Department: Macromolecular Science and Engineering ![[clear]](close-x.png "Remove this limiter")
40 matches in the database.
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1.
Arnoult, Olivier.
A NOVEL BENIGN SOLUTION FOR COLLAGEN PROCESSING.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► Collagen is the main protein constituting the extracellular matrix (ECM) of tissues…
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▼ Collagen is the main protein constituting the extracellular matrix (ECM) of tissues in the body (skin, cartilage, blood vessels…). It exists many types of collagen, this work studies only fibrillar collagen (e.g. collagen type I contained in the skin) that exhibits a triple helical structure composed of 3 α-helical collagen chains. This particular and defined hierarchical structure is essential to the biological and mechanical properties of the collagen.Processing collagen into scaffolds to mimic the ECM is crucial for successful tissue engineering. Recently collagen was processed into fibrous and porous scaffold using electrospinning process. However the solvent (HFIP) used for electrospinning is extremely toxic for the user and expensive. This work shows that HFIP can be replaced by a benign mixture composed of water, salt and alcohol. Yet only three alcohols (methanol, ethanol and iso-propanol) enable the dissolution of large quantity of collagen in the benign mixture, with a wide range of alcohol to buffer ratio, and conserve the collagen hierarchical structure at least as well as the HFIP. Collagen can be electrospun from the benign mixture into sub-micron fibers with concentrations as low as 6 wt-% for a wide range of alcohol to buffer ratio, with at least 10wt-% of salt, and any of the three alcohols. Specific conditions yield nano size fibers. After processing from HFIP or a benign mixture, collagen is water soluble and needs to 17 be chemically crosslink for tissue engineering application. Post-crosslinking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) results in the loss of the scaffold fibrous aspect and porosity, hence it is useless for tissue engineering. Such issue could be prevented by incorporating the crosslinker into the mixture prior to electrospinning. When EDC is used alone, collagen forms a gel in the mixture within minutes, preventing electrospinning. The addition of N-hydroxysuccinimide (NHS) in excess to EDC slows down the crosslinking reaction, enabling electrospinning. The study of one benign mixture shows that rheological and electrospinning characterizations correlate and that electrospinnability of collagen from the benign mixture stops for a storage modulus (G‘) of 500 Pa.
Advisors/Committee Members: Wnek, Gary.
Subjects: Polymers
Keywords: Collagen, Electrospinning, Fibers, Solvent, Crosslinking
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2.
Ayyer, Ravishankar.
Failure Processes in Polymers: Environmental Stress Crack Growth and Adhesion of Elastomeric Copolymers to Polypropylene.
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► In CHAPTER 1 slow crack propagation in MDPE pipe was studied in…
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▼ In CHAPTER 1 slow crack propagation in MDPE pipe was studied in air and Igepals at 50 °C to determine the possibility for fatigue to creep correlation in environmental liquids. The stepwise fatigue crack growth in air was preserved in Igepal solutions. Lifetime in Igepal was affected to a much smaller extent as compared to air. The correlation in air was previously established primarily for tests at 21 °C. The stepwise mechanism was verified in air at 50 °C. The crack growth rate under various loading conditions was related to the maximum stress and R ratio by a power law relationship. Alternatively a strain rate approach reliably correlated fatigue and creep in air at 50 °C except at R = 0.1 and frequency less than 1 Hz. In CHAPTER 2 the effect of concentration of Igepal CO 630 on slow crack propagation in MDPE pipe was investigated to determine whether the mechanism was conserved in creep and fatigue as required for the fatigue-to-creep correlation. The mechanism of crack propagation and lifetimes in creep and fatigue at R=0.1 at 50 °C were compared to those in air and water. The fatigue and creep behavior followed the same stepwise crack growth mechanism as in air at all the concentrations used. As the concentration increased to 0.01 vol. %, the creep lifetime decreased significantly whereas the lifetime in fatigue gradually increased. At higher concentrations the lifetime was similar in creep and fatigue. In CHAPTER 3 effect of R-ratio on kinetics and mechanism of environmental fatigue and creep crack growth was analyzed in an attempt to predict the environmental stress crack resistance at 50 °C. Same methodology was used as previously established for fatigue to creep formulation in air at 50 °C. The stepwise mechanism of crack growth in air was conserved in Igepal solutions as R-ratio approached to unity (creep) with few exceptions. At higher R-ratio, the lifetime decreased systematically in Igepal solutions relative to air and was defined as ‘Igepal transition time (ITT)’. It depended on concentration and molecular weight of Igepal. Both fatigue and creep crack growth rate in Igepal showed significantly higher crack growth rate after ‘ITT’ relative to air. To probe the Igepal effect on kinetics, fracture processes involved in first craze failure were compared to that in air.
Advisors/Committee Members: Hiltner, Anne.
Subjects: Engineering; Materials science; Polymers; Technology
Keywords: Environmental stress cracking; polyethylene pipe; Fatigue; Creep; Adhesion; Elastomers; Polypropylene
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3.
Buerkle, Lauren Elizabeth.
Tailoring the Properties of Supramolecular Gels.
Degree: PhD, Macromolecular Science and Engineering, 2012, Case Western Reserve University
► Supramolecular gels created from low molecular weight species (gelators) have gathered wide…
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▼ Supramolecular gels created from low molecular weight species (gelators) have gathered wide attention over the past few decades on account of their highly ordered assembly and ability to respond to external stimuli. These properties make such gels highly promising candidates for a diverse range of applications including biomaterials, viscosity modifiers, sensors, and liquid crystalline materials. We have focused on the design and tailoring of guanosine (the ribonucleoside of the nucleobase guanine) hydrogels. It is well known that in an aqueous environment, guanosine forms circular hydrogen-bonded quartets around a monovalent metal ion, most commonly potassium. These quartets then stack to form high-aspect ratio fibers that entangle and branch to form gels. Despite facile gel formation, crystallization of the guanosine molecules out of the gel is a common occurrence that leads to gel collapse within hours of fabrication. In addition, guanosine and related gelators often require a high potassium concentration or acidic pH to gel, which presents limited practical use in our target application of tissue engineering. We have focused on the modification and analysis of guanosine gels via an additive and/or a change in chemical structure to inhibit crystallization and promote gelation at physiological salt concentrations. Additionally, initial cell culture experiments suggest that these gel materials show great potential as an easily accessible and inexpensive tissue engineering scaffold. We also examined the potential for supramolecular gels for use in personal care formulations as electrolyte-resistant rheology modifiers for aqueous systems. Sugar-based gels fit the necessary criteria; however, many of these molecules also crystallize from the gel over time. We achieved lifetime stabilization again via a mixing approach and examined the resulting properties of the stabilized gels.
Advisors/Committee Members: Rowan, Stuart.
Subjects: Biomedical Engineering; Materials Science; Nanoscience; Organic Chemistry; Polymer Chemistry; Polymers
Keywords: Supramolecular hydrogels; guanosine; gluconamides; tissue engineering scaffolds
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4.
Burke, Kelly Anne.
Structure-Property Relationships in Main-Chain Liquid Crystalline Networks.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► Main-chain liquid crystalline networks were prepared from mesogenic dienes using two different…
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▼ Main-chain liquid crystalline networks were prepared from mesogenic dienes using two different synthetic routes. First, main-chain liquid crystalline copolymers were synthesized by polymerizing a mesogen with a nonmesogenic comonomer using acyclic diene metathesis (ADMET) chemistry. The resulting polymers form nematic phases, with composition dictating the glass transition and isotropization temperatures. Free-radical crosslinking through the unsaturated bonds in the polymer was demonstrated for a selected composition to lead to an elastomeric network. This two step process was employed to control the polymer properties before crosslinking and serves as a viable route to tailored nematic networks for applications as anisotropic adhesives.Liquid crystalline elastomers (LCEs) were prepared using a second synthetic route that employed hydrosilylation chemistry to react the mesogens with hydride-terminated poly(dimethylsiloxane) and a vinyl crosslinker. The resulting LCEs formed a smectic-C phase with transition temperatures that depend on mesogen composition. The mesogens impart two distinct active behaviors to the elastomers. The first of these is actuation, the reversible extension and contraction of the polymer when cooled and heated, respectively, through the mesogen isotropization transition. Actuation is dependent on the crosslink density of the material and can cause the samples to elongate as much as 30 % under tensile load. The second active behavior is shape memory, the ability to fix a temporary deformation and later recover the equilibrium shape by heating. The LCEs have excellent shape memory fixing and recovery ratios, both of which generally exceeded 95 %. The ability of a soft network to fix strains above room temperature is unusual and was investigated using a combination of thermal analysis, mechanical testing, and wide angle x-ray scattering, where it was found that strain is fixed by freezing the mesogens within the smectic layers. The LCE’s low modulus was exploited by reversible embossing, the localization of a temporary topography onto the LCE using shape memory. A microscale embossed topography was stable until erased by heating to recover the LCE’s flat, permanent shape. Possible applications of these LCEs include artificial muscles, smart shear-based actuators, and active substrates.
