Rozprawy doktorskie na temat „Polylactide- Synthesis”

Polylactide homopolymers with pendent carboxylic acid functional groups have been designed and synthesized to be studied as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest for a variety of biomedical applications including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications, it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties. The acid-functionalized silane endgroup was utilized as the dispersant anchor to adsorb onto magnetite nanoparticle surfaces and allowed the polylactide to extend into various solvents to impart dispersion stability. The homopolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces, and these complexes were dispersible in dichloromethane. The polylactide tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes. The resultant magnetite-polymer complexes were further incorporated into controlled-size nanospheres. The complexes were blended with poly(ethylene oxide-b-D,L-lactide) diblock copolymers to introduce hydrophilicity on the surface of the nanospheres with tailored functionality. Self-assembly of the PEO block to the surface of the nanosphere was established by utilizing an amine terminus on the PEO to react with FITC and noting fluorescence.
Ph. D.

This master’s degree project optimized the synthesis route to a functional lactide by increasing the total yield from 25 to 33 % and reducing the number of unit operations from 17 to 10. This was done by optimizing an existing synthetic pathway to better fit larger scale manufacturing. The monomer was also successfully copolymerized with ʟ-lactide and functionalized by attaching poly(ethylene glycol) units of varying chain lengths to the polylactide chain, which gives some antifouling properties to the copolymer. The resulting material, a functionalized polylactide, is an interesting material suitable for the use in medical implats, largely thanks to its versatility and ability to be tailored for a specific purpose.
I detta examensarbete optimerades en syntesväg till en funktionaliserad laktid genom att öka utbytet från 25 till 33 % samt minska antalet enhetsoperationer från 17 till 10 st. Detta gjordes genom att anpassa en befintlig syntesväg till tillverkning i större skala. Monomeren sampolymeriserades även med ʟ-laktid och funktionaliserades genom att polyetylenglykol av varierande kedjelängd fästes till polylaktidkedjan, vilket gav en hämmande effekt på celladheransen till materialets yta. Det resulterande materialet: En funktionaliserad polylaktid, är ett intressant material som lämpar sig för användning i medicinska implantat, mycket tack vare sin mångsidighet och möjligheten att utforma materialen för specifika ändamål.

Polylactide-siloxane triblock copolymers with pendent carboxylic acid functional groups have been designed and synthesized for study as magnetite nanoparticle dispersion stabilizers. Magnetic nanoparticles are of interest in a variety of biomedical applications, including magnetic field-directed drug delivery and magnetic cell separations. Small magnetite nanoparticles are desirable due to their established biocompatibility and superparamagnetic (lack of magnetic hysteresis) behavior. For in-vivo applications it is important that the magnetic material be coated with biocompatible organic materials to afford dispersion characteristics or to further modify the surfaces of the complexes with biospecific moieties.

The synthesis of the triblock copolymers is comprised of three reactions. Difunctional, controlled molecular weight polymethylvinylsiloxane oligomers with either aminopropyl or hydroxybutyl endgroups were prepared in ring-opening redistribution reactions. These oligomers were utilized as macroinitiators for ring-opening L-lactide to provide triblock materials with polymethylvinylsiloxane central blocks and poly(L-lactide) endblocks. The molecular weights of the poly(L-lactide) endblocks were controlled by the mass of L-lactide relative to the moles of macroinitiator. The vinyl groups on the polysiloxane center block were further functionalized with carboxylic acid groups by adding mercaptoacetic acid across the pendent double bonds in an ene-thiol free radical reaction. The carboxylic acid functional siloxane central block was designed to bind to the surfaces of magnetite nanoparticles, while the poly(L-lactide)s served as tailblocks to provide dispersion stabilization in solvents for the poly(L-lactide). The copolymers were complexed with magnetite nanoparticles by electrostatic adsorption of the carboxylates onto the iron oxide surfaces and these complexes were dispersible in dichloromethane. The poly(L-lactide) tailblocks extended into the dichloromethane and provided steric repulsion between the magnetite-polymer complexes.
Master of Science

PLA nanofibers were successively produced by thermo-responsive transformation of PLA particles in water. The morphological structure of the nanofibers could be optimized by the heat treatment as well as the incorporation of GO to the fiber surface. PLA/GO fiber demonstrated a more stable morphology and GO provided good compatibility between PLA and starch. Both PLA and PLA/GO fibers incorporated in starch films resulted in increased thermal stability and mechanical properties. However, the most favorable properties were assigned starch films containing high concentration of PLA/GO fibers. These films with completely green components could possibly be utilized in biodegradable packaging applications.

