Thesis (M.S.)--Rochester Institute of Technology, 1984. / Typescript. Includes bibliographical references (leaf 31).

New grades of fluoropolymers are available from DuPont that have been designed to relieve some of the processing problems associated with these materials. By nature, Teflon$\sp{\circler}$ is very viscous in the melt state, and only high energy processes allow material processing. These new grades of fluoropolymers are the first to be dissolvable, by perfluorinated solvents, and have opened up a whole new field of solution processing. It has been the aim of this work to investigate this new field of research. New solution processing techniques have been developed to create strong well-adhered coatings of fluoro-ethylene-propylene (FEP) copolymers to various substrate materials, ranging from 50nm to 100$\mu$m. By observing and exploiting upper and lower critical solution temperatures, solutions of concentrations up to 15 wt. % have been achieved, well above the 1 wt % solutions produced at DuPont. This enabled the formation of FEP coatings in one step, rather than attempting multiple layers to achieve greater thickness. Since these are experimental grades of FEP, physical properties have been investigated by thermal and x-ray analysis. In terms of coating properties, the coatings have shown remarkable adhesion properties measured by a unique self decohesion test approach. In order to define optimal uses for these materials as coatings, barrier properties have been measured. Permeability has been tested using carbon dioxide and air and Atlas cell corrosion tests have been run to compare the corrosion resistance among the copolymers being studied. Mechanical properties have also been characterized by holographic interferometry, which measures the in-plane residual stresses, and Instron testing, for tensile properties of the films. To improve coating quality, while taking advantage of the solution media, sol-gel reaction schemes have been modified by DuPont researchers to be carried out in these solvents in the presence of the dissolved FEP. The result is the formation of an SiO$\sb2$ network around the FEP molecules, producing a nano-composite material. This has been investigated with limited success on improving adhesion and other properties mentioned above.

This thesis describes the synthesis, polymerization, and characterization of poly(butylene terephthalate) (PBT) polymers as produced from cyclic oligomers of PBT using a stannoxane cyclic initiator. The properties of the resulting macrocyclic PBT polymer are compared to the properties of four commercial linear PBTs, covering the range of molecular weights for commercial polymers. The macrocyclic polymers are found to have unique properties in both the melt and the solid state. In the melt, the macrocyclic polymers are found to have significantly lower viscosities vs. the linear resins at equivalent molecular weight. The results reported herein show differences in the zero shear viscosity of macrocyclic and linear PBT melts at equivalent molecular weight that are much larger than the differences reported in the literature between macrocyclic and linear polystyrene melts. It is believed that the unique ring expansion polymerization used in this research has resulted in producing simpler cyclic molecules, having no catenation or knotting, than have been reported elsewhere. When crystallized, these cyclic molecules produce a semi-crystalline spherulitic structure. The spherulite formed is unique in that it is highly nucleated, rapidly crystallized, and found to be the same spherulitic form only previously reported as being produced by slow cooling or solvent crystallization processes. The crystalline structure from these macrocyclic molecules is believed to have a lower intercrystalline tie chain density than found in melt cooled linear PBTs. This macrocyclic polymer, produced from cyclic oligomers, is proposed as being capable of being used as a thermoplastic composite resin, with sufficiently low viscosity in the oligomeric state, and sufficiently high polymerization and crystallization rates, that a melt process is feasible. While being very brittle, the fracture toughness of cyclic PBT is found to increase when the macrocyclic structure is degraded, increasing by three times within ten minutes of thermal degradation in the melt. A new initiator is proposed in the thesis, capable of producing linear PBT from cyclic oligomers with the same reaction kinetics as the stannoxane initiator. Such a system is expected to be as tough as high molecular linear PBT, and have the chemical and heat resistant characteristics necessary for a new thermoplastic composite resin.