Advisors/Committee Members: Mather, Patrick.
Subjects: Polymers
Keywords: liquid crystalline; network; elastomer; main-chain; shape memory; actuation; polymer; structure-property relationship
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5.
Burnworth, Mark Gross.
Multifunctional Metallo-Supramolecular Matrials and Sensors.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► Supramolecular chemistry has become a rapidly growing field since the Nobel Prize…
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▼ Supramolecular chemistry has become a rapidly growing field since the Nobel Prize was awarded to the work of Lehn, Pedersen, and Cram in 1987 for their pioneering work on crown ethers and non-covalent host-guest interactions. Metal-ligand interactions represent a particularly useful and well-studied means of preparing supramolecular polymers from telechelic building blocks. This present work focuses on utilizing main-chain metallo-supramolecular polymers or small molecules, based on 2,6-bis(1’-methylbenzimidazolyly)pyridine (Mebip) ligands, to create materials aimed at applications such as light healable polymers, or the detection of chemical warfare agents. With the objective to develop new organic/inorganic hybrid materials, which combine good mechanical properties and other attractive properties with ease of processing, new classes of metallo-supramolecular polymers were explored. The general design approach merged the structure of known polymer systems, for example semiconducting polymers (poly(p-phenylene ethynylene)s) or thermally stable hydrocarbons (poly(p-xylyene)s), with the advantages of a dynamic (reversible) polymerization process, to allow access to materials that are otherwise difficult to process. The new telechelic metallo-supramolecular polymers could be readily solution-processed and represent illustrative examples for metallo-supramolecular polymers with good mechanical properties, while maintaining the properties of parent polymer. Polymers with the ability to repair themselves after sustaining damage are poised to extend the lifetime of materials used in a wide range of applications. Reported here is the development of metallo-supramolecular polymers that can be mended through exposure to light. Upon exposure to ultraviolet light, the metal-ligand motifs are electronically excited and the absorbed energy is converted into heat, causing reversible disengagement of the metal-ligand motif and a temporary reduction in the molecular weight. As a result, defects heal quickly, with high efficiency, and if needed repeatedly. A modular sensory system, for the detection of organophosphates, which utilizes a multi-metal/multi-ligand approach is presented. The sensing scheme relies on fluorescent sensor complexes of Mebip ligands and selected metal ions. Detection of organophosphates is accomplished through competitive coordination of the analyte with the metal. Mixing and matching consciously designed ligands and carefully selected metal ions allows the formation of sensor complexes, which allow organophosphate detection with high selectivity and sensitivity.
Advisors/Committee Members: Rowan, Stuart.
Subjects: Chemistry; Polymer Chemistry; Polymers
Keywords: metallo-supramolecular; supramolecular polymer; photoheal; organophosphate sensors; poly(p-phenylene ethynylene)s; poly(p-xylylene)s
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6.
Check, Casey.
Design, Synthesis and Characterization of Two-Dimensional Polyelectrolytes.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► A novel two-dimensional poly(1,3,5-phenylene-4,4’-biphenylene-2,2’-disulfonic acid) (CPPSA) was synthesized using palladium-catalyzed Suzuki coupling…
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▼ A novel two-dimensional poly(1,3,5-phenylene-4,4’-biphenylene-2,2’-disulfonic acid) (CPPSA) was synthesized using palladium-catalyzed Suzuki coupling in water. The postulated architecture is comprised of hexagonal, macrocyclic, 2-dimensional polymer sheets resembling a honeycomb. Such structures should exhibit a high driving force for 3-dimensional packing thereby creating materials with incompressible nano-channels which can retain water at very low relative humidity. Motivation for the design of such polymers is for use as significantly improved polymer electrolyte membranes for fuel cells. A series of model compound studies based on monomer 4,4’-dibromobiphenyl-2,2’-disulfonic acid were performed to determine the optimal reaction conditions for cyclopolymerization. Emphasis was placed on evaluating water-soluble boronate compounds, bases, and ligands/catalyst systems in order to obtain quantitative yield of model compound quaterphenyl-2’,2”-disulfonic acid. A kinetics model based off of the standard Suzuki coupling catalytic cycle was constructed to evaluate the rate of reaction based on the results of sampled model compound reactions. Cyclopolymerization reactions were run under pseudo high-dilution conditions with slow monomer addition. The resulting polymers showed usual physical properties including insolubility in water after condensing to the solid state. Subsequent ultrasonication with heating was shown to disperse the intractable solid polymers into “solutions” which could be used for film casting suggesting that their insolubility was due to aggregation and not from 3-dimensional crosslinking. Further supporting the postulated structural picture was the slow diffusion of water from CPPSA films into D2O in proton NMR experiments. Imaging of the CPPSA polymers by scanning electron microscopy (SEM) indicated evidence of layered structures formed by extensive aggregation. Atomic force microscopy (AFM) showed further evidence of stacking of planar structures into larger assemblies. Clear evidence of hexagonal polymeric structures was observed by scanning tunneling microscopy (STM). Measurements of the lattice spacing indicate a void size of ~18 – 20.5 angstroms, which is consistent with the theoretical value based on bond-length calculations and molecular modeling (19 – 21.5 angstroms). These preliminary imaging results suggest that the desired hexagonal polymer structure was obtained.
Advisors/Committee Members: Litt, Morton H.
Subjects: Polymer Chemistry
Keywords: poly(phenylenesulfonic acid); polyelectrolytes; macrocycle; Suzuki coupling kinetics
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7.
Chernykh, Andrey.
Main Chain Type Benzoxazine Polymers for High Performance Applications.
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► A new polymer with benzoxazine group in the main chain has been…
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▼ A new polymer with benzoxazine group in the main chain has been synthesized through the Mannich condensation of a difunctional phenol, formaldehyde and a diamine. Obtained polymer has weight average molecular weight of approximately 10,000 Da and a moderately broad polydispersity index. The new polymer is used to manufacturer self-supporting film of thermosetting resins. Aiming to obtain higher molecular weight, click chemistry approach has been applied to synthesize linear benzoxazine polymers. Three types of polymers have been prepared from dipropargyl- and novel diazide-functionalized benzoxazine monomers, showing a tremendous flexibility for applying click reaction to obtain various polymer architectures. The weight average molecular weight is estimated to be in the range from 50,000 to 100,000 Da which is significantly higher than the benzoxazine polymers which have been chain extended via Mannich reaction. Further developing approach of polycondensation of the monomers containing ozaxine rings, the oxidative coupling approach has been utilized in order to couple benzoxazines with terminal acetylene groups. A model benzoxazine compound containing diacetylene linkage exhibits unexpectedly low exothermic peak with the onset around 140°C, which is significantly lower than the temperature of conventional benzoxazine polymerization. The initial model studies have been made in order to understand this phenomenon and preliminary explanation is given. Extending this pathway to the difunctional propargyl- and ethynyl-functionalized benzoxazine monomers, a series of novel benzoxazine polymers containing diacetylene groups in the main chain have been synthesized. The weight average molecular weight of the polymers is achieved to be up to 50,000 Da. The effect of diacetylene moiety on the benzoxazine crosslinking behavior is even more pronounced for the obtained linear polymers showing exothermic peak with the onset at around 125°C and its maximum at 185°C. Upon crosslinking, polymers demonstrate outstanding thermal stability with char yield up to 72% and glass transition temperature above 350°C.
