Sodium ion batteries (SIBs) are emerging as an attractive energy storage technology due to the accessibility, global abundance and low cost of sodium. However, improving their energy density to reduce system weight, particularly for mobile applications, remains a challenge. Structural batteries address this issue by integrating energy storage and mechanical load-bearing functionality into a single material. Here, we present electrografting as a single-step method to uniformly coat individual carbon fibres with a 1.1 μm thick, chemisorbed PEG-acrylate/NaTFSI-based solid polymer electrolyte (SPE). This enables the fabrication of separator-less structural sodium batteries with high energy and power density. The SPE rapidly forms a passivating layer on the carbon fibre surface, exhibiting excellent electrochemical stability, thermal resilience, and low overall resistance. A post-synthesis leaching step is critical to remove unreacted monomer, thereby minimising irreversible first-cycle capacity loss and the SPE resistance. The resulting SPE-coated electrodes deliver high specific capacities (150 mAh g−1) and coulombic efficiencies >99% over 100 cycles. This approach opens new pathways for lightweight, high-performance structural and conventional sodium battery systems.

The thermodynamics of ring-opening polymerization (ROP) are central when predicting the chemical recyclability of aliphatic polyesters and polycarbonates. Conceptually, the enthalpy of polymerization, DH p, is widely understood as a measure of ring-strain for a given monomer. However, the ring-strain is commonly larger than DH p, generating the question of how the release of ring-strain energy during ring-opening transforms. In this work, we propose that DH p is the sum of the energy released by the ring-strain ðDH ring-strainÞ and the energy absorbed by the polymer conformations ðDH confÞ. Owing to the similar ring-strain, but vastly different DH p values, d-valerolactone, d-caprolactone, d-octalactone, and d-decalactone were used as model compounds to evaluate the energy cost of polymer conformational freedom. Polymer conformation, measured by ¹³C NMR, DSC, and molecular dynamics, results are in good agreement with the hypothesis and can explain previous literature observations i.e. positive DH p for systems with ring-strain, substituent effects, and solvent effects, that are difficult to understand when only using the analogy of ring-strain and DH p. We believe that our results provide a deeper understanding of the underlying thermodynamics and their interpretation in ROP.

Aliphatic polyesters synthesized via ring-opening polymerization (ROP) have properties competitive to incumbent plastic (PE, PP), while simultaneously opening up for chemical recycling to monomer (CRM). However, not all aliphatic polyesters are prone to undergo CRM, and the ability to shift the equilibrium between polymer and monomer is tightly associated with the initial monomer structure. The standard strategy to measure CRM is to evaluate the change in free energy during polymerization (triangle GROP). However, triangle GROP is only one-dimensional by assessing the equilibrium between initial monomer and polymer. But under active catalytic conditions, the depolymerization of polymers can lead to formation of larger rings, such as dimers, trimers, tetramers, and so on, via the ring-chain equilibrium (RCE), meaning that the real thermodynamic recycling landscape is multi-dimensional. This work introduces a multi-dimensional chemical recycling to all rings (CRR) via a highly active catalytic system to reach RCE. Thermodynamically triangle GRCE is completely different from triangle GROP. Using triangle GRCE instead of triangle GROP allows us to achieve CRR for polymers notoriously difficult to achieve CRM for, as exemplified within by CRR for poly(epsilon-caprolactone), poly(pentadecalactone), and mixed polymer systems. Overall, this work provides a new general concept of closing the material loop.

To mitigate the generation of plastic waste, chemical recycling strategies and chemically recyclable polymers need to be developed. Equilibrium ring-opening polymerization (ROP) has emerged as a promising approach to recycle polymers due to the inherent ring – polymer equilibrium nature, facilitating ring-closing depolymerization of polymers to recyclable rings. This thesis delves into the associated thermodynamics of ROP to accelerate the development of closed loop chemical recycling to ring strategies.