Ce travail a pour objectif principal la modification de la surface de nanoparticules de polymères par de nouveaux copolymères amphiphiles et biocompatibles, possédant différentes architectures. Les copolymères considérés dans cette étude sont composés d'une chaine hydrophile de poly(oxyde d'éthylène) (POE) et d'une chaîne hydrophobe à base de poly(ε-caprolactone) (PCL). A partir d'un POE coiffé par une unité ε-caprolactone et par un groupement méthoxy à ses extrémités α et ω, respectivement, (γPOE. CL), des copolymères amphiphiles greffés, PCL-g-POE, et un copolymère ternaire possédant une architecture en étoile ont été synthétisés. Des copolymères diblocs, POE-b-PCL, ont également été préparés. Les copolymères diblocs et greffés de POE et PCL, tensioactifs, ont été utilisés pour stabiliser et modifier la surface de nanoparticles polymères (NP), vecteurs potentiels pour la délivrance de principes actifs. L'effet des propriétés des copolymères (architecture, composition et quantité) sur la formation et la structure des nanoparticules, a été examiné. De plus, l'activation du complément, c. -à. -d. La furtivité des nanoparticules, en fonction de la composition et de l'architecture du copolymère utilisé a été étudiée. Un autre défi relevé dans ce travail est la fonctionnalisation de la surface de nanoparticules pas des motifs mannose afin de cibler des cellules dendritiques. A cet effet, des dérivés du mannose ont été fixés de manière covalente à l'extrémité de la poly(ε-caprolactone) et de copolymères diblocs POE-b-PCL. Ces derniers ont été utilisés avec succès pour modifier la surface de nanoparticules de polylactide
This work mainly aims at modifying the surface of polymer nanoparticles (NP) by novel biocompatible amphiphilic copolymers, composed of hydrophilic ethylene oxide (EO) units and hydrophobic ε-caprolactone (CL) units. Copolymers of different architectures have been considered, i. E. , diblock copolymers, graft copolymers and star-shaped copolymers. Poly(ethylene oxide) chains α-terminated by an ε-caprolactone group and ω-end-capped by a methoxy group (γPEO. CL) were synthesized and used, (i) as PEO macromonomers that were copolymerized by ring-opening polymerization (ROP) with ε-caprolactone (ε-CL) to give PCL-g-PEO graft copolymers, and (ii) as precursors for a AB-double headed PEO chain, that were used to initiate selectively the polymerization of two different monomers to form an ABC mikto-arm star copolymer. The amphiphilic PEO/PCL diblock and graft copolymers were used as stabilizers and surface modifiers of polymer nanoparticles (NP). The effect of the copolymer structural features (architecture, composition and amount) on the formation and structure of the NP was investigated. The complement activation, i. E. , the stealthiness of the nanoparticles, as a function of the composition and architecture of the copolymer used as a stabilizer was studied. Another challenge of this work was to decorate the surface of such NP by mannose moieties, which are suitable targeting probes for dendritic, mannose-receptor expressing cells. Therefore, mannose derivatives were covalently attached as α-end-group to poly(ε-caprolactone) and PEO-b-PCL diblock copolymers. It was found that the NPs' surface properties were strongly related to the glyco(co)polymers used for their preparation

