Browsing by Subject "polymers"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Data for Combining photocontrolled-cationic and anionic-group transfer polymerizations using a universal mediator: enabling access to two- and three-Mechanism block copolymers
    (2024-08-15) Hosford, Brandon M; Ramos, William; Lamb, Jessica R; jrlamb@umn.edu; Lamb, Jessica R; Lamb Research Group
    An ongoing challenge in polymer chemistry is accessing diverse block copolymers from multiple polymerization mechanisms and monomer classes. One strategy to accomplish this goal without intermediate compatibilization steps is the use of universal mediators. Thiocarbonyl thio (TCT) functional groups are well-known mediators to combine radical with either cationic or anionic polymerization, but a sequential cationic-anionic universal mediator system has never been reported. Herein, we report a TCT universal mediator that can sequentially perform photocontrolled cationic polymerization and thioacyl anionic group transfer polymerization to access poly(ethyl vinyl ether)-block-poly(thiirane) polymers for the first time. Thermal analyses of these block copolymers provide evidence of microphase separation. The success of this system, along with the established compatibility of radical polymerization, enabled us to further chain extend the cationic-anionic diblock using radical polymerization of N-isopropylacrylamide. The resulting terpolymer represents the first example of a triblock made from three different monomer classes incorporated via three different mechanisms without any end-group modification steps. The development of this simple, sequential synthesis using a universal mediator approach opens up new possibilities by providing facile access to diverse block copolymers of vinyl ethers, thiiranes, and acrylamides.
  • Thumbnail Image
    Item
    Development and Applications of Gold Nanoparticles and Elastomeric Polymers as Biomaterials
    (2021-07) Siehr, Allison
    This thesis is focused on the development and applications of two different types of biomaterials: nanoparticles and polymers. In chapter 1, I briefly review these biomaterials. In chapter 2, we develop gold nanoparticles (GNPs) that can be driven to either self-assemble or remain colloidally stable using coiled-coil protein interactions. Control over the GNP self-assembly or stability is critical for specific biomedical applications. In chapter 3, we use the self-assembling GNPs to inhibit human immunodeficiency virus type-1 (HIV-1) by adding a targeting ligand for HIV-1. However, we found our GNPs are weak inhibitors of HIV-1. Methods to improve the inhibitor design are then discussed. In chapter 4, a biomaterials-based approach is used to elucidate the structures of HIV-1 and human T-cell leukemia virus type-1 (HTLV-1). A GNP immunolabeling strategy is used to identify HIV-1 and HTLV-1 envelope proteins, critical for viral entry and targets for vaccine development. However, the immunolabelling strategy was not robust, and alternative methods to study envelope proteins are discussed. Lastly, in chapter 5, a novel elastomeric polymer is evaluated for biomedical applications. PLA-PβMδVL-PLA polymers were synthesized in this work and shown to exhibit elastomeric properties. Next, the polymers were found to be biocompatible and biodegradable both in vitro and in vivo. Overall, this thesis demonstrates the development and applications of both gold nanoparticles and elastomeric polymers as biomaterials.
