No description available.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 109-112). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 109-112). Also available on the Internet.

No description available.

Recycling is one of the most important strategies for combating plastic pollution. However, before plastic waste can be converted into other items, the different types of plastic present in it must be sorted, a time-consuming and expensive process. Indeed, it is often more cost-effective to manufacture new plastic materials than to recycle existing plastic waste. Researchers are therefore attempting to eliminate the sorting process altogether and directly recycle the mixed plastic waste. While this would lead to phase-separated mixtures with temporally evolving domains and poor fracture toughness properties, these problems could be mitigated to some extent by incorporating surfactant-like macromolecular compatibilizers, such as block copolymers or random copolymers (RCPs). These compatibilizers preferentially localize at polymer/polymer interfaces, lowering droplet coalescence and interfacial tension in the process. Moreover, the macromolecular structure of these compatibilizers enables them to form entanglement networks across the interface, thus enhancing stress transfer and fracture toughness. Nanoparticle (NP)-based compatibilizers have recently attracted attention due to their significantly stronger suppression of droplet coalescence under certain conditions. Unfortunately, while these compatibilizers work relatively well in oil/water emulsions, they perform poorly in immiscible polymer blends. This is because most polymer blends consist of hydrophobic components, making the NPs gravitate toward one of the bulk phases rather than the interface. Moreover, their rigid cores function as stress concentrators in polymer matrices, causing further deterioration to the fracture toughness properties of the blend. In this dissertation, we construct hybrid compatibilizers consisting of NP cores and outer grafted polymer layers. In this manner, the desired features of both macromolecules and NPs are combined into a single compatibilizer: the NP cores suppress droplet coalescence, while the polymer grafts direct the NPs to the interface and form entanglements. We investigate the effectiveness of these hybrid compatibilizers in three critical areas: NP localization control, droplet coalescence suppression, and fracture toughness enhancement. In each area, we perform systematic studies using an immiscible polymer blend composed of poly(methyl methacrylate) (PMMA) and polystyrene (PS) in order to find the optimal compatibilizing effect as a function of graft chemistry, graft molecular weight, and grafting density. We demonstrate that the most efficient hybrid compatibilizers are those with a surfactant-like architecture. For example, silica NPs sparsely grafted with PS chains can form a dense monolayer packing at the immiscible PMMA/PS interface. In this example, surfactancy is derived from a balance of enthalpic interactions: the silica core strongly interacts with the PMMA phase, while the PS grafted layer mixes intimately with the PS phase. The hydrophilic–lipophilic balance is readily controlled by varying the contact area of each interaction through the grafting density or the graft molecular weight. Similarly, we show that silica NPs grafted with surfactant-like polymer chains, such as styrene–methyl methacrylate RCPs, can also localize at the PMMA/PS interface. Here, surfactancy is derived mainly from the RCP grafts. There are two advantages to using RCP grafts. First, it allows for interfacial localization even if the grafted layer completely encapsulates the silica core (i.e., at high grafting densities). Second, RCP grafts can entangle on both sides of the interface and thus transmit stress more efficiently than PS grafts, which only entangle on the PS side of the interface. There are two advantages to using this latter approach. First, RCP grafts can entangle on both sides of the interface and thus transmit stress more efficiently than PS grafts, which only entangle on the PS side of the interface. Second, it allows for interfacial localization even if the grafted layer completely encapsulates the silica core (i.e., at high grafting densities). Our research shows that both forms of hybrid compatibilizers significantly outperform conventional ungrafted macromolecular compatibilizers in droplet coalescence suppression. Interestingly, coalescence can be suppressed even when the hybrid compatibilizers only partially cover the dispersed droplets. We believe that this is due to the grafted layers forming strong entanglement networks around the droplets that function as barriers to coalescence. Linear rheology experiments corroborate this reasoning: the low-frequency storage moduli of the compatibilized blends approach a plateau when the NP grafting density is increased, suggesting the presence of a network structure at the interface. For fracture toughness experiments, we employ RCP-grafted NPs to exploit their entanglement on both sides of the interface. We show that when a moderate grafting density is used, the fracture toughness of the PMMA/PS interfaces exceeds that of the interfaces compatibilized with ungrafted RCP analogs. This again results from the brush entanglement network at the interface. Specifically, in the moderate grafting density zone, RCP brushes form a more connected entanglement network than ungrafted RCPs and are thus more efficient at transmitting stress across the interface. In summary, we have developed a method for accurately controlling the localization of NP-based compatibilizers in immiscible polymer blends. We have also identified the grafting conditions under which these hybrid compatibilizers outperform conventional macromolecular compatibilizers in both droplet coalescence suppression and fracture toughness enhancement.

