Doctor of Philosophy, Case Western Reserve University, 2021, Materials Science and Engineering

Polymers are widely used in different industrial segments, such as food, automobile, chemistry, pharmaceutical, and aerospace. They are therefore ever-present in nearly all aspects of daily human life. Polymers are generally flammable and susceptible to ignition if they come into contact with a flame. Significant efforts have been made on the development of flame retardants in order to minimize the flammability impact of polymers on people and the environment. New approaches to reduce the flammability impact of polymers and make them more environmentally friendly are emerging. These include polymer nanocomposites, intumescent systems, char formers, polymer morphology modification, and additives found in natural renewable resources. Polybenzoxazines is a phenolic resin with molecular design flexibility known to have a highly char yield and low flammability. Flexible chemistry of benzoxazine allows developing benzoxazine with different structures to achieve the desired properties, all the while using greener material. Polybenzoxazine is very unique due to its intrinsically flame retarding nature. Chapter 1 will provide a broad overview of polybenzoxazine as well as general concepts of fire science. In Chapter 2, a detailed historical examination into the development of polybenzoxazines will be explored. A particular attention will be given to those adopted for flame retardation. Initially we will spotlight the use of classically known approaches then work forward and present more recent intrinsically flame retarded greener polybenzoxazines. In Chapter 3, an evaluation of the simple coating approach from a flame retardation point of view will be ascertained by evaluating how fire performs against the coated polyurethane foam. A unique green flame retardant nanocomposite has been developed. The nanocomposite is prepared using elastomeric benzoxazine as a matrix and a laponite as the filler. By using a single dip-coating, polyurethane foam is coated with a very thi (open full item for complete abstract)

Committee: Dr. Hatsuo Ishida (Committee Chair); Dr. Veronica Calado (Advisor); Dr. Márcio Nele (Committee Member); Dr. James Tien (Committee Member); Dr. Gary Wnek (Committee Member); Dr. Hatsuo Ishida (Advisor) Subjects: Aerospace Materials; Chemistry; Engineering; Materials Science; Organic Chemistry; Polymer Chemistry; Polymers

Doctor of Philosophy, Case Western Reserve University, 2021, Macromolecular Science and Engineering

Corrosion is a natural phenomenon that affects virtually every material, consumes billions of dollars annually worldwide and may result in catastrophic events. Coating is the most utilized technique to prevent corrosion. In this sense, epoxies are widely applied in all sectors of industry. Despite being high performance polymers, epoxies present issues, such as the use of toxic crosslinkers and long curing time. Benzoxazines are an emerging class of high performance self-curing thermosets. While typical monomers are based on mono- and difunctional derivatives, higher functional benzoxazines, prepared without using solvents, but purified with nontoxic solvents, are more desirable towards a greener synthesis of PBZ for high performance applications. Herein, we describe an environment-friendly approach to synthesizing a trifunctional benzoxazine from melamine, phenol, and paraformaldehyde. The chemical structure of the synthesized benzoxazine was confirmed by spectroscopic analyses, while the polymerization was monitored by thermal analysis. The synthesized xv benzoxazine monomer is, then, copolymerized with a commercial difunctional epoxy resin. We investigate the synergistic effect on improved thermal properties using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results showed that a glass transition temperature of up to 268 °C was obtained. A higher thermal stability was also achieved with an onset degradation of nearly 400 °C and char yield of 22 wt% at 800 °C. Later, the copolymer was combined with silica to produce anticorrosion coatings. Results revealed superhydrophobic surfaces with great scratch resistance and adhesion to steel substrate. Electrochemical test proved high effectiveness of the coatings as anti-corrosion barrier, with increasing performance with the incorporation of silica.

