those derived from terpenes (such as PLC), fatty acids, sugars, and lignin (Scheme 3b) [83, 84]. Intriguingly, in contrast to most other PCs, terpene‐ and glycerol‐derived polycarbonates possess functionalities (double bonds and hydroxyl groups, respectively) that allow for post‐polymerization adjustments of the polymer side‐chain, and thus their thermal, mechanical, and optical properties [85].

SCHEME 3.

(a) Differences in the depolymerization of rigid vs non‐rigid PCs. (b) Main classes of commercial and research‐oriented (biobased) PCs. (c) Different backbiting pathways and typical conditions.

BPA‐PC and PISC behave rather differently when depolymerized when compared to PPC and PCHC. Both BPA‐PC and PISC need an external nucleophile to initiate depolymerization (Scheme 3a), as their rigid structure does not allow for easy backbiting reactions starting from either chain end. In a backbiting scenario, an intramolecular nucleophilic attack of an O‐terminated PC (being either an alkoxide or carbonate) takes place onto the nearest electrophilic position in the polymer backbone (Scheme 3c). In general, PCs that are more easily depolymerized (for instance, at lower reaction temperatures) should be devoid of any (pro)nucleophilic impurities and/or catalyst residues upon processing around or above their T _g´s, as that could lead to undesired depolymerization at elevated temperatures, and consequently poorer material performance.

Recent reviews on the chemical recycling of more conventional PCs have been communicated [3, 6, 86, 87]. In the following sections, focus will first be put on the more frequently studied PCs, while backbiting processes taking place within the newer types of PCs will be specifically highlighted.

3.2. Commercial and Common Polycarbonates

Different backbiting routes are possible, giving rise to different products among which are epoxides (and CO₂), and cis or trans configured cyclic carbonates (Scheme 3c). The activation energy for the conversion of the PC into the trans cyclic carbonate is generally lower than for the epoxide [50]. The trans cyclic carbonate is the kinetic product of the reaction, while the formation of the epoxide (and concomitantly CO₂) is driven by thermodynamics. Nonetheless, exceptions are known, such as in the case of poly(cyclopentene carbonate), PCC [49, 50]. For PCC, the activation energy for epoxide formation is lower than for the trans cyclic carbonate. The backbiting of the O‐based nucleophile on the electrophilic vicinal carbon atom or the carbon center of the carbonate are S_N2‐ and S_NAc type substitutions, respectively [88]. Alkoxide attack on the nearest carbonate unit (path 1) affords the corresponding trans cyclic carbonate, while attack on the vicinal carbon (path 2) gives the epoxide with CO₂ extrusion. Depending on the reaction conditions (i.e., at high pCO₂ values), carbonate‐type backbiting affords the cis cyclic carbonate (path 3). In addition, a concerted decarboxylation‐alkoxide attack sequence can occur, affording the epoxide product with inversion of the original stereochemical configuration. Importantly, while trans cyclic carbonates feature a strained ring that allows for ROP, the cis mono‐cyclic carbonates are typically impossible to repolymerize as they are significantly more stable from a thermodynamic point of view than their respective PCs [88]. The cis cyclic carbonates may have applications as solvents and electrolytes, but are undesired as degradation products in the context of polymer circularity.

The reaction conditions greatly influence the depolymerization outcome, with the reaction temperature and CO₂ pressure being the principal parameters (Scheme 3c). In general, polymerization processes entail a decrease in entropy, and thus the depolymerization of polycarbonates is favored at high temperature and low pressure. At high CO₂ pressure and concentration, in situ present alkoxide‐terminated chain ends give rise to carbonate‐type backbiting that ultimately may lead to a cis‐configured cyclic carbonate product (path 3). In turn, alkoxide backbiting is favored under vacuum or dilute CO₂ conditions [50].

