Дисертації з теми "Polymer chain conformation"

This dissertation presents solid-state NMR studies of the chain conformation, dynamics and morphology of three adsorbed polymer systems: two random semi-crystalline copolymers, poly(ethylene-co-acrylic acid) (PEA) and poly(propylene-co-acrylic acid) (PPA), and an amorphous homopolymer, poly(n-butyl methacrylate) (PnBMA). Zirconia (ZrO2) was chosen as the substrate for all three polymers since the binding of carboxylic acids to this metal oxide is well understood. The choice of polymers was based on their particular bulk conformational and dynamic properties as well as their common use in polymer coatings. These studies are motivated by the general lack of a microscopic picture of adsorbed polymers, which can be provided by NMR, and the relevance of chain conformation and dynamics to important polymer film properties such as adhesion.
First the chain conformation and surface binding of adsorbed PEA as a function of acrylic acid content are characterized by 13C cross polarization - magic angle spinning (CP-MAS), 2D 1H- 13C wideline separation (WISE) and 1H spin diffusion NMR experiments and FTIR-PAS (Fourier transform infrared photoacoustic spectroscopy) measurements. The most important finding is that the chain conformation of adsorbed PEA is determined primarily by the sticker group density rather than the surface coverage. The second study of PEA concerns the chain dynamics in the bulk and adsorbed states. Variable temperature NMR experiments provide evidence that ethylene segments of adsorbed PEA form partially folded loops rather than flat extended trains. Finally 129Xe NMR studies, used to probe the morphology of adsorbed PEA, show a bulk-like signal only for the highest loadings.
The second system investigated, PPA, is another semi-crystalline random copolymer which binds to zirconia via carboxylate linkages. The 13 C CP-MAS NMR spectra of adsorbed PPAC unexpectedly show splittings normally associated with chain-chain packing in the crystalline regions of bulk polypropylene (PP). The splittings in the spectra of adsorbed PPAC, which are more resolved than in bulk PPA, are proposed to arise from recrystallization of the PP segments between sticker groups.
Finally the interfacial properties of an amorphous homopolymer, PnBMA were studied using 13C and 129Xe NMR to characterize adsorbed and filled samples. PnBMA binds to zirconia via the partial hydrolysis of the ester side chains. The remaining ester chains of adsorbed PnBMA are found to segregate to the polymer/air interface. Both adsorbed and ZrO 2-filled PnBMA show enhanced local segmental mobility. However, the 129Xe NMR measurements of the filled samples are consistent with restricted motion on a larger length scale which may be due to particle bridging.