Committee: Rigoberto Advincula Dr (Advisor); Gary Wnek Dr (Committee Chair); José Roberto d'Almeida Dr (Advisor) Subjects: Materials Science; Polymers

Doctor of Philosophy, Case Western Reserve University, 2018, Macromolecular Science and Engineering

Polybenzoxazines are relatively new but already commercialized thermosetting resin. The material has already gathered much attention from not only academia but also industry field due to its superior properties than conventional phenolic, epoxy and bismaleimide resins. However, many people focus on working towards high performance material, much less work has been done on the fundamental study on understanding the vibrational structure, ring-opening kinetics of oxazine ring, which will be a great guidance on future molecular design and higher performance material, resins, composites. Chapter 1: In this chapter, the previous work and current research interest are covered, which leads to my research motivation for understanding the vibrational structure, ring-opening kinetics of oxazine ring and hydrogen bonding effects on fast polymerization of 1,3-benzoxazines. Chapter 2: In this chapter, the characterization band of benzoxazines and polybenzoxazines in FT-IR spectra is reassigned. Polymerization of benzoxazine resins is indicated by the disappearance of a 960-900 cm-1 band in infrared spectroscopy (IR). Historically, this band was assigned to the C-H out-of-plane bending of the benzene to which the oxazine ring is attached. This study shows that this band is a mixture of the O-C2 stretching of the oxazine ring and the phenolic ring vibrational modes. Vibrational frequencies of 3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazine (PH-a) and 3-(tert-butyl)-3,4-dihydro-2H-benzo[e][1,3]oxazine (PH-t) are compared with isotope-exchanged and all-substituted compounds. Deuterated benzoxazine monomers, 15N-isotope exchanged benzoxazine monomers, and all-substituted benzoxazine monomers without aromatic C-H groups are synthesized and studied meticulously. The various isotopic-exchanges involved deuteration around the benzene ring of phenol, selective deuteration of each CH2 in the O-CH2-N (2) and N-CH2-Ar (4) positions on the oxazine ring, or simultaneous deuteration (open full item for complete abstract)

Committee: Hatsuo Ishida Dr. (Advisor); Gary Wnek Dr. (Committee Member); Lei Zhu Dr. (Committee Member); Daniel Lacks Dr. (Committee Member) Subjects: Chemistry; Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2016, Polymer Engineering

We investigated the effects of polymerization conditions, such as temperature, the polarity of the solvents, and microscale confinement during sol-gel transition, on the microstructure and physical properties of the resultant polymer aerogels. This work includes two main parts. (1) Studies of properties and formation mechanism of polybenzoxazine aerogels showing spherical and cylindrical building blocks; (2) Evaluation of properties of the aerogels obtained from the gel precursors synthesized in an oil-in-oil emulsion and a macroporous polymer host, in comparison to the normal aerogel monoliths. In the first part (Chapter III & Chapter IV), p-toluenesulfonic acid (TSA) was used as the catalyst for cationic ring opening polymerization of benzoxazine to produce polybenzoxazine (PBZ) aerogels. The PBZ aerogel building blocks (spheres vs. strands) and pore surface area show strong dependence on the solvent and the gelation temperature. The use of dimethyl sulfoxide (DMSO) and dimethylacetamide (DMA) led to spherical particle networks while fibrillar networks were obtained using N-methyl-2-pyrrolidone (NMP). In order to thoroughly understand the formation of these two types of networks, a combination of dynamic light scattering (DLS) and static light scattering (SLS) was used to monitor the growth of polymer networks during polymerization. The light scattering results revealed that polymer networks formed via nucleation and growth mechanism. In addition, the shape of building blocks was found to be associated with the concentration of the nuclei and the gelation time. In DMSO, a higher concentration of nuclei resulted a fast crowding of the building blocks that constituted the gel network. However, at low concentration of the nuclei and at long gelation times, the spherical building blocks evolved into cylinders by self-assembly and formed a fibrillar network when NMP was used as the solvent. Originally, the differences in the concentration of nuclei were due to the (open full item for complete abstract)

Committee: Sadhan Jana PhD (Advisor); Younjin Min PhD (Committee Chair); Bryan Vogt PhD (Committee Member); Li Jia PhD (Committee Member); Jiahua Zhu PhD (Committee Member) Subjects: Polymers

Doctor of Philosophy, Case Western Reserve University, 2014, Chemical Engineering

