No description available.

abstract: Aqueous solutions of temperature-responsive copolymers based on N-isopropylacrylamide (NIPAAm) hold promise for medical applications because they can be delivered as liquids and quickly form gels in the body without organic solvents or chemical reaction. However, their gelation is often followed by phase-separation and shrinking. Gel shrinking and water loss is a major limitation to using NIPAAm-based gels for nearly any biomedical application. In this work, a graft copolymer design was used to synthesize polymers which combine the convenient injectability of poly(NIPAAm) with gel water content controlled by hydrophilic side-chain grafts based on Jeffamine® M-1000 acrylamide (JAAm). The first segment of this work describes the synthesis and characterization of poly(NIPAAm-co-JAAm) copolymers which demonstrates controlled swelling that is nearly independent of LCST. The graft copolymer design was then used to produce a degradable antimicrobial-eluting gel for prevention of prosthetic joint infection. The resorbable graft copolymer gels were shown to have three unique characteristics which demonstrate their suitability for this application. First, antimicrobial release is sustained and complete within 1 week. Second, the gels behave like viscoelastic fluids, enabling complete surface coverage of an implant without disrupting fixation or movement. Finally, the gels degrade rapidly within 1-6 weeks, which may enable their use in interfaces where bone healing takes place. Graft copolymer hydrogels were also developed which undergo Michael addition in situ with poly(ethylene glycol) diacrylate to form elastic gels for endovascular embolization of saccular aneurysms. Inclusion of JAAm grafts led to weaker physical crosslinking and faster, more complete chemical crosslinking. JAAm grafts prolonged the delivery window of the system from 30 seconds to 220 seconds, provided improved gel swelling, and resulted in stronger, more elastic gels within 30 minutes after delivery. / Dissertation/Thesis / Ph.D. Bioengineering 2012

Ce travail concerne l’élaboration de nanocomposites à base de polystyrène/polyamide 6/argile montmorillonite (PS/PA6/MMT). Son but premier a été d’évaluer l’influence d’un copolymère polystyrène greffé polyamide 6 (PS-g-PA6), en tant qu’agent compatibilisant pour promouvoir une meilleure interaction PS-PA6, et son influence dans l’intercalation/exfoliation des argiles, d’une part ; évaluer les structures et les propriétés des nanocomposites obtenus. Deux sortes d’argile montmorillonite ayant différents modificateurs organiques, bien que cinq sortes de PS-g-PA6 contenant différentes quantités de PA6 et différentes masses molaires de greffés ont étés utilisés. Deux compositions de mélange PS/PA6 ont été préparées, 50/50 et 80/20 % en poids. Les quantités d’argile et de PS-g-PA6 utilisées dans les mélanges ont étés 5 et 3% en poids, respectivement. Les images obtenues par microscopie électronique à balayage (MEV) ont montré qu’une inversion de phase a lieu entre les deux compositions, sus les conditions de procédé utilisées, le PS étant la phase mineure à 50/50 %. Les images de MEV ont également révélé que les copolymères et l’argile ont un effet synergique dans la compatibilization des mélanges PS/PA6, dans les deux compositions. La capacité de compatibilization des copolymères est fortement affectée par ses masses molaires et ses quantités de PA6, que promeuvent différents degrés de nouvellement des chaines dans l’interface PS/PA6. De manière générale, les copolymères contenant une plus grande quantité de PA6, associés à l’argile qui meilleure itérât avec la PA6 présentaient des meilleures propriétés / This work aimed the preparation and characterization on polystyrene / polyamide 6 / montmorillonite clay (PS/PA6/MMT) nanocomposites. The goal was to evaluate the influence of the addition of polystyrene graft copolymer with polyamide 6 (PA6-g-PS) with potential to act as a coupling agent, promoting better interaction between PS and PA6, and to study the structures and properties of obtained nanocomposites. Two types of montmorillonite clay, organically modified with different modifiers, as well as five types of PS-g-PA6 copolymer, possessing different amounts of PA6 and grafts with different molecular weights, were employed. Two PS/PA6 blends compositions were prepared, 50/50 and 80/20 wt%. The chosen amount of clay and PS-g-PA6 were 5 and 3% by weight, respectively. Images obtained via scanning electron microscopy (SEM) showed a phase inversion occurring between the two compositions, being PS the dispersed phase in 50/50% composition. SEM images also showed that the addition of copolymers and clay have a synergistic effect on the compatibilization of the blends PS/PA6 in both compositions. The copolymers coalescence ability is strongly affected by their molecular weight and their amount of PA6, which provides different levels of folding of the chains at the interface PS-PA6.The best results were obtained in systems where it was added concomitantly clay and copolymer. Rheology and TEM results showed that the molecular weight of copolymers influence the interfacial tension in mixtures. In general, copolymers containing larger amounts of PA6, associated with clay that best interacts with PA6, showed the best results