The controllable design of magnetic nanocarriers is essential for advanced in vivo applications such as magnetic resonance image-guided therapeutic delivery and alternating magnetic field-induced remote release of drugs. This work describes the fabrication of polymer-stabilized nanoparticles encapsulating imaging and therapeutic agents and delineates relationships among materials parameters and response. The effect of aggregation of magnetic iron oxide nanoparticles in aqueous suspension was characterized using a well-defined core-corona complex comprised of a superparamagnetic magnetite nanoparticle stabilized by terminally-anchored poly(N-isopropylacrylamide) (PNIPAM) corona. The modified Vagberg density distribution model was employed to verify that the complexes were individually dispersed prior to aggregation and was found to accurately predict the intensity-weighted hydrodynamic diameter in water. Aggregation of the complexes was systematically induced by heating the suspension above the lower critical solution temperature (LCST) of the polymer, and substantial increase in the NMR transverse relaxation rates was noted. Controlled clusters of primary iron oxide nanoparticles stabilized by the biodegradable block copolymer, poly(ethylene oxide-b-D,L-lactide) were fabricated by a scalable, rapid precipitation technique using a multi-inlet vortex mixer. Quantitative control over iron oxide loading, up to 40 wt%, was achieved. Correlations between particle parameters and transverse relaxivities were studied within the framework of the analytical models of transverse relaxivity. The experimental relaxivities typically agreed to within 15% with the values predicted using the analytical models and cluster size distributions derived from cryo-transmission electron microscopy. Hydrophilic-core particles assembled using the poly(ethylene oxide-b-acrylate) copolymer and at similar primary nanoparticle sizes and loadings had considerably higher transverse (r2) and longitudinal (r1) relaxivities, with r2s approaching the theoretical limit for ~ 8 nm magnetite. Block copolymer nanoparticles comprised of poly(D,L-lactide) and poly(butylene oxide) cores were utilized to encapsulate the poorly water-soluble antiretroviral drug, ritonavir, at therapeutically-useful loadings. Controlled size distributions were achieved by incorporation of homopolymer additives, poly(L-lactide) or poly(butylene oxide) during the nanoparticle preparation process. Nanoparticles either co-encapsulating a highly hydrophobic polyester poly(oxy-2,2,4,4-tetramethyl-1,3-cyclobutanediyloxy-1,4-cyclohexanedicarbonyl) within the core or possessing crosslinkable groups around the core were also successfully fabricated for potential sustained release of ritonavir from block copolymer carriers.
Ph. D.

The general aim of this work was to study the different routes that can be taken in order to generate a polymer-nanocomposite taking into account the current knowledge in this scientific domain. Consequenlty, four routes were studied: The first route starts from the preformed inorganic phase, i. E. Fumed silica, and the polymer matrix, i. E. Poly(lactic acid) (PLA). The second route starts from the preformed inorganic filler and PLA monomer, i. E. L-Lactide, in order to in-situ polymerize the L-Lactide in the presence of the fumed silica. The third route starts from the preformed polymer matrix, i. E. PLA, and the use of alkoxysilane as precursors for in-situ generation of an inorganic-rich phase into the polymer. The fourth and last route combines the generation of the inorganic-rich phase and the polymerization of the organic monomer. The objectives of this work focused on the chemical paths and processes instead of the final properties of the resulting nanocomposites. Due to the very broad series of PLA-based nanocomposites which could be generated from the different routes, we choose to have a special attention on the chemistry(ies) involved. Finally, the different routes leading to various types of PLA-nanocomposites in terms of molar mass, crystallinity and morphology were reported. The key point for having a high better state of dispersion seems to depend on the process as we demonstrated that the extrusion step offers high shear enabling a good dispersion. Moreover, it was shown that compatibility between the PLA matrix and the inorganic phase can be tailored by the functionality of the nanofiller surface or the functional groups of an interfacial agent
L’acide polylactique génère depuis quelques années un engouement certain puisqu’il apparaît comme un des biopolymères les plus aptes à remplacer les polymères issus de l’industrie pétrolière. Toutefois, afin de pouvoir prétendre remplacer ces polymères dans les applications tel que l’emballage, etc. , les propriétés mécanique se doivent d’être au moins égale. Il est maintenant bien reconnu qu’il est possible d’accroitre une multitude de propriété en nanostructurant à l’aide d’une phase inorganique les polymères. Cependant il existe plusieurs possibilité quand au procédé choisi. Ici on se propose d’étudier la production d’un nanocomposite à base d’acide polylactique et d’une phase inorganique siliconée en utilisant différentes voies de production. En premier lieu, la synthèse in-situ du PLA en présence de silice pyrogénée a été étudiée tout en faisant varier la compatibilité par la fonctionnalisation en surface. Ensuite la génération de la phase inorganique à partir de précurseur alkoxysilane a été menée directement dans l’acide polylactique fondu par extrusion réactive avec l’ajout ou non d’agent d’interface. Puis les deux voies ont été combinées afin de générer la phase inorganique dans le monomère fondu (L-Lactide) puis de polymériser celui-ci dans le même réacteur. Enfin ces trois voies ont été comparées entre elles et avec le simple mélangeage dans le fondu de silice pyrogénée avec l’acide polylactique en extrusion