The relatively easy change in reaction conditions can hence be leveraged to favor either PC synthesis or its depolymerization, and usually the more challenging to prepare PCs tend to be more easily depolymerized and vice versa. Such types of PCs possess a relatively low ceiling temperature (T _c), which is the temperature at which the polymer decomposes into its constituent monomers [89, 90]. In order to be able to regenerate the original polymer, high‐selective depolymerization towards epoxide and CO₂ provides a way to have both monomers undergoing catalytic ROCOP requiring, however, a dedicated pressure reactor. Alternatively, when a repolymerizable cyclic carbonate (trans) can be selectively targeted, more easily adaptable ROP is envisaged, which can be carried out in simpler reactor set‐ups.

The cyclodepolymerization of PPC, one of the most widely available and potentially biobased polycarbonates produced via ROCOP has not been extensively studied so far, with only a handful of reports on its selective catalytic conversion into propylene carbonate (Scheme 4a). In a pioneering contribution from Kuran and co‐workers, PPC was converted at 30°C into propylene carbonate (yield not reported) using ZnEt₂ as a catalyst [91]. More recently, air‐stable ZnCl₂ was applied as a catalyst (T = 160°C, 16 h) by Byers, achieving a 92% yield of PC [46]. A similar outcome (99% yield of PC) was achieved under Co‐catalysis at 180°C in 20 h [47], while borane catalysis afforded the same yield, though at a lower temperature and in shorter times (105°C, 2 h) [92, 93].

SCHEME 4.

(a) Reported work on the catalytic depolymerization of PPC via backbiting reactions. (b) PC substituent effects on the depolymerization selectivity. (c) The effect of the depolymerization conditions and catalyst structure on the chemo‐selectivity.

Darensbourg and co‐workers studied the influence of the PC main chain substituents on the outcome of the depolymerization reaction using Cr^III(salen) complexes as catalysts (Scheme 4b) [48, 49, 50, 57, 88]. As a general trend, on one hand, PCs originating from monosubstituted epoxides (e.g. PO) results in the preferential formation of epoxide products; on the other hand, the increase in strain in polymer originating from bicyclic epoxides (e.g., CPO) favors cyclic carbonate formation. This is well reflected in the sharp 3‐to‐20‐fold increase in the activation energy to form the trans cyclic carbonate for PCs with acyclic substituents, with the depolymerization of PCC being an exception due to thermodynamic constraints. The same conclusions were drawn by Lu and co‐workers, who used CrCl₃/nBu₄NN₃ as a binary catalyst while increasing the ring‐size of the cyclic group from 5‐to‐7 in the PC, thereby observing a drastic increase in the selectivity for trans cyclic carbonate (Scheme 4b) [60].

The reaction conditions and the nature of the catalyst can also have a tremendous impact on the selectivity of the depolymerization reaction. Williams, Buchard, and co‐workers showed that bimetallic catalysts (di‐Mg^II or heterobimetallic Mg‐Co based), compared to single‐site Zn(OAc)₂ or TBD under similar conditions (120‐140°C, toluene/neat), induce the depolymerization of a series of polycarbonates affording the corresponding epoxide or the trans cyclic carbonate in up to 99% selectivity (Scheme 4c) [53, 54, 55, 94]. In the proposed mechanism, the bimetallic catalyst is able to simultaneously coordinate and activate both a carbonate and an alkoxide to favor the formation of an epoxide product. This catalytic system thus delivers a different product (epoxide) than the one reported by Darensbourg using monometallic Cr^III(salen) type catalysts [48, 49, 57, 88].

The effect of the catalytic system was also scrutinized by Lu and co‐workers (Scheme 4c) [51]. At high temperature (200°C) and for relatively short times (20‐40 min), applying vacuum, poly‐cyclohexene carbonate, PCHC was selectively converted into its trans carbonate (99%) using either MgCl₂, Zn(OAc)₂, or a Co^III(salen) complex as a catalyst. In contrast, with a Cr^III‐centered salen complex, the chemo‐selectivity of the reaction changes towards the epoxide (99%). The authors propose a pathway that involves first the formation of a trans cyclic carbonate, which then decomposes via decarboxylation into the epoxide product. This is an illustrative example of how a catalyst and conditions can drastically modify the outcome of the depolymerization of a given PC.