Only recently has external reflectance infrared spectroscopy been used to acquire structural information at the molecular level at air-liquid interfaces, and particularly to characterize in situ molecular chains adsorbed at the air-water interface. This technique has been applied for the determination of chain orientation, chain conformation and packing density of small molecules such as phospholipids, fatty acids and fatty alcohols on the surface of water, and more recently of macromolecular systems. Vibrational spectroscopy, a nondestructive technique, is especially successful in the determination of the conformational order or disorder of alkyl chains (e.g. trans/gauche ratio) as well as in the evaluation of coil, helical or extended conformations in poly(amino acids). In this thesis work, the construction of a microcomputer controlled Langmuir trough optically coupled to a FT-IR instrument has allowed the direct investigation of molecular films spread at air-liquid interfaces. Order-disorder transitions and relaxation behaviors in vinyl comb-like polymeric Langmuir films have been examined using simultaneously external reflection infrared spectroscopy and surface tensiometry. The structures of several poly(amino acid) films have also been studied as a function of surface packing density at the air-water interface.

Trends in the adsorption of poly(N-methyl-N ′-((±)-α-phenylethyl)carbodiimide), poly-R/S, and poly(N-methyl-N ′-((–)-α-phenylethyl)carbodiimide), poly- S, to native silicon oxide were shown to be influenced by the polymer's conformation in solution (worm-like and rigid, respectively), solvent quality, molecular weight, and process conditions. High affinity adsorption isotherms were measured for poly-R/S adsorbed from toluene to silica and the adsorbed amount increased with molecular weight. The adsorbed amount of poly-R/S and poly-S from THF was influenced by both solvent quality and the conformation of the polymer in solution. For both polymers, adsorbed from THF, the XPS and contact angle data indicated that the adsorbed amount decreased with molecular weight and the adsorbed amount, for equal molecular weights, of poly-S was greater than poly- R/S. Using AFM, the adsorbed films of both polymers were shown to dewet during the evaporation of solvent. The extent of dewetting is shown as a function of solvent quality, temperature, and experimental processes. The size and dimensions of the surface structures after dewetting were shown to increase with molecular weight. Using organosilane chemistry, lyophobic silicon-supported monolayers of tris(trimethylsiloxy)chlorosilane (tris(TMS)), 10-(carbomethoxy)decyldimethylchlorosilane (CMDCS), diphenyldichlorosilane (DPDCS), and mixed binary monolayers of tris(TMS) with CMDCS were prepared; followed by adsorption of poly-R/S and poly-S to the monolayers. Relative to silica, both polymers have little affinity to adsorb to surfaces composed mostly of methyl (tris(TMS)) or methylene (CMDCS) groups. Furthermore, the adsorbed amount increased with molecular weight but decreased with chain rigidity. In addition, the adsorbed films dewetted upon solvent evaporation. Vapor phase modification of silica with DPDCS was shown by AFM to form patchy surface structures. Both polymers were shown to have a higher affinity for the DPDCS modified surfaces compared to adsorptions performed on tris(TMS) and CMDCS surfaces. Adsorption experiments with poly-R/S and poly-S to surfaces composed of hydrolyzed CMDCS (H-CMDCS) indicated an increase in the adsorbed amount with increasing amount of H-CMDCS. Adsorbed films of poly-R/S on native silicon oxide were prepared for studying the effect of thermal decomposition on the adsorbed polymer film. Using real-time FT-IR and TGA, the decomposition rates were measured, but experimental conditions are shown to influence the data. Topography analysis, by tapping mode AFM, of the decomposed adsorbed films indicated changes in the surface structure with thermal exposure. In addition, with thermal exposure the adsorbed film became weakly attached to the substrate. Nonetheless, thermal decomposition can be used to modify an adsorbed film of poly-R/S.

