Browsing by Subject "Polymer"

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Accessing Model, Functional Polyolefins and Polyolefin Copolymers with Ring-Opening Metathesis Polymerization
(2022-11) Dingwell, Claire
Polyolefins are the most widely used commercial polymer available due to their low cost and excellent properties. Functionalized polyolefins with polar functional groups are desirable targets for more complex materials benefiting from the excellent properties of polyolefins, but these materials are challenging to synthesize using traditional polymerization methods. Ring-opening metathesis polymerization (ROMP) is a useful tool for achieving this goal as the catalysts are often tolerant to a wide range of functional groups, and the polymerizations are typically well-controlled making polymers with moderate dispersities. Chapter 2 describes the synthesis of epoxy-telechelic polyalkenamers and polyolefins made by ROMP of a cyclooctene-based monomer with difunctional chain-transfer agents. These polymers can then be rapidly photocured into model elastomers with few dangling-end defects and tunable properties based on the degree of saturation and the prepolymer molar mass. Appendix A shows the synthesis of similar elastomers made from polymers containing epoxide groups along the backbone of the polymer chain to explore the contributions of dangling-end defects to the mechanical properties of the final material. Chapters 3 and 4 describe the synthesis of a gas barrier polymer, an ethylene vinyl alcohol (EVOH) copolymer, made by ROMP of 3-functional cyclooctene. Chapter 3 explores the effect of regioregularity, given by ROMP of cyclooctenes with substituents in the 3 position, on the barrier properties of EVOH with the goal of decreasing the oxygen permeability of EVOH with high ethylene content while maintaining low water permeability. Chapter 4 discusses the additional effects of stereoregularity on the properties of a similar EVOH polymer. Appendix B describes the attempted synthesis of a disubstituted ROMP monomer for the synthesis of EVOH copolymers containing a higher vinyl alcohol copolymer content compared to the polymers made in Chapters 3 and 4. Finally, Appendix C presents the compilation and discussion of data from learning experience reports, an anonymous accident reporting system from the joint safety team.
Cationic Polymers and Polymeric Micelles as Plasmid DNA and CRISPR-Cas9 Ribonucleoprotein Delivery Vehicles
(2019-11) Tan, Zhe
Millions of people are currently suffering from genetic diseases and disorders worldwide and the traditional protein-based treatments are both expensive and require repetitive injections to maintain long-term effects. Gene therapy, as an alternative, holds great potential by direct delivery of genetic materials such as nucleic acids and genome editing machineries into human body to achieve long-term therapeutic protein expression, malfunctioning gene silencing, and native gene alternation. As a crucial step towards gene therapy, the delivery of genetic materials remains a major challenge, and affordable, efficient, and well-defined delivery vehicles are urgently needed. Synthetic polymers have been explored as plasmid DNA delivery vehicles for decades owing to their low production cost, chemical flexibility, low immunotoxicity, and the ability to encapsulate biomacromolecules. However, the precise control of polymeric vehicle properties by structure-tuning is a general challenge. Hence, the fundamental understanding of polymeric vehicle’s structure-property relationships is of great importance. In addition, polymers as well-documented nucleic acid delivery vehicles, are largely underexplored for their ability to encapsulate, stabilize and deliver RNA-protein conjugates, such as CRISPR/Cas9 ribonucleoprotein, a recently emerged versatile genome editing tool, presumably due to the inherent structural differences between long, semiflexible DNA and globular RNA-protein payload. Herein, several classes of polymeric delivery vehicles were synthesized and investigated, namely, cationic linear polymers, block copolymers, and polymeric micelles. Initially, a systematic comparison of linear polymers and micelles were performed, and vehicle architecture were shown to largely affect DNA complexation ability, complex physical properties, and biological performance. Later on, polymeric micelles were explored as well-defined CRISPR/Cas9 ribonucleoprotein delivery vehicles, and the solvent condition was found to be a key factor that affect particle complexation and gene-editing efficiency. Finally, polymers with liver-targeting ability and cellular membrane-penetration property have been developed and studied for their gene delivery efficiency and cytotoxicity.
Characterization of pi-conjugated polymers for transistor and photovoltaic applications
(2012-12) Paulsen, Bryan D.
pi-Conjugated polymers represent a unique class of optoelectronic materials. Being polymers, they are solution processable and inherently "soft" materials. This makes them attractive candidates for the production of roll-to-roll printed electronic devices on flexible substrates. The optical and electronic properties of pi-conjugated polymers are synthetically tunable allowing material sets to be tailored to specific applications. Two of the most heavily researched applications are the thin film transistor, the building block of electronic circuits, and the bulk heterojunction solar cell, which holds great potential as a renewable energy source. Key to developing commercially feasible pi-conjugated polymer devices is a thorough understanding of the electronic structure and charge transport behavior of these materials in relationship with polymer structure. Here this structure property relationship has been investigated through electrical and electrochemical means in concert with a variety of other characterization techniques and device test beds. The tunability of polymer optical band gap and frontier molecular orbital energy level was investigated in systems of vinyl incorporating statistical copolymers. Energy levels and band gaps are crucial parameters in developing efficient photovoltaic devices, with control of these parameters being highly desirable. Additionally, charge transport and density of electronic states were investigated in pi-conjugated polymers at extremely high electrochemically induced charge density. Finally, the effects of molecular weight on pi-conjugated polymer optical properties, energy levels, charge transport, morphology, and photovoltaic device performance was examined.