To provide an alternative to experimental wet lab trial and error approaches, a computational model based on molecular dynamics was created to theoretically determine the thermodynamics of ROP for different monomers. The atomistic insight that the model provided, supported by experimental data and literature observations, led to a newly proposed understanding of the enthalpy and entropy of ROP. Particularly, the enthalpy of polymerization is hypothesized to contain an energy term that accounts for polymer conformations in addition to the already established ring-strain energy. Next, to enhance chemical recycling,thermodynamic terms that describe the full ring-chain equilibria (RCE)involving rings of different sizes was developed. The benefit of including all rings and RCE thermodynamics was exemplified through the efficient chemical recycling of polymers under conditions that are inconceivable using ROP equilibrium thermodynamics. The RCE was further studied using random walk statistics from which a method to calculate the involved equilibrium thermodynamics from theory was established. A drawback of RCE systems, is the necessity of active catalysts, which cause an abundance in backbiting reactions. Such side reactions make it hard to control the architecture of copolymers. To provide the necessary conditions to create block, tapered, or random copolymers at will, despite abundant backbiting, an equation based on polymerization kinetics was derived. The equation was validated experimentally and copolymers of various copolymer architectures were synthesized accordingly. The theories developed in this thesis may assist in the understanding of ROP and technological advancement for chemical recycling.

För att minska mängden plastavfall som genereras och lagras, behöver kemisktåtervinningsbara polymerer och återvinningsstrategier utvecklas. Ringöppningspolymerisation, som är en jämviktsreaktion, har identifierats som en lovande metod för kemisk återvinning av polymerer. Detta beror på den jämvikt som uppstår mellan monomer/cykliska strukturer och polymer, vilken möjliggör effektiva ringslutningsreaktioner. Denna avhandling undersöker termodynamiken som är kopplad till ringöppningspolymerisation i syfte att främja utvecklingen av strategier för kemisk återvinning till monomer och andra cykliska strukturer.

För att minska behovet av experimentellt arbete utvecklades en beräkningsmodell baserad på molekyldynamiksimuleringar, för att teoretiskt bestämma termodynamiken för ringöppningspolymerisation av olika monomerer. Modellen, tillsammans med experimentellt framtagna data och litteraturvärden, gav atomistisk insikt och ledde därmed till en ny förståelse av entalpi och entropibegreppen i ringöppningspolymerisation. Framförallt klargjordes det att polymerisationsentalpin inkluderar ett energibidrag från polymera konformationer, utöver den kända ringspänningsenergin. För att öka möjligheten till kemisk återvinningen utvecklades också en utökad termodynamisk beskrivning av ring-kedja-jämvikter (RCE) där ringar större än monomer inkluderades. Fördelarna av detta tillvägagångssätt framgår av den effektiva kemiska återvinningen av polymerer under förhållanden som konventionell termodynamik inte kan beskriva. RCE analyserades vidare med hjälp av slumpvandringsmodeller och en teoretisk metod för att beräkna jämviktsparametrar etablerades. En nackdel med RCE-system är behovet av aktiva katalysatorer som ofta leder till ”backbiting”-reaktioner, och därmed svårigheter i att kontrollera arkitekturen hos sampolymererna. För att möjliggöra kontrollerad syntes av block-, gradient- eller slumpmässiga sampolymerer trots detta, härleddes en ekvation baserad påpolymerisationskinetik, som validerades experimentellt och dess parametrar användes för att framställa sampolymerer med fördefinierade arkitekturer. Förhoppningen är att de teorier som utvecklats i denna avhandling kan bidra till förståelsen av ringöppningspolymerisation och tekniska framsteg inom kemiskåtervinning.

Defined macromolecular architecture using anionic ring-opening copolymerization (ROcP) of lactones and cyclic carbonates offers facile routes toward copolymers with unique material properties, ranging from thermoplastic to elastomeric. However, monomers with a slow ROP rate are hampered by competing backbiting reactions, scrambling the macromolecular sequence, and, thereby, a loss of material properties occurs. We here solve this issue by controlling the rate of backbiting. Through our approach, we show how block structures previously inaccessible can be synthesized from monomers with vastly different ROP rates, covering small lactones and even including macrolactones. This control can also be extended beyond block structures to include random and gradient architectures by tuning monomer concentration to the relative ROP and backbiting rate.

