No description available.

No description available.

Changes in the crystallite size distribution during the isothermal crystallization of linear polyethylene fractions were studied using low frequency Raman spectroscopy. Increases in the crystallite size and broadening distributions were observed as a function of time for all molecular weights studied. Large increases in size occurred even after most of the isothermal crystallinity had formed. The rate of increase was faster for higher crystallization temperatures, while the process was retarded for higher molecular weights. The existing theories for crystallite thickening were found to be insufficient to explain all of the experimental results. These experimental observations could be rationalized if the thickening occurred by a partial melting process. The observed increases in thickness were found to correlate very well with increases in calorimetric melting points. The extrapolation of this thickness-melting point data to obtain an equilibrium melting point was complicated by the possibility of changes in the crystallite's surface free energy. The use of melting temperature-crystallization temperature plots was found to be a better method of extrapolation. The best estimate of the equilibrium melting point of polyethylene was determined to be 146(DEGREES)C. / Source: Dissertation Abstracts International, Volume: 44-06, Section: B, page: 1847. / Thesis (Ph.D.)--The Florida State University, 1983.

Source: Dissertation Abstracts International, Volume: 37-12, Section: B, page: 6164. / Thesis (Ph.D.)--The Florida State University, 1976.

In my PhD polymer microarrays have been central in discovery of new materials for cardiovascular repair, cartilage tissue engineering and bacteria resistant medical devices. This has led to the work described in the following four chapters of my thesis. In the first part of my thesis polymers for the development of novel heart valve leaflets were identified. Diseased heart valves are currently replaced with the either synthetic or bioprosthetic (acellular xenografts) valve prostheses. While synthetic prosthesis have excellent durability, thromboembolic complications are frequent, requiring patients to undergo lifelong anti-coagulation therapy. On the other hand, the leaflets of bioprosthetic valves undergo structural deterioration, resulting in the patients having to undergo follow-up replacement surgeries. In order to overcome these shortcomings, the aim of this part of my PhD was to discover polymers that will enable the development of a ‘bio-synthetic’ heart valve, with the durability of synthetic valves and the biocompatibility of bioprosthetic vales. Polymers that bind valve interstitial cells (cells with a plastic fibroblast / myofibroblast phenotype that renew the extracellular matrix components of the valve leaflets) and also enable stable expression of key markers were identified. Immunohistochemistry and RNA expression analysis identified polymers for coating 3-D scaffolds, with the coated scaffolds showing excellent cell invasion, viability and maintenance of valve interstitial cell markers. To mimic the regions of the valve leaflets with differing stiffness, the response of valve interstitial cells to substrate stiffness was studied with various crosslinked gels. Thus, polymeric gels, prepared with the same chemical composition but with different Young’s modulus (covering 3 orders of magnitude) showed valve interstitial cell attachment with the cells showing differing behaviour based on the stiffness of the gels. In the second part of this thesis, polymers were identified for cartilage repair. Hyaline articular cartilage has very low potential for self-renewal, therefore cell-based therapies with autologous chondrocyte implantation are desired. Due to limited availability from biopsies, chondrocytes have to be expanded by in vitro culture; and fully defined synthetic culture substrates are essential for regulatory approvals. Using the high throughput approach I identified ‘hit’ polymers that allowed adhesion, proliferation and long-term culture of primary human chondrocytes and also chondrocytes derived from Mesenchymal stem cells. 2-D scale-up identified 2 lead polymers that supported long-term attachment and maintenance of chondrocyte markers. Since prolonged monolayer culture is known to induce loss of chondrocyte phenotype (dedifferentiation), 3D versions of the polymers were prepared and their potential for their long-term maintenance of chondrocytes via immunohistochemistry and RNA expression was demonstrated. The 3D gels were also used to encapsulate chondrocytes and their long-term maintenance of phenotype within these matrices, offers the exciting possibility of using these matrices for cartilage regeneration. The third part and fourth parts of the thesis focussed on reducing medical device associated infections. Thus polymers identified that prevented binding of a variety of bacteria including clinical isolates from infected medical devices, were used to coat two commercially available central venous catheters resulting in up to 96% reduction in bacterial binding. This non-binding was enhanced by the generation of polymeric nanocapsules containing the anti-bacterial eugenol (or its natural source clove oil). A coating consisting of eugenol nanocapsules entrapped within an interpenetrating network of the best bacteria repellent polymer, allowed slow-release of eugenol and further improved its performance.