Combined Application of Density Functional Theory and Molecular Mechanics Sampling Techniques to study Chemical Systems, from Intramolecular Rearrangements to Polymerization Reactions
(2023-05) Chiniforoush, Sina
Modern techniques in computational chemistry have allowed for the investigation of a diverse array of problems in chemistry and material sciences. However, one of the main challenges in the use of these techniques is the trade-off between computational cost and chemical accuracy. Methods like density-functional theory (DFT) are often accurate, but at the expense of higher computational resources. Methods like molecular mechanics (MM) are less computationally expensive, but fail to describe important features of chemical systems. While the study of chemical systems of relatively small size can often be carried out using methods like DFT, some of these systems have a high number of conformational degrees of freedom despite their relatively small size, and it’s often not possible to accurately describe important characteristics of these systems without capturing these all possible conformers. In this case, using MM-based sampling methods followed by DFT computations can allow for a relatively accurate description of these systems. This work contains three studies. In chapter 2, the mechanistic details of Newman-Kwart rearrangement under oxidative conditions is explored using DFT, and using theoretical predictions, modifications to the Newman-Kwart substrate are proposed to increase reactivity. In chapter 3, a combination of MM sampling methods and DFT are used to evaluate the temperature sensitivity of 19F chemical shifts in a library of organofluorine compounds screened for temperature sensing, and computations were used to successfully predict the chemical shift temperature sensitivity of these compounds, and finally used to guide the synthesis of more temperature sensitive compounds. In chapter 4, the same combination of DFT and MM techniques were used to describe two Aluminum-based ring-opening transesterification polymerization (ROTEP) catalysts, and a variety of the features of these catalysts, including the origin of their stereoselectivity, the mechanism of the inversion of catalyst chirality, and the relative stereoselectivity of the catalysts in the initiation stage, and the mechanism of stereoselectivity in the propagation stage, were described.
Compatibilization of polyolefin blends
(2015-08) Thurber, Christopher
Polymer blends are used to access unique combinations of properties beyond those of neat homopolymers. Blends confer flexibility in tailoring a specific material to a given application, and in some cases, they can lend improved properties compared to their constituent materials. Some examples of blend-synergistic properties in the literature include toughness enhancement, increased chemical resistance, increased modulus, and improved processability. Given the breadth of properties that can be improved by blends, they are employed extensively in commercial products, with more than a third of all polymer resins used in blends (Utracki, 2003). Most polymer pairs are immiscible, thus their blends require compatibilization to aid dispersion in the melt state and to transfer stress across interfaces in the solid state. Block copolymers have proven to be successful compatibilizers, in both premade and reactively formed systems. This thesis focuses mainly on reactive systems. The reaction at immiscible polymer interfaces is kinetically limited and most reactions are too slow for applications, so general methods of increasing interfacial reaction rate have been investigated. This work also seeks to find new tools for measuring localization and conversion in polymer blends, with the ultimate goal of making useful, economical materials, and understanding the resulting structures. This thesis attempts to further our knowledge of compatibilization of polyolefin blends in particular. Chapter 2 attempts to create facile reactive compatibilization schemes for polyolefins with poly(methyl methacrylate). Chapters 3 and 4 examine the use of catalysts to increase interfacial reaction rate between functional polyethylene and polylactide. Chapter 3 demonstrates stannous octoate catalyst is localized at the interface, and blends show better compatibilization than those with a more active but non-localized tin chloride dihydrate catalyst. Chapter 4 uses cobalt octoate catalyst to increase interfacial reaction rate by ~90-fold and the extension at break of polylactide majority blends to ~200%. Structural dependence of copolymers on compatibilization efficiency in polypropylene/polyethylene blends is investigated in Chapter 5. Finally, a small scale coextruder is created using a dual-bore capillary rheometer, with the potential to examine the effect of flow on copolymer localization, catalyst localization, and interfacial reaction rate (Chapter 6).