La cellulose, un biopolymère renouvelable, peut remplacer les matériaux non biodégradables dans les applications industrielles. Elle est d'abord dissoute, puis transformée (par exemple en fibres) et enfin « régénérée » (recristallisation par ajout d'eau). Cependant, la dissolution de la structure cristalline très stable nécessite des solvants agressifs et polluants, au contraire des liquides ioniques (IL). Cette thèse étudie le processus de dissolution et l'état dissous pour deux liquides ioniques sélectionnés comme solvants efficaces. Nous étudions la structure et la conformation des chaînes de cellulose par la diffusion des rayons X et des neutrons. Les signaux sont très faibles (< 1 cm⁻¹), en raison de la forme fine des bâtonnets, du faible contraste et de la difficulté à mesurer en raison de la grande sensibilité à l'eau. Le chapitre 1 résume l'état de l'art sur les solutions dans des solvants industriels et dans les liquides ioniques, et sur les études de diffusion, de la lumière, des rayons X et des neutrons, montrant des situations diverses. Le chapitre 2 présente la préparation des échantillons et les techniques. Le chapitre 3 présente des études de Diffusion des rayons X aux Petits Angles (DXPA), réalisées à l'aide de spectromètres sur synchrotron, à flux élevé et à faisceau étroit. Nous avons d'abord étudié la cellulose microcristalline (MCC, degré de polymérisation DP = 200 unités) dans deux IL à base de butyl-méthyl-imidazolium : acétate (BmimAc) ou chlorure (BmimCl). Différents régimes sont attendus à partir d'études rhéologiques. - Dans le régime dilué (0,005 - 0,02 g/g). La diffusion est ajustée au facteur de forme P(q) d'une chaîne en forme de bâtonnet, entourée d'une coquille de densité différente de celle du solvant, avec éventuellement une grande longueur de persistance (> 7 nm). - Pour des concentrations plus importantes, dans des cas encore bien dissous, un facteur de structure révèle des répulsions inter-chaînes faibles, sans alignement fort. - A des concentrations plus élevées, la diffusion suggère une séparation de phase liquide-liquide. - Enfin, aux concentrations les plus élevées, des cristaux non dissous sont détectés à grand q (WAXS), un grand avantage de notre technique. La coexistence avec les cristaux a été étudiée pendant le gonflement de films ou de fibres de cristaux de nanocellulose, par balayage en faisceau étroit d'un gradient de concentration. L'effet d'un faible pourcentage d'eau ajoutée a été testé, les Il bons solvants étant assez hygroscopiques. Au-delà de quelques pour cent d'eau, une diffusion beaucoup plus forte suggère de fortes fluctuations de concentration, ou une structure biphasique, utile pour comprendre les premières étapes de la « régénération » (recristallisation) par ajout d'eau. Les courbes de diffusion de cellulose d'autre origine et de poids moléculaire également faible (rayonne, nanocristaux - CNC) sont similaires à celles du MCC. Celle de la cellulose bactérienne montre aussi une identité complète à l'échelle locale, mais avec des agrégats indépendants visibles aux moyens q. Le chapitre 4 présente les mesures : - de Diffusion des Neutrons aux Petits Angles (DNPA) aux faibles concentrations, le profil de DNPA est celui de la DXPA, ce qui permet une évaluation complémentaire des densités de longueur de diffusion. Par extrapolation à la fraction zéro de cellulose deutérée, nous avons tenté d'extraire la fonction intra-chaîne S₁(q)~P(q), et la fonction inter-chaîne S₂(q). Des difficultés sont apparues à faible q en raison de la forte remontée de la cellulose deutériée bactérienne. A q élevé il y a accord avec la DXPA. - de Diffusion de Neutrons aux Grands Angles (DNGA) suit les corrélations à courte échelle. Nous avons effectué différentes deutériations : soit le cation Bmim, soit l'anion Ac, soit les deux. Par comparaison nous discutons de l'absorption possible des anions acétate sur les chaînes
Cellulose, a renewable bio-polymer, can replace non-biodegradable materials in various technological applications. Industrially, it is first dissolved, then processed (e.g. by spinning), and finally “regenerated” (recrystallization by adding water). However, dissolution from the very stable crystal structure requires harsh, pollutant solvents for individual chains to stay in solution. Ionic liquids (ILs) have emerged as non - polluting effective solvents. This thesis aims at the dissolution process and dissolved state checking how the two selected ILs are successful solvents, which is controversial. Our approach is to study structure and conformation of cellulose chains by X-Ray and neutron scattering, which are very weak (< 1 cm⁻¹), due to the small volume of the thin rod, the low contrast and difficult to measure due to high sensitivity to water. Chapter 1 summarizes the state of the art on solutions of cellulose in different widely industrially used solvents, in ionic liquids, and in scattering studies, light, X-rays and neutrons, showing various states of dispersion. Chapter 2 presents the preparation of the samples and the techniques. Chapter 3 reports Small Angle X rays Scattering (SAXS) studies, using high flux and narrow beam synchrotron spectrometers. We first monitored MicroCrystalline Cellulose (MCC, Degree of Polymerisation DP ≈ 200 units) in two Butyl-methyl-imidazolium based ILs: acetate (BmimAc), or Chloride (BmimCl). Different regimes are assumed from rheological studies. -In the dilute regime (0.005 – 0.02 g/g). Scattering is fitted to the form factor P(q) of a rod-like chain, surrounded by a shell of density different from the one of the solvent, with possibly a large persistence length (> 7 nm). -For larger concentrations, in yet well dissolved cases, a structure factor unveils soft interchain repulsions, without strong alignment. -At higher concentration, the scattering suggests a liquid-liquid phase separation -Finally, at the highest concentrations, non-dissolved crystals are detected at large q (WAXS), a great advantage of our technique. The coexistence with crystals was also investigated during swelling in nanocellulose crystals films or fibers, through narrow beam scanning of a concentration gradient. The effect of a small percentage of added water was tested, the IL good solvents for cellulose being quite hygroscopic. Above a few per cent of water, much stronger scattering suggests strong concentration fluctuations, or biphasic structure, useful to understand the first stages of the “regeneration” (recrystallization) step performed by adding water, to obtain the final products. Cellulose of other origin and similarly small molecular weights (in rayon, and CNC), superimpose their scattering on the one of MCC. Bacterial cellulose scattering superposes only at large q (hence a complete identity at local scale), but shows an additional strong low q upturn, due to independent aggregates. This opens the way to neutron scattering experiments using deuteriated cellulose, which is available only in a bacterial form. Chapter 4 reports the measurements of: -Small Angle Neutron Scattering (SANS) shows for low concentrations a profile similar to SAXS, allowing a complementary evaluation of the Scattering Length Density of cellulose. Using extrapolation at Zero Deuteriated Cellulose Fraction, we attempted the extraction of the intrachain function S₁(q)~P(q), the interchain function S₂(q). Difficulties appeared at low q due to the strong upturn, while high q showed agreement with the SAXS measurement of the form factor below c*. -Wide Angle Neutron Scattering (WANS) was used to track the correlations at short scale. Different solvents were used in which either the Bmim cation, or the anion Ac, or both, were deuteriated using our own synthesis processes. Comparisons enable us to discuss about possible absorption of the acetate anions on the cellulose chains