Chapter 1 is the main introduction of this work and it features the two main concepts of this study. First living polymerisation techniques are introduced with a special focus into RAFT and ROP. Secondly solution self-assembly is briefly discussed. In Chapter 2 we describe the synthesis of an amphiphilic block copolymer where the two blocks are connected through a reversible bond. A Diels-Alder (DA) adduct consisted of a maleimide-furan pair was chosen as the reversible linker. The solution self-assembly of this polymer was studied by TEM and DLS giving rise to the unexpected formation of cylindrical micelles. In Chapter 3 the main objective was to synthesise new amphiphilic block copolymers without the DA motif in order to investigate their self-assembly behaviour compared to those for DA containing polymers obtained in Chapter 2. To further understand this self-assembly behaviour our method has been extended to the synthesis of other hydrophilic blocks and end group modified polymers. In addition, some key properties of the polymers synthesised have been investigated. In Chapter 4 our main goal is to understand the origins of the cylindrical micelle formation seen in Chapter 2. We investigated the aggregation behaviour under the aqueous thermal conditions in which the PTHPA block hydrolysis is performed. Studies at different concentrations and solvent mixtures provide valuable information regarding the self-assembly mechanism. In addition, the polymers with modified end groups and the triblock copolymers synthesised in Chapter 3 are studied and all the results compared. In Chapter 5 we explore the living crystallisation driven self-assembly of PLA-b- PAA block copolymers in aqueous media towards the formation of cylindrical micelles of controlled length. Interestingly, in many of the unstained TEM images presented in this work the particles demonstrate a non-uniform contrast along their width. This unexpected result is fully investigated in Chapter 6.