Complexation of DNA with Polycationic Micelles
(2018-08) Jiang, Yaming
Interpolyelectrolyte complexation is a ubiquitous phenomenon that plays vital roles in biological systems and in design of responsive materials. However, precise control of polyelectrolyte complexes (PEC) has been challenging, particular for DNA-polycation complexes designed for gene delivery applications. Incorporating polyionic micelles is a promising strategy to tune PEC properties, but has been under-utilized in designing polymeric gene delivery vehicles. Herein, cationic micelles self-assembled from amphiphilic block polymers are complexed with double stranded DNA. The structure, composition, and stability of the resulting "micelleplexes" are characterized to probe the fundamental physics that govern the formation and properties of micelleplexes. With cationic AB+ micelles, complexation of linear semiflexible DNA and flexible poly(styrenesulfonate) were compared and the influence of polyanion chain flexibility was extracted and discussed. DNA length was found to strongly influence the size, composition, and colloidal stability of micelleplexes, whereas DNA topology (linear or circular supercoiled) has minimal influence. To improve the colloidal stability and reduce the size of micelleplexes that are composed of multiple micelles connected by bridging DNA chains, AB+C micelles with hydrophilic nonionic outer coronas of varying length were designed. The addition of the outer nonionic corona dramatically improves the colloidal stability of micelleplexes over a much wider charge ratio, and the outer corona length closely correlates to micelleplex size, zeta potential, and the average number of micelles per micelleplex. In addition, AB+C micelleplexes adopt a beads-on-a-string structure that resembles the organization of DNA in chromatin. Lastly, structure, composition, and stability of micelleplexes were closely compared with those of another typically studied family of DNA complexes, "polyplexes", which form between DNA and cationic homopolymers or AB+ diblock copolymers with a hydrophilic nonionic A block. Compared to the polyplexes, micelleplexes showed more than a 4-fold increase in gene transfection efficiency, which was attributed to the high positive charge content of micelleplexes.
Cure induced stress generation and viscoelasticity in polymer coatings.
(2010-01) O’Neal, Daniel Jeffrey
Coatings solidified by free-radical polymerization and crosslinking (curing) reactions initiated with ultraviolet (UV) light do so quickly and at room temperature. Low viscosity monomer or oligiomer makes the use of volatile solvent unnecessary, decreasing energy use and making the process more environmentally friendly but photoinitiators can be toxic, limiting certain applications. Stress may be generated by a changing specific volume during cure, and stress-induced defects are undesirable. The goal of this research is to understand stress generation in UV irradiated coatings and to model stress generation and viscoelasticity seen during curing. Two new mathematical models were created to accomplish viscoelastic stress modeling. The first, a network model, uses a two-dimensional network of one-dimensional elements to replicate deformation in the coating. The second uses continuum momentum conservation and linear viscoelastic equations. Inertial forces can be neglected and a substitution performed, making the solution more rapid and simple with standard finite element methods. Stress generation in uniformly cured coatings depends on how quickly the specific volume and physical properties change. Reaction kinetics, volume, and stress are calculated simultaneously. Rapid initiation from high initiator concentration or UV light intensity delays volume change, generating more stress because the volume changes with a higher modulus. An optimum curing schedule would insure the actual specific volume and its equilibrium value remain the same. Inhomogeneities in the substrate or the presence of defects change the stress field. Knowing forces on the coating boundaries suggests defect locations and types. Probing the types of geometries and surface roughnesses seen in different types of coatings shows that restricted deformation increases stress concentrations and surface forces seen. Also, avenues for reducing stress via relaxation are discussed. The two-dimensional stress profiles used in these analyses are not possible to measure experimentally, making computational modeling essential. The models developed and methodology presented may be extended to other UV cured coatings or to other methods of coating solidification. Process windows of allowable final conversion-stress-energy-time states suggest what tradeoffs must be made to meet constraints.
Evaluation of the SafeLane™ Overlay System for Crash Reduction on Bridge Deck Surfaces
(Minnesota Department of Transportation Research Services Section, 2010-03) Evans, John F.
The winter performance of the SafeLane™ commercial overlay system has been evaluated at four installations on bridge decks in the state of Minnesota. The study was conducted over a period of a total of three years. Analyses included mechanical and chemical testing of the components, chloride analysis as a function of depth, friction by skid test and visual inspection. At one site plow operator’s comments were gathered to access retention of deicing chemicals from event to event. All sites were included in a comparison of accident frequency before and after overlay installation.