Advisors/Committee Members: Ishida, Hatsuo.
Subjects: Polymers
Keywords: benzoxazine; main chain polymer
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8.
Chung, Taekwoong.
New Shape Memory Effects in Semicrystalline Polymeric Networks.
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► Shape memory polymers (SMPs) have attracted much research interest as a type…
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▼ Shape memory polymers (SMPs) have attracted much research interest as a type of smart material that possesses the capacity to undergo rapid changes of their shape and size under a specific or tailored environment. Herein, we prepared semicrystalline polymers-based networks such as poly (cyclooctene) (PCO), poly (epsilon-caprolactone) (PCL) and poly (ethylene glycol) (PEG) networks in order to explore their shape memory effects and thermomechanical properties as well as the possibilities for their applications. Interestingly, besides so-called one-shape memory effect that can be manipulated and fixed to a temporary shape under specific conditions of temperature and stress, and subsequently relax to the original shape on heating, the semicrystalline polymer networks exhibit a reversible two-way shape memory effect, revealing crystallization-induced elongation on cooling and melting-induced contraction on heating. These thermally induced reversible two-way shape memory effects were systematically explored with respect to the crosslinking density of networks and the applied stress.In order to develop a shape memory network with temperature sensing capability, we incorporated appropriately tailored chromogenic cyano-OPVs into cross-linked PCO via guest-diffusion to create phase-separated blends in which the dye’s emission properties are dominated by excimer fluorescence. Heatng to the temperature above melting temperature and cooling below the crystallization temperature of PCO led to reversible optical changes through dissolution or agregation of the dye molecules. These optical changes happened in conjuction with shape changes of PCO networks For an application of shape memory network in bone tissue engineering, we fabricated novel shape memory nanocomposite scaffolds base on PCL and nano-hydroxyapatite (nano-HAP) using thiol-ene photopolymerization and salt leaching technique. The shape memory property, morphologies and biomineralization of the scaffolds were characterized. In addition, the effect of biomineralization on shape recovery of the deformed PCL-HAP scaffolds was studied. These results suggest the possibility that these shape memory scaffolds can be tailored to fit bone defects and can maintain the tailored shape as well as achieve bioactive properties by apatite growth on the surface. We anticipate that the shape memory network systems studied for this dissertation will have the potential for many technological applications in various fields where shape memory effects are needed.
Advisors/Committee Members: Mather, Patrick T.
Subjects: Polymers
Keywords: shape memory polymers; semicrystalline polymer networks; two-way shape memory effects
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9.
Gawryla, Matthew Daniel.
Low Density Materials through Freeze-Drying:Clay Aerogels and Beyond….
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► Clay aerogels and other ice templated materials belong to a family of…
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▼ Clay aerogels and other ice templated materials belong to a family of materials with properties similar to those of conventionally foamed polymers including low density, high porosity and low thermal conductivity. The ice templating process represents an environmentally friendly method for producing light weight alternatives to typical polymer foams. The properties of these materials can be controlled using many variables such as component shape, size, and chemistry. Sub-micron scale fillers are able to be incorporated into the lamellar structure while larger particles are deposited on the surfaces. The molecular weight and chemistry of the reinforcing polymer also plays a significant role in the structure and properties seen in these materials. Controlling the directionality of ice crystallization, as well as nucleation, provides an additional level of manipulation with which the properties can be tailored. In addition to providing stand alone structural materials, ice templated materials can provide a foundation for developing novel clay/polymer nanocomposite materials. The nanocomposites created via ice templating exhibit properties comparable to those seen in organically modified clay/polymer composites without the need for organic modification of the clay.
Advisors/Committee Members: Schiraldi, David.
Subjects: Materials science; Plastics; Polymers
Keywords: Aerogel; Clay; Polymer; Composite; Insulation; Ice Templating
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10.
Guo, Qiongyu.
POSS-Based Biodegradable Polymers for Stent Applications: Electroprocessing, Characterization and Controlled Drug Release.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► Polyhedral oligosilsesquioxane (POSS)-based biodegradable polymers were investigated as stent coating for drug…
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▼ Polyhedral oligosilsesquioxane (POSS)-based biodegradable polymers were investigated as stent coating for drug delivery from drug-eluting stents and as polymeric scaffold for fully bioabsorbable stents. A highly efficient and precise electrospraying technique, one of the electrostatic processing techniques, was developed for the stent coating application. The roughness of stent coatings produced was varied conveniently by the electrospraying technique utilizing different electrospraying mode or Coulombic fission, and was further modified using post-treatments of pure solvent electrospraying or vapor welding. Abluminal stent coatings were achieved utilizing the targeting nature of the charged electrospraying droplets to avoid luminal coating on stents by applying nonconductive materials temporarily contacting the inner surface of the stents.Long-standing questions of paclitaxel (PTx)-polymer blend miscibility and interactions were studied for particular polymer blends using characterization methods. It was found that paclitaxel is amorphous in all proportions in the blends of paclitaxel with POSS-based thermoplastic polyurethanes (POSS TPUs), and serves as an antiplasticizer by increasing the blend Tg gradually from the polymer Tg up to the substantially higher Tg of amorphous paclitaxel. The polyethylene glycol (PEG) segment incorporated in POSS TPUs exhibited specific hydrogen-bonding interactions with the paclitaxel and promoted the miscibility in the blends. Highly adjustable release of paclitaxel was achieved from both thermoplastic stent coatings utilizing P(DLLA-co-CL)-based POSS TPUs, and thermoset stent coatings employing PLGA-POSS end-linked thiol-ene network. Using a newly-developed drug release approximation model describing the entire drug release profile, paclitaxel release mechanisms from these biodegradable stent coatings were interpreted quantitatively, including the effects of polymer glass transition temperature, polymer initial molecular weight, degradation, coating swelling, POSS content, drug concentration, and coating thickness. Fully bioabsorbable shape-memory stents were fabricated using four cost-effective methods, including dipping coating method, fiber tube fabrication using electrospinning technique, which is another electrostatic processing method, mesh tube welding, and stent writing extrusion. The stent mechanical testing methods to characterize the radial stiffness and collapse pressure of stents were also improved using dynamic mechanical analysis (DMA) combined with a newly-designed stent compression holder.
Advisors/Committee Members: Mather, Patrick T.
Subjects: Biomedical research; Polymers
Keywords: POSS; biodegradable polymer; drug delivery; drug-eluting stents; polymeric stent; drug release modeling; paclitaxel; electrostatic processing; electrospraying; electrospinning; coating roughness; miscibility; specific interactions; shape memory
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11.
Gupta, Mohit.
Enhancing the Value of Commodity Polymers Part 1. Structure-Property Relationships in Composite Materials Based on Maleated Polypropylene/Inorganic Phosphate Glasses Part 2. New Value-Added Applications for Polyesters.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► The first part of the thesis (Chapters 2 & 3) describes a…
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▼ The first part of the thesis (Chapters 2 & 3) describes a new class of organic polymer/inorganic glass composite materials with property improvements that are impossible to achieve with classical polymer blends or composites. These materials exhibit good processability, superior mechanical performance, good thermal stability, and have excellent gas barrier properties. Low glass transition temperature phosphate glasses (Pglass) are used as inorganic fillers and slightly maleated polypropylene is used as the organic polymer matrix. The Pglass, which was dispersed as spherical droplets in the unoriented composites can be elongated into high aspect ratio platelets during the biaxial stretching process. Biaxially oriented films exhibited a brick wall type microstructure with highly aligned inorganic platelets in a ductile organic matrix and the oxygen barrier properties are significantly improved due to presence of Pglass platelets as impermeable inclusions. Mechanical properties of the biaxially oriented films showed significant improvements compared to neat polymer due to uniform dispersion of the Pglass platelets. Properly dispersed and aligned platelets have proven to be very effective for increasing the composite modulus. These developed materials therefore show promise to help fulfill the ever increasing demand for new advanced materials for a wide variety of advanced packaging applications because of their gas barrier properties, flexibility, transparency, mechanical strength and performance under humid conditions.The second part of the thesis (Chapters 4 & 5) describes new value-added applications for polyesters. Chapter 4 reports a novel process for the decolorization of green and blue colored PET bottle flakes using hydrogen peroxide. The decolorized flakes were characterized for color, intrinsic viscosity values. Decolorized flakes exhibited color values similar to those of colorless recycled PET and even though IV values decreased, bleached flakes still exhibit useful molecular weight. The consumption of H2O2 during the bleaching process was quantified by titrating the residual peroxide using a standard solution of potassium permanganate. Chapter 5 reports synthesis of ductile amorphous polymers which change their color as a function of mechanical deformation. Cyano–OPV moieties were covalently incorporated into the backbone of amorphous polyester PETG. The materials exhibit a significant color change upon compression consistent with efficient breakup of the dye aggregates upon deformation and therefore can be useful for technological applications that require smart coatings with integrated scratch detectors.