Additive manufacturing provides unmatched control and diversity over structural design of polymeric, ceramic and metallic parts. Nevertheless, until recently, the toolbox of polymeric feedstocks for light based additive manufacturing limited employment of printed parts for applications necessitating high thermomechanical performance. Development of synthetic pathways permitted the first additive manufacturing of high performance poly(amide imides) via ultraviolet assisted direct ink write (UV-DIW) printing. Precursor resins exhibited prerequisite rheology and reactivity for UV-DIW and produced organogels were well-defined and self-supporting. Thermal treatment induced drying and imidization of the precursor organogels to form the desired poly(amide imide) structures. During post-processing the parts displayed linear isotropic shrinkage as low as 26% and exhibited competitive thermomechanical properties. Following expansion of the high performance backbones available for additive manufacturing, simplification of synthetic rigors was undertaken. This investigation facilitated the evolution of the first photocurable and processable small molecule polyimide precursors. These supramolecular carboxylate ammonium nylon salts, coined polysalts, allowed for additive manufacturing of both high performance polyimides and polyetherimides using vat photopolymerization (VP). The use of small molecule precursors over previously investigated polymeric precursors displayed much lower solution viscosities yielding reduction of organic solvent loading, inducing lower overall shrinkage. Polysalts provide a stimulating platform for rapid and facile printing of high performance polyimides in the future. Surveying the excellent carbonization behavior for aromatic polyimides spurred translation of known 2D protocols to post-processing of printed polyimides. Applying pyrolysis methodologies to parts produced using VP and UV-DIW induced efficient carbonization at 1000 °C. Remarkably, the carbonized parts retained structure and did not display cracks or pore formation. Raman spectroscopy indicated production of disordered carbon via the utilized pyrolysis protocol, in line with literature on carbonization of PMDA-ODA polyimide at 1000 °C. Electrical testing indicated production of conductive materials following pyrolysis, with carbonization temperature modulating the performance. The excellent thermal stability, transport properties, and known mechanical performance of carbonaceous materials may enable application of these printed objects in customized electronics and aerospace environments. Exploration of drop-in monomeric units permitted a multi-pronged research program into augmentation of mechanical, rheological and transport properties of high performance polyetherimides (PEIs). Installation of sodium or lithium substituted disulfonated monomers via classical two-step polyimide synthesis afforded two series of sulfonated polyetherimides (sPEI). The sPEIs exhibited robust thermal properties, with high sulfonate mol% inducing Tg > 300 °C. X-ray scattering experiments revealed the development of domains via inclusion of the sulfonate moieties, with low mol% producing larger domain spacing. The larger domains present in the low mol% sPEIs yielded improved ionic liquid uptake within 2 d, yielding improved ionic conductivities at room temperature relative to high mol% samples. The observed conductivities indicated potential of the sPEIs as battery electrolytes, but further ionic liquid incorporation is required for competitive performance. Development of a poly(ethylene glycol) (PEG) bearing macromonomer facilitated synthesis of PEIs and PI graft copolymers. When coupled with 4,4'-(4,4'-isopropylidene-diphenoxy)diphthalic anhydride (BPADA) and meta-phenylene diamine (mPD), the PEG-grafted materials exhibited signs of phase mixing at low mol% incorporation of macromonomer, with a single observable Tg depressed from neat BPADA-mPD. Doping of the PEI-g-PEG with lithium salts allowed for production of polymeric films that displayed good ionic conductivities at room temperatures. Extension of the PEG macromonomer into fully aromatic PIs yielded phase separated materials even at modest loadings, >2.5 mol%. The formed PEG-g-PMDA-ODA contained thermally stable PI main-chains with thermally labile graft chains, which when thermally treated induced facile quantitative PEG removal. Remarkably, the thermally treated materials retained flexibility, even at >60 wt.% PEG removal. Further investigations aim to explore use of novel PEIs in energy storage as well as low density and dielectric materials. / Doctor of Philosophy / High performance polymers enjoy wide use in microelectronics and aerospace industries due to high thermal stability and excellent mechanical performance. However, processing restrictions hinder manufacturing of 3-dimensional objects of many high performance polymers suitable for extreme environments. Additive manufacturing, also known as 3D printing, has garnered attention in both academic and industrial settings over the last four decades due to the unmatched control over part design and internal structure, but the material arsenal for additive manufacturing of polymers lacks options for applications demanding high thermal stability. The first half of this dissertation aimed to promote translation of high performance polymeric chemistries to suitable feedstocks for additive manufacturing. By designing and developing novel chemical pathways, traditional processing limitations were circumvented and high performance polymers, such as poly(amide imides) and polyimides, were successfully processed via light based additive manufacturing. Likewise, by investigating carbonization dynamics of polyimides and expanding current additive manufacturing techniques for processing of fully aromatic polyimides, complex 3D carbonaceous materials were obtained. These carbon objects present extreme thermal stability and electrical conductivity, advantageous for aerospace and electronic industries. Additionally, investigations allowed for development of synthetically facile routes for expanding the available polyimide backbones for additive manufacturing via use of small molecule precursors. The second half of the dissertation explored novel polyetherimide and polyimide reagents for production of functional materials. Harnessing ionic building blocks permitted synthesis of a series of thermally robust polyetherimides displaying promise for energy storage. Similarly, coupling previous literature for ion conduction in solid polymer electrolytes for battery applications with thermally stable and flame resistant polyetherimides enabled synthesis of a series of innovative graft copolymers with good room temperature ionic conductivities. Lastly, pairing of thermally labile polymers with thermally resistant polyimide backbones allowed for development of an exciting platform for obtaining highly insulting and flexible films for electronics applications. Outlined future work aims to probe the formation of pores in the obtained polymer