  • Thumbnail Image
    Item
    Solution properties of polymers in ionic liquids
    (2019-07) Kharel, Aakriti
    Ionic liquids (ILs) are emerging as promising solvents for polymers. They exhibit excellent chemical and thermal stability, favorable ionic conductivity, and negligible vapor pressure, making them attractive alternatives to traditional solvents. Moreover, adding polymers to ILs provides mechanical integrity to these solvents while retaining their transport properties, enabling their use in various applications such as polymer electrolytes, gas separation, and energy storage. However, the use of these materials would benefit from a thorough understanding of the polymer behavior in this relatively new class of solvent. This work focuses on developing a fundamental understanding on solvation behavior of two model polymers in ILs by characterizing their structural, dynamic, and thermodynamic properties. In the past years, various simulation approaches have reported conflicting conformational characteristics of poly(ethylene oxide) (PEO) in an IL. As much as simulation studies are on-going, experimental work to guide simulation models are lacking. This work focused on assessing the excluded volume exponent, v, for PEO in an IL by measuring the dependence of PEO coil size on polymer molecular weight. Since this system is not viable in light scattering, small-angle neutron scattering (SANS) was utilized instead. Therefore, a wide range of accessible molecular weights (10 to 250 kg/mol) of perdeuterated polymers (d-PEO) were synthesized by anionic polymerization, for enhanced contrast in SANS. The dependence of coil size on polymer molecular weight was assessed to yield v ≈ 0.55 at 80 °C, which indicates that PEO adopts a slightly swollen, flexible coil conformation in the IL. The results clarified the uncertainty surrounding PEO coil dimensions in IL, and also successfully guided the development of new simulation models. This work was further extended to examine the tunability of coil dimensions by varying the ionic liquid components. Altering both the cation and anion of the IL changed the solvent quality, but the anion seemed to exert a more pronounced effect. The temperature dependence of coil dimensions was moderate, however, the coil size varied insignificantly in ternary mixtures of PEO, IL, and a binary salt. The static and dynamic properties of a range of molecular weights (20 to 160 kg/mol) of poly(benzyl methacrylate) (PBzMA) were assessed in four different ionic liquids over a wide temperature range (27 °C ‒ 155 °C), primarily using light scattering. The relevant structural, dynamic, and thermodynamic parameters were examined as a function of concentration, temperature, and molecular weight. Some interesting observations were revealed. The phase behavior study showed a potential shift of the critical composition to polymer-rich region, as opposed to lower concentrations of polymer commonly observed in polymer solutions. The second-virial coefficient (A2) remains surprisingly positive, even at temperatures close to the phase separation, where A2 < 0 is anticipated. Furthermore, A2 shows a stronger dependence on molecular weight than commonly observed for polymers in good solvents. On the dynamic side, the diffusion virial coefficients remained mostly positive, further corroborating the good solvent behavior of A2. The excluded volume exponents (v≈ 0.52 ‒ 0.55) obtained from the dependence of hydrodynamic radii on molecular weight also revealed good solvent characteristics of these ILs.
  • Thumbnail Image
    Item
    Tunable Polymers as Specialized Excipients for Oral Drug Delivery
    (2016-08) Ting, Jeffrey
    For the continued advancement of modern pills and tablets in oral drug administration, spray–dried dispersions (solid–solid mixtures of amorphous drugs and polymers) have the potential to elevate poor drug solubility by orders of magnitude through drug supersaturation, thereby enhancing the therapeutic potency, oral bioavailability, and safety of accessible, lifesaving medicines worldwide. However, drug formulation efforts of these materials often employ Edisonian trial–and–error tactics with limited molecular– level understanding of the underlying interactions between polymers and drugs. Herein, a rational approach to establish fundamental structure–property relationships is presented using well–defined, modular polymer platforms. Specifically, Chapters 3–5 describes the synthesis, characterization, and performance properties of a multicomponent acrylic polymer, inspired by hydroxypropyl methylcellulose acetate succinate (HPMCAS). By strategically varying the precise monomeric incorporation, microstructure, and chemical character of these HPMCAS analogs, we systematically examined how specific polymeric attributes produce stable, amorphous spray–dried dispersions with various hydrophobic drugs at increasing drug loadings. Chapter 6 extends these ideas for precision drug formulation, a concept that specialized polymers can be judiciously constructed around drugs of high therapeutic interest. High–throughput synthesis and screening tools expedited this process, akin to molecular evolution methods in biology and genetics; in vitro and in vivo results show the remarkable versatility and ability of designer polymers to controllably solubilize drugs. Altogether, this simple but universal approach combining synthetic and predictive ingredients enables the establishment of robust guidelines to meet unfulfilled needs in the pharmaceutical landscape.