Advisors/Committee Members: Schiraldi, David.
Subjects: Polymers
Keywords: Phosphate Glasses, Gas Permeability
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12.
Henry, Milliman W.
REINFORCEMENT OF MELT-BLEND COMPOSITES; POLYMER-FILLER INTERACTIONS, PHASE BEHAVIOR, AND STRUCTURE-PROPERTY RELATIONSHIPS.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► In recent years POSS (polyhedral oligomeric silsesquioxanes) has been incorporated into a…
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▼ In recent years POSS (polyhedral oligomeric silsesquioxanes) has been incorporated into a number of polymers as a copolymer, graft or as a melt-blend. The advantages gained from using POSS come from its hybrid organic-inorganic nature whose inorganic core provides molecular reinforcement while its variety of functionalization schemes allow for reaction or other interactions with the host polymer. Previous work has shown the ability of POSS to reinforce polymers when incorporated through grafting or copolymerization, but there is a lack of understanding of how to obtain successful reinforcement when using POSS as a melt-blend additive. One hypothesis is that a high degree of POSS-polymer interactions are necessary which promote a pseudo-grafted structure yielding results similar to that of copolymer system. The first part of this thesis (Chapters 2 and 3) will address the role of POSS-polymer interaction in reinforcement. Specifically, Chapter 3 will discuss a new approach to predicting these interactions through the determination of Hansen solubility parameters. This approach however does not take into account the role of processing. Chapter 4 will address this by evaluating the structure-property relationships in melt-spun fiber composites. Finally, Chapter 5 will discuss a different field of polymer composites, polymer clay aerogels. In this work the use of these low-density composites as an oil absorbing media will be discussed.
Advisors/Committee Members: Schiraldi, David.
Subjects: Polymers
Keywords: Polymer composites, polymer blends, structure-property relationships, phase behavior, solubility parameters
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13.
Jin, Lin.
Applications of Polybenzoxazines for Improvement in Processability and Property.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► Polybenzoxazines obtained from the polymerization of benzoxazine monomers or oligomers has been…
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▼ Polybenzoxazines obtained from the polymerization of benzoxazine monomers or oligomers has been used for various applications: to simplify the technology adopted for protection, to improve the processability of high performance material and to replace the environmental hazards in resins.Novel siloxane-containing benzoxazine oligomers with benzoxazine rings in the main chain have been synthesized and mixed with octasilane polyhedral silsesquioxane (OctaSilane POSS) and glass sphere to form a thermo-oxidatively stable coating on a carbon/carbon composite after polymerization and baking. The coating method is very simple and inexpensive compared with the conventional approaches, such as chemical vapor deposition. The effectiveness of the coating has also been demonstrated. A new class of benzoxazine-containing monomers, namely bis(benzoxazine-maleimide)s have been synthesized to improve the poor processability of bismaleimides. A new approach of using high boiling point nonpolar solvent has been developed to prepare the monomer, which is difficult to synthesize using the traditional method of synthesizing benzoxazines. In the meantime, by the combination of two types of polymers: benzoxazine and bismaleimides, high thermally stable thermosets with high Tg have been obtained. Benzoxazine monomers have also been introduced into vinyl ester resins to replace styrene for environmental concern. With the incorporation of allyl-containing benzoxazines, the dynamic mechanical property and the thermal stability of the resins have been improved, while the processibility of the resin is maintained.
Advisors/Committee Members: Ishida, Hatsuo.
Subjects: Polymers
Keywords: Benzoxazine; Polym; Bis; Resins; pC-ala; OctaSilane; OctaSilane POSS
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14.
Johnson, Jack Royce III.
POLYMER BLENDS, COMPOSITES AND AEROGEL MODIFICATION BY INNOVATIVE APPROACHES.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► This dissertation covers a wide array of polymer science, from investigating the…
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▼ This dissertation covers a wide array of polymer science, from investigating the barrier properties of polymer blends for commercial products and their specifications to using novel approaches to incorporate glassy inorganic materials within a polymer matrix for high density data storage materials to using common materials in new ways to increase the use range of low density clay aerogels to using bioinspired chemistry to develop reinforcement of current materials and bone replacement materials. Chapter 2 discusses the advances in oxygen barrier materials through innovative approaches to modifying the refractive index change induced by biaxial orientation by simple melt blending procedures. Chapter 3 discusses an approach to developing 3D data storage devices by the blending of common optical polymers with inorganic chalcogenide glasses. Chapter 4 discusses the vast mechanical improvement of a polymer/clay aerogel composite material by a simple dip coating procedure. Chapters 5-7 involve the use of biomineralization for various purposes. In Chapter 5 a polyethylene imine/clay aerogel is coated by a silica layer to impart vastly superior mechanical properties, while a layering approach modestly improves mechanical performance. In Chapter 6 a polyacrylic acid/clay aerogel is subjected to CaCO3 deposition, showing the ability to grow large amounts of CaCO3 in relatively short times. Chapter 7 discusses an electrophoretic mineralization approach to collagen hydrogels.
Advisors/Committee Members: Schiraldi, David.
Subjects: Polymers
Keywords: biomineralization, polymer blends, data storage, oxygen barrier, clay, aerogel
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15.
Kamdar, Akshay R.
Miscibility and Structure-Property Relationships in Some Novel Polyolefins.
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► In the first chapter, miscibility of homogeneous propylene/ethylene (P/E) copolymers of relatively…
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▼ In the first chapter, miscibility of homogeneous propylene/ethylene (P/E) copolymers of relatively narrow molecular weight distribution was studied as a function of constituent comonomer content. Polymers with up to 31 mol% ethylene were blended in pairs in order to vary the comonomer content difference. Copolymers of molecular weight about 200 kg/mol were miscible if the difference in ethylene content was less than about 18 mol%, and immiscible if the ethylene content difference was greater than about 20 mol%. Blends with constituent composition difference in the range of 18 20 mol% exhibited partial miscibility in the melt.In the second chapter, the effect of chain microstructure on the miscibility and phase behavior of ethylene-octene (EO) copolymer blends was studied. Binary blends of two statistical copolymers (EO/EO blends) that differed in comonomer content were compared with blends of an EO with an olefinic blocky ethylene-octene copolymer, OBC (EO/OBC blends). Two EOs of molecular weight about 100 kg/mol were miscible if the difference in octene content was less than about 10 mol% and immiscible if the octene content difference was greater than about 13 mol%. The blocky nature of the OBCs reduced the miscibility and broadened the partial miscibility window of EO/OBC blends compared to EO/EO blends. The EO/OBC blends were miscible if the octene content difference was less than 7 mol% and immiscible above 13 mol% octene content difference. In the third chapter, the adhesion of some ethylene-octene copolymers to polypropylene (PP) and high density polyethylene (HDPE) was studied in order to evaluate their suitability as compatibilizers for PP/HDPE blends. A one-dimensional model of the compatibilized blend was fabricated by layer-multiplying coextrusion. The microlayered tapes consisted of many alternating layers of PP and HDPE with a thin tie-layer inserted at each interface. The thickness of the tie-layer varied from 0.1 to 14 microns, which included thicknesses comparable to those of the interfacial layer in a compatibilized blend. A blocky copolymer (OBC) consistently exhibited better adhesion to PP than statistical copolymers (EO). Inspection of the crack-tip damage zone revealed a change from a continuous plastic damage zone in tie-layers 2 microns or thicker to a highly fibrillated damage zone in thinner tie-layers.
Advisors/Committee Members: Baer, Eric.