Novel perfectly alternating segmented copolymers containing imide junction points were synthesized via terminal amine-anhydride coupling from poly(dimethylsiloxane)s and either poly(arylene ether)s or polyimides. The copolymers were characterized in solution and the solid state. The -(-A-B-)-n architecture and molecular design of these linear systems afforded thermodynamically microphase separated systems which gave rise to interesting copolymer properties. Each controlled molecular weight oligomeric segment, or homopolymer, was initally synthesized with reactive endgroups and fully characterized prior to copolymerization. Thus, anhydride-terminated poly(dimethylsiloxane)s were prepared via cationic ring-opening polymerization in the presence of a "monofunctional" bis-norbornane anhydride disiloxane endcapping species. Aromatic amine-terminated engineering thermoplastics were synthesized through either nucleophilic aromatic substitution in the presence of a “monofunctional” aminophenol endcapper (as for poly(arylene ether ketone)s and poly(arylene ether sulfone)) or by solution imidization using a controlled excess of the diamine monomer. A solution imidization method was developed for the segmented copolymerization that simplified the typically two-step, two-solvent method into a one-step approach with a single solvent. Thus, a previously described condensation catalyst, 2-hydroxypyridine, was utilized which was demonstrated to be essential in obtaining high molecular weight copolymers. These segmented copolymers generally were fibrous and highly soluble in many common organic solvents. Creasable, transparent, solution-cast films were readily prepared. Thermal and morphological analyses demonstrated that the copolymers exhibited phase separation, and displayed lower and upper Tg's as a result of the two components employed. At short hard block lengths, uper Tg's were somewhat depressed, implying partial miscibility. / Master of Science