In dieser Arbeit wurden auf Substratoberflächen adsorbierte Polymermoleküle mit Rasterkraftmikroskopie (RKM) untersucht. Dabei war die Form der Moleküle (Konformation) von besonderem Interesse. Sie ist von zentralerer Bedeutung in der Polymerphysik und wird üblicherweise in Lösung und mit Streumethoden untersucht. Polymerkonformationen auf Oberflächen sind heutzutage noch wenig untersucht. Üblicherweise wird das Verhalten nach dem so genannten Wormlike-Chain Modell angenommen. Es basiert auf der Annahme, dass die Kettenbiegung nur aus thermischen Fluktuationen resultiert, so dass sich die Kettenform durch statistische Mechanik beschreiben lässt. Es wurden für verschiedene Modellsystem einzelne Moleküle hochaufgelöst abgebildet und die Konformation aus den Bildern bestimmt. Es hat sich gezeigt, dass die idealisierte Vorstellung des Wormlike-Chain Modells tatsächlich nur für wenige der untersuchten Systeme erfüllt ist. Abweichende Konformationen sind oft auffallend regelmäßig: entweder sinusartig mäandrierte oder spiralförmig gedrehte. Beide Charakteristika lassen sich aus dem Prozess der Adsorption erklären, was zeigt, dass die Moleküle auf dem Substrat immobil sind, so dass eine thermische Relaxation der Konformation verhindert ist. Konformtionen lassen sich mit RKM nicht nur beobachten, sondern auch gezielt verändern (Nanomanipulation). Für dendronisierte Polymere konnte so gezeigt werden, dass es einen glasartigen Zustand für das einzelne Molekül gibt. In diesem Zustand verhält sich das Molekül nicht mehr wie eine bewegliche Kette, sondern formstabil, ähnlich einem makroskopischen festen Körper.
In this work single polymer molecules adsorbed onto substrate surfaces were investigated by scanning force microscopy (SFM). The focus was on the shape (conformation) of the molecules, which is of central importance in polymer physics. It is commonly investigated in solutions and with scattering methods. Conformations on surfaces are only little investigated thus far. Often a behavior according to the so-called worm-like chain model is assumed. It is based on the assumption that chain bending results entirely from thermal fluctuations so that the overall chain shape can be described by statistical mechanics. For several model systems single molecules were imaged and the conformation was determined from the images. It was found that the idealistic wormlike chain behavior is only valid for a few systems. Deviations are often remarkable regular: either sine-like undulated or spiral wound. Both characteristics can be explained from the process of adsorption, indicating that molecules are immobile on the substrate so that thermal relaxation is inhibited. Conformations can not only be imaged using the SFM, but also changed in a defined way (nanomanipulation). Manipulation experiments with dendronized polymers the existence of a glassy state for the single polymer. In this state the molecule no longer behaves as a flexible chain but remains its shape, similar to a macroscopic solid body.

Chemically identical but topologically different cyclic and linear polymers not only result in marked differences in dynamics, but also lead to unique transport properties of their blends, where cyclic polymers have chances to be threaded onto the linear polymers. This dissertation addresses the effect of ring architecture on dynamics using different time/length scale techniques: self-diffusion coefficients, NMR spin-spin relaxation time (T2) and bulk viscosity. In deuterated water, synthesized cyclic poly(oxyethylene) (CPOE) (400-1500 g/mol) diffused faster than corresponding linear POE (LPOE) and linear POE dimethyl ether (LPOEDE). However, the self-diffusion coefficients in melts were arranged in the following manner: LPOEDE > CPOE > LPOE, in excellent agreement with T2 and viscosity data, showing topological and chain end effects. Compared to LPOEDE, both CPOE and LPOE had higher activation energies for viscosity with less dependence on the molecular weight. In the blends of CPOE and LPOE for 900 and 1500 g/mol, the diffusion coefficient and viscosity in melts were higher and lower than the values predicted by a binary mixing rule, respectively. These deviations were attributed to the threading conformation, and the weight fraction of the threaded chains for 1500 g/mol was estimated by a three-term mixing rule. This threading conformation also appeared to influence such important bulk properties as the glass transition and spherulitic growth rate of the blends.

Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第14871号
工博第3139号
新制||工||1470(附属図書館)
27293
UT51-2009-K667
京都大学大学院工学研究科高分子化学専攻
(主査)教授 伊藤 紳三郎, 教授 長谷川 博一, 教授 金谷 利治
学位規則第4条第1項該当

La fonction d'autocorrelation orientationnelle a ete ajutee au modele de diffusion et perte generalisee (gdl). La signification physique des temps de correlation relatifs aux modeles conformationels a ete precisee et l'influence de la structure du polymere sur ces parametres a ete demontree. Etude de l'interaction entre la sonde fluorescente et le polymere et etude theorique de son influence sur la dynamique de chaine

Plusieurs indices suggèrent que le repliement du chromosome et la régulation de l’expression génétique sont étroitement liés. Par exemple, la co-expression d’un grand nombre de gènes est favorisée par leur rapprochement dans l’espace cellulaire. En outre, le repliement du chromosome permet de faire émerger des structures fonctionnelles. Celles-ci peuvent être des amas condensés et fibrillaires, interdisant l’accès à l’ADN, ou au contraire des configurations plus ouvertes de l’ADN avec quelques amas globulaires, comme c’est le cas avec les usines de transcription. Bien que dissemblables au premier abord, de telles structures sont rendues possibles par l’existence de protéines bivalentes, capable d’apparier des régions parfois très éloignées sur la séquence d’ADN. Le système physique ainsi constitué du chromosome et de protéines bivalentes peut être très complexe. C’est pourquoi les mécanismes régissant le repliement du chromosome sont restés majoritairement incompris.Nous avons étudié des modèles d’architecture du chromosome en utilisant le formalisme de la physique statistique. Notre point de départ est la représentation du chromosome sous la forme d’un polymère rigide, pouvant interagir avec une solution de protéines liantes. Les structures résultant de ces interactions ont été caractérisées à l’équilibre thermodynamique. De plus, nous avons utilisé des simulations de dynamique Brownienne en complément des méthodes théoriques, car elles permettent de prendre en considération une plus grande complexité dans les phénomènes biologiques étudiés.Les principaux aboutissements de cette thèse ont été : (i) de fournir un modèle pour l’existence des usines de transcriptions caractérisées in vivo à l’aide de microscopie par fluorescence ; (ii) de proposer une explication physique pour une conjecture portant sur un mécanisme de régulation de la transcription impliquant la formation de boucles d’ADN en tête d’épingle sous l’effet de la protéine H-NS, qui a été émise suite à l’observation de ces boucles au microscope à force atomique ; (iii) de proposer un modèle du chromosome qui reproduise les contacts mesurés à l’aide des techniques Hi-C. Les conséquences de ces mécanismes sur la régulation de la transcription ont été systématiquement discutées
Increasing evidences suggest that chromosome folding and genetic expression are intimately connected. For example, the co-expression of a large number of genes can benefit from their spatial co-localization in the cellular space. Furthermore, functional structures can result from the particular folding of the chromosome. These can be rather compact bundle-like aggregates that prevent the access to DNA, or in contrast, open coil configurations with several (presumably) globular clusters like transcription factories. Such phenomena have in common to result from the binding of divalent proteins that can bridge regions sometimes far away on the DNA sequence. The physical system consisting of the chromosome interacting with divalent proteins can be very complex. As such, most of the mechanisms responsible for chromosome folding and for the formation of functional structures have remained elusive.Using methods from statistical physics, we investigated models of chromosome architecture. A common denominator of our approach has been to represent the chromosome as a polymer with bending rigidity and consider its interaction with a solution of DNA-binding proteins. Structures entailed by the binding of such proteins were then characterized at the thermodynamical equilibrium. Furthermore, we complemented theoretical results with Brownian dynamics simulations, allowing to reproduce more of the biological complexity.The main contributions of this thesis have been: (i) to provide a model for the existence of transcrip- tion factories characterized in vivo with fluorescence microscopy; (ii) to propose a physical basis for a conjectured regulatory mechanism of the transcription involving the formation of DNA hairpin loops by the H-NS protein as characterized with atomic-force microscopy experiments; (iii) to propose a physical model of the chromosome that reproduces contacts measured in chromosome conformation capture (CCC) experiments. Consequences on the regulation of transcription are discussed in each of these studies

Here, we report on a new temperature responsive polymer brush system with a terminal “click” functionality. Bifunctionalized poly(N-isopropylacrylamide) (PNiPAAm) with distinct functional end groups was synthesized by atom transfer radical polymerization (ATRP) and grafted to a modified silicon substrate. The presence of the active terminal alkyne functionality is validated using an azide-modified rhodamine B (N3-RhB) via copper(I) catalyzed alkyne–azide cycloaddition (CuAAC). The optical properties and swelling dynamics of an N3-RhB modified PNiPAAm brush are analyzed in dry state and in situ by VIS-spectroscopic ellipsometry (SE). The best-fit results are obtained using a Gaussian oscillator model and are confirmed by UV/VIS-spectroscopy. We observed evidence of interactions between the aromatic residues of the dye and the PNiPAAm amide groups, which significantly affect the swelling behavior of the modified polymer brush
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Here, we report on a new temperature responsive polymer brush system with a terminal “click” functionality. Bifunctionalized poly(N-isopropylacrylamide) (PNiPAAm) with distinct functional end groups was synthesized by atom transfer radical polymerization (ATRP) and grafted to a modified silicon substrate. The presence of the active terminal alkyne functionality is validated using an azide-modified rhodamine B (N3-RhB) via copper(I) catalyzed alkyne–azide cycloaddition (CuAAC). The optical properties and swelling dynamics of an N3-RhB modified PNiPAAm brush are analyzed in dry state and in situ by VIS-spectroscopic ellipsometry (SE). The best-fit results are obtained using a Gaussian oscillator model and are confirmed by UV/VIS-spectroscopy. We observed evidence of interactions between the aromatic residues of the dye and the PNiPAAm amide groups, which significantly affect the swelling behavior of the modified polymer brush.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