Graphene synthesis & graphene/polymer nanocomposites
(2012-11) Liao, Ken-Hsuan
Graphene, a two-dimensional carbon sheet with single-atom thickness, has recently attracted significant interest due to its unique mechanical and electrical properties. It has been reported that incorporation of graphene in polymers can efficiently improve the materials’ electrical and mechanical properties. For reliable integration of graphene into practical graphene/polymer nanocomposites, it is essential to have a simple, reproducible and controllable technique to produce graphene on a large scale. We successfully developed a novel, fast, hydrazine-free, high-yield method for producing single-layered graphene. Graphene sheets were formed from graphite oxide by reduction with de-ionized water at 130 ºC. Over 65% of the sheets are single graphene layers. A dehydration reaction of exfoliated graphene oxide was utilized to reduce oxygen and transform C-C bonds from sp3 to sp2. The reduction appears to occur in large uniform interconnected oxygen-free patches so that despite the presence of residual oxygen the sp2 carbon bonds formed on the sheets are sufficient to provide electronic properties comparable to reduced graphene sheets obtained using other methods. Cytotoxicity of aqueous graphene was investigated with Dr. Yu-Shen Lin by measuring mitochondrial activity in adherent human skin fibroblasts using two assays. The methyl-thiazolyl-diphenyl-tetrazolium bromide (MTT) assay, a typical nanotoxicity assay, fails to predict the toxicity of graphene oxide and graphene toxicity because of the spontaneous reduction of MTT by graphene and graphene oxide, resulting in a false positive signal. An appropriate alternate assessment, using the water soluble tetrazolium salt (WST-8) assay, reveals that the compacted graphene sheets are more damaging to mammalian fibroblasts than the less densely packed graphene oxide. Clearly, the toxicity of graphene and graphene oxide depends on the exposure environment (i.e. whether or not aggregation occurs) and mode of interaction with cells (i.e. suspension versus adherent cell types). Ultralow percolation concentration of 0.15 wt% graphene, as determined by surface resistance and modulus, was observed from in situ polymerized thermally reduced graphene (TRG)/ poly-urethane-acrylate (PUA) nanocomposite. A homogeneous dispersion of TRG in PUA was revealed by TEM images. The aspect ratio of dispersed TRG, calculated from percolation concentration and modulus, was found to be equivalent to the reported aspect ratio of single-layered free standing TRG. This indicates TRG is mono-layer-dispersed in the matrix polymer. How graphene/polymer nanocomposite glass transition temperatures (Tg) vary was investigated in this study. First we surveyed the literature. No changes in Tg were observed for graphene/polymer nanocomposites synthesized via physical blending processes such as solvent or melt blending, except aqueous blending. In contrast, chemical blending processes such as in situ polymerization or chemically modified fillers yielded significant Tg increases in graphene/polymer nanocomposites. We attribute these results to bonding interactions at the interfaces between matrix polymers and fillers. Physical blending processes cannot provide enough interaction at the interfaces, whereas chemical blending processes can yield strong interaction such as covalent bonds. Aqueous blending of graphene or graphene oxide nanocomposites with water soluble matrix polymers also cause Tg increases, even though the blending processes involve no chemical reactions. The reason for this exception is that hydrogen bonding forms between fillers (graphene oxide or reduced graphene) and water soluble matrix polymers. We then measured Tg in PMMA. We used isotactic PMMA (i-PMMA) and syndiotactic-rich atactic PMMA (a-PMMA) to make TRG/PMMA nanocomposites using solvent blending and in situ polymerization in order to investigate the stereo-regularity and processing effects on the Tg. A Tg increase was found in i-PMMA and in situ PMMA but not in a-PMMA. The results can be explained by the thin film confinement effect of polymer. We attribute the Tg increase to both a higher interaction density and a stronger hydrogen bonding at the interfaces. We have studied the elastic modulus of graphene oxide with various oxygen content. We used in situ AFM nano-indentation to measure the influence of oxygen on the elastic modulus of graphene oxide with various carbon/oxygen (C/O) ratios. The results show that chemical reduction (lower oxygen contents) decreases the elastic modulus of graphene oxide. We speculate that chemical reduction of oxygen atoms of epoxy groups on graphene oxide surface removes the bridging effect between carbon atoms, which leads to more flexible sheets.
Hybrid solar cells from polymers and silicon nanocrystals.
(2009-12) Liu, Chin-Yi
This thesis is concerned with the application of silicon nanocrystals (Si NCs) in photovoltaic devices. Two types of novel solar cells, hybrid solar cells and Si NCs-only thin-film photovoltaic devices, have been developed. Hybrid solar cells are made from polymers and Si NCs. The first hybrid solar cells were fabricated by using poly- 3(hexylthiophene) (P3HT) which has a good hole mobility and matches the energy band alignment of Si NCs. The solar cell performance of Si NCs/P3HT devices was studied as a function of the weight ratio of Si NCs/P3HT and Si NC size. Three groups of Si NCs were used in this study: Si NCs 3-5 nm in diameter, 5-9 nm in diameter, and 10-20 nm in diameter. The open-circuit voltage and short-circuit current increased by using the smallest size NCs due to the high surface-area-to-volume ratio and quantum confinement effect. Those results indicate that Si NCs are a good candidate as an electron acceptor in hybrid solar cell application. To improve the efficiency of Si NCs/P3HT hybrid solar cells, we started to optimize the fabrication conditions by modification of the polymer concentration, usage of postproduction heat treatment, and application of different metal electrodes. After optimization, a hybrid solar cell from 50wt% (weight ratio) Si NCs/P3HT annealed at 150 °C for 2 hours with aluminum (Al) electrodes had a power conversion efficiency of 1.47% with a fill factor of 0.47, short-circuit current of 3.8 mA/cm2, and open-circuit voltage of 0.8 V under air mass 1.5 direct (AM 1.5D) one sun illumination. To understand the hole mobility of P3HT before and after post-production heat treatment, a hole-only device was fabricated by depositing gold (Au) electrodes, which block electron injection from the electrodes to Si NCs. The results suggest that the hole mobility of 50wt% Si NCs/P3HT film increases one order of magnitude after heat treatment, due to improved crystallinity in the P3HT, which can