A novel class of biobased cross-linked polymers combining the molecular structure of both chitosan (CTS) and polybenzoxazine (PBZ) is synthesized via blending in aqueous media. The benzoxazine precursors, main-chain type benzoxazine polymer and star-like telechelic benzoxazine, are synthesized through Mannich condensation reaction of phenols and primary amines, in the presence of either formaldehyde or paraformaldehyde. Synergistic improvements in the thermal and mechanical properties of biobased cross-linked polymers are observed due to presence of oxazine-ring which provides more crosslinking density. Furthermore, utilization of these newly developed crosslinked polymers in adsorption of CO2 has been investigated. Various nanocomposite aerogels have been fabricated using either sodium montmorillonite (Na-MMT) or graphene oxide (GO), and their carbon aerogels (CAs) show superior CO2 adsorption capacity. Firstly, new nanocomposite aerogels have been synthesized from clay-reinforced CTS/polybenzoxazine via freeze-drying. Scanning electron microscopy is used to verify that the addition of clay leads to layered structure in the hybrids. Carbonization of the developed aerogels was performed to increase the surface area and to enhance the structure of the aerogels. Combination of Na-MMT in the cross-linked polymers increases the CO2 adsorption capacity from 2.1 mmol g-1 to 5.7 mmol g-1, depending on the benzoxazine concentration. The Freundlich isotherm model provides a good fit of the adsorption data with hybrid aerogels. Secondly, CTS/GO monoliths show an increase in the adsorption capacity of CO2 from 1.92 to 3.48 mmol g-1 with 10 wt% GO at ambient conditions. Doubling the concentration of GO from 10 to 20 wt% increases the adsorption capacity only 20 %. To improve this system, hybridization of the two different cross-linked polymers with 10 wt% GO is applied to develop novel nanocomposite aerogels. Significant enhancements in the mechanical and thermal propertie (open full item for complete abstract)

Committee: Syed Qutubuddin Dr. (Advisor); Hatsuo Ishida Dr. (Advisor); Chung-Chiun Liu Dr. (Committee Member); R. Mohan Sankaran Dr. (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, Case Western Reserve University, 2014, Chemical Engineering

Polymeric surfactants attracted considerable attention in recent years for applications such as personal care product and stabilization of emulsions and suspensions. The characteristic properties of polymeric surfactants originate from the formation of aggregates through the association of the hydrophobic alkyl chains in aqueous solution, within a narrow concentration range. The aggregates are called micelles, and the narrow concentration range above which micelles are formed in the solutions is called the critical micelle concentration (cmc),. The characteristics of micelles are easily controlled by changing the solution conditions such as temperature, concentration and ionic strength, and by changing the surfactant properties such as chain length, hydrophobic volume and head group area. In present work, a novel platform of anionic polymeric surfactants, poly(4HBA-oca-Na+), poly(4HBA-dea-Na+), and poly(4HBA-doa-Na+), has been synthesized by polymerizing benzoxazine monomers that are synthesized by reacting an aliphatic amine of variable chain length (C8, C10 and C12), with 4-hydroxybenzoic acid and paraformaldehyde. The structures of the monomers and polymeric surfactants are confirmed by NMR and FTIR. The ring-opening polymerization and thermal behavior of the benzoxazine monomers are studied by DSC and TGA. Size exclusion chromatography (SEC) coupled with Viscotek triple detection technique is used to characterize the molecular weight distribution of polybenzoxazine surfactants. The influence of the structure on the surface activity is investigated by measuring the surface tension of aqueous solutions of the polymeric surfactants using the Wilhelmy plate method. The tensiometry results indicate that the adsorption at the air/water interface is similar for the octylamine, decylamine and dodecylamine-based surfactants. Increasing the alkyl chain length from C8 to C12 does not significantly affect the surface tension at the critical micelle concentration ( (open full item for complete abstract)

Committee: SYED QUTUBUDDIN (Advisor); DANIEL LACKS (Committee Member); MOHANN SANKARAN (Committee Member); HATSUO ISHIDA (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, Case Western Reserve University, 2013, Chemical Engineering