博士
國立清華大學
化學工程學系
94
Abstract In this research, the effects of the solvent nature, concentration of solution and temperature which affect the morphology of MEH-PPV polymer chains in solution state were inquired. We discover, in spite of solvent nature and the molecular weight of MEH-PPV, the existence of aggregation phenomenon even in ultra dilute solution as the amount of molecular chains of MEH-PPV larger than 109/ml, it implicates aggregations could be a colligative property which depends only on the number of solute molecular chains. Because molecular chains’ self-assembling make the effective conjugated length increasing, therefore results in photoluminescence (PL) spectrum red shift, it implicates the aggregation has a lot of significant meaning in photophysical properties. We also discover, below the aggregated concentration region, the intensity of photoluminescence increases as the solute molecular weight increases, it implicates the intensity of photoluminescence depends on the size of luminescence particles. The affinity of solvent nature to the side chain and backbone of MEH-PPV decides the type and degree of aggregation of solvent molecular chains. Aromatic solvents such as toluene and chlorobenzene have good affinity to the backbone of MEH-PPV, so the main chains’ aggregation were forbidden attributed to the aromatic solvent filling up among the main chains, but allow the side chains’ aggregation. On the contrast, aliphatic solvents such as chloroform and tetrahydrofuran (THF), THF especially, have good affinity to the side chain of MEH-PPV, so the main chains’ aggregation proceed in the way of adamant zipper-like aggregation as the concentration of solution was increased, which could not be capable deaggregated by means of the heating process. Although when MEH-PPV was dissolved in toluene we have learned from our temperature-dependent SANS experiments which exhibits the good thermal reversibility, as heating the aggregated cluster deaggregate and as cooling the deaggregated segments aggregate again, but not include THF system due to entirely different aggregation structure.

Anisotropic molecules confined on a spherical or other curved surface can display coupled positional and orientational orderings, which make possible applications in physics, chemistry, biology, and material science. Therefore, controlling the order of such system has attracted much attention recently. Several distinct conformations of rod-like or chain-like molecules confined on a spherical surface have been predicted, including states such as tennis-ball, rectangle, and cut-and-rotate splay. These conformations have four +1/2 defects and are suggested to dominate over the splay conformation that has two +1 defects. For the purpose of investigating the conformations of 2-fold anisotropic molecules confined on the spherical surface, the author of this thesis utilizes the Onsager model to study the system of rigid rods and conducts Monte Carlo simulations on the bead-bond model to research the system of semiflexible polymer chains. At low surface coverage density, no particular pattern of the molecules would form. However, coupled positional and orientational ordering begins to emerge beyond a transition density. On the basis of the numerical solutions of the Onsager model of rigid rods, the splay conformation is shown to be the only stable state. On the other hand, Monte Carlo simulations on a polymer system indicate that the ordered state always accompanies the tennis-ball symmetry. With comparison to the continuous isotropic-nematic transition of a fluid of hard rods embedded in a flat two-dimensional space, the disorder-order transition for both the system of rigid rods and the system of polymer chains confined on the spherical surface has first-order phase-transition characteristics.