Subjects: Engineering; Plastics; Polymers
Keywords: polyolefins; copolymers; polypropylene; polyethylene; adhesion; gradient refractive index optical lens
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16.
Khariwala, Devang.
STRUCTURE-PROPERTY RELATIONSHIPS IN MULTILAYERED POLYMERIC SYSTEM AND OLEFINIC BLOCK COPOLYMERS.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► The dissertation focuses on structure-property relationships in several polymeric systems. In part…
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▼ The dissertation focuses on structure-property relationships in several polymeric systems. In part I, the effect of tie-layer thickness on delamination behavior of polypropylene/tie-layer/Nylon-6 multilayers is examined. Various maleated polypropylene resins were compared for their effectiveness as tie-layers. Delamination failure occurred cohesively in all the multilayer systems. Two adhesion regimes were defined based on the change in slope of the linear relationship between the delamination toughness and the tie-layer thickness. The measured delamination toughness of the various tie-layers was quantitatively correlated to the damage zone length formed at the crack tip. Exciting new developments in polyolefin synthesis give rise to olefinic block copolymers with properties typical of thermoplastic elastomers. Part II of the dissertation describes the material science of these unique polymers as characterized by thermal analysis, x ray diffraction, microscopy, and tensile deformation. The block copolymers synthesized by chain shuttling technology consist of crystallizable ethylene-octene blocks with low comonomer content and high melting temperature (hard blocks), alternating with amorphous ethylene-octene blocks with high comonomer content and low glass transition temperature (soft blocks). Blocky ethylene-octene copolymers differ from random copolymers in their rapid rate of crystallization and in the formation of space-filling spherulites even when the crystallinity is as low as 7 %. The crystallization kinetics of these copolymers in terms of bulk crystallization and spherulite growth rate is compared.
Advisors/Committee Members: Baer, Eric.
Subjects: Polymers
Keywords: Structure Property relationships, adhesion, interdiffusion, block copolymers, polyolefins, coextrusion
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17.
Knight, Pamela Tiffany.
Polyester-based Biodegradable Systems Incorporating POSS.
Degree: PhD, Macromolecular Science and Engineering, 2010, Case Western Reserve University
► Two new families of hybrid polyester-based systems incorporating polyhedral oligosilsesquioxane (POSS) are…
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▼ Two new families of hybrid polyester-based systems incorporating polyhedral oligosilsesquioxane (POSS) are introduced. First, synthesis of tunable polyester-based polyurethanes is presented. Changes in the soft block composition made through variation of the initiator and cyclic ester co-monomers showed direct control of the final glass transition temperature. Incorporating POSS into the hard segments yielded semicrystalline materials with excellent elasticity above Tg, not typically seen in other biodegradable materials. Based on the soft block composition, these polyurethanes could be tuned to be either brittle or elastic films, with strain-at-failure values ranging from 15% to over 900%. The films were also robust and exhibited a Young’s modulus as a high as 1 GPa and yield stress up to 30 MPa. Absorption of water was found to soften the material, however, as well as decrease Tg by more than 10 °C. Hydrolysis for all samples was observed when incubated in PBS buffer at 37 °C, with the degradation rate dependant on the hydrophilicity of the soft block.The second degradable polyester family was synthesized from POSS-initiated PLGA oligomers cured into a cross-linked network. Increasing POSS inclusion increased the crystallinity of the networks while decreasing the degradation rate due to its hydrophobic and nonhydrolyzable properties. It was found that co-curing PLGA oligomers with and without POSS in the backbone could be utilized to create networks with a reduced POSS loading level, at a given cross-link density, allowing tuned crystallinity. Hydrolytic degradation of the co-cured networks was slower than for the PLGA homonetwork, but still led to complete degradation after 14 weeks in PBS buffer. POSS-containing networks exhibited excellent one-way shape memory and this property could be used to fix a temporary shape that was then largely maintained during degradation. All aforementioned materials were subjected to an in vivo biodegradation and biocompatibility study. Both material and cellular changes during degradation were assessed. Results from the histological analysis were favorable and all POSS-based materials were considered biocompatible. Material changes observed during degradation included chain scission (molecular weight loss), increased crystallinity, and loss of film integrity after eight weeks of implantation.
Advisors/Committee Members: Mather, Patrick.
Subjects: Biomedical research; Polymers
Keywords: polyhedral oligosilsesquioxane; biodegradable; polyester; biocompatible
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18.
Kumpfer, Justin Richard.
Utilizing Metallosupramolecular Polymers as Smart Materials.
Degree: PhD, Macromolecular Science and Engineering, 2012, Case Western Reserve University
► This dissertation focuses on the preparation and properties of a number of…
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▼ This dissertation focuses on the preparation and properties of a number of metallosupramolecular polymers, which combine the processability and mechanical properties of polymers with the functionality of metals. Ditopic 2,6-bis(N-methylbenzimidazol-2ʹ-yl)pyridine (Mebip) ligand end-capped metallosupramolecular polymers coordinated with Zn2+ and Eu3+ metal-ions and their resulting stimuli-responsive properties were initially investigated. These polymers were found to exhibit thermo- and chemo-responsive properties directly related to the Eu3+ content. Structure-property relationships were investigated using detailed rheological and morphological studies which revealed that the nature of the polymer core strongly influences the mechanical properties and degree of phase separation of the metal-ligand complexes. This work was expanded upon using a crosslinkable polymer core to form metallosupramolecular polymer films which show shape-memory properties. The shape-memory behavior was able to be triggered using temperature, UV light, or solvents and the shape fixing was tailorable using different metal-ions and counterions. Continued investigations into the use of different metal-ions yielded mechanically stable vapochromic materials by blending small-molecule Mebip:Pt2+ complexes into a series of polymethacrylates. The use of a polymer matrix revealed that the films also displayed piezochromic properties. Pt2+ was then used to form metallosupramolecular polymers with the ditopic macromonomers previously studied to give films which assemble via Pt – Pt interactions. Thin films of the Pt2+- containing polymers were utilized as templates in the formation of Pt nanoparticles with <5 nm diameter by reduction using electronsgenerated from an extracted discharge from an atmospheric microplasma. The particle size and density was found to be directly related to the polymer core and exposure time. Finally, a side-chain Mebip-functionalized polymer blended into a polymer matrix was compression molded with a polymer blend containing Zn2+ to form a metallosupramolecular polymer network at the polymer-polymer interface. Spectroscopy was used to confirm that formation of the metallosupramolecular polymer occurred within 5 mins at the processing temperature (210 °C) and microscopy confirmed the location of the metallosupramolecular polymer to be at the interface between the two polymer layers.
Advisors/Committee Members: Rowan, Stuart J.
Subjects: Polymer Chemistry; Polymers
Keywords: metallosupramolecular polymers; self-assembly; smart materials
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19.
Kunzelman, Jill Nicole.
Polymers with Integrated Sensing Capabilities.
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► This dissertation is focused on the creation and characterization of new types…
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▼ This dissertation is focused on the creation and characterization of new types ofchromogenic polymers, which change their absorption and/or fluorescence characteristics in response to an external stimulus. These optical sensor materials rely on chromophores that display pronounced color changes upon self-assembly as a result of charge-transfer interactions and/or conformational changes. When these chromophores are incorporated into a polymer of interest, the relative amounts of dispersed and aggregated molecules (and therefore their optical appearance) can be initially tuned by controlling the extent of aggregation via the materials composition and the processing protocol employed; the phase-behavior is changed in a predefined manner upon exposure to a specific stimulus. This sensing scheme was exploited in a number of different polymer matrices, leading to a variety of sensor types including mechanochromic, thermochromic, moisture-sensing, and shape-memory materials that allow visualization of the set/release temperature. Important design fundamentals of “aggregachromic” sensor dyes are discussed and chemical structure is related to type of interactions (hydrophobic, π-π, charge-transfer) and self-assembly/color relationships. The knowledge is used to control behavior such as piezochromism, aggregation rate, and intramolecular-excimer-formation.
Advisors/Committee Members: Weder, Dr. Christoph.
Subjects: Chemistry; Plastics; Polymers; Technology
Keywords: cyano-OPV; excimer; charge-transfer complex; sensor; thermochromic; mechanochromic; aggregachromic; piezochromic; moisture-sensing; shape-memory; chromogenic; color change
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20.