3.3. Emerging PCs and Unique Depolymerization Strategies

The Chen group found that a PC derived from a hybrid epoxide/lactone monomer could be rapidly depolymerized at 160°C (5‐15 min) into the corresponding epoxide by Cr^III catalysis, or into the cis cyclic carbonate in the presence of TBD (Scheme 4c) [95]. Marks and co‐workers developed a protocol to selectively depolymerize well‐studied PCHC into the corresponding epoxide or cyclic carbonate (99%) under Ln‐catalysis by varying the reaction conditions (Scheme 4c) [58]. At 140°C, under a static vacuum, they achieved 99% selectivity towards the epoxide, while at the same temperature using a dynamic vacuum, the selectivity was driven towards the trans carbonate (99%). The authors suggest that two competing depolymerization pathways are occurring based on experimental and computational analysis: low‐energy, reversible cyclic carbonate formation and a rate‐limiting irreversible decarboxylation.

Poly(limonene carbonate), PLC has emerged as a fully biobased polycarbonate alternative with post‐polymerization functionalization potential and sustainable material development (Scheme 5a). The double bonds in PLC provide sites for post‐modification of the polymer (generally not possible in the case of other biobased PC) and thus fine‐tuning and optimizing the polymer properties. The synthesis [14, 96, 97, 98] and depolymerization of PLC have triggered much interest from various research groups in recent years. Koning and co‐workers selectively depolymerized PLC into limonene oxide (LO, >98%) at 110°C using TBD as the catalyst (Scheme 5a, top) [61]. A similar outcome was achieved by the Williams's group using a di‐Zn complex as catalyst under milder conditions (80°C) [99]. In contrast, Kleij and co‐workers depolymerized PLC into the corresponding trans cyclic carbonate (LC) in 60% yield using TBD at 80°C (Scheme 5a, below) [62]. Both DFT and experimental data (control reactions, GPC analysis) supported a mechanistically divergent process involving both end‐group activation and main‐chain scission (i.e., a random cleavage along the polymer backbone with H₂O as a pronucleophile) pathways. Computational comparison revealed that both pathways are competitive and offer a potential reactivity framework for other types of PCs. Notably, trans‐LC could be efficiently polymerized via ROP at 80°C into PLC with a similar M _n, Ð, and isomeric repeat‐unit ratio using TBD as catalyst in the presence of an alcohol initiator.

SCHEME 5.

(a) Depolymerization for PLC. (b) Degradation of particular PCs. (c) Depolymerization of PCs obtained by ROP or from ROCOP of CO₂ and oxetanes.

A more specific type of PC was prepared by Liu, Lu, and co‐workers via ROCOP of an N‐containing epoxy pyrrolidine and CO₂ under Cr^III or Co^III catalysis (Scheme 5b) [11, 100]. Remarkably, using a Cr^III(salen) complex as a catalyst, the envisioned PC was synthesized (TOF up to 100 h^{− 1}) at 60°C and depolymerized at 100°C without the need for additives [11]. Zhang synthesized a PCHC variant with a unique cyclic structure comprising sequential carbonate groups apart from cyclohexyl units (Scheme 5b) [56]. This PC was depolymerized into cyclohexene oxide and CO₂ using a multi‐nuclear Zn catalyst, achieving 99% selectivity at 150°C. Another example of a selective depolymerization of PCHC was reported by Kerton and co‐workers using B(C₆F₅)₃ as the catalyst at 105°C (Scheme 5b) and providing cis cyclohexene carbonate in 91% yield. The latter example is unique in the sense that it contrasts with other reported methods that provide either trans cyclohexene carbonate or cyclohexene oxide as the primary product [53, 58], and the rationale for the observed discrepancy may be found in the occurrence of a multi‐step degradation of PCHC in the presence of B(C₆F₅)₃.