No description available.

Microfluidics covers the science of manipulating small quantities of fluids using microscale devices with great potential in analysis, multiplexing, automation and high-throughput screening. Compared to conventional systems, microfluidics benefits from miniaturization resulting in shortened time of experiments, decreased sample and reagent consumptions as well as reduced overall costs. For microfluidic devices where further weight and cost reduction is additionally required, stimuli-responsive hydrogels are particularly interesting materials since they can convert an environmental stimulus directly to mechanical work without any extra power source. Hydrogels are used as chemostats, micropumps, and chemo-mechanical valves in microfluidics. Existing studies about hydrogels for flow control reported on hydrogels responsive to only one stimulus, including temperature, pH value, and solvent. Combining temperature and pH stimuli within one material is an interesting approach, which allows internal as well as external flow control and broadens potential applications. Among the variety of temperature- and pH-responsive monomers, N-isopropylacrylamide (NiPAAm) and acrylic acid (AA) are considered as ideal building blocks to obtain a hydrogel with pronounced stimuli response. There are different architectures for realizing a temperature- and pH-responsive hydrogel with NiPAAm and AA (e.g. copolymer gels, interpenetrating polymer networks (IPNs), semi-IPNs, or graft copolymer gels). Each approach has its inherent benefits and disadvantages. Grafted hydrogels with a temperature-responsive backbone and pH-responsive graft chains are a promising architecture overcoming drawbacks of copolymer gels (loss of thermoresponsive behavior due to the comonomer), interpenetrating polymer networks (IPNs, difficult fabrication of structured particles via soft lithography), and semi-IPNs (leakage of penetrating polymer). However, studies about multi-responsive grafted hydrogels for flow control in microfluidics are comparatively rare and further research is needed to emphasize their real potential. For this reason, the overall aim of this work was the synthesis of temperature- and pH-responsive grafted hydrogels based on NiPAAm and AA for flow control in microfluidics. This required the synthesis of a pH-responsive macromonomer by RAFT polymerization. As a suitable chain transfer agent with a carboxylic acid group for an end-group functionalization, 2-(dodecyl-thiocarbonothioylthio)-2-methylpropionic (DTP) acid was employed. The approach towards the synthesis of the pH-responsive macromonomer based on two key steps: (i) attaching a functional group, which retains during RAFT polymerization, and (ii) conducting the RAFT polymerization to synthesize the pH-responsive macromonomer. In total, four functionalizations for the macromonomer were investigated, including allyl, unconjugated vinyl, acrylamide, and styrene. End-group analysis and solubility tests revealed that macromonomers with a styrene functionalization are suitable for the synthesis of graft copolymer gels. A series of grafted net-PNiPAAm-g-PAA-styrene hydrogels with a PNiPAAm backbone and PAA-styrene graft chains (Mn = 4200 g/mol, Mw/Mn = 1.6) were prepared and characterized. The main goal was to identify suitable stimuli for an application as a chemo-mechanical valve and to show reversibility of the swelling and shrinking process. Importantly, the temperature sensitivity should be retained, while a pH response needs to be introduced. Equilibrium swelling studies quantified with the response ratio revealed that a grafting density of PAA-styrene between 0.25 and 1 mol-% provides a suitable response towards temperature, pH, salt, and solvent. Furthermore, the swelling and shrinking process is highly reproducible over four consecutive cycles for all four stimuli. In order to evaluate the swelling kinetics of grafted net-PNiPAAm-g-PAA-styrene hydrogels, the collective diffusion model extended by a volume specific surface was applied. The determined cooperative diffusion coefficients of net-PNiPAAm-g-PAA-styrene indicated faster response time with increasing PAA-styrene content. Remarkably, net-PNiPAAm-g-PAA-styrene containing 1 mol-% PAA-styrene exhibited an accelerated swelling rate by a factor of 9 compared to pure net-PNiPAAm. Rheological analysis of net-PNiPAAm-g-PAA-styrene showed that an increasing graft density leads to decreasing mechanical stability. The photopolymerization experiments showed that the gelation time linearly increases with the grafting density. Grafted net-PNiPAAm-g-PAA-styrene hydrogels were tested in two fluidic setups for flow control. A straightforward fluidic platform was developed consisting of a fluid reservoir, an inlet channel, an actuator chamber and an outlet channel. The actuator chamber was filled with crushed hydrogel particles. Accordingly, the fluid flow was directed by the active resistance of the hydrogel particles in the actuator chamber (i.e. swelling degree) and allowed flow control by the local environmental conditions. Flow rate studies showed that the fluid flow throttles when the inlet channel was provided with a solution in which the hydrogel swells (pH 9 buffer solution at room temperature). In contrast, the hydrogel-based valve opens immediately when a solution was used in which the hydrogel collapses. The advantageous properties of net-PNiPAAm-g-PAA-styrene were highlighted by using pH, salt and solvent stimulus in one experiment. Remarkably, the opening and closing function was reversible over six consecutive cycles. As part of a collaboration project with the chair of polymeric microsystems within the Cluster of Excellence Center for Advancing Electronics Dresden (A. Richter and P. Frank), membrane assures hydraulic coupling in a chemo-fluidic membrane transistor (CFMT) and grafted net-PNiPAAm-g-PAA-styrene hydrogels were combined to emphasize the potential of both systems. Flow rate studies showed that 4 different stimuli can be used to control the opening and closing state of the CFMT. Multiple opening and closing cycles revealed no considerable changes in the valve function emphasizing a high potential for an application in microfluidics.

