Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 1 crystallinity, and the conditions of degradation. 73-75 PCL is degraded by hydrolysis of its ester linkages in physiological conditions. Therefore PCL has been used in many fields such as scaffolds in tissue engineering, in long-term drug delivery systems, in microelectronics, as adhesives, and in packaging. 76-81 PCL has been approved by Food and Drug Administration (FDA) to be used in the human body as a drug delivery device, suture, or adhesion barrier. PCL can be synthesized by the polycondensation of hydroxycarboxylic acids. 82 But high molecular weight PCL is usually made by the ROP of ε-caprolactone (ε-CL) that is industrially produced from the oxidation of cyclohexanone by peracetic acid (Figure 1.4.1). Three different catalytic systems, including metal-based, enzymatic, and organic systems, can 59, 83-85 be used to catalyze the polymerization of ε-CL. 1.4.2 Polyglycolide Figure 1.4.1 Preparation of poly(ε-caprolactone) Polyglycolide or polyglycolic acid (PGA) is a biodegradable, thermoplastic polymer and the simplest linear, aliphatic polyester. PGA has a glass transition temperature between 35-40 and its melting point is reported to be in the range of 225-230 . The degree of crystallinity of PGA is around 45-55%. 86 High molecular weight PGA is insoluble in almost all common organic solvents. However PGA is soluble in highly fluorinated solvents like hexafluoroisopropanol and hexafluoroacetone sesquihydrate. PGA was used to develop the first synthetic absorbable suture with the tradename of Dexon by the Davis & Geck subsidiary of the American Cyanamid Corporation in 1962. 87 It is naturally degraded in the body by hydrolysis and is absorbed as water-soluble monomers, completed between 60 and 90 days. PGA and its copolymers with lactic acid, ε-caprolactone, or trimethylene carbonate, are widely used as a material for the synthesis of absorbable sutures and are being evaluated in the biomedical field, such as implantable medical devices, tissue engineering or controlled drug delivery. 88 PGA can be prepared starting from glycolic acid by polycondensation or the ROP of glycolide. But the polycondensation yields a low molecular weight product. The most ‐ 16 ‐
- 17 - Polymerization and Applications of Biodegradable Polyesters common synthesis route to produce a high molecular weight PGA is ROP of "glycolide", the cyclic diester of glycolic acid (Figure 1.4.2). Glycolide can be prepared by heating low MW PGA under reduced pressure, collecting the diester by means of distillation. ROP of glycolide can be catalyzed using different catalysts, including antimony, zinc, tin, aluminum, calcium, and lanthanide compounds. Stannous octoate is the most commonly used catalyst, since it is high efficient and approved by the FDA as a food stabilizer. 89 Figure 1.4.2 Ring-opening polymerization of glycolide to produce polyglycolide. 1.4.3 Poly(lactide-co-glycolide) . Using the PGA and PLA properties as a starting point, it is possible to copolymerize the two monomers to extend the range of homopolymer properties. Copolymers of glycolide with lactide (PLGA) have been developed for medical device, tissue engineering and drug delivery applications. 90-92 It is important to note that there is not a linear relationship between the copolymer composition and the mechanical and degradation properties of the materials. For example, a copolymer of 50% glycolide and 50% D,L-lactide degrades faster than either homopolymer. 93 PLGA with 25-70% glycolide are amorphous due to the disruption of the regularity of the polymer chain by the other monomer. PLGA of 90% glycolide and 10% lactide was developed by Ethicon as an absorbable suture material under the trade name Vicryl. It absorbs within 3-4 months but has a slightly longer strength-retention time. 93 PLGA is produced by the copolymerization of lactide and glycolide under ring-opening polymerization catalyst (Figure 1.4.3). Figure 1.4.3 Synthesis of poly(lactide-co-glycolide).
Page 1 and 2: Catalytic Synthesis and Characteriz
Page 3 and 4: Preface Biodegradable polyesters ha
Page 5 and 6: Chapter 3 Polymerization of Lactic
Page 7 and 8: Chapter 1 Polymerization and Applic
Page 9 and 10: - 3 - Polymerization and Applicatio
Page 13 and 14: 1.2.2 Aluminum Catalysts - 7 - Poly
Page 17 and 18: 1.3 Polylactide 1.3.1 Introduction
Page 19 and 20: - 13 - Polymerization and Applicati
Page 21: 1.3.4 Application of PLA Figure 1.3
Page 27 and 28: 1.5.1.4 Polyaniline (PANi) - 21 - P
Page 47 and 48: 1.6.1 Radical Polymers for Organic
Page 51 and 52: initialization of the device by app
Page 55 and 56: 1.6.2.4 Others - 49 - Polymerizatio
Page 63 and 64: 182. R. B. Weller, J. Invest. Derma
Page 65 and 66: Chapter 2 Synthesis and Electrochem
Page 67 and 68: Synthesis and Electrochemistry of S
Page 73 and 74:
Synthesis and Electrochemistry of S
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Page 77 and 78:
Page 79:
Page 84 and 85:
Chapter 3 3.1 Introduction Poly(lac
Page 86 and 87:
Chapter 3 polydispersity index (PDI
Page 88 and 89:
Chapter 3 aluminum based complexes
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Chapter 3 3.5 Conclusions Co(III) c
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Chapter 3 22. Z. H. Tang, X. S. Che
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Chapter 4 4.1 Introduction Stimulus
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Chapter 4 the proton of methenyl gr
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Chapter 4 attributed to the amide g
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Chapter 4 4.4 Thermal Properties Th
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Chapter 4 Figure 4.8 MTT assay for
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Chapter 4 The 1 H NMR and 13 C NMR
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Chapter 4 Cell viability (%) = (Asa
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Chapter 5 Synthesis of Triblock Cop
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5.2 Synthesis of Triblock Copolymer
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Sample Table 1. Feed and result com
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= 25 μm. B: MTT assay for the cyto
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‐ 109 ‐ Synthesis of Triblock C
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‐ 111 ‐ Synthesis of Triblock C
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Chapter 6 6.1 Introduction Since th
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Chapter 6 6.3 Synthesis of MPEG-b-P
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Chapter 6 used to characterize the
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Chapter 6 Figure 6.6 Cyclic voltamm
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Chapter 6 vivo cytotoxicity was als
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Chapter 6 NMR. Characterization of
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Chapter 6 CO2 for 24 h. RSC96 cells
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Chapter 7 Conclusion and Future Pro
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‐ 131 ‐ Conclusion and Future P
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‐ 133 ‐ Conclusion and Future P
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13. Xuan Pang, Xuesi Chen, Xiuli Zh
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Acknowledgments The present thesis
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