Depolymerization strategies for PCs prepared from the ROP of six‐membered cyclic carbonate or the ROCOP of oxetanes and CO₂ are presented in Scheme 5c. Generally, high depolymerization selectivity towards a six‐membered cyclic carbonate can be achieved. This chemo‐selectivity does not seem to depend on the type of polycarbonate and/or the applied catalysts that so far included Cr^III(salen) complexes, ZnCl_2, or DBU [68, 89, 92, 101, 102]. One early example reported by Darensbourg [68] demonstrated that a more flexible PC with two β‐positioned substituents undergoes partial but selective Cr^III(salen) induced depolymerization affording a 70:30 mixture of the starting, but lower (average) molecular weight PC and a six‐membered cyclic carbonate (Scheme 5c, upper left). Byers reported the selective depolymerization of PTMC into TMC (85%) using a combination of ZnCl₂ and PEG600 while applying a vacuum [45]. The Reineke laboratory showed that a similar PC as used by Darensbourg degrades into a six‐membered cyclic carbonate with very high selectivity (>99%) in the presence of DBU as catalyst at 90°C [89].

Endo and co‐workers systematically investigated the effect of substituents on the equilibrium of six‐membered cyclic carbonates and their respective PCs (Scheme 5c, middle) [102]. As a general trend, they found that polymers bearing bulkier R¹ and R² substituents were more easily depolymerized into their corresponding six‐membered cyclic carbonates using tBuOK as a simple base catalyst at 20°C. A rather interesting approach to large‐scale synthesis (>100 g, >60% yield) of a six‐membered cyclic carbonate (2‐allyloxymethyl‐2‐ethyltrimethylene carbonate, AOMEC) was developed by Albertsson (Scheme 5c, lower part) [103]. They combined in a one‐pot bulk reaction approach trimethylolpropane allyl ether, diethyl carbonate, and NaH, providing, after application of vacuum (to remove EtOH) and high temperature (200°C), a functionalized PC that depolymerizes under these conditions, giving AOMEC. The latter monomer underwent easy, controlled, and fast ROP towards the same PC in the presence of TBD. Their work was further extended by surmising that the reaction conditions (type of solvent, temperature, pressure) have a significant effect on the monomer‐polymer equilibrium [104]. Tailoring those conditions, the AOMEC‐PC equilibrium could be favored towards the polycarbonate using bulk polymerization at 30°C, while the monomer was the major reaction component at 82°C (CH₃CN) at 0.5 M concentration.

Cai, Zhu and co‐workers designed chemically recyclable polycarbonates starting from seven‐membered bicyclic carbonates [105]. Initially, polycarbonates featuring six‐membered fused rings with M _n´s of up to 673 kg/mol and high thermal stability (T _d > 300°C) were synthesized via ROP under yttrium catalysis ([Y]) using BnOH as the initiator. The resulting PCs could be completely depolymerized at room temperature under basic conditions (MeOK) into their corresponding cyclic dimers. These dimers were repolymerized into the same PCs at 150°C in the presence of catalytic MeOK (Scheme 5c, bottom). In a follow‐up contribution, the same group developed a similar procedure using Zn‐based catalysts [106].

As a last example, the Kleij group prepared polycarbonates from six‐membered bicyclic carbonates with a variety of functionalities, including vinyl, allyl, ester, and alkenes such as styrene and cyclic olefins (Scheme 5c, lower part) [107]. A representative example was subjected to depolymerization in the presence of TBD as a catalyst in toluene at 110°C, giving rise to 56% mass recovery and a product mixture containing 85% of an oxetane product and 15% of its corresponding 1,3‐diol. The oxetane product here resembles the same type of product (i.e., a cyclic ether) observed in many depolymerization processes and holds promise to degrade PC derived from larger ring carbonates towards re‐polymerizable oxetane monomers.