Supercritical carbon dioxide (scCO2) has been widely studied as an environmentally friendly alternative to organic solvents in many applications. This thesis will describe specific routes for both melt and solid-state processing of polymers in scCO2-mediated environments. The primary goal is to analyze the influence of scCO2 on the final properties of polymers as well as to design novel processing routes using scCO2 that could allow access to well-defined structures and novel materials, and processing of “intractable” polymers. Most of the fiber-drawing studies of polymers in scCO2 have focused on permeable conditions, where the plasticization process of scCO 2 dominates the interaction and the effect of the imposed hydrostatic pressure is negligible.1–3 In this thesis, the interactions of scCO2 with solid state polymers under non-permeable conditions are investigated through the drawing behavior of highly crystalline, highly oriented, polymorphic fibers (UHMWPE) within this environment. The high-pressure environment appears to stabilize the crystal structure of the fiber, which in this case is the major component. As a consequence, scCO2-treated samples display a constant mechanical and thermal response compared to air-drawn samples that show significant temperature dependence in their behavior. In addition, the interactions of scCO2 with polymers in the melt are analyzed by designing a modified processing system that allows to process polymers in scCO2. Using this system, the foaming process of polyethylene in scCO2 is studied, and scCO2-assisted polymer processing is then applied to high molecular weight polymers, including fluoropolymers and high molecular weight polyolefins, as a novel processing-route. The success of this method is based on the effect of scCO2 on the melting behavior of semicrystalline polymers, along with its large plasticizing properties observed primarily in fluoropolymers. Finally, the feasibility of preparing polymer-clay nanocomposites by this route using a variety of approaches is also studied. The use of polymers with controlled hydrophilicity, as well as the introduction of chemically designed hydrophilic polymers or compatibilizers that enhance the interaction between the polymer and the clay have been used to understand the effect of scCO2 on the melt intercalation process as well as on the final structure and morphology of these systems.

The main objective of this dissertation was the synthesis and modification of thermotropic liquid crystalline copolyesters to be blended with isotropic engineering thermoplastics such as PET. There has been a lot of interest in the last several years in the blending of thermotropic LCPs with engineering thermoplastics to form in situ composites. Yet, due to the typically high melt transitions of highly aromatic thermotropic LCPs, several methods have been studied in this dissertation to reduce the melt transitions of LCPs to within the processing window of engineering thermoplastics. Three series of thermotropic, aromatic copolyesters derived from EHQ, PHQ, HQ, EG, and TA were synthesized, and characterized by PLM, DSC, NMR, TGA, and solution viscometry. It was shown that the melt transition was effectively reduced through the copolymerization of the monomers. For melt blending with engineering thermoplastics, such as PET, the transition temperatures for the Series III samples were too high, while some of the Series I and II copolymers with low amounts of PT units had thermal transitions in the range which would make them more favorable for blending. Several different liquid crystalline copolyesters were thermally post-treated successfully to increase their degree of randomness. Both poly(ethoxyphenylene terephthalate-co-ethylene terephthalate)s and poly(phenylphenylene terephthalate-co-ethylene terephthalate)s were thermally randomized. It was found that increased randomness numbers caused decreased melt transition temperatures and crystallization temperatures. The more random sequence distributions also resulted in a decreased crystallinity of the copolyesters as observed by reduced enthalpies of fusion and crystallization. Two different LC copolyesters, poly(EPT-co-ET) and poly(PPT-co-ET), were solution blended with PET using a mixture solvent of TFAA/Chloroform. Four different samples of each LC copolyester, with varying degrees of randomness, were used in the blends. The blends were characterized by DSC, polarized light microscopy, and rheological testing. It was observed that the melt viscosity of the blend had a strong dependence on the degree of randomness of the LC copolymer used. The copolyesters with high degrees of randomness caused a reduction of the melt viscosity.