Thesis advisor: Jeffery A. Byers
Chapter 1. Poly(lactic acid) (PLA) is a biodegradable polymer derived from renewable resources that has garnered much interest in recent years as an environmentally friendly substitute to conventional petroleum-derived engineering polymers. PLA has many applications in textiles, packaging, compostable consumables, and biomedical devices, as PLA displays excellent biocompatibility. This polymer is primarily produced from the ring-opening polymerization of lactide, a cyclic dimer of lactic acid. This introductory chapter highlights mechanistic features of this ring-opening polymerization reaction as well as metal-based catalysts that have been reported for lactide polymerization. In addition, switchable catalysis is an emerging field that has gained interest with polymer chemists for the potential of creating original polymer compositions and architectures. The utilization of redox-switchable catalysis to control lactide polymerization is discussed in this chapter. Chapter 2. Bis(imino)pyridine iron bis(alkoxide) complexes have been synthesized and utilized in the polymerization of (rac)-lactide. The activities of the catalysts were particularly sensitive to the identity of the initiating alkoxide with more electron-donating alkoxides resulting in faster polymerization rates. The reaction displayed characteristics of a living polymerization with production of polymers that exhibited low molecular weight distributions, linear relationships between molecular weight and conversion, and polymer growth observed for up to fifteen sequential additions of lactide monomer to the polymerization reaction. Mechanistic experiments revealed that iron bis(aryloxide) catalysts initiate polymerization with one alkoxide ligand, while iron bis(alkylalkoxide) catalysts initiate polymerization with both alkoxide ligands. Oxidation of an iron(II) catalyst precursor lead to a cationic iron(III) bis(alkoxide) complex that was completely inactive towards lactide polymerization. When redox reactions were carried out during lactide polymerization, catalysis could be switched off and turned back on upon oxidation and reduction of the iron catalyst, respectively. In addition, preliminary investigations of copolymerization reactions of lactide with ethylene are reported. Chapter 3. A cationic iron(III) complex is active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex is inactive. Cyclohexene oxide polymerization could be "switched off" upon in situ reduction of the Fe(III) complex and “switched on” upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the complex: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY-NMR studies. Chapter 4. Formally iron(I) bis(imino)pyridine monoalkoxide complexes were synthesized through protonolysis of a bis(imino)pyridine iron alkyl species with p-methoxyphenol or neopentyl alcohol. The resulting complexes were characterized by X-ray crystallography, 1H NMR, EPR, and Mössbauer spectroscopy, and preliminary characterization of the electronic structure of these complexes is discussed. These iron complexes were found to be highly active catalysts for the polymerization of various cyclic esters and carbonates, with the iron mono(neopentoxide) complex being much more active and giving more narrow molecular weight distributions than the mono(aryloxide) complex. The bis(imino)pyridine iron neopentoxide complex was highly active in particular for the polymerization of ε-caprolactone (CL), giving full conversion within 10 minutes at room temperature in toluene, making it one of the most active iron complexes reported for this transformation ([Fe]:[CL] = 1:2000). Comparison of the polymerization activity of these iron mono(alkoxide) complexes with the analogous iron(II) bis(alkoxide) complexes is reported
Thesis (PhD) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Polylactic acid (PLA) resins of various molecular weights and molecular weight distributions were synthesized. Linear, narrow molecular weight distribution (MWD) PLA resins were synthesized, as well as resins containing both high molecular weight branched structures and low molecular weight chains and oligomers. Narrow MWD resins were synthesized for use as adhesives for corrugated paperboard and broad MWD resins were synthesized for use as a waterborne coating. PLA resins were dispersed for use as a waterborne coating. Success has been made at forming films utilizing various plasticizers and surfactants as well as polyvinyl alcohol as dispersing agents. A cold dispersion procedure realized the most success, as a 15% PLA waterborne formulation was achieved. Standard test methods show a high degree of grease resistance for the formulated coatings. A hot melt adhesive was also formulated utilizing blends of narrow MWD resins of various molecular weights. The hot melt adhesive showed a high degree of success as failure occurred at the substrate for the materials tested.

The aim of this thesis is the investigation of modeling and optimization particularities of tubular polymerization reactors. The original work is divided in two sections, the first treating a modeling and optimization study of tubular reactors for methyl methacrylate polymerization in solution, and the second, an experimental and theoretical study of L-lactide reactive extrusion. In the first section, reactor simulations in similar operating conditions were performed in order to select a representative kinetic model among the published kinetic models for MMA solution polymerization. Two widely used numerical algorithms, one based on Pontryagin's Minimum Principle and the other a Genetic Algorithm, were compared for an average-complexity optimization problem. The results showed a superior robustness of the Genetic Algorithm for this category of problems. The second part of the thesis deals with the modeling and optimization of L-lactide reactive extrusion. A kinetic model is proposed and its parameters estimated using nonlinear estimation numerical procedures based on experimentally measured data. Reactive extrusion experiments were performed in representative operating conditions. The Llactide/ polylactide flow in the extruder was characterized by simulation using the commercial software LUDOVIC®. The simulated residence time distributions characteristics are used to model the reactive extrusion process of two approaches, an axial dispersion model and a compartment model, based on compartments whose characteristics are deduced from the simulations using LUDOVIC®. The modeling results are in good agreement with the measured data in the same operating conditions.