The thesis constitutes investigations from two distinct areas of research. One part deals with controlling and modulating the conformation of linear polymer in solution. Folding of a polymer chain has been achieved by utilising weak non-covalent interactions interaction like metal ion binding, charge-transfer complex formation and solvophobic effect in tandem. The second part of the thesis deals with synthesis and characterization of end-functionalized polymers prepared by melt-transesterification. The thesis is divided into five chapters. Chapter 1 provides a general introduction on foldamers – a class of polymers that adopts an ordered conformation in solution and various approaches to obtain end-functionalized polymers. Chapter 2 describe the attempts to improve the association constant (based on earlier works reported by Ghosh and Ramakrishnan) between the external folding agent and the polymer repeat unit. The polymer used in this study constitutes an electron deficient pyromellitic dimide units (PDI) linked with a flexible oxyethylene glycol spacer. An electron rich dialkoxy naphthalene (DAN) serves as the folding agent which forms a charge-transfer (C-T) complexation with the electron deficient aromatic units (PDI) in the polymer backbone and effects the folding. The folding agent has the metal ion as its integral part and this aids the interaction between electron-deficient and electron-rich aromatic units by complexing with oxyethylene glycol spacer. Thus folding is due to the synergistic effect of C-T complex formation and metal ion binding. Further a new polymer with larger -surface area of electron acceptor units was prepared with naphthalene dimide (NDI) unit instead of PDI unit which is expected to show higher folding propensity. Chapter 3 explores the possibility of modulating the folding of the donor acceptor (D-A) polymer. A D-A polymer consist of adjacently placed DAN and PDI units linked by an oxyethylene glycol spacer. Folding of the D-A polymer is effected in the presence of suitable metal ion that binds to the oxyethyleneglycol spacer. Random copolymers with segments of alternately placed D-A pairs and segments that is devoid of D-A pairs were prepared. Depending on composition of the random copolymer, the stack length was shown to be modulated as evident from UV-visible and NMR titration experiments. Following a similar approach, a two step folding of the synthetic polymer was demonstrated. The synthesis and characterization of end functionalized polyesters by melt transesterification is discussed in chapter 4. Well defined linear polymer with propargyl group as the end functionalizable group is prepared by the polycondensation of AB type monomer whereas polycondensation of AB2 type monomer leads to peripherally functionalized hyperbranched polymer. Azide-alkyne ‘click’ reactions carried out at the chain end of linear polyester with fluorophores allowed the estimation of the molecular weight by UV-visible and fluorescence spectroscopic method which is compared with estimation from 1H-NMR. Similarly the glass-transistion temperature of hyperbranched polyester is modulated by the peripheral functionalization with various organic azides by ‘click’ reaction. Chapter 5 gives the conclusion and future directions based on the findings from the thesis work.

The thesis constitutes investigations from two distinct areas of research. One part deals with controlling and modulating the conformation of linear polymer in solution. Folding of a polymer chain has been achieved by utilising weak non-covalent interactions interaction like metal ion binding, charge-transfer complex formation and solvophobic effect in tandem. The second part of the thesis deals with synthesis and characterization of end-functionalized polymers prepared by melt-transesterification. The thesis is divided into five chapters. Chapter 1 provides a general introduction on foldamers – a class of polymers that adopts an ordered conformation in solution and various approaches to obtain end-functionalized polymers. Chapter 2 describe the attempts to improve the association constant (based on earlier works reported by Ghosh and Ramakrishnan) between the external folding agent and the polymer repeat unit. The polymer used in this study constitutes an electron deficient pyromellitic dimide units (PDI) linked with a flexible oxyethylene glycol spacer. An electron rich dialkoxy naphthalene (DAN) serves as the folding agent which forms a charge-transfer (C-T) complexation with the electron deficient aromatic units (PDI) in the polymer backbone and effects the folding. The folding agent has the metal ion as its integral part and this aids the interaction between electron-deficient and electron-rich aromatic units by complexing with oxyethylene glycol spacer. Thus folding is due to the synergistic effect of C-T complex formation and metal ion binding. Further a new polymer with larger -surface area of electron acceptor units was prepared with naphthalene dimide (NDI) unit instead of PDI unit which is expected to show higher folding propensity. Chapter 3 explores the possibility of modulating the folding of the donor acceptor (D-A) polymer. A D-A polymer consist of adjacently placed DAN and PDI units linked by an oxyethylene glycol spacer. Folding of the D-A polymer is effected in the presence of suitable metal ion that binds to the oxyethyleneglycol spacer. Random copolymers with segments of alternately placed D-A pairs and segments that is devoid of D-A pairs were prepared. Depending on composition of the random copolymer, the stack length was shown to be modulated as evident from UV-visible and NMR titration experiments. Following a similar approach, a two step folding of the synthetic polymer was demonstrated. The synthesis and characterization of end functionalized polyesters by melt transesterification is discussed in chapter 4. Well defined linear polymer with propargyl group as the end functionalizable group is prepared by the polycondensation of AB type monomer whereas polycondensation of AB2 type monomer leads to peripherally functionalized hyperbranched polymer. Azide-alkyne ‘click’ reactions carried out at the chain end of linear polyester with fluorophores allowed the estimation of the molecular weight by UV-visible and fluorescence spectroscopic method which is compared with estimation from 1H-NMR. Similarly the glass-transistion temperature of hyperbranched polyester is modulated by the peripheral functionalization with various organic azides by ‘click’ reaction. Chapter 5 gives the conclusion and future directions based on the findings from the thesis work.