enhance hybrid solar cell efficiency. Literature has reported that the compatibility of polymers and nanocrystals plays an important role in hybrid solar cell efficiency. Although P3HT is a good hole conductor and light absorber in solar cell applications, other polymers should be tested to find the best compatibility for Si NCs. Knowing this, P3HT was replaced by poly [2-methoxy-5- (3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) in 3-5 nm Si NCs/MDMO-PPV hybrid solar cells. Although Si NCs/MDMO-PPV devices have a higher open-circuit voltage than Si NCs/P3HT devices, the power conversion efficiency of Si NCs/MDMO-PPV devices is not as high as that of Si NCs/P3HT devices. To understand the reasons for the low efficiency from Si NCs/MDMO-PPV devices, the hole mobility of MDMO-PPV, energy band alignment between MDMO-PPV and Si NCs, and absorption spectrum of MDMO-PPV were studied and compared to those of P3HT. To measure the hole mobility of MDMO-PPV, Au electrodes were again utilized to block electron injection into the Si NCs. The results show that the hole mobility of MDMOPPV is lower than that of P3HT. The absorption spectrum of MDMO-PPV (400-600 nm) is narrower than that of P3HT (400-650 nm) so that exciton generation in P3HT is more efficient than in MDMO-PPV under AM 1.5 conditions. Additionally, MDMO-PPV has a lower highest occupied molecular orbital level than P3HT so the efficiency of hole injection from Si NCs into MDMO-PPV may not be as efficient as for P3HT. These reasons explain why the efficiency of Si NCs/MDMO-PPV devices is not as good as Si NCs/P3HT devices. From Si NC solution processing, we found that 10-20 nm bare Si NCs without any surface modification can form a stable cloudy colloid with 1,2-dichlorobenzene. This colloid can be spin-cast onto an ITO substrate to form a continuous and dense thin film. A Schottky photovoltaic device consisting of a single layer of intrinsic Si NCs was fabricated in a glove box to verify that films can be cast from colloid Si NCs. This photovoltaic device has a sandwich structure with a 250 nm Si NC layer between ITO and Al electrodes. Under AM 1.5D one sun illumination, the Si NC Schottky device showed a significant photovoltaic response with a power conversion efficiency of 0.02%, a fill factor of 0.26, short circuit-current density of 0.148 mA/cm2, and open-circuit voltage of 0.51 V. This result suggests that the solution processing of bare Si NCs can be a new way to manufacture low-cost and high-quality silicon-based thin films.
Immunological benefits of a novel polycaprolactone-polyorthoester-based therapeutic vaccine in a mouse model of glioma
(2014-08) Grinnen, Karen Lynn
Cancer immunotherapy has led to significant improvement in the survival of patients with previously untreatable malignancies. The use of therapeutic vaccines is a promising form of immunotherapy, but their efficacy remains ambiguous. Much of the difficulty in identifying the optimal formulation and delivery is related to the complicated nature of the immune response, where it is uncertain which aspects would be most effective in destroying cancer cells. In this thesis, a novel polymeric delivery system, involving poly (caprolactone)-co-poly (ortho ester) [PCL-POE], was used to deliver tumor antigens and adjuvants in a controlled manner. We hypothesized that persistent release of tumor antigens from the biodegradable polymer would result in an increase in the number and persistence of anti-tumor lymphocytes in the effector state. To test this hypothesis, vaccines were administered to mice and the time dependent immunological response was evaluated. The polymeric delivery system resulted in an in vitro release profile characterized by a burst release of both antigen and adjuvant followed, in both cases, by a much slower phase of release. We also observed that the slow release provided by the PCL-POE polymer stimulated prolonged maturation of dendritic cells, activation and persistence of anti-OVA antibodies and antigen-specific T cells following a single vaccination. The vaccine system was also tested in a mouse model of glioblastoma multiforme (GBM). We observed a significant, potentially translatable increase in overall survival.
Interfacial coupling between immiscible polymers: flow accelerates reaction and improves adhesion.
(2011-10) Song, Jie
As the workhorses of the plastics industry, polyolefins are consumed in the largest volume of all types of polymers. Despite their wide use, polyolefins suffer from poor adhesion and compatibility with other polar polymers due to their intrinsic low polarity and lack of functional groups. The first goal of this study is to enhance interfacial adhesion between polyolefins with other polymers through coupling reaction of functional polymers. We have used functional polyethylenes with maleic anhydride, hydroxyl, primary and secondary amino groups grafted through reactive extrusion. Functional polyolefins dramatically improved the performance of polyolefins, including adhesion, compatibility, hardness and scratch resistance, and greatly expand their applications. The second goal is to understand the factors affecting adhesion. We systematically investigated two categories of parameters. One is molecular: the type and incorporation level of functional groups. The other is processing condition: die design in extruders, reaction time and temperature. The interfacial adhesion was measured with the asymmetric dual cantilever beam test and T-peel test. The extent of reaction was quantified through measuring anchored copolymers via X-ray photoelectron spectroscopy. A quantitative correlation between adhesion and coupling reaction was developed. A coextruded bilayer system with coupling reaction at interfaces was created to clarify processing effects on the kinetics of coupling reactions. For the reaction between maleic anhydride modified polyethylene and nylon 6, the reaction rate during coextrusion through a fishtail die with compressive/extensional flow was strikingly almost two orders of magnitude larger than that through a constant thickness die without compressive flow. The latter reaction rate was close to that of quiescent lamination. We attribute the reaction acceleration through the fishtail die to the large deformation rate under the compressive/extensional flow condition. The deformation generated stretched chains leading to complimentary functional groups exposed to each other and forcing reactive species to overcome the interfacial diffusion barrier. We also found reaction acceleration through a fishtail die for the coupling of functional PE with thermoplastic polyurethane. This work illustrates that enhancing the compressive/extensional flow during polymer processing may create opportunities for increasing adhesion and designing new reactions and products.