During the past 20 years, a number of aliphatic polyesters have aroused considerable interest due to their biodegradability and biocompatibility, since their use would to reduce the quantity common non-biodegradable polymers (for example PET). In this scenario, studies (both academic and industrial) have been focused on one polymer in particular: polylactic acid (PLA). It is biodegradable, biocompatible and compostable and derives from renewable resources such as corn, potato, cane molasses and beet sugar; it belongs to the family of aliphatic polyesters commonly obtained from α-hydroxy acids which includes other kinds of polymers such as polyglicolic acid or polymandelic acid. PLA was synthesized for the first time by Carothers in 1932 and it was introduced in the market for medical applications at the end of 1960; in the last ten years its good mechanical properties, comparable to those of polystyrene, and an increasing interest for biodegradable polymers have made it interesting for others industrial applications especially in packaging applications as an environmental friendly substitute of traditional plastics. PLA is certainly the most promising and interesting biodegradable polymer for large scale applications for which could be assumed a gradual and progressive replacement of traditional materials coming from hydrocarbon, but there are many aspects such as thermal resistance, impact resistance, gas barrier properties that need to be improved because, at present, are lower than those of traditional polymers. The present PhD project aimed at the synthesis and the study of the properties of new biocompatible polymeric materials based on PLA, focusing the attention on to two main aspects that may have an effect on the final properties of the polymer: the control of the molecular architecture through the use of appropriate chain regulators able to modify the macromolecular structure and he use of nanoparticles, used as such or modified on the surface, added to the polymer matrix. Complex macromolecular architectures give to the materials special properties (for example low melt viscosity, shear sensitivity) that allow the increase of the fields of applications regarding to traditional polymers, while the possibility to use nanometric fillers could represent a new solution in composite materials field; in fact the high surface area of nanoparticle can reduce the amount of fillers added to the polymer improving the properties of the materials even with low percentage of mineral ( 5% w/w). In this work several PLAs with modified macromolecular architecture (star, tree and tree-star) have been synthesized to evaluate the effect of different structure on molecular and rheological properties. Different comonomers have been chosen to obtain complex structures. SEC analyses on samples synthesized with different comonomers show the effect of multifunctional comonomers on the molecular properties of the PLA, especially on the polydispersity index of the system. Star structures show a decrease of polydispersity index, while tree polymers have higher polydispersity than the one of linear PLA. Rheological analyses show the different viscosity of systems having complex macromolecular architectures in comparison with linear PLA. A more complex system is represented by tree-star polymer, obtained using a combination of two or more comonomers; these polymers have a very complex structure, which requires a careful control of feed, allowing to obtain a wide range of PLA with different rheological behavior. The molecular weights and the viscosity of the materials can be modulated changing the comonomers ratio obtaining a wide range of materials with different properties. Nanocomposites with percentages form 0.5% to 5% w/w of different fillers, montomorillonite and nanosilica, have been synthesized. The effects of nanoparticles on molecular properties of PLA are confirmed by the rheological analyses: increasing the amount of fillers complex viscosity decreases, but for low quantity (0.5% and 1% w/w) the viscosity of nanocoposites is higher than pure PLA even if the Mn values are lower. The use of nanoparticles can also modify thermal behavior of PLA; pure PLA has a very slow kinetic of crystallization that leads to a very low tendency of this polymer to form crystals during the cooling phase, therefore the material has an high amorphous phase with a clear and large glass transition. For this reason nanocomposites have been analyzed both with dynamic and in isothermal scanning to study the crystallization process, a very important aspect for the processing and the properties of the polymers, in order to evaluate difference from standard PLA. Nanosilica act as nucleating agent promoting the crystallization process of PLA, while materials containing Cloisite have a large amount of amorphous phase, probably because lamellas are not well separated, and only some samples crystallize during the cooling phase: but anyway the process has very low intensity and is very slow. The surface modification of nanoparticles can reduce the problem caused by the different surface energy between the organic phase (polymer) and the mineral phase (nanoparticle) but can also lead to a variation of material properties. Different organosilanes were used as coupling agents to modify the surface of nanoparticles. Modified nanoparticles were characterized with different techniques to determine both quantitatively and qualitatively the presence of silane on the particle. Titration was used to have quantitative results about the yield of surface modification reaction. Filler-polymer interaction and dispersion of the mineral is improved in presence of the coupling agents, as shown in TEM analysis. The modification of nanoparticles, in particular silica, promotes the crystallization process of the polymer; increasing the amount of silane higher crystallization temperature and crystallization heat are observed and also all crystallization processes are faster in presence of high quantity of silane due to a higher homogeneity of the system. TGA analyses show that all nanoparticles improve thermal stability of PLA. All samples have been synthesized without stabilizers to verify the action of fillers on thermal stability of PLA. The most interesting behavior has been observed in presence of pure silica with a very interesting increase of the degradation temperature. The use of modified silica also decreases the rate of the degradation. PLA nanocomposites have been used to prepare polymeric films by casting to evaluate the permeability of these materials towards different gases, like O2, CO2 and water vapor, in order to evaluate the effect of crystallynity and nanoparticles on this property.

