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Title Page

Contents

ABSTRACT 10

CHAPTER 1. Introduction 12

1.1. Carbon Dioxide as a Chemical Storage Material and its Utilization 13

1.1.1. Applications of CO₂ in Chemical Synthesis 15

1.1.2. Copolymerization of CO₂ and epoxide 17

1.1.3. Poly(Propylene Carbonate) 18

1.2. Recent Catalyst Developments for CO₂/epoxide Copolymerization 19

1.2.1. Single Component Salen Catalysts 20

1.3. Double Metal Cyanide Catalysts 23

1.4. Immortal CO₂/epoxide Copolymerization 24

1.5. References 24

CHAPTER 2. Thermal and Weathering Degradation of Poly(propylene carbonate) 27

2.1. Introduction 28

2.2. Results and discussion 29

2.2.1. Degradation in the presence of catalyst residue 29

2.2.2. Thermal stability of PPC after removal of catalyst residue 30

2.2.3. Weathering degradation 32

2.2.4. Degradation mechanism 34

2.2.5. Polymer chains grown from peroxide 35

2.2.6. Thermal and weathering degradation of pure PPC not containing peroxide unit 37

2.3. Conclusions 39

2.4. Experimental 40

2.4.1. General remarks 40

2.4.2. Weathering Test 40

2.4.3. Peroxide detection 40

2.5. References 40

CHAPTER 3. Catalyst Modification for Immortal CO₂/Propylene Oxide Copolymerization 42

3.1. Introduction 43

3.2. Result and Discussion 44

3.2.1. Modification of Complex 1 for CO₂/propylene oxide immortal polymerization 45

3.2.2. Degradation of poly(propyelene carbonate) due to H₂O₂ formed during catalyst preparation 47

3.3. Conclusions 48

3.4. Experimental 48

3.4.1. General Remarks 48

3.4.2. Synthesis of Complex 3 by air oxidation 49

3.4.3. Synthesis of Complex 3 by oxidation with AgOAc under inert condition. 49

3.5. References 50

CHAPTER 4. Incorporation of Ether Linkage in CO₂/Propylene Oxide Copolymerization by Dual Catalysis 51

4.1. Introduction 52

4.2. Results and Discussion 53

4.2.1. Homopolymerization and CO₂-copolymerization of PO using DMC catalyst 53

4.2.2. CO₂/PO copolymerization using dual catalyst of DMC and 2 54

4.2.3. Characterization of copolymers 57

4.3. Conclusions 61

4.4. Experimental 61

4.4.1. General remarks 61

4.4.2. Preparation of double metal cyanides (DMC) catalyst 61

4.4.3. Typical procedure for CO₂/ propylene oxide copolymerization using dual catalyst of 2 and DMC 62

4.5. References 63

CHAPTER 5. Prepartion of Low Molecular-Weight Poly(propylene oxide-co-propylene carbonate)-diols Using Double Metal Cyanide Catalyst for Polyurethane Formation 65

5.1. Introduction 66

5.2. Results and Discussion 67

5.2.1. Preparation of DMC catalysts by the conventional method. 67

5.2.2. Preparation of DMC catalysts using H3Co(CN)6.(이미지참조) 69

5.2.3. Preparation of low molecular-weight poly(PC-co-PO)-diols using various chain transfer agents. 71

5.3. Conclusions 77

5.4. Experimental 78

5.4.1. General Remarks. 78

5.4.2. Preparation of DMC catalysts (DMC-1, DMC-2, DMC-3) by the conventional method. 78

5.4.3. Preparation of H3Co(CN)6(이미지참조) 78

5.4.4. Preparation of double metal cyanide catalyst (DMC-4) using H3Co(CN)6.(이미지참조) 79

5.4.5. A typical procedure for CO₂/PO copolymerization using DMCs. 79

5.4.6. A typical procedure for formation of polyurethane. 80

5.5. References 81

Appendix 83

ABBREVIATION 103

RESEARCH PUBLICATIONS 105

초록보기

 Transformation of carbon dioxide to organic compounds or polymeric materials is recently attracting both academic and industrial interests. We are at the midst of a huge increase of CO₂emission due to human activities and rapid depletion of petroleum based carbon feed stokes. Hence these transformations have both economical and environmental benefits. Among these transformations, CO₂/propylene oxide copolymerization to produce poly(propylene carbonate) (PPC) may have high potential to replace current petroleum derived polymers, thus considerably utilize cheap and waste CO₂to valuable and sustainable products.

High molecular-weight poly(propylene carbonate) (PPC) is intact when it is stored in an ambient air or in a water for 8 months once the catalyst is completely removed. The catalyst-free pure PPC is also thermally stable below 180 ℃. At 200 ℃, substantial alteration is observed on the GPC curve. Main degradation mechanism of the pure PPC is an attack of the chain-ended hydroxyl group onto a carbonate linkage, through which the molecular weight distribution is broadened by simultaneous formation of low and high molecular weight fractions. Incomplete removal of hydrogen peroxide, generated during the catalyst preparation results in a prepared polymer contains a substantial amount of polymer chains grown biaxially from the hydrogen peroxide, which resulted in more severe thelmal degradation. Experiments conducted in weathering chamber at high temperature (63 ℃) and high humidity (50%) revealed another degradation process involving chain scission through an attack of water molecule onto the carbonate linkage - additionally operates, which progressively and temporally lowers molecular weight.

H₂O₂was generated during catalyst preparation by the action O₂and 2,4-dinitrophenol during the preparation of salen Co(II) complex. Chain transfer reaction to H₂O₂affects the stability of PPC. A cheap and inexpensive method for the catalyst preparation was generated. The new catalyst is not sensitive to protic compounds and supports immortal polymerization. Anaerobic condition for the preparation of the catalyst was developed to avoid the generation H₂O₂. Explosive DNP was replaced by NO₃¯ and AgOAc was used for oxidation.

Carbon dioxide (CO₂)/propylene oxide copolymerization using dual catalysts composed of Salen-cobalt(III) complex bearing four quaternary ammonium salts (a highly active poly(propylene carbonate) catalyst) and a double metal cyanide (DMC. a highly active poly(propylene oxide) catalyst) affords poly(propylene carbonate-co-propylene oxide) through shuttling of the growing polymer chains between the two catalyst sites. Results of ¹H NMR, ¹³C NMR, DSC studies support formation of genuine poly(propylene carbonate-co-propylene oxide), not a mixture of poly(propylene carbonate) and poly(propylene oxide). The carbonate fraction is variable by tuning the ratio of the two catalysts and the CO₂pressure.

Low molecular weight poly(PO-co-PC)-diols was used in polyurethane industry. Diols having carbonate linkage of 65% and average molecular weight (Mn) 2000 g ㏖-1 can find suitable place in polyurethane industry. As the new Double metal cyanide catalyst is working well with wide range of carboxylic acids as chain transfer agents. low MW poly(PC-co-PO)-diols can be prepared by addition of various carboxylic acids. These promising diols were used in preparation of polyurethane. The preparation method of catalyst includes by removing K-ions at the initial stage. 30-35 % ether linkage give flexibility to polymer backbone.

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