Polyimides are a family of heterocyclic polymers that have received extensive evaluation as adhesives, fibers, films, moldings, composite matrices, insulators, coatings, membranes, and resists. their outstanding thermal stability, excellent mechanical and electrical properties, and chemical resistance make them attractive for many applications.;This research developed ether-containing polyimides for three applications: liquid crystalline polyimides as processing aids, polyimides for microelectronic applications, and polyimides for harsh environments. The approach consisted of three primary activities: (1) developed novel diether dianhydrides for polyimide fabrication, (2) designed, characterized, and evaluated polyimide architectures based on the material application requirements, and (3) provided extensive structure-property relationships utilizing a number of unique groups in the polymer backbone and their contributions to the resultant polymer features.;Several novel extended diether dianhydrides were synthesized. When these flexible dianhydrides were combined with rigid diamines, an alternating flexible/rigid polymer backbone resulted and hence the potential was created for liquid crystallinity. Other favorable components of liquid crystallinity, such as flexible spacers, rigid groups, and bulky groups, were incorporated into these novel dianhydrides and polymers therefrom. The potential liquid crystalline polyimides developed exhibited crystallinity and other desirable properties, but data were inconclusive regarding their liquid crystallinity. Extensive knowledge was gained in the synthesis of novel dianhydrides and their precursors. Additionally, structure-property relationships based on a variety of novel dianhydride moieties resulted.;High performance polymer film and coating materials are increasingly being used by the electronic circuit industry. Electrical behavior is critical for polymers used in these applications. Materials are needed with substantially lower dielectric constants. Fluorinated dianhydrides and polyimides therefrom were synthesized to achieve lower dielectric constants. Additionally, a series of polyimide copolymers were developed for use as semi-conductor stress relief layers, interlayer dielectrics, and encapsulants. Several combinations were achieved that optimized mechanical, physical, and chemical properties required for the applications.;Polyimides for use in harsh environments evaluated new and existing polyimides through physical, mechanical, and chemical means to determine possible substitutes for wire and cable insulation. These candidates have other utility in applications requiring hydrolytic stability. Also, squaric acid containing polyimides were developed and evaluated for potential space applications. These polyimides exhibited a combination of attractive properties, especially their resistance to the radiation component of geosynchronous orbit.

High-field {dollar}\sp{lcub}13{rcub}{dollar}C and {dollar}\sp1{dollar}H NMR spectroscopies were used to investigate some unusual features of the molecular microstructure of poly(vinyl chloride) (PVC).;Several model monochloroalkenes were synthesized in order to determine {dollar}\sp{lcub}13{rcub}{dollar}C shift increments for the replacement of H by Cl at positions that are near an isolated internal double bond. These increments then were used to predict the {dollar}\sp{lcub}13{rcub}{dollar}C shifts of the internal allylic chloride structure in PVC. The predictions were not satisfactory, because, as expected, the increments were not additive.;It was shown that during conventional VC polymerization, the chloroallylic chain end (-CH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}Cl) does not copolymerize with the monomer and is not destroyed by a mechanism involving allylic rearrangement, macroradical addition, and chlorine-atom {dollar}\beta{dollar}-scission to produce a -CHClCH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}CHCl- structure. Nevertheless, that mechanism was found to operate during the preparation of a special type of PVC (made at 0{dollar}\sp\circ{dollar}C with (t-Bu){dollar}\sb2{dollar}Mg initiation) which contained the rearranged chain end, -CH{dollar}\sb2{dollar}-CHClCH=CH{dollar}\sb2,{dollar} at an abnormally high concentration.;During the preparation of PVC under subsaturation VC pressures, small amounts of a 1,3-di(2-chloroethyl) branch structure were found to be formed by a "double backbiting" mechanism involving two intramolecular H abstractions in succession. The presence of this structural defect was established by the 125.77-MHz {dollar}\sp{lcub}13{rcub}{dollar}C NMR spectra of reductively dechlorinated PVC specimens. at 55-80{dollar}\sp\circ{dollar}C, the two backbites leading to the defect differ substantially in relative rate, in that the backbiting:addition rate ratio is larger for the second backbite by a factor of 15-16, irrespective of temperature. No evidence was obtained for the presence of the 2-ethyl-n-hexyl branch structure that would have resulted from double backbiting by an alternative route. These findings were confirmed by spectral comparisons with the {dollar}\sp{lcub}13{rcub}{dollar}C shifts of two separately synthesized models, 9,11-diethylnonadecane and 9-(2-ethyl-n-hexyl)heptadecane.;Polymerizations of VC were performed in the presence of two potential transfer agents, trans-1-chloro-2-hexene and trans-1,5-dichloro-2-pentene. Preliminary examination of the resulting polymers by high-field NMR provided evidence for the destruction of the -CH{dollar}\sb2{dollar}CH=CHCH{dollar}\sb2{dollar}Cl chain end, during polymerization, by a mechanism involving H abstraction to form the -CH{dollar}\sb2{dollar}CH=CHC{dollar}\sp{lcub}\cdot{rcub}{dollar}HCl radical, followed by the addition of that species to VC in order to give the -CH{dollar}\sb2{dollar}CH=CHCHClCH{dollar}\sb2{dollar}- structure.