The research goal of this work was dedicated to improvement of the properties and enhancement of the application potential of commodity polymer based on polyolefins by choosing different synthesis routes to create new structures and materials. More precisely, the presented study explores different aspects of metallocene and post-metallocene catalyzed olefin polymerization leading to synthesis of novel copolymers and nanocomposites. The first part of this thesis deals with controlled polymerization of α-olefins catalyzed by post-metallocenes. Bis(phenoxyamine) zirconium complexes with [ONNO]-type ligands bearing cumyl (bPA-c) and 1-adamantyl (bPA-a) ortho-substituents were applied. For the polymerization catalyzed by bPA catalyst quasi-living kinetic character is proposed. The bPA catalyst was applied for synthesis of block copolymers by employing the strategy of sequential monomer addition. The blocky structure of the copolymer was successfully achieved and confirmed by NMR techniques. Moreover, the monomodal distribution of molar mass in SEC chromatogram confirmed the absence of homopolymers. In the second part of the work new defined comb-like copolymers (CLC) having a poly(10-undecene-1-ol) (PUol) backbone and densely grafted poly(ε-caprolactone) (PCL) side chains are presented. These copolymers were synthesized in two steps by means of metallocene polymerization followed by ring opening polymerization. Copolymers with varied and adjustable graft length (PCL segments) were synthesized. It was proved that the melting and crystallization temperatures of the CLC correlate with the PCL side chain length, i.e. longer chains result in higher Tm and Tc,o values. The melting enthalpy was found to be asymptotically dependent on the length of PCL side chains. The bulk morphology of the comb-like copolymers is proposed to be lamellar as judged from the TEM micrographs. The third part of the thesis is focused on the synthesis of polypropylene nanocomposites via in situ polymerization. Thereby, organomodified aluminumphosphate with kanemite-type layered structure (AlPO-kan) has been used as novel filler. Melt compounding composites were prepared for comparison purposes to evaluate the influence of in situ synthesis on the dispersion quality of the filler in polymer matrix. Melt compounding of neat AlPO-kan with PP did not lead to formation of nanocomposites. TEM images show macro-composites with the lamellar solid remaining agglomerated. On the contrary, in situ polymerization of propene yielded materials with exfoliated nanocomposite morphology. In XRD, diffractions of the AlPO-kan pilling of layers are not detectable. It can be concluded that the primary existing layers are delaminated. Very fine distribution of the filler in the polypropylene matrix has been impressively demonstrated by TEM.

