Doctor of Philosophy, University of Akron, 2024, Chemical Engineering

Thermoplastic elastomers (TPE) are a set of materials with characteristics of elastomers and thermoplastics. There is an increasing demand for polymers to be processed into three dimensional porous constructs for tissue engineering. Aliphatic polyester-based, poly(butylene succinate-co-dilinoleic succinate) (PBS-DLS) and polyisobutylene-based, poly(alloocimene-b-isobutylene-b-alloocimene) thermoplastic elastomer copolymers and their development will be presented for end use as biomaterial-based therapies in this dissertation. Electrospun fibrous scaffolds are favored for tissue engineering for their micro-structured networks creating a high surface area to volume ratio and this high interconnected porosity. These properties help mimic natural tissue structure for better tissue integration and diffusion through the network. Applying thermoplastic elastomers as scaffolds offers materials whose material properties can be tailored for specific applications. This dissertation presents work to advance biodegradable aliphatic copolymers for tissue scaffolds, and polyisobutylene copolymers for drug delivery. Cardiac soft tissue regenerations strategies employ biodegradative copolymers for cell delivery. Completely bio-based and biodegradable PBS-DLS copolymers have shown great potential for coiled 3D scaffolds for cardiac applications. This dissertation presents the kinetics of a step enzymatic polycondensation of PBS-DLS copolymers with varying feed ratios. 1H NMR and SEC results found that hydrophobic soft segment DLS was incorporated into the hard segment PBS within the first 3 hours. After which, the pressure was increased during second stage and complete DLS incorporation and high Mn oligomers occurred between 24 and 48 hours. MALDI-ToF analysis showed that the lower molecular weight fractions cyclic formation of long PBS sequences are favored during early stages of reactions. Poly(styrene-b-isobutylene-b-styrene) is currently used as the coating on the Taxus coronary (open full item for complete abstract)

Committee: Nic Leipzig (Advisor); Judit Puskas (Committee Member); Ge Zhang (Committee Member); Bi-min Newby (Committee Member); Donald Visco (Committee Member); Chrys Wesdemiotis (Committee Member) Subjects: Biochemistry; Biomedical Engineering; Chemical Engineering; Engineering; Health Care; Materials Science; Medicine; Nanoscience; Nanotechnology; Surgery

Doctor of Philosophy, University of Toledo, 2021, Engineering

Thermoplastic elastomers (TPEs) are a class of materials known for their low Young's modulus and high yield strain. Their applications range from adhesives and seals to automotive parts, footwear, and medical components. This dissertation aims to develop new applications for styrenic TPEs in areas of stimuli sensing and winter safety. First, TPEs with controlled volumetric shape change sensitive to heat and chemical vapors are developed through the concept of dynamic porosity. Dynamically porous films are developed mainly from poly(styrene-ethylene/butylene-styrene) (SEBS) using an eco-friendly CO2 manufacturing method. It is shown that omnidirectional pore size changes above a glass transition temperature (Tg) for polystyrene (PS) physical crosslinks (i.e. 125 °C), which imparts the films with a controlled pore density and a porous-to-solid transition (PST). The tunable PST at a specific temperature is also concomitant with an opaque-to-transparent transition (OTT) useful for indication/detection of temperature. The PST and OTT concepts were further exploited for developments of actuators and vapor responsive films. The second part of this dissertation describes the development of an unconventional and facile strategy for crafting dynamically porous TPEs with an ability to undergo a PST in response to applied mechanical contact pressure at ambient conditions. The PST is shown to be reversible for multiple cycles by applying an in-plane stretch on the activated non-porous films. The PST transition leads to a three orders of magnitude reduction of pore density, resulting in a strong OTT contrast, which can act as a visual indicator for pore reversion and re-generation. Finally, it is shown that the pore reversion can be exploited to locally control the films' mechanical and heat transfer characteristics. Given thousands of injuries involved with ice, sleet, or snow during winter, the development of surfaces with enhanced grip on such slippery surfaces would be deem (open full item for complete abstract)

Committee: Reza Rizvi (Advisor) Subjects: Engineering; Materials Science; Mechanical Engineering; Polymers