Linear Polymer Affinity Agents for the Intrinsic SERS Detection of Food Safety Targets
(2018-07) Szlag, Victoria
This dissertation explores the use of polymer affinity agents for the surface-enhanced Raman spectroscopy (SERS) detection of food safety targets. First, current molecular motifs used as affinity agents in intrinsic surface-enhanced Raman spectroscopy (SERS) sensors are reviewed. By comparing antibody, aptamer, small molecule, and polymer affinity agents, the largely unresearched potential of polymer affinity agents (chemical customization, tunable length, ease of production, opportunity for multiplexing) is highlighted. The first proof of concept work of this dissertation targets the detection of the bioterror agent, ricin B-chain (RBC) in water and liquid food matrices. An N-acetyl-galactosamine glycopolymer capture layer was designed and applied to create a SERS sensor. The sensing scheme’s detection limit (20 ng/mL) is well below that of the predicted oral exposure limit. The RBC was detected in two types of juice, and a computed normal Raman spectrum of the glycomonomer supports polymer–RBC intermolecular interactions at the functional group level. Subsequent work focuses on the translation of this sensing scheme from the detection of proteins to the detection of small molecules relevant to food safety. Because interactions between a small molecule target and a polymer affinity agent are less specific than those that were leveraged in the RBC work, the development of a rapid affinity agent screening method was deemed necessary. A potent carcinogenic metabolite of a fungal pathogen that can infect food and feedstocks, aflatoxin B1 (AFB1), was used as a model target. Seven homopolymers of nitrogen-inclusive poly(N-(2-aminoethyl) methacrylamide) (pAEMA) and their oxygen analogs, poly(2-yydroxyethyl methacrylate) (pHEMA) were synthesized to be evaluated as AFB1 affinity agents based on hypothetical hydrogen bonding interactions and optimal polymer length. An isothermal titration calorimetry (ITC) method was development for rapid affinity agent screening and good agreement was observed between the ITC results and follow-on SERS sensing experiments. A final polymer series (poly(N-acryloyl glycinamide), pNAGA) was designed for the capture of AFB1 and was used to explore the influence of polymer molecular weight (2.0 – 5.2 kDa), attachment chemistry (thiol vs. trithiocarbonate), and order of addition (pre- vs. post- functionalization of the substrate) on the sensitivity of AFB1 detection. The best polymer chain length (pNAGA22), anchoring chemistry (thiol), and polymer/toxin assembly scheme (in-solution) allowed detection of 10 ppb AFB1 in water (below the FDA regulatory limit of 20 ppb), a hundred-fold improvement over SERS sensing without the pNAGA affinity agent. This dissertation concludes with the advantages, disadvantages, and future perspectives of polymers used as analytical affinity agents. Adjustment of surface attachment moieties, the use of crosslinkers with target affinity, and application to other signal transduction mechanisms are emphasized a potential areas for continuing work.
Phase Behavior of ternary polymer blends: asymmetry, segregation strength, and coexisting phases
(2013-02) Habersberger, Brian McLean
The bicontinuous microemulsion phase, found in ternary polymer blends containing immiscible A and B homopolymers and an amphiphilic A-B diblock copolymer, has attracted interest due to its combination of properties that make it attractive for use as a template for nanoporous materials. While recent work has demonstrated that a variety of materials can be templated from a single blend system, future work may demand incorporation of a variety of polymers into microemulsion-forming blends. Such systems fall beyond the currently understood model phase behavior for ternary blends. In this thesis, the effect of well-controlled nonidealities and other extensions of ternary blend phase behavior are described. Systems were designed to investigate the influence of conformational asymmetry – a difference in the radius of gyration per molar volume of two polymers – on blend phase behavior. Previous work suggested that the influence was significant, and resulted in a broad region of a hexagonally symmetric phase in the vicinity of the microemulsion. This behavior could inhibit the process of capturing of microemulsion for templating purposes, so it is important to understand conformational asymmetry’s influence. A related series of systems was designed to investigate the effect of increased segregation strength by using amphiphilic diblocks of varying molecular weight. Finally, a previous study incorporating an ABA triblock, C homopolymer, and ABABA–C amphiphilic hexablock was expanded to incorporate ordered components, allowing for hierarchical microphase separation. This study demonstrates that model ternary blend phase behavior can be extended to systems containing more complex linear polymer architectures. Additionally, two phenomena observed in these systems were investigated in detail. First, light scattering was observed in the vicinity of the order-disorder transition of blends; this scattering is a result of coexisting ordered and disordered phases. Finally, catalytic hydrogen-deuterium exchange on polyolefins was investigated. The reaction conditions described provide a facile method of preparing isotopically labeled chains and give insight into the mechanism of exchange.