This communication reports a unique ultra-large sheet formation through hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone and flexible poly(ethylene oxide) (PEO) side chains. The hierarchical self-assembly process involved a distinctive morphological transition of 1D helical to 2D superstructures. The graft copolymer offers a new chance for the challenging bottom-up fabrication of ultra-large self-assembled nanosheets in solution, as well as a novel system for fundamental studies on 2D self-assembly of polymers.

Le sujet de cette thèse concerne l’élaboration de copolymères greffés possédant un squelette poly(1,4-butadiène) et une haute densité de greffons polaires. La synthèse de copolymères à squelette strictement poly(1,4-butadiène) et possédant une haute densité de greffons selon un enchaînement strictement tête-à-tête a été réalisée par polymérisation par ouverture de cycle par métathèse (ROMP) de monomères cyclobutène 3,4-disubstitués. Le choix des greffons polaires s’est porté sur des poly(Ɛ-caprolactone)s (PCL) et des poly(L-lactide)s (PLLA) obtenus par polymérisation par ouverture de cycle (ROP). Ces polyesters aliphatiques qui présentent une biocompatibilité élevée et une (bio)dégradation rapide, sont utilisés dans de nombreuses applications biomédicales. De plus, les copolymères greffés à greffons polyester peuvent donner accès à des nanomatériaux poreux suite à leur organisation en solution ou à l’état solide, suivie de l’hydrolyse des chaînes polyester.Les copolymères greffés poly(1,4-butadiène)-g-polyester ont été synthétisés selon les stratégies grafting through et grafting from, à partir d’inimers (initiator-monomer) cyclobutène portant une ou deux fonctionalités alcool, capable d’amorcer la ROP du L-lactide ou de l’ Ɛ-caprolactone. La stratégie grafting through a, dans un premier temps, été étudiée. Des macromonomères polyester de type PCL ou PLLA ont été synthétisés. La ROMP de ces macromonomères a conduit à des copolymères greffés poly(1,4-butadiène)-g-polyesters en forme d’étoile de structure définie et dont la densité des greffons est parfaitement contrôlée. La stratégie grafting from a, quant-à-elle, permis d’accéder à des copolymères greffés en forme de peigne. L’organisation des architectures macromoléculaires obtenues a été visualisée par microscopie à force atomique (AFM) et microscopie électronique à transmission (TEM). / The objective of this work was the preparation of graft copolymers with a poly(1,4-butadiene) backbone and a high density of polar grafts. We used a consecutive Ring-Opening Metathesis Polymerization (ROMP)/Ring-Opening Polymerization (ROP) route to prepare poly(1,4-butadiene)-g-polyesters from cyclobutenyl macromonomers bearing one or two polyester segment(s) derived from L-lactide (L-LA) or Ɛ-caprolactone (Ɛ-CL). Poly(L-lactide)s (PLLA) or poly(Ɛ-caprolactone)s (PCL) are important polymers as they are easily (bio)degradable and have tremendous applications as engineering plastics and within the biomedical field. An attractive feature of polyester-grafted copolymers is their potential to act as building blocks for nanomaterials synthesis thanks to the hydrolytically degradable polyester grafts. Cyclobutenyl polyester macromonomers bearing one and two PCL or PLLA arms have been successfully prepared by organocatalyzed ROP of Ɛ-CL or L-LA from a cyclobutenyl alcohol acting as an initiator. Subsequent "grafting through" by ROMP using Grubbs’ second generation catalyst afforded poybutadiene brushes featuring pendant polyester (PLLA or PCL) side-chains. This efficient ROP/ROMP two-step approach has thus allowed the synthesis of well-defined poly(1,4-butadiene)-g-polyester copolymers. The synthesis of graft copolymers via the grafting from approach by ROMP and ROP was also studied. ROMP of 3,4-disubstituted cyclobutenes containing one and two initiating hydroxyl sites for ROP was first investigated with ruthenium initiators. The resulting well-defined poly(1,4-butadiene)s were then used as macroinitiators for the ROP of L-LA or Ɛ-CL. After the ROP, brush copolymers with high molecular weight have been obtained and characterized by microscopy.