3.4. Novel Types of Heteroatom‐based PCs

Sulfur‐containing polycarbonates are a class of polymers in which sulfur atoms are incorporated into the backbone or side chains of the PC. These analogues often exhibit enhanced thermal stability, higher refractive indices, and improved resistance to degradation compared to conventional polymers [108, 109]. Additionally, their recycling potential makes S‐containing polycarbonates a promising focus for sustainable material development. For instance, Plajer and co‐workers reported that sulfur‐containing poly‐dithiocarbonates derived from the ROCOP of CS₂/oxetane under Cr^III/K catalysis undergo depolymerization under conditions not effective for their oxygen‐based analogues. The synthesized polymer could then be depolymerized under basic conditions into the corresponding cyclic thiocarbonate, which, in turn, was re‐polymerized via ROP using TBD and BnOH as the catalyst and initiator, respectively [110].

In contrast, in a subsequent study, the same group showed that related poly‐thioimidocarbonates derived from the ROCOP of phenyl isocyanate/oxetane cannot be depolymerized under similar conditions. This difference in reactivity is likely because of a higher kinetic stability of the thioimidocarbonate group towards backbiting and, thus, depolymerization [111]. To date, CS₂, COS, thiiranes, dimethyl trithiocarbonate, elemental sulfur (S₈), and RNCS have all been used as monomers to prepare S‐containing (poly)carbonate analogues (Scheme 6a). Their polymerization routes are often similar to the ROCOP of epoxides with CO₂, with a catalyst and an initiator being involved in the catalytic process. On the other hand, unlike traditional oxygen‐based ROCOP systems, these sulfur‐containing monomers are often engaged in multiple propagation pathways, namely scrambling reactions, giving rise to a variety of isomeric linkages/products depending on the relative positioning of the oxygen, sulfur, and sometimes even nitrogen atoms (Scheme 6b) [112, 113, 114, 115, 116, 117]. The scrambling reactions here refer to processes that are connected to nucleophile‐induced backbiting steps, causing redistribution of carbonate and thiocarbonate units. These scramblings are typically promoted under thermal and/or catalytic conditions, particularly in the presence of bases or metal catalysts, and result in significant structural rearrangements within the polymer chain.

SCHEME 6.

(a) S‐containing monomers and organic carbonates. (b) Mechanistic model from Darensbourg for the O‐for‐S exchange reactions through scrambling. (c) Mechanistic scrambling model reported by Plajer.

Darensbourg proposed a mechanism for these scrambling reactions (Scheme 6b) [114]. At first, an initiator (here, a boronate species) ring‐opens the epoxide, which in turn attacks CS₂, and subsequently cyclization occurs. Then, the nucleophilic addition of an alkoxide onto the dithio cyclic compound affords a thiolate, which attacks a second molecule of CS₂ and generates a fully S‐based carbonate analogue. The backbiting of latter anionic and linear species produces a cyclic trithiocarbonate. Several other pathways (equilibria) are concomitantly possible, giving rise to a variety of products as represented under Scheme 6b. In addition to these scrambling reactions, polymerizations (propagation) can occur at each alkoxide/thiolate stage and will depend on the relative rates of intra‐ vs. inter‐molecular reactions.

Importantly, other groups formulated different mechanistic hypotheses explaining the formation of the S‐containing species, thereby providing an alternative rationale for the scrambling manifold [116, 117]. Overall, differences in the reaction conditions, relative bond strengths, and nucleophilicity between S‐ and O‐species influence the process outcome [115, 118]. The (partial) exchange of O‐ for S‐atoms in carbonate macromolecules can affect the polymer thermal stability, and is appealing for potential applications in dynamic or recyclable materials. A recent study by Plajer's laboratory provided experimental and computational evidence that carbon disulfide/epoxide copolymerization can be envisioned as a series of structurally related insertion events that are interlinked by a central oxygen/sulfur scrambling reaction at the propagating chain end (Scheme 6c) [115]. The authors presented a complex scenario that involves a series of insertion reactions of CS₂ and epoxide, followed by intramolecular rearrangements.