Polymer Reservoirs to Solubilize Hydrophobic Drugs
(2018-08) Li, Ziang
Research and development of new drug delivery formulations for hydrophobic drugs hold great promise for patients worldwide in the ever-growing pharmaceutical industry. A large portion of the drugs, both in the current market and the development pipeline, suffer from low aqueous solubility, therefore limiting their efficacy for oral administration. One effective way to resolve this problem is the use of an amorphous solid dispersion (ASD), a blend of drug and polymer. An ideal polymer candidate can kinetically stabilize the dispersed drug in its amorphous form in the solid state, while enhancing drug solubility and dissolution in the solution state. Despite recent advances in polymer development for oral drug delivery, the structure-property relationships and the underlying solubility enhancement mechanisms are not fully understood for ASDs. The goals of this dissertation are to develop effective polymers for oral drug delivery, and more importantly, to elucidate the mechanism(s) of drug solubility and dissolution enhancement by using well-defined polymer platforms. Specifically, three model systems were designed and synthesized, including blends of a commercially available polymer and self-assembled micelles in Chapter 3, micelle-forming statistical copolymers and diblock polymers in Chapter 4, and chemically crosslinked polymer nanogels in Chapter 5. It was observed universally in all these three systems that hydrophobic drugs can be sequestered in the slightly hydrophobic polymer reservoirs, and that the drug-polymer partitioning is stronger when the polymer chains are more crowded. The partitioning inhibits drug nucleation and crystal growth in aqueous solution, resulting in enhanced drug solubility. This mechanism is supported by a battery of state-of-the-art characterization experiments, including light scattering, nuclear Overhauser effect and diffusion ordered spectroscopy, cryogenic transmission electron microscopy, small-angle X-ray scattering, and in vitro dissolution tests. Potential applications of the discovered mechanism and the characterization experiments to other drug/polymer systems are discussed as future directions.
Polymer-Based Ion Gels as a Versatile Platform of Solid Electrolytes
(2018-07) Tang, Boxin
Ion gels are a versatile class of functional materials. Combining the excellent electrical properties such as high ionic conductivity and capacitance of the ionic liquid (IL) and the mechanical integrity of the polymer, the composite materials have led to a variety of applications such as electrolyte-gated transistors (EGTs), electroluminescent, and electrochromic soft materials. This thesis is built up from previous research on the electrical and mechanical properties of the ABA triblock polymer-based ion gels and continues to improve properties of the materials for electrochemical device applications. In the first part of the thesis work, the objective is to improve the existing ABA triblock polymer systems with poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA) as the IL-solvating midblock by combining the merit of the low Tg from PEO and hydrophobicity from PMMA into one system. As a result, poly(styrene-b-ethyl acrylate-b-styrene) (SEAS) triblock polymer was developed. The ion gels made with SEAS demonstrate similarly high ionic conductivity as the PEO-based ion gels, which are significantly improved from those of the PMMA-based ion gels. By shortening the midblock size of the triblock polymer, a synergistic improvement of both the ionic conductivity and the modulus can be achieved. Additionally, the EGTs made by SEAS-based ion gels demonstrate superior stability under humidity compared with EGTs made by SOS-based ion gels. In the following two projects of the thesis work, the polymer platform changes from petroleum-based polymers with hydrocarbon backbones to renewable aliphatic polyesters with the potential aim of EGTs in biocompatible applications. To achieve the ion gels, both physical and chemical crosslinked-systems have been explored. The physically crosslinked ABA aliphatic polyester triblock ion gels demonstrate good mechanical integrity and can be successfully printed under similar conditions as the previous systems, and demonstrate improved ionic conductivity from the PMMA-based ion gels. In addition, the resulting ion gels also demonstrate efficient hydrolytic degradation under basic condition. In a different approach, chemically crosslinked poly(lactide) (PLA)-based ion gels can be synthesized from a facile one-pot method. Owing to a smaller volume fraction in ion-insulating domain, the ion gel demonstrates an excellent ionic conductivity at low polymer concentration. Meanwhile, the ion gel also possesses a high toughness owing to the chemical crosslinks. The thin chemically crosslinked PLA-ion gels can be laminated onto EGTs via a cut-and-stick method. On the other hand, the bulk ion gel demonstrates a good electromechanical response with high electromechanical sensitivity with the applied strain and a low hysteresis between stretching and unstretching.