This communication reports a unique ultra-large sheet formation through hierarchical self-assembly of a rod–coil graft copolymer containing a rigid polyphenylene backbone and flexible poly(ethylene oxide) (PEO) side chains. The hierarchical self-assembly process involved a distinctive morphological transition of 1D helical to 2D superstructures. The graft copolymer offers a new chance for the challenging bottom-up fabrication of ultra-large self-assembled nanosheets in solution, as well as a novel system for fundamental studies on 2D self-assembly of polymers.

The research goal of this work was dedicated to improvement of the properties and enhancement of the application potential of commodity polymer based on polyolefins by choosing different synthesis routes to create new structures and materials. More precisely, the presented study explores different aspects of metallocene and post-metallocene catalyzed olefin polymerization leading to synthesis of novel copolymers and nanocomposites. The first part of this thesis deals with controlled polymerization of α-olefins catalyzed by post-metallocenes. Bis(phenoxyamine) zirconium complexes with [ONNO]-type ligands bearing cumyl (bPA-c) and 1-adamantyl (bPA-a) ortho-substituents were applied. For the polymerization catalyzed by bPA catalyst quasi-living kinetic character is proposed. The bPA catalyst was applied for synthesis of block copolymers by employing the strategy of sequential monomer addition. The blocky structure of the copolymer was successfully achieved and confirmed by NMR techniques. Moreover, the monomodal distribution of molar mass in SEC chromatogram confirmed the absence of homopolymers. In the second part of the work new defined comb-like copolymers (CLC) having a poly(10-undecene-1-ol) (PUol) backbone and densely grafted poly(ε-caprolactone) (PCL) side chains are presented. These copolymers were synthesized in two steps by means of metallocene polymerization followed by ring opening polymerization. Copolymers with varied and adjustable graft length (PCL segments) were synthesized. It was proved that the melting and crystallization temperatures of the CLC correlate with the PCL side chain length, i.e. longer chains result in higher Tm and Tc,o values. The melting enthalpy was found to be asymptotically dependent on the length of PCL side chains. The bulk morphology of the comb-like copolymers is proposed to be lamellar as judged from the TEM micrographs. The third part of the thesis is focused on the synthesis of polypropylene nanocomposites via in situ polymerization. Thereby, organomodified aluminumphosphate with kanemite-type layered structure (AlPO-kan) has been used as novel filler. Melt compounding composites were prepared for comparison purposes to evaluate the influence of in situ synthesis on the dispersion quality of the filler in polymer matrix. Melt compounding of neat AlPO-kan with PP did not lead to formation of nanocomposites. TEM images show macro-composites with the lamellar solid remaining agglomerated. On the contrary, in situ polymerization of propene yielded materials with exfoliated nanocomposite morphology. In XRD, diffractions of the AlPO-kan pilling of layers are not detectable. It can be concluded that the primary existing layers are delaminated. Very fine distribution of the filler in the polypropylene matrix has been impressively demonstrated by TEM.