Over the years there have been many studies on the theoretical and phenomenalogical aspects of starblock, di- and tri-block copolymer systems with very narrow molecular weight distributions. However, in many real multiblock systems the effect of such variables as; chemical composition distribution, molecular weight distribution and block architecture, among others, are not very well understood. The key to gaining a better understanding of these systems lies in the use of synthetic and process controlled variables. Seven different systems were used to study the effect of various synthetic and process controlled variables. The poly(butene sulfone) (PBS)-polydimethylsiloxane (PDMS) graft copolymers were synthesized by a free radical technique which involves the terpolymerization of butene, SO, and hexenyl functionalized polydimethylsiloxane macromonomers. The surface and bulk morphologies of a series of PBS-g-PDMS compolymers with 1, 5, 10, and 20K PDMS graft molecular weights at 5 and 20Wt.% PDMS incorporation. Additionally, for each graft molecular weight and at each composition, copolymers with a low and a high degree of polymerization of the PBS backbone were analyzed. A two phase morphology was found to exist with PDMS domain size increasing with increasing PDMS graft length. The type of morphology observed was dependent on PDMS composition, and in some cases the degree of polymerization and average number of grafts/backbone. These factors were also found alter the nature of the surface morphology and the related surface properties. The effect of PDMS segment molecular weight, the chemical nature of the polyimide segment, the procedure used to imidized the polyimide and processing conditions on the structure-property relationships in a series of polyimide-PDMS containing approximately 15Wt.% PDMS was studied. It was determined that as the polarity of the polyimide segment increased the morphology shifted to texture with lower surface/volume ratios. Casting the copolymers from an NMP solution favored a more discrete morphology than the thermally treated compression molded samples. The modulus was found to increase as the degree of phase separation increased with increasing PDMS segment size at constant composition. In addition, the solution cast films were found to have a higher modulus than the compression molded analogs. The morphology of a series of methacrylate based block ionomer was investigated. The effect of ionic block length, the architecture of the segments, and variations in the nature of ionic group were studied. SAXS revealed the presence of multiple scattering maxima in the dilbock materials. Both highly ordered and disordered region were observed from TEM analysis. The observed spacing from TEM measurements and SAXS were in good agreement. The interdomain spacings between the ionic domains were found to be a strong function of ionic block length. / Ph. D.

During the past few years, studies involving the synthesis, characterization, and structure-property relations of especially well-defined or "model" block and graft copolymers have received increasing interest among academic and industrial communities. The well-defined nature of such polymers makes them ideal subjects for both fundamental studies and specialty polymer applications. This study addresses the synthesis and characterization of well-defined block and graft copolymers through the use of reactor systems and permeability instrumentation designed specifically for this purpose. The engineering design, construction, operation, and in some cases automation of the above instrumentation is discussed in detail. Examples of the synthesis and permeability characterization of several especially interesting multiphase graft and star block copolymers are provided to demonstrate the utility of the instrumentation described. The primary focus of this work has been to address the effects of varying degrees of microphase separation and morphological development on the physical properties of well-defined block and graft copolymers and their hydrogenated derivatives. The application of gas permeability as an especially sensitive probe of morphology in well-defined poly(methylmethacrylate) -poly(dimethylsiloxane) graft copolymers has been given special emphasis. The synthesis these graft copolymers has been accomplished by the copolymerization of model, methacrylate-functional, poly(dimethylsiloxane) CPDMS) "macromonomers" with methylmethacrylate, using conventional free-radical and novel anionic and group transfer techniques. These techniques are described and referenced with chemical characterization provided. The resulting graft copolymers have PDMS-modified surface and bulk morphologies that dominate particular physical property responses and provide for interesting structure-permeability studies. The characterization of these copolymers to demonstrate their well-defined nature has been performed with a focus on the application of gas permeability as an especially sensitive morphological probe. A review of the relevant literature is followed by detailed experimental procedures, a summary and discussion of results, and descriptive appendices. The appendices include details concerning the design, fabrication, and automation of instrumentation to perform volumetric, equilibrium sorption experiments and computer programs for the acquisition and analysis of permeability data. / Ph. D.

The synthesis of novel well defined graft copolymers is now possible with the recent advent of the macromonomer technique. Copolymers with narrow molecular weight distributions of the backbone as well as the grafts are possible. The anionic alkyl- lithium initiated ring opening polymerization of the hexamethylcyclotrisiloxane has been investigated to prepare polymers of controlled molecular weights and narrow molecular weight distributions. This technique was extended to the preparation of macromonomers and from these macromonomers the synthesis of graft copolymers. These siloxane macromonomers were then incorporated into acrylic and styrenic copolymers via free radical and anionic techniques. A series of graft copolymers were characterized by a variety of methods. The resulting copolymers exhibit interesting thermal properties dependent on graft molecular weight and composition. Well-defined morphologies were observed by TEM analysis, indicative of the unique structures prepared. Graft copolymers offer unique possibilities of structure property relationships, often forming two phase morphologies that give rise to properties of both constituents. This allows the preparation of polymers designed to give optimal characteristics. / Ph. D.