碩士
國立清華大學
化學工程學系
95
My study includes two following parts. The first is to improve Yamamoto polycondensation to yield high molecular weight poly(para-phenylene)s (PPPs) and to characterize their properties. PPPs are one of the most important classes of conjugated polymers and have been the subject of extensive research, particularly as active materials for use in light-emitting diodes (LEDs) and solar cell. These materials have been particular interest as potential blue emitters in such devices. The two main polycondensation methods used are the Suzuki polycondensation of aryl halides with arylboronic acids and the Yamamoto polymerisation of aryl dihalides using nickel(0) reagents. Generally speaking, the Suzuki method yield higher molecular weight than the Yamamoto procedure, but is synthetically more demanding (refer to arylboronic acids). To improve Yamamoto method, Using THF as reaction solvent to substitute for DMF and toluene used in common Yamamoto polycondensation, the reaction reactivity can be increased resulting from good solubility for both Ni catalysts and polymers. We can obtain high-molecular weight PPP as Suzuki polycondensation did. Then we synthesize three high-molecular weight PPP derivatives: mono-substituted alkoxyl group (mR8O-PPP), di-substituted alkoxyl group (dR8O-PPP), and Cz capping on the ends of alkoxyl group (Cz-PPP), and to study their structure-property relationships. The incorporation of long alkyl-chain substitute on side chain can pack in order in thin film as cast from THF and thus increase conjugation; Cz on the ends of alkoxyl group for Cz-PPP can destroy the order pack in thin film and thus reduces conjugation. While doping with 8 wt% Ir-G complex, Cz-PPP has less phase separation because the Cz on the ends of alkoxyl group exhibits excellent chemical compatibility with guest material. The device (ITO/PEDOT/Polymer : dopant /CsF/Ca/Al) based on this material exhibits stable green emission (spectrum remains unchanged upon successive operation) and luminous efficiency of 14.31 cd/A (13.6 V, 0.85 mA/cm2), and the highest luminance of 3882 cd/m2 (24.8 V , 107.6 mA/cm2). And we can obtain better balance of carrier by inserting TPBI as hole-blocking layer. The second is to determine the conformation of single conjugated polymer chain. A technique for grafting a polymer to a solid metal or semiconductor surface is essential for the development of such applications. This is because the chemical and electrical connectivity between a polymer terminus and an electrode surface may have an important influence on effective electron or photon signal transportation. A high density polymer grafted on a surface is commonly called a polymer brush, and such polymers have been well investigated such as surface modification. In contrast, a low-density grafted polymer is useful for observing nanostructures and physical properties at a single polymer chain level. As a methodology for polymer grafting, we use two-phase (water-toluene) reduction of AuCl4- by sodium borohydride in the presence of an alkanethiol, the gold particles of average 2.6 nm diameters bearing a surface of thiol have been prepared and characterized by TEM and UV-Vis absorption. Then we synthesized end-functionalized PFO bearing thiolacetate (SH-PFO). Furthermore, with the chemisorption of thiolacetate modified polymer on a gold particle surface, we visualized the polymer connection onto particle surfaces by AFM and clearly observed dumbbells-type nanohybrids that consisted of the polymer bridging between two Au nanoparticles.

The development of solution-processable semiconducting polymers has brought mankind’s long-sought dream of plastic electronics to fruition. Their potential in the manufacturing of lightweight, flexible yet robust, and biocompatible electronics has spurred their use in organic transistors, photovoltaics, electrochromic devices, batteries, and sensors for wearable electronics. Yet, despite the successful engineering of semiconducting polymers, we do not fully understand their molecular behavior and how it influences their doping (oxidation/reduction) properties. This is especially true for donor-acceptor (D-A) p-systems which have proven to be very efficient at tuning the electronic properties of organic semiconductors. Historically, chain-length dependent studies have been essential in uncovering the relationship between the molecular structure and polymer properties. Discussed here is the systematic investigation of a complete D-A molecular series composed of monodispersed and well-defined conjugated molecules ranging from oligomer (n=3-21) to polymer scale lengths. Structure-property relationships are established between the molecular structure, chain conformation, and redox-active opto-electronic properties for the molecular series in solution. This research reveals a rod-to-coil transition at the 15 unit chain length, or 4500 Da, in solution. The redox-active optical and electronic properties are investigated as a function of increasing chain-length, giving insight into the nature of charge carriers in a D-A conjugated system. This research aids in understanding the solution behavior of conjugated organic materials.

The nature of the solvent plays an important role in the conformation and orientation of polymers in solution. A particularly interesting case is when the solvent itself possesses order, such as when dissolving the polymer in a LC. In this dissertation, the morphology and diffusion behavior of the conjugated, stiff polymer MEH-PPV, (poly[2-methoxy-5((2-ethylhexyl)oxy)-1,4-phenylenevinylene]), in liquid crystal (LC) solvents have been investigated. Using polarization sensitive fluorescence correlation spectroscopy, it was found that in a nematic LC the polymer molecules are extended and highly aligned parallel with the nematic director. The conformation and orientational order of MEH-PPV increase with chain stiffness as a result of an interplay among the conformational entropy, solvation anisotropy, and bending energy of the polymer chains. In the smectic phase, about 10% of the MEH-PPV molecules are aligned perpendicular to the director in between the smectice layers, an effect not previously observed for a polymer solute. When applying an external electric field across the LC cell, the LC director changes orientation from a planar to a homeotropic alignment. The MEH-PPV chains remain aligned parallel with the LC director with applied field in the bulk of the LC device. However, the local structure near the LC-substrate interface is more complex. Single molecule polarization distributions measured as a function of distance from the LC device interface allow us to use MEH-PPV as sensitive local probe to explore complex structures in anisotropic media. Furthermore, diffusion anisotropy of the polymer solute in a LC solvent was studied by a novel two-beam cross-correlation technique. The diffusion anisotropy was observed to be about 2. This value is comparable to the diffusion anisotropy of the solvent and suggests that, despite the high degree of alignment, the solute diffusion is governed by the solvent and not the solute.

