The work presented in this thesis is divided into four chapters. Chapter I describes the control of the crystallization behavior of syndiotactic polystyrene (sPS) by chemical modification of sPS using sulfonation. In Chapter II, preparation of wood-ceramic composites through sol-gel processes is described. Chapter III describes the end-functionalization of poly(ethylene oxide)s (PEOs), and the interfacial properties of the functionalized PEOs. Finally, the distribution of chain conformation of PEO in the liquid state is discussed in Chapter IV. Direct sulfonation of highly stereoregular syndiotactic polystyrene (sPS) has been accomplished in chloroform. The degree of sulfonation can be effectively controlled. The crystallization behavior of sulfonated sPS is considerably different than the unmodified polymer. The crystallinity and the crystallization kinetics of sPS decrease with increasing extent of modification. Wood-ceramic composites were prepared by introducing a ceramic component into pine, a softwood, through sol-gel processes. Several ceramic precursors, including SiCl$\sb4$, Si(OCH$\sb3)\sb4$, and CH$\sb3$SiCl$\sb3$, were used. The ceramic content introduced into the wood structure can be controlled by varying the reaction time and the moisture content of wood. The modification of wood by CH$\sb3$SiCl$\sb3$ in supercritical CO$\sb2$ penetrated the entire wood structure, generating a macroscopically uniform distribution of the ceramic component in wood. Samples with one or both ends of monodisperse PEO functionalized with perfluorodecanoyl groups (PEO$\sp{\rm F}$ or PEO$\sp{\rm F2}$) were synthesized and blends of these end-capped PEOs with PEOs of the same molecular weight (M$\sb{\rm n}$$\sim$2000 - $\sim$16000) were prepared as cast films. Due to the lower surface energy of the fluorocarbon end groups, the modified PEOs preferentially adsorb to the free polymer surface. The surface concentration of the perfluoroalkyl end groups was measured by XPS which indicates that perfluoroalkyl chain ends adsorb to the polymer surface in a reasonably close-packed fashion (at all molecular weights) and leave a zone depleted of fluorine immediately beneath the highly fluorinated surface region. There is only a slight effect of molecular weight on surface fluorine content indicating a "stretched brush" conformation for the higher molecular weight samples. The adsorption of these polymers at the air-water interface was studied as well. The packing density and the orientation angle of the fluorinated chain end segregated at the interface were assessed by external reflectance IR. Isotropic Raman spectra of PEO in aqueous solution and in the melt were simulated by superposing calculated spectra resulting from a series of normal coordinate calculations performed for an ensemble of conformers, and compared with the corresponding experimental results. The conformational distribution for poly(ethylene oxide) in the molten state favors the tgg' conformer, and the aqueous solution of poly(ethylene oxide) contains mostly tgt conformers. The results for PEO were supported by measurements and computations made using 1,2-dimethoxyethane as a model.

In recent years, supercritical fluids (SCF), specifically carbon dioxide (CO2), have been tested and applied as alternative solvents for polymer processing and modification. The principal utility of CO2 in heterogeneous polymer systems lies in the sorption of significant mass fractions of CO2, which influence properties that are driven by free volume. The effects include depressed glass transition temperatures, enhanced transport within the dilated polymer and decreased viscosity. The exploitation of these effects in multicomponent systems requires an understanding of the influence of compressible fluid sorption on polymer-polymer compatibility that to date has been unexplored. In this dissertation, it is demonstrated for the first time, that sorption of SCF's can induce phase segregation in polymer systems exhibiting Lower Critical Solution Temperature-type (LCST) behavior at temperatures hundreds of degrees below the ambient pressure transition. For LCST systems, the relative compressibilities of the components play a dominant role, which can be exacerbated by sorption of SCF's. For example, fluorescence quenching experiments indicate that sorbed gas (CO2) depresses the LCST's of blends of polystyrene/poly (vinyl methyl ether) (PS/PVME) by over 100°C at modest pressures (around 20 bar) of the gas with negligible dependence on temperature and molecular weights of the polymer components. Absorbed CO2 has similar effects on blends of deutrated-polybutadiene/polyisoprene as studied by Small Angle Neutron Scattering. The phase behavior of PS/PVME in the presence of CO2 has been modeled using the Sanchez-Lacombe equation of state, which indicates that the polymer blend phase separation is driven primarily by the selective dilation of PVME by CO2 relative to PS. Ethane, with a weaker selectivity also induces phase separation in PS/PVME system, but is significantly different from the effect of CO2 with respect to temperature and polymer molecular weights, indicating the role of selectivity of poor solvents that is superimposed on compressibility effects. Finally, the design, development and application of neutron reflectivity to high-pressure systems for in situ measurements are discussed including results on swelling of thin homopolymer films and investigations of the phase behavior of a diblock copolymers of polystyrene and poly (n-butyl methacrylate) that exhibit Lower Disorder-Order Transition (LDOT).

