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Development of Sustainable CO2 Polymerization : Discovery of Highly Efficient Zn-gallate Catalyst and Its Application to Polymerization Using CO2 and Epoxides

  • 성기혁 (아주대학교 일반대학원)

초록/요약

Sustainable utilization of CO2 as a chemical feedstock represents a critical pathway toward mitigating anthropogenic climate change while advancing a circular carbon economy. This dissertation establishes low-toxic, non-noble transition metal catalysis as a versatile platform for synthesizing CO2-incorporated polymers with controlled architectures and tunable properties. While CO2-based polycarbonates offer substantial environmental advantages through massive CO2 fixation, conventional catalytic systems present inherent limitations: heterogeneous zinc catalysts achieve high carbonate incorporation (high fCO2) at the cost of prohibitively low catalytic activity, whereas double metal cyanide (DMC) catalysts exhibit superior productivity but incorporate minimal CO2. This work systematically addresses these trade-offs through five integrated research contributions. Chapter 1 reviews the background of CO2 utilization in commercial polymer processes, and heterogeneous catalysts including Zn-based dicarboxylates and double metal cyanide catalysts applied in polymer industry, and polyurethanes prepared using CO2 based polyols. Chapter 2 describes the development of an ultrathin Zn-gallate catalyst that simultaneously achieves exceptional catalytic activity (3.01 kg/g-cat) and substantial CO2 incorporation (fCO2 = 0.97, 98% selectivity) in propylene oxide/CO₂ copolymerization—a ~360-fold improvement over canonical heterogeneous benchmarks (zinc glutarate). The unique 1–2 nm nanosheet architecture exposes abundant active sites and facilitates ready exfoliation, resulting in high densities of accessible catalytic centers. Mechanistic elucidation via combined DFT calculations and targeted polymerization experiments reveals that lattice Zn–OH groups initiate polymer growth through ring-opening of propylene oxide (PO), with rate-limiting CO2 insertion into Zn-alkoxide intermediates. Chain-transfer agent screening demonstrates precise control over molecular weight (Mₙ = 3.3–889 kg/mol) via carboxylic acids, alcohols, and anilines, with kinetic insights indicating bimetal-cooperative mechanisms at proximal Zn centers. Chapter 3 addresses the inherent mechanical brittleness of high-fCO2 polycarbonates by incorporating lactide—a biodegradable monomer—via random and block terpolymerization with PO and CO2. Both single-pot (yielding PLA content of 9.4–36 wt%) and sequential protocols (accessible range of 15– 76 wt% PLA) maintain high catalytic productivities (0.7–3.6 kg/g-cat). Critically, a random terpolymer with modest PLA content (9.4 wt%) demonstrates mechanical properties exceeding low- density polyethylene (LDPE) under identical testing conditions, with tensile strength of 20 MPa and elongation at break of 679%—establishing these CO2-derived materials as viable petroleum-free alternatives for commodity applications. Chapter 4 pioneers the first synthesis of polyurethanes from CO2-based polyols prepared via the heterogeneous Zn-gallate catalyst. Low-molecular-weight polycarbonate diols are generated through 1,4-butanediol-mediated alcoholytic cleavage of high-Mn PPC, circumventing the traditional requirement for homogeneous catalysts to achieve high fCO2. Systematic characterization (FT-IR, DSC, TGA, Shore hardness, tensile testing) establishes comprehensive structure–property relationships between polyol composition (functionality, fCO2, molecular weight) and polyurethane thermal- mechanical properties, demonstrating that CO2 content, polyol hydroxyl functionality, and hard- segment composition collectively govern phase separation, hydrogen bonding, and mechanical performance. Collectively, this dissertation validates earth-abundant zinc combined with polyphenolic ligands as a robust, scalable platform for high-performance CO2 utilization. The demonstrated capacity to synthesize functionalized polyols, block copolymers with controlled architecture, and low-branched polyglycerols from renewable or captured CO2 establishes a foundation for advancing circular carbon economy manufacturing while generating polymers competitive with petroleum-derived alternatives. These catalytic approaches integrate laboratory innovation with the practical requirements of sustainable materials production, thereby contributing to both climate mitigation and the transition toward carbon dioxide-based polymer chemistry. Keywords: CO2 fixation, heterogeneous catalysis, layered zinc hydroxide, Zn-gallate, polycarbonate, lactide terpolymerization, polyurethane, ring-opening polymerization, structure–property relationships, sustainable polymers

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목차

Chapter 1. CO2-Based Polycarbonates and Polyols for Polyurethane Applications: Catalysts, Properties, and Commercial Outlook 1
1.1 CO2 Utilization in Commercial Polymerization Processes 2
1.2 Heterogeneous Catalysts Used in Commercial Polymerization Using Epoxides and CO2 4
1.2.1 Zn-based Heterogeneous Catalysts 4
1.2.2 Double Metal Cyanide Catalysts 7
1.3 Applications of CO2-polyols: Sustainable Polyurethane Synthesis 11
1.3.1 Polyurethane Synthesis Using Low to Moderate-CO2 Poly(ether carbonate) Polyol 12
1.3.2 Polyurethane Synthesis Using High-CO2 Polycarbonate Polyol 16
1.4 Scope of Thesis 20
Chapter 2. Ultrathin Zn-Gallate Catalyst: A Remarkable Performer in Propylene Oxide/CO2 Copolymerization and Understanding Polymerization Mechanism 22
2.1 Introduction 23
2.2 Results and Discussion 24
2.2.1 Preparation and Optimization of LZH based Zn Catalyst 24
2.2.2 Characterization of Zn-gallate 26
2.2.3 Zn-gallate Catalyzed PO/CO2 Copolymerization 31
2.2.4 Zn-gallate Catalyzed PO Homopolymerization 34
2.2.5 Macrostructure Analysis of PPC 36
2.2.6 Influence of CTA 37
2.2.7 Influence of CO2 Pressure 40
2.2.8 Influence of Monomers 41
2.3 Mechanism Study 42
2.3.1 Computational Calculation 42
2.3.2 Plausible Mechanism 45
2.4 Conclusion 46
Chapter 3. Zn-gallate Catalyzed Synthesis of High-Performance CO2-Polymers with Tunable Composition and Architecture 48
3.1 Introduction 49
3.2 Results and Discussion 50
3.2.1 Zn-gallate Catalyzed Polymerization of PO, CO2 and Lactide 50
3.2.2 Sequential Polymerization 53
3.3 Mechanical Properties of Copolymers 55
3.4 Mechanistic Aspects 56
3.5 Conclusion 57
Chapter 4. Synthesis of Sustainable Polyurethanes from CO2-Polyols 58
4.1 Introduction 59
4.2 Results and Discussion 61
4.2.1 Alcoholytic Cleavage of PPC 61
4.2.2 CO2-polyol Based Polyurethanes 64
4.2.3 Thermal Properties of CO2-polyol Based Polyurethanes 69
4.2.4 Mechanical Properties of CO2-polyol Based Polyurethanes 71
4.3 Conclusion 74
Chapter 5. Experimental Details 75
References 85
Curriculum Vitae 96
Abstract (Korean) 101

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