Doctor of Philosophy, Miami University, 2021, Chemistry and Biochemistry

Polymer synthesis and modification have become one of the key research areas in recent industrial development. Dynamic chemistry and photochemistry are two different aspects that could benefit polymeric materials to improve their properties. Photochemistry allows polymerization and modifications of thermal-sensitive monomers to be carried out under mild reaction conditions. Photochemical modifications such as photo-labile cleavages often aid preventing side reactions in reactive monomers and protect the fidelity of the polymers. A novel photolabile monomer, 2-{[(benzyloxy)carbonyl]amino}ethyl 2-methylprop-2-enoate (ONBAMA) was synthesized and explored the deprotection under different wavelengths of light. It was found that ONBAMA yield well-controlled polymers and they can be used in post-polymer modifications upon UV irradiation. Often photochemical reactions are carried out using external light sources such as lasers, LEDs, and UV lights. However, the limited penetration efficacy and reaction vessel geometries can limit the efficiency of photopolymerization and light-mediated modifications. The introduction of an internal light generation is an effective way of overcoming these limitations. In the second chapter, a bi-phasic system was introduced employing the chemiluminescence reaction in the bottom phase and photo-induced polymerization in the top layer as a new concept for using internal light sources in polymerization. Phenyl vinyl ketone (PVK) is known as a photo-responsive molecule. Due to the presence of the acetophenone subgroup, PVK is known to undergo Norrish-type reactions. PVK is known to undergo the Norrish type I process under blue light to generate radicals to initiate polymerization and the Norrish type II process to degrade the poly(PVK). The fourth chapter focuses on using the photoinitiation and degradation of the PVK monomers in synthesizing block polymers and photodegradable thermoplastic elastomeric materials respectively. Dynam (open full item for complete abstract)

Committee: Dominik Konkolewicz Dr. (Advisor); Scott Hartley Dr. (Committee Chair); Richard Taylor Dr. (Committee Member); Rick Page Dr. (Committee Member); Zhijiang Ye Dr. (Committee Member) Subjects: Organic Chemistry; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2019, Polymer Science

Research into rubber reinforcement using β-sheet nanocrystals in this dissertation is divided into two major parts: thermoplastic elastomer (TPE) and thermoset vulcanizate. The study of β-sheet nanocrystals reinforced thermoplastic elastomers starts from the β-alanine trimer grafted styrene-butadiene rubbers (SBR) with different grafting densities. The nanocrystals in these two samples are rod-like with the longest dimension of a few tens of nanometers. This is in contrast to the fibrous crystals observed in most of the synthetic segmented TPEs. The rod-like nanocrystals are highly effective in reinforcing the elastomers. High strength, and high extensibility are achieved simultaneously. The rod-like morphology observed in the above SBR and in other oligo(β-alanine)-grafted elastomers studied in the Jia laboratory was attributed to the high chain density of a layer of polymer brush covalently attached to the nanocrystal surface. To demonstrate this, β-alanine trimer-grafted polyisobutylenes with different chain densities on the crystal surface were synthesized in order to control the morphology of β-sheet nanocrystals. TEM and SANs were used to confirm the formation of fibrous and particulate crystals in the soft polyisobutylene continuous phase. The SANS data have provided direct evidence of the existence of a layer of brush-like chains on the surface of crystals. The differences in mechanical and dynamic mechanical properties of TPEs containing β-sheet nanocrystals with different morphologies are less significant than expected. The structure change of the nanocrystals during extension is significant, indicated by the hysteretic behaviors of the β-alanine trimer-grafted polyisobutylenes. Surprisingly, IR and DSC indicate a lack of obvious hydrogen-bond breakage and preservation of the β-sheet crystals when the elastomers are stretched to various tensile strains. A fracture recoil model is proposed to explain the reinforcing mechanism of β-sheet crystals. A few (open full item for complete abstract)

Committee: Li Jia (Advisor); Mark D. Foster (Committee Chair); Gary R. Hamed (Committee Member); Abraham Joy (Committee Member); Kevin Cavicchi (Committee Member) Subjects: Morphology; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2015, Polymer Science

Linear poly(styrene-b-isobutylene-b-styrene) (l-SIBS) and arborescent poly(styrene-b-isobutylene-b-styrene) (arb-SIBS) are a type of polyisobutylene-based thermoplastic elastomers (PIB-based TPE) characterized by an excellent mechanical, thermal and chemical stability, low permeability and excellent biostability and biocompatibility. PIB-based TPE are prepared by living carbocationic polymerization with sequential monomer addition which allows to obtain narrow molecular weight distribution and to synthesize a wide variety of architectures. These materials have been extensively used for biomedical applications, however they have a unique combination of properties, not available in any other TPE, that make them suitable for potential uses in other areas as well. This work reports the evaluation of three new potential technological applications for l-SIBS and arb-SIBS. In the first part of this work a new method for the preparation of a flexible piezoelectric polymer by incorporating a bent-core liquid crystal (BLC) in a PIB-based TPE, l-SIBS was shown. The polymer composite material containing 10 wt. % of BLC showed a piezoelectric charge constant d33 (~1 nm V-1) greater than commercially available piezoelectric ceramics. Small angle X-ray scattering (SAXS) results show that the liquid crystal–polymer composite becomes aligned during compression molding leading to macroscopic polarization without electric poling. In the second part of this work l-SIBS and arb-SIBS were sulfonated to prepare block copolymer ionomers. The materials were successfully sulfonated to various sulfonation degrees (SD), and characterized for water uptake and ionic conductivity. This modification significantly increased water uptake of both S-l-SIBS and S-arb-SIBS; the associated proton conductivity of the S-l-SIBS increased with the SD, however it did not rise at the desirable levels. For the S-arb-SIBS low values of proton conductivity were obtained, possibly due to the limited solub (open full item for complete abstract)