The same group, in collaboration with Darensbourg, systematically investigated the outcome of ROCOP of epoxides using different sulfur sources under Cr^III/Rb^I heterobimetallic catalysis and unified conditions (Scheme 7a, left) [118]. They found that CSO was the most rewarding S‐source in terms of chemo‐selectivity in the polymerization reaction, which allowed for to selectively prepare perfectly alternating copolymers. In contrast, the utilization of thioanhydrides and CS₂ showed significantly lower selectivity, with increasing O/S‐scrambling and small molecule heterocyclic by‐product (cf., Scheme 6a) formation. As a testament to their commitment to the relatively novel area of S‐based polymers, they also reported two further approaches towards the co‐polymerization of CS₂ or elemental sulfur (S₈) with epoxides or phthalic thioanhydride, both under LiOR catalysis (Scheme 7a, right) [113, 119]. These latter processes afford poly(OSO‐alt‐S _x ) polysulfite and semi‐aromatic poly(ester‐alt‐S _x ) macromolecules, respectively. The mechanistic investigations of these manifolds revealed that alkyl oligosulfide intermediates from S₈ ring opening are better nucleophiles for the ROCOP of epoxides compared to the trithiocarbonates obtained from CS₂ addition, thus providing sequence selectivity [113]. In both cases, cross‐linked, recyclable networks were prepared using reversible disulfide linkages, which could be rapidly broken (in minutes) by the addition of a thiol such as iBuSH under basic conditions.

SCHEME 7.

(a) The influence of different S‐based monomers on the polymerization selectivity. (b) Transesterification of S‐based macromolecules. (c) Upcycling and selective synthesis of S‐containing polymers.

Ren and co‐workers produced polytrithiocarbonates via polycondensation of dithiols and dimethyl trithiocarbonate (Scheme 7b) [120]. This synthetic strategy features excellent compatibility with a wide range of monomers, including aliphatic, heteroatomic, and aromatic dithiols, enabling the synthesis of polytrithiocarbonates with diverse macromolecular structures. Notably, these polytrithiocarbonates could be easily depolymerized via transesterification in the presence of a small molecule thiol (MeSH) under basic conditions at 40°C to give the corresponding dimethyl trithiocarbonate and dithiol monomers, which can be repolymerized to the initial polymers without changing the material properties.

Zhang, Zhang, and co‐workers developed a method for the chemical recycling of polypropylene carbonate (PPC) to sulfur‐containing polymers using COS as the S‐source at 140°C. In this approach, DBU or tBuOK functions as a base catalyst (Scheme 7c, upper left) [66]. Their proposed mechanism involves first the depolymerization of PPC into PC (propylene carbonate), which then undergoes decarboxylation to give propylene oxide (PO). Next, the cycloaddition from COS to PO occurs, followed by a second decarboxylation step to elect propylene sulfide. The last step is the ring‐opening polymerization of propylene sulfide to produce sulfur‐containing polymers with a thioether content in the range 72%–100%. Another example of an S‐containing polymer was reported by Komber and Werner et al. They prepared highly regio‐regular and alternating polythiocarbonates obtained from CS₂ and terminal epoxides (Scheme 7c, lower part left) [116]. Under solvent‐free conditions at room temperature and using LiOtBu as initiator, the authors obtained polymers with molecular weights up to 109 kg/mol. The initiator loading proved to be crucial as loadings higher than >0.5 mol% afforded cyclic dithiocarbonate as an increasingly formed product. In principle, these latter polymers should also be susceptible to transesterifications using thiols as reagents.