This master’s thesis deals with plasticization of poly(3-hydroxybutyrate), polylactid acid and their blend. It explores effect of chemical structure of plasticizer on mechanical properties of this polymer blend and on its diffusion from the polymer blend. Syntheses of plasticizers based on oligomeric polyadipates, citrates, lactate and esters of 2 ethylhexanoic acid with poly(ethyleneglycol) were carried out. Molecular weight distribution of synthesized plasticizers was determined using gel permeation chromatography. Poly(3-hydroxybutyrate), polylactid acid and their blend were plasticized with synthesized and commercial plasticizers. From commercial, chosed plasticizers were based on citrates and ester of 2-ethylhexanoic acid with poly(ethyleneglycol). Thermal stability of selected commercial plasticizers in polylactid acid was studied using thermogravimetry. Diffusion of plasticizers from poly(3-hydroxybutyrate), polylactid acid and their blend during exposure to 110 °C was also investigated. Mechanical properties of prepared blends were tested by tensile test. Almost all used plasticizers showed positive softening effect in blend. The highest elongation at break was detected for the blend with commercial acetyltributylcitrate, where elongation at break reached 328 % relative to 21 % for neat non-plasticized blend.

碩士
國立臺灣科技大學
材料科學與工程系
102
In this thesis, polylactide with various molecular weights and molecular weight distributions were synthesized by solution ring opening polymerization. Molecular weight was controlled by varying the ratio of L-lactide monomer to palmityl alcohol initiator and tin(II) octanoate was used as a catalyst for precise control over molecular weight. Anhydrous toluene was used as a non-reactive solvent to prevent the contamination of catalyst. Besides, we also try to obtain the standard molecular weight of PLA (greater than 100,000 g/mol) to compare with commercial PLAs. Properties of different molecular weights of PLA were characterized by gel permeation chromatography, thermogravimetric analysis, differential scanning calorimety, and 1H NMR spectroscopy.

碩士
國立陽明大學
醫學工程研究所
90
Because of the excellent biocompatibility and biodegradability of polylactide (PLA), medical products made of PLA, such as sutures, have been used for about 30 years. Therefore, the safety of this kind of material has been confirmed. One of the major differences between biomaterials and ordinary materials is that biomaterials require strict sterilization treatment. The sterilization process should be chosen very carefully, to avoid causing any severe damages of the products. The effects of gamma irradiation on PLLA have been examined using electron paramagnetic resonance (E.P.R.) spectroscopy. By analyzing the decay curves of the E.P.R. signal intensities for PLLA annealed at various temperatures, one can study the reaction kinetics of free radicals generated by γ irradiation. The E.P.R. spectrum of γ- irradiated PLLA (irradiated at room temperature) show a quartet pattern, suggesting that free radicals produced by hydrogen abstractions from methine groups. This kind of free radicals may cause crosslinking. Free radicals decay in vacuum can be fitted well as a second order reaction. The fitting is even better if the reaction is modeled by a modified second order reaction. Free radicals decay in air can be fitted well as a first order reaction. The reaction rate constants of free radicals increase with increasing temperature, while decrease with increasing doses of exposure. Results of thermal analysis of DSC indicate that γ-irradiation has little effects on the melting temperature, Tm, of the specimens, while the glass transition temperature, Tg, decreases with increasing dose. The results suggest that the chain scissions due to gamma irradiation are mainly occurred at the amorphous regions of the polymer.