Designing the next generation of circular plastics can contribute to preventing environmental pollution and the loss of embedded value. In light of this, assessing the thermodynamic parameters, i.e., the polymerization enthalpy (ΔH<inf>p</inf>) and entropy (ΔS<inf>p</inf>) of ring-opening polymerization, is becoming increasingly important as these directly connect to the chemical recyclability of polymers. However, determining the thermodynamics currently requires the synthesis of each monomer and polymer structure, consuming large amounts of time and chemicals, making it unfeasible to screen a myriad of different structures to find polymers with optimal properties and recyclability. In silico methods could mitigate these issues and drastically increase the rate at which new recyclable plastics can be developed. We demonstrate how the collision frequency between the reactive groups in polymers and monomers, derived from nonreactive (i.e., no chemical changes) molecular dynamics simulations, can be used for the simultaneous computation of ΔH<inf>p</inf> and ΔS<inf>p</inf> with respective 3.5 kJ mol^-1 and 6.7 J mol^-1 K^-1 average deviation from experimental data.

A combined experimental and theoretical investigation revealed mechanistic differences in the ring-opening polymerization (ROP) behavior of macrocyclic carbonates (MCs, 11-membered to 15-membered MCs). The study employs urea and potassium methoxide as the catalytic system for ROP. Besides the polymerization rate correlating with the ring size, where smaller rings have a faster polymerization rate, both the thermodynamic stability of the conformer and the stability of the transition state affect the polymerization rate. An experimental kinetic evaluation revealed a deviation between the polymerization rate of the 11-membered MC and the rest of the MCs. Computational investigation using density functional theory showed that the thermodynamic stability of the 11-membered MC differs from others, with a population distribution more toward the usually less energetically disfavored (E,Z)conformer, while the larger rings showed a preference for the Z,Z-conformation. In the transition state, the (E,Z)-conformer was found to be lower in energy compared to the (Z,Z)-conformation, which leads to a lower Gibbs free energy of activation for nucleophilic attack on the (E,Z)-conformation (Delta G(+/-) = 18.3 kcal center dot mol(-1)) compared to macrocycles with the more stable (Z,Z)-conformation (19.8 kcal center dot mol(-1)). The rate-determining step for the 11-membered MC with (E,Z)-conformation relates to the nucleophilic addition, while the rate-limiting step for the larger 15-membered MC corresponds to the ring-opening step. Linking the thermodynamic conformer stability of cyclic monomers to their inherent polymerization behavior is essential for the future design of selective catalysts for ROP.

Selective, active, stable, and general catalysts for the controlled ring-opening polymerization of (macro)lactones are central in our pursuit of a more benign material economy. Within, we explore the formation of an activated lactone initiator (ALI) based on ZnEt2-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an air-stable and selective initiator/catalyst, yielding linear polymers with one ß-keto ester and one alcohol end-group. Ring-opening polymerization (ROP) with high activity and control was found for unsubstituted (macro)lactones (ω-pentadecalactone (PDL), hexadecanolide (HDL), δ-valerolactone (δVL), and ε-caprolactone (εCL)) and cyclic carbonate trimethylene carbonate (TMC). A particular focus was placed on studying the ALI for the polymerization of strainless PDL and strained εCL. In contrast, ALI-ROP could not polymerize lactones containing substituents on the terminal carbon, indicative of the coordination insertion features of the polymerization. This work explores selective catalysts with high control, fast kinetics, and superb air stability towards the next generation of greener materials.

Zwitterionic Lewis pair (LP) catalysis is potent towards the polymerization of lactone monomers to form cyclic polymers. In pursuit of faster polymerization kinetics, the use of weaker Lewis acids, such as diethylzinc (ZnEt2), has hitherto been suggested. However, the strong Brønsted base character of ZnEt2 brings the question of the actual initiation mechanism. Here, the ZnEt2-1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) LP was studied as catalyst for the initiation and polymerization reactions of ω-pentadecalactone (PDL), ϵ-caprolactone, δ-valerolactone, and γ-butyrolactone. Collective MALDI-ToF MS, NMR, FT-IR, and Ubbelhode viscometry studies revealed a polymerization mechanism proceeding through deprotonation of the α-protons on the lactone and not zwitterionic ring-opening, yielding an anionic propagation mechanism and linear polymers. The polymerization kinetics display an initiation period that correlates to ethyl decomposition on ZnEt2 and the initiation period is shortened by increasing the reaction temperature, Lewis base equivalents, and the lactones, e.g. ϵ-caprolactone, δ-valerolactone, and γ-butyrolactone in the system.