As a final example, Darensbourg, Wooley, and co‐workers investigated the effect of temperature on the outcome of the co‐polymerization of a D‐xylose‐based oxetane monomer and COS (Scheme 7c, right) [121]. They found that at temperatures >40°C, S‐for‐O exchange reactions occurred, modifying the structure and properties of the polymer. Notably, the tuning of catalyst/co‐catalyst ratio and reaction temperature were both key to fine‐tune the selectivity towards one or another type of S‐based polymer.

There is an effort needed to realize an easier recycling of these S‐containing polymers under attractive and sustainable process conditions. Chemical recycling of S‐containing polyesters and related macromolecules has already been demonstrated a few times [122, 123, 124], but so far only one example is known for the chemical recycling of poly‐trithiocarbonates [120]. Therefore, there is a need to produce degradable S‐derived polymers at a higher level of comprehension. Promising examples of a mechanistic rationalization of scrambling reactions have thus far been reported. However, a more generic understanding of how the nature of the catalyst, in combination with process parameters such as reaction temperature and concentration, and how these play an active role in facilitating a chemo‐selective (de)polymerization is warranted to provide clearer structure‐performance relationships that allow for predicting process outcomes.

4. Conclusion and Outlook

Depolymerization strategies involving PCs and related polymers have evolved from harsh pyrolysis to more practical and fine‐tuned (catalytic) methods with distinct reactivity, selectivity, and scalability profiles. Pyrolysis and hydrolysis approaches require harsher conditions and usually give complex product mixtures, making them energy‐intensive and poorly selective. In contrast, chemically guided solvolytic routes (e.g., alcoholysis, aminolysis) operate typically under milder, often metal‐free conditions to regenerate the virgin monomers and/or value‐added small synthons useful towards upcycling. These latter initiatives have already demonstrated to be applicable at the gram scale without loss of efficiency, underscoring their future potential.

Catalytic pathways represent the most sustainable option towards efficient depolymerization, offering tunable, closed‐loop recycling opportunities. For linear aliphatic PCs, base strength, the nature of the polymer chain‐ends, and metal‐based stabilization of oxo‐anion chain ends during the process are important parameters to control the “unzipping” of the PC structure, giving five‐ and six‐membered cyclic carbonates. Geometrically more constrained alicyclic PCs derived from cyclic epoxides show a richer mechanistic landscape that is controlled by the type of catalyst, ring size, ring substituents, and the presence of heteroatoms in the epoxide precursor. Depolymerization processes have thus far been developed, allowing for steering the degradation to either the epoxide or a trans‐configured cyclic carbonate. The option to switch between both products by changing the reaction conditions using the same catalyst is rather appealing and practical. Advanced catalysts, including dinuclear Mg^II and hetero‐dinuclear Mg^II‐Co^II complexes, multinuclear Zn^II compounds, and organocatalysts such as TBD, have enabled selective monomer recovery in both solution phase and in the solid‐state. In limited cases, chemical upcycling of CO₂‐based PCs has also been achieved, offering ways to valorize the original polymer atoms in different fields of chemical and material science.

Despite considerable progress in the area, there remain various obstacles that need to be addressed. The scope of robust, cost/effective and selective catalysts is rather limited, and those known in the area usually work well for a limited number of PCs and/or related polymers. The development of easily adjusted catalyst structures that can depolymerize alkyl, aryl, and more complex types of PCs would be a welcome addition. Moreover, catalytic processes will need to be further challenged and tested on real‐world mixed waste streams and integrate biotechnological approaches, techno‐economic assessment, and life‐cycle analyses to uncover the potential for realistic tech‐transfer. In this regard, there is a large gap in our understanding of already developed routes towards the depolymerization of PCs. This is an aspect that requires future focus while taking into account the relative cost of any newly designed and preferably biobased monomer. The potential production scale at which existing and new monomers are available needs to be better mapped out, whereas a broader diversity in constitutional variation and functionality will allow for a more reliable structure‐performance analysis.