碩士
逢甲大學
纖維與複合材料學系
104
Micelles have been frequently used as carriers for drug delivery. In general, micelles suffered from severe problems regarding their colloidal stability in human blood, which appreciably limits their clinical applicability. In this context, crosslinked micelles consisting of biodegradable polyethylene glycol-b-polylactide were prepared to enhance the colloidal stability of resulting micelles. To introduce covalently bonded crosslinkages into micelles, polyethylene glycol-b-poly(allyl functional polylactide-co- polylactide) (PEG-b-poly(ALA-co-LA)), a biodegradable amphiphilic copolymer, have been synthesized via a rational synthetic route. The chemical structures of PEG-b-poly(ALA-co-LA) were well analyzed through various analysis methods. Following the synthesis, the PEG-b-poly(ALA-co-LA)s a were changed from amphiphilic copolymers to non-crosslinked micelles (NCLMs). Sequentially, these NCLMs were crosslinked via UV-induced radical chain polymerization, resulting in the crosslinked micelles (CLMs). In PBS buffer , CLMs were observed to have enhanced colloidal stability than NCLMs according to their change in particle size and particle uniformity. The in vitro drug release results indicated that CLMs released their loaded drugs in a slower and more sustained manner as compared with NCLMs. Moreover CLMs displayed insignificant cytotoxicity in MES-SA cells. As a consequence, CLMs have been verified as a non-toxic and highly biocompatible material for the use of biodegradable carriers.

碩士
國立中興大學
化學工程學系所
99
In this study, we have combined the chemical processing of PLA-diol-2000 into polyurethanes (PUs) in our design of new green materials. PLA-diol-2000 of 1,800 molecular weight was synthesized from 1,4-butanediol and L-lactide through ring-opening polymerization, and was used as the key component of soft segment of PUs. Other common raw materials used in our formulation developments were diol of polyethylene-butylene-adipate (RS-956), polytetramethylene ether glycol (PTMEG), isophorone diisocyanate (IPDI), 1,4-butanediol (1,4-BDO) and 1,4-butanediamine (1,4-BDA). The suitable process for synthesis of PUs with PLA-diol-2000 was studied, and the characteristics of synthesized PUs containing PLA-diol-2000 were analyzed, including molecular weights, thermal properties and mechanical properties. From this study, we have come up with PUs possessing balanced properties that exhibit excellent biocompatibility and biodegradability. This is achieved by the combination of PLA-diol-2000/PTMEG/RS-956 (in ratio of 1/1/3, respectively) as the soft segment constituents with BDO and BDA (in ratio of 1/1, respectively) as the hard segment ingredients in our formulation. The green materials show great potential for use in the special medical applications.

碩士
國立臺灣大學
高分子科學與工程學研究所
102
Different kinds and constructions of polyurethanes are synthesized with different diisocyanates, polyols and chain-extenders by polycondensation in this research. And then, synthesized polyurethanes are made to stable dispersants according to suitable solvents. After all dispersants are synthesized, we discussed their characterizations, and interforces with several gathered inorganic materials which can be dispersed well in indicate dispersants. Synthesis and application of dispersants are mainly divided into two parts. The first part is about synthesization of star shape and comb shape Polylactic Acid Polyurethane(PLA-PU) dispersants. Since buying PLA on the market is not easy, we use direct synthesization in this research. PLA polyol are synthesized with Lactic acid and ethylene glycol by dehydration and polymerization. After PLA polyol are synthesized, star shape dispersants are centered with Trimethylolpropane and comb shape dispersants are centered with Xylitol, and both are synthesized with Isophorone diisocyanate(IPDI) and finally with different proportions of PLA polyol, Poly Ethylene Glycol(PEG) and Poly Properlene Glycol(PPG) in the branches. Grain-shape materials like TiO2 and SiO2 are well-dispersed in these PLA-PU dispersants. In order to check the effects in dispersants, the samples are examined by Transmission Electron Microscope(TEM), Dynamic Light Scattring(DLS) and several instruments in this research, which proved that Grain-shape materials are well-dispersed in PLA-PU dispersants. For applications, these PLA-PU dispersants can be added in spray, dye and ink etc. for its excellent and exact dispersion effects even if the solutions stand for a long time. The second part is about synthesization of waterborne polyurethanes(WPU) dispersants with IPDI, different proportions of PEG, PPG, and finally chain-extenders by emulsification and polymerization. Layer inorganic materials are dispersed in these WPU dispersants, like graphite can be dispersed to several slices of graphene. In order to check the effects in dispersants, the samples are examined by TEM, X-ray Diffraction(XRD), UV/VIS Spectrophotometer and several instruments in this research, which proved that layer inorganic materials are well-dispersed in these WPU dispersants. For applications, these WPU dispersants can be added in pigments, electronic materials, lubricants and several industrial materials for dispersants can promote inorganic materials’ thermal property, conductivity, transparency and many properties.