碩士
國立臺灣大學
高分子科學與工程學研究所
100
We employed all-atom molecular dynamics simulation and quantum mechanical methods to explore the relationship between molecular conformation and UV absorption spectra of polythiophene-based conducting polymers. The UV spectrum of 3HT monomer was observed in blue-shift, because of the deviation from coplanar of main chain; the D4QT was found in red-shift, due to the torsional deviation and competitive effect between conjugated main and side chain. In the ordered state, the P3HT and PDBT chains experience the pi-pi interaction and result in more coplanarity for main chain. Thus, they show significantly red-shift with increasing repeated unit. The absorption spectrum of PD3QT was shown in single peak, because the competitive effect of restricting electron could not be offseted and the coplanarity between side and main chain could be maintained. The torsional angle of PD4QT were shown in symmetry and located in 115o and 245o. Hence, the red-shift of PD4QT is more significant than PD3QT and shown in two peaks of spectrum. In the disordered state, the chain conformation is shown in coil conformation within dilute solution and the persistence length in disordered state is shorter than in ordered state. The persistence length of P3HT, PDBT, PD3QT and PD4QT are located in 3 to 5 repeated units by theoretical calculation. Therefore, the UV spectra for P3HT and PDBT or PD3QT and PD4QT are similar. Besides, our simulated spectrum for P3HT in disordered state showed the excellent agreement with experimental data. These results illustrate our methods is reliable.

博士
國立臺灣大學
化學研究所
99
Chapter I describes the development of side-chain functionalized polymers containing metal ion-responsive units with flexible/rigid backbone structures that have potential in developing metal ions sensory materials or self-assembly into hierarchical ordered structures. Poly-norbornene based homopolymer derived from ring-opening metathesis polymerization (ROMP) is regarded as rigid backbones because of the bicyclic constraints of norbornene. Decrease of backbone rigidity can be achieved through the alternating copolymerization of an appropriate cyclic olefin comonomer. A balance of ring strain and steric hindrance of the comonomers plays a key role in constructing alternating backbone structures. Thus, the incorporation of hydrocarbon or ether spacers into copolymers efficiently keeps two metal ion-chelators away from each other to prevent self-quenching of the dye molecules and makes a difference in polymer solubility that copolymers with ether linkage in the backbone chain enhance solubility in organic solvents. The use of 7-membered and 14-membered heterocyclic olefin comonomers results in no and lower levels of alternation behavior suggesting that low ring strain comonomer could not undergo cross-propagation with norbornene monomer. Chapter II describes that oligo-L-lysine based octamer PGLM8 containing metal ion-chelators in the side chains is of interest because the restricted rotation of peptide bonds provides a rigid backbone structure. PGLM8 adopts a stable helix conformation due to the formation of intramolecular sandwich-type complexes with four equivalents strontium ions through metal-coordination interaction at i, i + 4 spacing. The addition of more than four equivalents strontium ions results in the deformation of helix structure with a concomitant fluorescence enhancement. It is found that the presence of other alkaline earth metal ions such as Ca2+ and Ba2+ also promote the helix formation; other metal ions such as Na+, K+, and Pb2+ cannot induce the conformation transition, indicating that alkaline earth metals are suitable side chain cross-linking agents due to their higher charge density and coordination geometry. Chapter III describes the development of acridinium salt-based chromofluorescent probes for the detection of anions – fluoride and acetate. Analytes that form covalent bonds with receptors to trigger highly selective reactions and induce changes in fluorescence emission or absorption are being used to design target-specific chromogenic/fluorogenic probes. A nucleophilic attack occurs at the highly electron- deficient C9 position of acridinium salts more readily than at the corresponding position in their pyridinium or quinolinium counterparts. Our strategy is using this reaction feature to develop acridinium-based chromogenic and fluorescent sensors ACD1–ACD4 for effective anion sensing and delineate the sensing mechanisms for F–, AcO– ions, and halides. Both of F– and AcO– ions act as nucleophiles to attack at the C9 position of acridinium moiety inducing pronounced changes in UV-vis absorption and fluorescence emission while halides only exert collision quenching of acridinium. Anion selectivity can be achieved through controlling the steric congestion around the reactive site. As a matter of fact, our designed fluorescent probes successfully differentiate fluoride and acetate and the sensing action of the probes is reversible, which is an important feature for fluorescent probes.