Committee: Judit E. Puskas Dr (Advisor); Gary R. Hamed Dr. (Committee Member); Mesfin Tsige Dr. (Committee Member); Darrell H. Reneker Dr. (Committee Member); Thein Kyu Dr. (Committee Member) Subjects: Materials Science; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2014, Polymer Science

Polyisobutylene due to its unique properties, such as exceptional chemical, oxidative and thermal stability, low gas permeability and biocompatibility (bioinert), is a widely used material in applications ranging from oil additives to biomaterials. The objective of this dissertation was to study the copolymerization of alloocimene, a renewable monomer, and isobutylene under the traditional butyl rubber polymerization conditions: H2O/AlCl3 initiating system in methyl chloride solvent at -95 °C. It was our hypothesis that polyalloocimene would lead to improved filler interaction. Our work led to the discovery of the first two-phase (emulsion) living isobutylene polymerization system, solving the problems associated with solution living isobutylene polymerization systems: the use of unique and commercially not available initiators, expensive coinitiator at high concentrations and poor heat transfer due to the high viscosity of the reaction mixture even at low polymer concentrations (15wt%). High molecular weight copolymers, Mn = 200,000 to 400,000 g/mol, with molecular weight distribution of Ð = 1.5 to 2.1, were prepared containing 9 to 30 wt% alloocimene at 80 to 90 % conversion. The copolymerization of alloocimene and isobutylene was found to be living up to 40 % conversion, or 6.5 minutes, resulting in a diblock polymer structure, consisting of a polyalloocimene-rich first block and a polyisobutylene second block. Tri- and tetrablock copolymers were prepared by sequential monomer addition technique. Both di- and multiblock structures showed thermoplastic elastomeric properties. This is the first example of a diblock copolymer thermoplastic elastomer. This is also the first copolymerization system allowing the preparation of tri- and tetrablock copolymer polyisobutylene-based thermoplastic elastomers using an inexpensive polymerization system. Diblock copolymers showed outstanding reinforcement with carbon black: the ultimate tensile strength increased from 2- (open full item for complete abstract)

Committee: Judit Puskas Dr (Advisor); Gary Hamed Dr (Committee Chair); Matthew Becker Dr (Committee Member); Mesfin Tsige Dr (Committee Member); Avraam Isayev Dr (Committee Member) Subjects: Polymer Chemistry; Polymers

PhD, University of Cincinnati, 2001, Arts and Sciences : Chemistry

This work focused on examining and characterizing the reinforcement of thermoset and thermoplastic elastomers, such as natural rubber, epoxidized natural rubber and elastomeric polypropylene. The reinforcement was achieved through the formation of composites of these elastomers with reinforcing fillers by applying some of the latest techniques. One of the techniques is the combination of elastomeric materials with thermosetting resins, specifically natural rubber and cardanol-formaldehyde resins, to improve mechanical properties, such as toughness and thermal properties, such as high-temperature resistance. The natural product cashew nut shell liquid was used to obtain the cardanol, which was then used to prepare cardanol-formaldehyde (CF) resole and novolak resins. The curing behavior of systems containing natural rubber and cardanol-formaldehyde resins was established. The incorporation of cardanol-formaldehyde resins into natural rubber provided significant improvements in tensile strength, while maintaining the thermal stability of the elastomer. Various nanocomposites of epoxidized natural rubber, cis-1,4 polyisoprene and elastomeric polypropylene were successfully prepared by using montmorillonite clays as a reinforcing filler. Conditions were established for dispersing clay nanolayers into these elastomers. The clay filler-elastomer and clay filler-filler interactions were studied by using dynamic mechanical analysis. Such interactions were found to strongly depend on the clay organic modifiers and the polarity of the elastomers was found to have a major effect on the final properties of these nanocomposites. The dispersion of clay fillers into the elastomer matrix was examined by X-ray diffraction techniques. Mechanical property measurements showed that several organo-clays provided very strong reinforcing effects. For non-polar elastomers, organo-modified clays were found to behave more like "carbon black". For polar elastomers, the intercalation of the ela (open full item for complete abstract)

Committee: Dr. James E. Mark (Advisor) Subjects: Chemistry, Polymer