Lai, Chuan-Yar.
STRUCTURAL PHENOMENA OF MULTILAYERED POLYMERIC FILMS.
Degree: PhD, Macromolecular Science and Engineering, 2012, Case Western Reserve University
► Coextrusion through a series of layer multiplying elements has enabled the production…
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▼ Coextrusion through a series of layer multiplying elements has enabled the production of films containing tens to thousands of layers with individual layer thicknesses down to the nanoscale. This technology allows for interesting studies of polymers, and it can be used as a tool to create novel products such as polymeric gradient refractive index (GRIN) lenses. It has been utilized to better understand the confined crystallization of several semicrystalline polymers and its effect on their barrier properties, and to investigate interdiffusion between polymers. To further our understanding, and evaluate these confined semicrystalline materials for packaging applications, the resulting mechanical properties were investigated. Alternating layers of poly(ethylene oxide) (PEO) with either poly(ethylene-co-acrylic acid) (EAA) or polystyrene (PS) showed unexpected results. Though crystallinity and layer composition were constant, the intensity of the PEO glass transition decreased dramatically with layer thickness. By considering the changes in crystalline morphology that accompanied layer confinement, it was possible to completely account for this reduction using standard mechanical models. The deformation mechanism of PEO was also found to shift as layer thickness was decreased from typical axial alignment of the crystalline fraction, as seen in bulk materials, to nonuniform micronecking mechanisms found in solution-grown single crystals. Multilayer coextrusion has also enabled the fabrication of novel polymeric GRIN lenses comprised of poly(methylmethacrylate) (PMMA) and poly(styrene-co-acrylonitrile) with 17 mol% acrylonitrile (SAN17). The interdiffusion of these two miscible materials was examined to better understand its effect on film optical properties. Though a single additive value requires optical thicknesses less than or equal to a quarter-wavelength of light, some films exhibited such behavior with thicknesses 5x greater than expected, though layer resolution was still present.
Advisors/Committee Members: Baer, Eric.
Subjects: Polymers
Keywords: multilayered, nanolayers, mechanical properties, interdiffusion
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21.
Langhe, Deepak.
POLYMER CRYSTALLIZATION IN DROPLETS AND CONFINED LAYERS USING MULTILAYERED FILMS.
Degree: PhD, Macromolecular Science and Engineering, 2012, Case Western Reserve University
► Crystallization of polypropylene (PP) droplets produced by thermal break up of multilayered…
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▼ Crystallization of polypropylene (PP) droplets produced by thermal break up of multilayered films was investigated. Droplets produced from 12 nm PP layers resulted into exclusive homogeneous nucleation, which is usually viewed as the initial step during polymer crystallization. The structure, thermodynamics and crystallization kinetics of the droplets were analyzed to understand the homogeneous nucleation process. The stability of the homogeneously nucleated droplets was further probed by thermal treatment. Ability to produce homogeneous nucleation provided an opportunity to add various nucleating agents to the droplets and investigate the nature of heterogeneous nucleation. Effect of various nucleating agents on the crystallization of PP droplets is also discussed. In another approach, confined crystallization of a low crystallinity polymer, syndiotactic PP (sPP), was achieved by “forced assembly” coextrusion process. The crystal orientation was controlled by melt recrystallization of sPP layers under the hard confinement of polycarbonate. A transition from in-plane to on-edge lamellar orientation was observed with decreasing crystallization temperature. Controlled melt recrystallization of sPP layers was successfully used to manipulate the lamellar orientation of sPP and control the gas transport properties over one order of magnitude. Additionally, the effect of confinement on the physical aging and structural relaxation of a glassy polymer, polystyrene (PS), under the hard confinement of polycarbonate (PC) was also investigated in the thermally reset multilayered films.
Advisors/Committee Members: Baer, Eric.
Subjects: Polymers
Keywords: fractionated crystallization; isotactic polypropylene; heterogeneous nucleation; homogeneous nucleation; confined crystallization; multilayered films; syndiotactic polypropylene; physical aging; polystyrene
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22.
Lin, Yijian.
Structure-Property Relationship of Polyolefins Used as Packages and Adhesives.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► Polyolefins are among the most abundantly used polymeric materials in the world.…
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▼ Polyolefins are among the most abundantly used polymeric materials in the world. The structure-property relationship of polyolefins, especially for package and adhesive applications, is the primary focus of this dissertation. In part I, structure-property relationship of biaxially oriented polypropylene (BOPP) films for package application was investigated. The clarity of BOPP films was strongly dependent on the thermal history during processing. The clearest film was obtained by orienting a quenched unoriented sheet at the lowest temperature. Oxygen permeability was reduced by biaxial orientation processing. The decrease in permeability was attributed to reduced mobility of amorphous tie molecules. A single one-to-one correlation between the oxygen permeability and the intensity of the dynamic mechanical beta-relaxation was demonstrated for all the films used in the study. In order to further decrease the oxygen permeability of BOPP films, the layer-multiplying coextrusion with a subsequent biaxial orientation was used to generate the nanoparticles in situ by transforming a spherulitic polymer into impermeable, high aspect ratio lamellae that resemble polymer single crystals. The platelet-like single lamellae were homogeneously dispersed and highly oriented in BOPP films. Very substantial increases in gas barrier and gas selectivity were imparted to BOPP films while also increasing tear strength without sacrificing clarity. In Part II, some polyolefin elastomers used as adhesives or compatibilizers for polypropylene (PP) and high density polyethylene (HDPE) were studied. The compatibilizer was preferentially located at the interface between the PP matrix and the dispersed HDPE particles. The blend compatibilized with an olefin block copolymer (OBC) had the best combination of low brittle-to-ductile temperature and high toughness. This improved mechanical performance was attributed to the sufficient interfacial adhesion provided by the compatibilizer. The interfacial adhesion was measured in terms of the delamination toughness by peeling PP/compatibilizer/HDPE microlayered tapes. By treating the delamination damage zone as an Irwin plastic zone, it was demonstrated that a critical delamination stress controlled the delamination toughness. A quantitative correlation was established between the adhesion strength and mechanical performance.
Advisors/Committee Members: Baer, Eric.
Subjects: Polymers
Keywords: tie-layers; BOPP; HDPE; nano-BOPP; Films; OBCs
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23.
Li, Zheng.
Structural Studies of Natural and Synthetic Macromolecules Stabilized by Metal Ion Binding.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► Metal ions can interact with both natural and synthetic macromolecules to produce…
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▼ Metal ions can interact with both natural and synthetic macromolecules to produce changes in their structure and conformation. This thesis addresses structure-property relationships in several classes of macromolecular materials which fit this description. In Chapter II, the gelation mechanism of 50/50 w/w mixtures of guanosine (G) and 2',3',5'-tri-O-acetylguanosine (TAcG) in aqueous 0.354 M KCl is investigated using static light scattering (SLS), polarized and depolarized dynamic light scattering (VV and VH DLS), small-angle neutron and X-ray scattering (SANS and SAXS), and viscometry. The results indicate sol and microgel phases coexist up to the macroscopic gel point. An unusual transient contribution to the gel modulus is attributed to fibrillar species trapped within the gel network. In Chapter III, a class of stimuli-responsive metallo-supramolecular gels self-assembled in good/poor solvent mixtures from metal ions and a ditopic macromonomer consisting of oligoethylene glycol end-capped with a 2,6-bis(1'-methylbenzimidazolyl)-4-pyridine ligand (MeBIP) is studied by SAXS and differential scanning calorimetry (DSC). An evolution from turbid to transparent gels with increase of good solvent content is shown to be due to the formation of a solvent-swollen lamellar structure. In Chapter IV, with the goal of developing redox-active assembly of supramolecular polymers in solution, we describe structural studies using viscosity, SAXS, SLS and DLS of the supramolecular polymers formed via binding of Cu(II) and Cu(I) ions to a ditopic macromonomer consisting of polytetrahydrofuran end-capped with MeBIP ligands. The results demonstrate differences in the molecular weight of the metallo-supramolecular polymers formed at fixed stoichiometry via Cu(II)-MeBIP versus Cu(I)-MeBIP binding. Chapter V describes structural characterization by SAXS of a cruciform base-paired ribonucleic acid (RNA) complex, which catalyzes an RNA splicing reaction. Comparison of the radii of gyration (Rg) of mutant complexes versus the wild type indicates a preference for one of four possible magnesium ion-driven folded conformers. Energy minimized atomistic structures are generated for the wild type and mutant complexes. Since the juxtaposition of catalytically-active groups in the selected conformer differs from that found in the native activated spliceosome, the results suggest a chaperoning role for spliceosomal proteins in ensuring the correct tertiary stacking of the base-paired helices.