Sulfur‐containing polycarbonate analogues are very promising in high‐value applications such as high‐refractive‐index optical materials, flame retardants, biomedical applications, and temperature‐resistant materials due to their favorable optical, mechanical, and thermal properties. In addition, being in some cases more easily depolymerized, they show promise as more sustainable alternatives to polycarbonates. Additional examples of applications for “exotic” and underexplored types of carbonates are drug‐delivery systems [65] and platform chemistry involving multi‐angle upcycling of the original polymer atoms into a variety of small molecule building blocks after depolymerization [19].

The documented enzymatic and microbial‐induced degradation of some aliphatic PCs suggests that engineered biocatalysts could complement chemical recycling approaches. Combined chemical/enzymatic or chemical/photo‐assisted approaches can be envisioned that create new synergies for hybrid plastic and polymer degradation. These interdisciplinary approaches are truly underexplored, though they offer possible routes to selectively decompose plastic waste streams without having to first separate the individual types of polymers often present in consumer materials.

Next‐generation depolymerization methods and processes must embrace circularity by design and combine very high atom efficiency and life‐cycle performance studies to turn PC waste into a resource contributing to a future sustainable plastics economy.

Conflicts of Interest

The authors declare no conflicts of interest.

Biographies

Davide Rigo is currently an EU‐Marie Curie funded postdoctoral researcher at the Institute of Chemical Research of Catalonia (ICIQ) in Tarragona (Spain). Previously, he received a joint PhD (2022) from the Università Ca’ Foscari di Venezia (Italy), the University of Sydney (Australia), and the Università degli Studi di Trieste (Italy) under the supervision of Maurizio Selva and Thomas Maschmeyer. He has had postdoctoral appointments at Aalto University (Mikhail Balakshin) and at the National Renewable Energy Laboratory (NREL, Gregg Beckham) in Golden, USA. His interests are in the catalytic valorization of biomass, and the upgrading of it towards macromolecular applications.

David H. Lamparelli is a senior researcher in the Department of Chemistry and Biology of the University of Salerno (Italy). He received his PhD in 2022 and then carried out postdoctoral work on sustainable polymers and their degradation at the Institute of Chemical Research of Catalonia (ICIQ) in Tarragona (Spain). He received the 2022 Cinzia Chiappe Award from the Italian Chemical Society for the best PhD thesis in green chemistry. His research interests span the areas of homogeneous catalysis, new sustainable polymer development and material science.

Antonio Buonerba is an Associate Professor of Chemistry and Spectroscopy in the Department of Chemistry and Biology at the University of Salerno (Italy). Among his research interests are the development of novel functional polymers for applications in catalysis, biomedical devices, and designing sustainable routes to various polymers. He is the author of over one hundred journal contributions and holds several patents on new polymeric material development and biomedical nano‐devices.

Carmine Capacchione is a Full Professor at the Department of Chemistry and Biology of the University of Salerno (Italy). He obtained his PhD (2003) from the University of Salerno with Prof. A. Proto as advisor. He carried out postdoctoral work at Salerno and in Heidelberg as an Alexander von Humboldt fellow (2005‐2006, Germany, Prof. Lutz Gade). His interests are in the area of the development of new metal catalysts and their use in the preparation of new elastomeric materials, new block copolymers using a combination of polymerization techniques, and studying the mechanisms involved in these processes.

Arjan W. Kleij is an ICREA Professor and Group Leader at the Institute of Chemical Research of Catalonia (ICIQ) in Tarragona (Spain). His research interest spans the areas of organic, polymeric and catalytic chemistry, with a main focus on the use of carbon renewables in fine‐chemical synthesis and biopolymer development. He received the 2023 European Award for Sustainable Chemistry (EuChemS) and currently leads the EU‐funded project “D‐Carbonize”. He is an Associate Editor of the leading sustainability journal Green Chemistry (RSC).

Data Availability Statement

Data sharing not applicable, no new data generated.