Molecular imprinting is a rapidly developing technique for preparation of polymeric materials that are capable of molecular recognition for selective separation and chemical identification. to prepare molecularly imprinted polymers (MIPs), a functional monomer and a crosslinker are polymerized in the presence of a template molecule. Then the template is extracted leaving sites which are complementary in both shape and chemical functionality to those of the template. This resin then becomes capable of selectively absorbing the template species. Because of MIPs' stability, predesigned selectivity, and easy preparation, they have been used for separation, sensor, drug development and directed synthesis.;In this study, we focused on characterizing and understanding the mechanism underlying formation and recognition of MIPs. Three resins imprinted with 4-hydroxybenzoic acid, 3-hydroxybenzoic acid and 6-methoxy-alpha-methyl-2-napthaleneacetic acid ((S)-naproxen) were prepared in a free radical polymerization. Hydrogen bonding between the template and functional monomer is the main interaction: it not only controls the template molecules in and out of the binding sites, but also contributes a high concentration of specific binding sites in the resulting polymer resin. After polymerization, the amount of template that can be effectively removed during each extraction was quantified in the naproxen imprinted system. For comparison, another resin was prepared under the same condition without the presence of the template, which was designated as NIP.;The binding experiments were performed for the affinity and selectivity tests. The MIP showed a special affinity for the template, but not for other analytes, which is consistent with the principle that an imprinted resin's recognition ability is dependent on the analyte's size, shape, and functionality. The NIP had similar affinities for the analytes and thus it could not differentiate among them. The binding behavior of the MIP is characterized by an association constant and the density of each kind of site using a simple two-binding-site model with one kind of sites special for the template and the others being more general with similar affinities as the NIP. The binding sites common to both the imprinted resin and the non-imprinted resin were found to have higher affinity but are less numerous than the sites unique to the imprinted resin.

The purpose of this research was to prepare nanocomposite materials comprised of exfoliated clay particles in a polyimide matrix. Poly(amide acid)/organoclay solutions and polyimide/organoclay films were prepared and the clay dispersion was characterized by visual inspection, XRD, and TEM. Mechanical measurements and certain thermal characterization measurements were also obtained. The research began by attempting to repeat the procedures set forth in the literature. Most of the polyimide/organoclay nanocomposites were being prepared by mixing prepared poly(amide acid) solutions with organoclay solutions. This simple mixing technology was used in the preparation of various polyimide/organoclay hybrid formulations. In-situ polymerization, which involved performing the polymer synthesis in the presence of the organoclay, replaced simple mixing with increased success. Although the in-situ polymerization technique was successful at exfoliating clay particles in certain polyimides, the organoclay degraded at the polyimide cure temperature. In order to raise the use temperature, the aliphatic surfactants found in commonly used organoclays were replaced with aromatic surfactants. The dispersion of the clay was more difficult with the aromatic surfactants. It was facilitated by reducing the charge on the clay surface. This was achieved by replacing some of the cations that reside on the surface of the clay particles with lithium ions in the interior of the particles. The in-situ polymerization of APB-BPDA poly(amide acid) in the presence of an aromatic organoclay with a cation exchange capacity (CEC) of 0.57 meq/g and subsequent cure to the polyimide yielded a film with a high level of clay dispersion.

An in situ measurement technique that isolates the mobility of charge carriers is described and analyzed. The technique allows significant improvement over conductivity measurements to monitor changes in the physical properties and state of a material as it cures. This is essential in systems where Ni, the number of charge carriers, cannot be assumed constant such as during cure of epoxies, urethanes and polyimides.;Currently, there is an assumption made in the literature that the number of charge carriers present in a curing material is constant when conductivity is used as an in situ measurement technique to monitor changes in mobility. Ion mobility, time of flight (ITOF) measurements, which are described here, are an appropriate technique to isolate and measure particle mobility due to changes in the state of the material. The ITOF technique, coupled with the measurement of sigma, the ionic conductivity, allows one to measure separately changes in the mobility and the number of charge carriers due to curing or changes in temperature. This is possible since conductivity is the product of the number of charge carriers and their mobility. Length of pulse, strength of applied field, sensor geometry, and temperature/viscosity are examined to determine optimum parameters of measurement for both a simple non-curing system, and more complex, hydrogen-bonded epoxy.;The second focus of this thesis is our recently developed single stage in situ synthesis of hybrid membranes comprised of nanometer-sized metal and metal oxide particles in polyimides. The major goal is development of polymer based structural materials designed to achieve exceptional performance properties regarding gas permeability and gas separation selectivity, particularly in regard to their thickness, modulus, and strength to weight ratio. We investigate hybrid inorganic-polyimide films where the nanoparticle inorganic phases are of two types: (1) nanometer-sized rare earth (lanthanum, gadolinium and holmium) oxide molecular clusters and (2) nanometer-sized palladium and silver metal clusters. For the polymeric phase we used aromatic poly(amic acid)s-polyimides because of their strength and chemical and thermal stability.