Advisors/Committee Members: Jamieson, Alexander.
Subjects: Polymers
Keywords: Metallo-supramolecular Polymers; Guanosine Hydrogel; Model Spliceosome; Light Scattering; X-ray and Neutron Scattering
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24.
LI, ZHENLONG.
DYNAMICS OF POLYMER SELF-ASSEMBLY BY COMPUTER SIMULATION.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► We studied the self-assembly dynamics of two polymeric systems, block copolymer micelles…
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▼ We studied the self-assembly dynamics of two polymeric systems, block copolymer micelles and supramolecular polymer solutions using computer simulation. Dissipative Particle Dynamics simulations were applied to study the equilibrium properties, kinetics of micellization and equilibrium chain-exchange in A2B3 and A4Bx(x=4,6,8) diblock copolymer micelle solutions. The critical micelle concentration, micelle aggregation number distribution and micelle structure were found to agree well with previous experimental and theoretical studies. The time-evolution of micelles from unimers is found to follow three stages: unimer consumption, equilibration of the number of micelles progressing mainly by the fusion/fission mechanism and slow adjustment of the weight-average aggregation number by micelle fusion, unimer and small aggregate exchange. The effect of polymer concentration, hydrophobic interaction energy and block length on the kinetics of micellization were also considered. By performing micelle hybridization simulations, we found the equilibrium chain exchange follows a first-order kinetic process and the characteristic time, mainly determined by chain expulsion and does not depend on polymer concentration. The chain exchange characteristic time, τ, increases exponentially with core block length, NA and interaction parameter between blocks, χAB as τ ~ exp(0.67χABNA). We also found that in contrast to theoretical predictions, chain exchange between micelles occurs more rapidly for micelles with a longer corona-block length due to a higher compatibility of diblock copolymers and therefore a lower potential barrier for chain expulsion. Using coarse-grained molecular dynamics simulations we studied the equilibrium and rheological properties of dilute and semi-dilute solutions of head-to-tail associating supramolecular polymers with our newly-developed model for spontaneous reversible association. We found that for a given spacer length all shear-rate-dependent reduced viscosity data collapse into one master curve with two power-law regions with increasing slopes due to change of the degree of self-assembling under shear. The equilibrium viscosity is found to obey a power-law scaling dependence with exponent 1.5 on oligomer volume fraction, in agreement with experimental observations for several dilute or semi-dilute solutions of supramolecular polymers, implying that dilute and semi-dilute supramolecular polymer solutions exhibit high polydispersity, but may not be sufficiently entangled to follow the reptation mechanism of relaxation, expected for wormlike micelles.
Advisors/Committee Members: Dormidontova, Elena.
Subjects: Polymers
Keywords: self-assembly dynamics, block copolymer micelles, supramolecular polymer, computer simulation, DPD simulation, Molecular Dynamics simulation, micelle dynamics, viscosity
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25.
Lott, Joseph Robert.
Design, Synthesis and Incorporation of Functional Additives into Multilayered Polymer Films.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► This dissertation is focused on the synergistic combination of the nanostructured architectures…
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▼ This dissertation is focused on the synergistic combination of the nanostructured architectures of coextruded multilayered polymer films and tailored functional additives to create novel and useful functional optical material systems. Layer multiplying coextrusion was used to create layered polymeric systems with hundreds to thousands of layers with individual layer thicknesses in the range of 90 nanometers to 20 microns. If transparent polymers of different refractive index are employed, these films can display characteristics of one dimensional photonic crystals whose reflection and transmission characteristics can be readily tailored via the geometry and refractive indices. The experiments shown in this thesis demonstrate that the functionality and range of possible applications for these layered polymeric systems can be greatly expanded through incorporation of functional additives, which can take the form of nanoparticles, small organic species, and tailored polymers. Thus, properties such as refractive index, fluorescence, sensing ability, stimuli responsiveness, and optical upconversion were controlled in multilayered films using a variety of polymer hosts and functional additives. These components were united to develop a number of technologically relevant optical systems including terahertz photonic crystals, all-polymer distributed Bragg reflector and distributed feedback lasers, stimuli responsive mechanochromic sensors, materials for three dimensional optical data storage, and the first and a number of subsequent solid-state optical upconversion systems. The combination of fabrication methods which are amenable to rapid, inexpensive, large-scale industrial production with materials performance that is competitive with current state of the art systems in a number of high-tech applications means the concepts explored herein should have an ever expanding impact in years to come.
Advisors/Committee Members: Weder, Christoph.
Subjects: Chemistry; Materials Science; Nanoscience; Nanotechnology; Optics; Organic Chemistry; Plastics; Polymer Chemistry; Polymers
Keywords: photonic crystals, coextrusion, multilayered films, polymer lasers, triplet-triplet annihilation, upconversion, excimer, fluorescent sensors
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26.
Makowski, Brian Thomas.
Functionality via Confinement of Photo-Responsive Materials.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► This dissertation focuses on imparting unique functionality to nano-structured architectures, such as…
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▼ This dissertation focuses on imparting unique functionality to nano-structured architectures, such as photonic crystals and polymer colloids, via incorporation of photo-responsive materials. When the photo-responsive material is a nonlinear optical chromophore, it is possible to achieve a dynamic optical band gap that can be utilized in all-optical switching devices. Chromophores were optimized to elicit large optical nonlinearities while their physico-chemical characteristics were adapted for facile melt-infiltration into 2D macroporous silicon templates. Chromogenic, excimer-forming dyes were also studied, and were used to impart sensing ability to polymeric, spray-coatable particles. The complexation of the excimer-forming dyes was manipulated by imbibing a maximum amount of dye into the particles using a solution-based swelling/deswelling process, with the dye fluorescing in its monomer state. Exposure to chemical vapors induces particle coagulation, and an expulsion of dye, providing striking visual contrast from monomer- to excimer-based emission. Thermotropic materials were also studied which exploit the temperature-dependent refractive index difference between the matrix of a polymer composite with that of constituent polymer particles. The main goals of this dissertation were to design nonlinear optical chromophores for suitable infiltration into nano-structured architectures, to maximize the amount of photo-responsive materials that can be incorporated, and to create new functional devices based on the incorporation of photo-responsive materials into nano-structured architectures and to study their properties.
Advisors/Committee Members: Weder, Christoph.
Subjects: Polymers
Keywords: polymer, nonlinear optical chromphores, photonic crystals, optical sensors, thermotropic materials, opals
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27.
Marsh, Timothy Edward.
High Performance Hyperbranched Polymers For Improved Processing And Mechanical Properties In Thermoset Composites.