A new class of high-performance resins combining the molecular structure of both traditional phenolics and benzoxazines is developed. The monomers are synthesized through Mannich condensation reaction of methylol-functional phenols and primary amines, in the presence of paraformaldehyde. The network structure is built utilizing simultaneous addition and condensation polymerization through benzoxazine and resole chemistry. The presence of methylol groups accelerates the polymerization with improved thermal properties of the produced polymer. The polymers show high glass transition temperature, Tg (274-311°C) and excellent thermal stability compared to the traditional polybenzoxazines. The non-isothermal DSC analysis using Kissinger and Ozawa methods show that polymerization reactions of methylol monomer exhibits lower apparent non-elementary activation energy (83.6 and 93.5 KJ/mol) compared to the unfunctionalized monomer (94.1 and 101.4 KJ/mol). The thesis shows an optimum solution to overcome the historic limitations of using phenolic/urethane materials. The limitations include the slow reaction kinetics of the isocyanate and phenolic compounds along with poor thermal stability of the produced urethane linkages. The new approach is based on reacting methylol benzoxazines with isocyanates and polyols to form polybenzoxazine/polyurethane copolymers. The incorporation of benzoxazine in the copolymer shifted the decomposition temperature to (285-300 °C) with char yield of (18-53%), depending on the benzoxazine content. In addition, the thesis deals with the preparation of high thermally conductive coating for electronic components. For this purpose, boron nitride nanosheet (BNNS) is used as a model system to be dispersed in benzoxazine monomer. Composite of the commercial BN embedded into methylol benzoxazine monomer was used as a control. BNNS systems exhibit higher thermal conductivity values than the BN systems. The SEM images show that dispersion and distributio (open full item for complete abstract)

Committee: Syed Qutubuddin Dr. (Advisor); J. Adin Mann Dr. (Committee Member); R. Mohan Sankaran Dr. (Committee Member); David Schiraldi Dr. (Committee Member) Subjects: Chemical Engineering

Master of Science in Polymer Engineering, University of Akron, 2009, Polymer Engineering

Shape memory polyurethanes (SMPUs) have attracted much attention from academic and industrial researchers due to strong potential in biomedical and consumer applications. Some of the limiting factors of these materials are low recovery stress (RS) and shape recovery (SR). Fundamental studies have focused on the improvement of RS and SR values using primarily two approaches. The first utilizes the nanocomposite route by which a few weight percentages of nanofillers are added to SMPU in order to increase the modulus and consequently to obtain enhancement in recovery stress. Although successful in the case of SMPU with amorphous soft segments, the nanofillers caused reduction in crystallinity of crystalline soft segment leading to deterioration of shape memory properties of SMPUs. In the second approach, chemical additives are added which either chemically bond with SMPU chains or form a separate phase and offer much stronger modulus than the soft and hard segments of SMPU. This second approach was followed in the current study.Polybenzoxazine (PB-a) was incorporated into a thermoplastic polyurethane (PU) formulation, anticipating that it would play a similar role to hard segment and improve the shape memory properties. It was found that benzoxazine monomer formed miscible blends with the prepolymer derived from 4,4'-methylenebis (phenyl isocyanate) (MDI) and poly (tetramethylene) glycol (PTMG) with average molecular weight of 650 g/mol. This allowed chain extension of prepolymer using 1,4-butanediol (BD) as in the synthesis of regular polyurethanes. The benzoxazine was later polymerized into polybenzoxazine (PB-a) by thermal curing at 180 °C in 3 hrs. The results of this study showed that both RS and SR increased with the addition of benzoxazine. A specimen with 17 wt. % benzoxazine produced the best RS and SR values with 13 MPa and 93%, respectively compared to RS of 6.8 MPa and SR of 72% for polyurethane. The deformation conditions were also found to exert significa (open full item for complete abstract)

Committee: Sadhan Jana PhD (Advisor) Subjects: Polymers