Quinine Copolymer Reporters For Enhanced Gene Editing And Raman Imaging
(2022-01) Van Bruggen, Craig
After decades of development, gene therapy has finally reached the forefront of medicine and has led to new cures for genetic disorders and the development of life-saving vaccines. The field has been buoyed by the development of more precise and user-friendly targeted nucleases, such as those used for clustered regularly interspersed palindromic repeats (CRISPR)-based editing. These useful gene-editing technologies, however, are still stymied by the challenge of delivering exogenous nucleic acids and proteins into the cells of interest. The emerging gene therapy industry is investing heavily in developing more efficient and safe non-viral vehicles as alternatives to costly and immunogenic viral vectors. Cationic polymers are promising non-viral vectors due to their manufacturing scalability, their chemical stability, and their synthetic tunability. Improvements in delivery efficiency are necessary, however, for widespread adoption of polymeric vehicles for gene therapy. One challenge in improving performance, however, is the difficulty and limited methodology for elucidating the intracellular mechanics of polymeric vehicles. In this thesis, I describe my research focused on the development of a novel quinine-containing polymer, called a Quinine Copolymer Reporter (QCR), that enhanced transient transfections of cultured cells with plasmids and improved gene editing of cultured cells through the simultaneous delivery of the CRISPR-associated protein Cas9 and DNA donor template. In addition, I describe collaborative research performed with colleagues in the research group of Prof. Renee Frontiera that characterized a band in quinine’s Raman spectrum that is diagnostic of its chemical environment. Using this chemical sensitivity in conjunction with Raman microscopic imaging, we help elucidated the intracellular unpackaging mechanisms of the QCR-nucleic acid complexes.
Reductively degradable polymeric biomaterials
(2015-01) Partlo, Walter Eugene
Polymers were synthesized that included functional groups that allowed for the triggering of polymer degradation via reduction of the present azide groups. This degradation was demonstrated and characterized.
Renewable Aliphatic Polyester Block Polymer Thermoplastic Elastomers
(2014-04) Martello, Mark
The performance of thermoplastic elastomers is predicated on their ability to form mechanically tough physically crosslinked elastomeric networks at low temperatures and be able to flow at elevated temperatures. This dissertation focuses on renewable aliphatic polyester block polymers with amorphous polylactide (PLA) and their performance as TPEs. The goal of this work was to enhance the mechanical toughness of PLA containing TPEs; fundamental properties ranging from chemical composition and phase behavior, molecular architecture and melt processability, to melt polymerization strategies were investigated. ABA triblock polymers with PLA end-blocks and rubbery mid-blocks from substituted lactones comprised of poly(6-methyl-ε-caprolactone)(PMCL), poly(δ-decalactone), and poly(ε-decalactone)(PDL) were produced by sequential ring-opening polymerizations in the bulk. The bulk microstructure of symmetric PLA-PMCL-PLA and PLA-PDL-PLA triblock polymers formed long-range ordered morphologies and the interaction parameter of the repeat units was determined. High molar mass triblocks exhibited elastomeric behavior with good tensile strengths and high elongations. Small triblocks were coupled to produced (PLA-PDL-PLA)n multiblock polymers with high molar mass and accessible order-disorder transitions allowing for melt processing via injection molding. The mechanical toughness of the multiblocks was comparable to the high molar mass triblocks. The controlled polymerization of renewable δ-decalactone was accomplished with an organocatalyst at low temperatures in the bulk to maximize the equilibrium conversion of the monomer.
Stress development in particulate, nano-composite and polymeric coatings.
(2009-09) Jindal, Karan
The main goal of this research is to study the stress, structural and mechanical property development during the drying of particulate coatings, nano-composite coatings and VOC compliant refinish clearcoats. The results obtained during this research establish the mechanism for the stress development during drying in various coating systems. Coating stress was measured using a controlled environment stress apparatus based on cantilever deflection principle. The stress evolution in alumina coatings made of 0.4 micron size alumina particles was studied and the effect of a lateral drying was investigated. The stress does not develop until the later stages of drying. A peak stress was observed during drying and the peak stress originates due to the formation of pendular rings between the particles. Silica nanocomposite coatings were fabricated from suspension of nano sized silicon dioxide particles (20 nm) and polyvinyl alcohol (PVA) polymer. The stress in silica nano-composite goes through maximum as the amount of polymer in the coating increases. The highest final stress was found to be ~ 110MPa at a PVA content of 60 wt%. Observations from SEM, nitrogen gas adsorption, camera imaging, and nano-indentation were also studied to correlate the coatings properties during drying to measured stress. A model VOC compliant two component (2K) acrylic-polyol refinish clearcoat was prepared to study the effects of a new additive on drying, curing, rheology and stress development at room temperature. Most of the drying of the low VOC coatings occurred before appreciable (20%) crosslinking. Tensile stress developed in the same timeframe as drying and then relaxed over a longer time scale. Model low VOC coatings prepared with the additive had higher peak stresses than those without the additive. In addition, rheological data showed that the additive resulted in greater viscosity buildup during drying.

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