A new design protocol and energy absorption models are proposed for polymeric foam that improve material and absorber geometry selection for impact conditions encountered in service. Design diagrams are constructed that show the energy absorption of uniaxial and trapezoidal absorber geometries as a function of product geometry, foam density, and strain rate for closed cell polyethylene (PE) and polystyrene (EPS) packaging foams. Design constraints including load spreading, buckling, creep, and material costs are addressed. Energy absorption models for plate, cylindrical, and spherical product geometries generate design data that account for the increased stress and energy absorption resulting from deformation of foam adjacent but external to the region directly below the product (i.e., load spreading). The models partition the energy absorption into polymer deformation and gas compression components, require only easily obtainable uniaxial compression data, and agree within fifteen percent of measured values. Additionally, a systematic examination of the effect of processing parameters on EPS fracture and energy absorption characteristics addresses the influence of cracks frequently observed in impacted commercial EPS components. The energy absorbed during compression increases with increasing toughness because compression induced fracture is reduced. Lower fracture toughness allows longer cracks, which decreases the energy absorbed, possibly resulting in damage to the packaged product. The toughness increases as a function of increased molding time and pressure because of increased fusion. Fusion is characterized by quantitative fractography and is correlated with toughness.

In this study three examples of solid-solid phase transitions in polymers have been investigated with vibrational spectroscopy. The effects of a high strength electric field on the microstructure of piezoelectric copolymers of vinylidene fluoride and trifluoroethylene has been studied. The application of an electric field is found to produce changes in dipolar orientation and also changes in chain conformation, and these are measured by infrared spectroscopy below and above the Curie transition temperature. Electrical poling behavior is examined for two copolymer compositions which show substantial differences in structure and Curie temperature, and infrared analysis provides a means to determine the differences in dipole orientation and chain conformation distribution for these two copolymers. Infrared spectroscopy is employed to determine the content of $\alpha$ and $\beta$ phases of PVDF for two highly drawn blends and also for PVDF homopolymer. The effects of annealing on the phase content and segmental orientation are measured. Highly drawn PVDF samples are used for determination of the transition dipole moment directions of selected vibrational bands. The microstructure of different phases of syndiotactic polystyrene has also been studied. A normal coordinate analysis is performed for the all trans conformation of syndiotactic polystyrene using nonredundant coordinates and force constants for the phenyl ring. Force constants for the chain have been obtained from studies of saturated hydrocarbons. Assignment of the infrared and Raman bands and their polarization characteristics is made upon comparison of the calculated results with the observed spectra obtained from coextruded films. Annealing the coextruded films increases the overall segmental orientation as the crystallinity increases. The theoretical modulus of a single chain has been calculated from the dispersion curive of the longitudinal acoustic branch near the Brillouin zone center. The kinetics of the irreversible phase transition in syndiotactic polystyrene has been measured as a function of temperature and annealing history, in order to determine the effect of thermal history on the transition behavior. (Abstract shortened with permission of author.)

The overall goals of this research were to establish better selection criteria for the use of polymeric coatings and to develop unique material characterization techniques to measure the properties of thin polymer films. The main focus was on establishing structure/processing/property relationships for novel anisotropic polyimide coatings and measuring their in-plane and out-of-plane properties. This involved understanding the effect of processing conditions on the state of stress and on the material properties, and determining the anisotropic elastic constants. The materials investigated were a variety of polyimides, including some novel fluorinated polyimides. Extensive processing and testing of these materials has been carried out. Residual and thermal stresses have been measured using the technique of vibrational holographic interferometry. The stresses have also been measured under different temperature, humidity, and processing conditions. These polymers are very anisotropic with widely different in-plane and out-of-plane properties. The primary goal of this research was the determination of anisotropic elastic constants--tensile moduli, shear moduli and Poisson's ratios--to aid in reliable modeling of polymers in actual applications. All these constants have been determined using existing as well as new unique techniques. The structure/processing/property relationships for these materials have also been investigated. The anisotropy in properties results from a preferred in-plane orientation in polyimides. The effect of polymer structure, film thickness, and processing conditions on the orientation, and hence on the material properties, has been studied. The material properties have been evaluated by physical, mechanical, and thermal testing. The orientation has been characterized by wide angle x-ray diffraction (WAXD) and birefringence measurements. Another important aspect of reliability of polymeric coatings is the adhesion between coating and substrate. The adhesion of these polyimides to a silicon wafer substrate has been evaluated by a self-delamination method. The improvement in adhesion strength of the polyimide-silicon interface by using a silane coupling reagent has been studied.