Degree: PhD, Macromolecular Science and Engineering, 2009, Case Western Reserve University
► Hyperbranched polymers, specifically hyperbranched poly(arylene ether ketone imide)s (HBPAEKI), are here studied…
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▼ Hyperbranched polymers, specifically hyperbranched poly(arylene ether ketone imide)s (HBPAEKI), are here studied as blend additives in thermoset composites to improve processing and ultimate performance properties of the composite. Monomer synthesis for HBPAEKI was further advanced in this work leading to higher yields, fewer reactions, and shorter production times. A five step synthetic method with an overall yield of 12% was reduced to a three step process with an overall yield of 38%. Polymer was synthesized under varying conditions and end group chemistry for use in thermoset blends. NMR characterization allowed for the assignment of chemical shifts in monomer and cataloguing of shifts in polymer for use in future work to characterize degree of branching.Cure kinetics of blends of HBPAEKI are explored through the use of differential scanning calorimetry (DSC) and chemorheology using small angle oscillatory shear. In a phenylethynyl terminated imide oligomer (PETI) thermoset resin, reactive phenylethynyl endcapped PAEKI (PEPAEKI) was found to retard cure while non reactive alkyl endcapped PAEKI was found to accelerate cure in DGEBA/DAH epoxy systems. Minimal effect was seen on early stage blend viscosity. Composite properties tested focused on the effect on bulk fracture and interfacial shear strength. No significant effect was seen in fracture toughness by SENB. XPS was used to verify that PEPAEKI was surface active to DGEBA/DDS epoxy/air interfaces to the complete exclusion of the epoxy at the surface. Evidence was also seen consistent with surface activity in alkyl endcapped PAEKI in DGEBA/DAH systems, although the contrast is much lower. Effect of alkyl endcapped HBPAEKI on interfacial shear strength was examined through the use of t-peel and single fiber fracture (SFF) techniques. In some systems, t-peel indicates a clear improvement in peel force, proportional to the blend concentration. In SFF, interfacial shear strength was found to be equal or slightly reduced in the blends, although the difference was within experimental error.
Advisors/Committee Members: Mather, Patrick T.
Subjects: Polymers
Keywords: hyperbranched; hyperbranched polymer; composite; interface; rheology; cure acceleration; surface segregation; surface activity; dendrimer
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28.
McKenzie, Blayne M.
Metallo-Responsive Liquid Crystalline Monomers, Polymers and Networks.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► This dissertation focuses on the preparation and properties of a number of…
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▼ This dissertation focuses on the preparation and properties of a number of liquid crystalline derivatives of the 2,6-bisbenzimidazolylpyridine (Bip) ligand and incorporation of these mesogens into polymers and networks for metallo-responsive polymer actuators. First, a versatile one-pot synthetic platform for the preparation of a range of functionalized Bip derivatives is presented. This protocol significantly reduces the cost and time of previous synthetic routes, while facilitating scale up to multi-gram quantities in good yields (63-90%). Via this platform, a series of liquid crystalline monomers with chemo-responsive properties has been prepared and studied. Tailoring the size of the aromatic core and the length of two pairs of alkyl substituents allows the preparation of calamitic mesogens with a range of tunable thermal liquid crystalline transitions and phase geometries. Depending on the length of the alkyl substituents, the binding of lanthanide- and/or transition metal salts results in either a transition from a nematic or smectic liquid crystalline state to an isotropic material or the manifestation of a metallomesogen. From these monomers, thiol-ene and metathesis chemistry were utilized to prepare oligomeric, polymeric and network liquid crystalline materials. A liquid crystalline elastomer has been prepared which displays soft shape memory, as flexibility is retained in both the permanent and temporary shapes. By incorporating the metallo-responsive mesogen into the backbone of the network polymer, a material which exhibits thermal shape memory behavior as well as light and metal-ion triggered recovery has been accessed. While the metallo-network itself does not exhibit further shape memory properties, this behavior is recovered upon removal of the metal ions from the Bip binding sites.
Advisors/Committee Members: Rowan, Stuart.
Subjects: Chemistry; Organic Chemistry; Polymer Chemistry
Keywords: liquid crystals, shape memory, stimuli-responsive, actuator, elastomer
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29.
Mendez, James D.
Conjugated Polymer Networks and Nanocomposites.
Degree: PhD, Macromolecular Science and Engineering, 2011, Case Western Reserve University
► Conjugated Polymer Networks and Nanocomposites Abstract By JAMES DENNIS MENDEZ This dissertation…
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▼ Conjugated Polymer Networks and Nanocomposites Abstract By JAMES DENNIS MENDEZ This dissertation is based on an experimental study, which explored two different approaches to the design and synthesis of conjugated polymer systems with improved electrical transport properties. The first approach sought to improve the local charge transport through structural variation of the polymer. It was hypothesized that hyperbranched and cross-linked conjugated structures would offer better charge-transport characteristics than linear macromolecules, on account of the reduced importance of interchain transport in the former. Thus, hyperbranched versions of a commonly used semiconducting conjugated polymer, poly (p-phenylene ethynylene) (PPE), were synthesized and the charge transport properties were investigated using a time-of-flight technique and fluorescence quenching. The results show that the high molecular weight hyperbranched materials offer charge transport characteristics that are better than the linear polymer but are still soluble in common organic solvents. Similarly, the wellknown electrically conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was cross-linked with several conjugated cross and non-conjugated cross-linkers. The concentration and structure of the cross-linker was systematically varied to explore the influence on the electrical conductivity. Optimized compositions resulted in materials which displayed an electrical conductivity of up to ~800 S/cm; this corresponds to a conductivity increase of up to 36% compared to linear PEDOT prepared under identical conditions. The second approach sought to improve the charge transport on a macroscopic scale by producing nanocomposites based on electrically active nanorods in a polymer matrix. The (semi)conducting nanofibers were produced by decorating cellulose nanorods derived from sea tunicates with the electrically conducting polymer PEDOT and a fullerene derivative as example of an n-type semiconductor. The incorporation of these electrically conducting nanorods into inert as well as semiconducting polymer matrices resulted in a very low percolation threshold upon formation of percolating nanofibers network. This is concomitant with a remarkable conductivity (in the case of PEDOT) and high fluorescence quenching efficiency (in the case of the fullerene).
Advisors/Committee Members: Weder, James.
Subjects: Polymers
Keywords: polymer; PEDOT; polythiophene; cellulose; tunicate; PPE
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30.
Meng, Linghui.
Polymer Biomaterial Constructs For Regenerative Medicine and Functional Biological Systems.
Degree: PhD, Macromolecular Science and Engineering, 2012, Case Western Reserve University
► The use of collagen as a biomaterial is currently undergoing a renaissance…
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▼ The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The excellent biocompatibility and safety due to its biological characteristics, such as biodegradability and weak antigenicity, make collagen a primary material resource in medical applications. Described herein is work towards the development of novel collagen-based matrices, with additional multi-functionality imparted through a novel in-situ crosslinking approach. The process of electrospinning has become a widely used technique for the creation of fibrous scaffolds for tissue engineering applications due to its ability to rapidly create structures composed of nano-scale polymer fibers closely resembling the architecture of the extracellular matrix (ECM). Collagen-PCL sheath-core bicomponent fibrous scaffolds were fabricated using a novel variation on traditional electrospinning, known as co-axial electrospinning. The results showed that the addition of a synthetic polymer core into collagen nanofibers remarkably increased the mechanical strength of collagen matrices spun from the benign solvent system. A novel single-step, in-situ collagen crosslink approach was developed in order to solve the problems dominating traditional collagen crosslinking methods, such as dimensional shrinking and loss of porous morphology, and to simplify the crosslinking procedure for electrospun collagen scaffolds. The excess amount of NHS present in the crosslinking mixture was found to delay the EDC/collagen coupling reaction in a controlled fashion. Fundamental investigations into the development and characterization of in-situ crosslinked collagen matrices such as fibrous scaffolds, gels and sponges, as well as their biomedical applications including cell culture substrates, wound dressings, drug delivery matrices and bone regeneration substitutes, were performed. The preliminary mice studies indicated that the in-situ crosslinked collagen matrices could be good candidates for wound healing and skin regeneration. Polyelectrolyte fibrous tubes of highly-crosslinked poly (acrylic acid) were fabricated by means of electrospinning as polymer models for functional biological systems, with special attention to the axon cortical layer and its cation-exchange properties. The processing parameters of fiber formation and the reversible phase transitions of PAA tubes according to monovalent-divalent ion exchange in solution were systematically investigated. The results showed that the neutralized PAA tubes were responsive to calcium ions, exhibiting significant shrinkage that could be reversed with a chelator such as citrate. Study of such phase transitions may help to better understand the electrophysiological processes known as nerve excitation and conduction in the nervous system, and the resulting PAA tubes might be used as polymer models of artificial axons for potential tissue engineering and nerve repair applications.
Advisors/Committee Members: Wnek, Gary.
Subjects: Biomedical Research; Chemical Engineering; Chemistry; Nanotechnology; Polymers
Keywords: Tissue Engineering, Electrospinning, Collagen, In-situ Crosslinking, Wound Healing, Poly (acrylic acid), Nanofiber
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