This thesis investigates the macroscopic yield behavior and microscopic energy absorption mechanisms in single and multiphase polymers. One unique aspect is the evaluation of polymers under multiaxial loading conditions. This is important because in many applications polymers are subjected to complex loading conditions and hence optimal design requires experimental evaluation and modeling of behavior under multiaxial stress states. This work has resulted in a more quantitative understanding of yield and energy absorption in the different polymers considered. Multiaxial stress states are achieved using thin-walled hollow cylinder specimens. The hollow tubes are simultaneously subjected to internal pressure and axial load, leading to biaxial stress states. Stress states ranging from uniaxial compression to equibiaxial tension are interrogated using the same specimen geometry, a procedure uncovering true material behavior. In the first part of this study, a generalized model for the yield behavior of single-phase polymers is evaluated for a polycarbonate system. The generalized model accounts not only accounts for viscoelasticity (i.e., rate and temperature dependence) but also the effect of pressure on yield behavior. The effects of physical aging on the behavior of amorphous polycarbonate are also highlighted. For rubber-modified polymers, existing models for both macroscopic yield behavior and the onset of microscopic damage (e.g., cavitation) are evaluated under multiaxial conditions (chapter 3). Serious discrepancies are found for both cases, prompting an investigation into the nature of energy absorption mechanisms in the materials. Apart from the chosen rubber-modified systems, a toughening mechanism in the form of overlapping parallel cracks is identified to be generic to a range of polymers (chapter 4). The last part of the thesis (chapter 5) involves a quantitative investigation of interactions in overlapping crack patterns. This effort is vital, because for better design of materials, the interaction has to be related to intrinsic material properties. The interactions in an infinite 2D array of parallel and overlapping cracks are analyzed using a complex stress function method. The size and number density of cracks in the array are related to intrinsic material properties and conditions for damage stability are identified.

Nanocomposites are of interest for numerous applications such as catalysis, photonic band gap materials, and waveguides. Ionomers and diblock copolymers have previously been used as templates for ordered nanocomposites. However, these processes have been limited to reactions within thin films or coprecipitation methods from solution due to mass transport limitations of ceramic and metallic precursors within the solid templates. This issue has been addressed by fabricating ordered nanocomposites using phase selective deposition of precursors into supercritical carbon dioxide (SC-CO2) swollen polymeric templates. SCCO2 is an effective plasticizing agent for most polymers and enhances mass transport of the precursors into polymeric templates while preserving the initial template morphology. By proper choice of template material, the precursor can be selectively bound within one phase of the template and reacted to produce the desired material. The resulting composite contains nanoparticles arranged in an ordered morphology dictated by the template over bulk dimensions. Polymer/ceramic and polymer/metal nanocomposites have been successfully synthesized using this technique.

Poly(4-methyl-1-pentene) (PMP) films were surface-selectively chlorinated, controlling the extent and the depth of modification with chlorine vapor pressure, photointensity and reaction time. Chlorinated PMP samples were analyzed with surface and bulk sensitive techniques to chose reaction conditions for selected modification types. Gas permeability studies with the selected membranes showed that a thick layer of densely chlorinated PMP was needed to change the gas barrier properties of a PMP membrane. The decrease in flux through the highly and deeply chlorinated PMP membrane was more pronounced in cases of large gas molecules resulting in improvements in selectivity of the membrane. PMP membranes were also surface-selectively oxidized to yield a carboxylated PMP surface (PMP-COOH). Alternating ultrathin layers of poly(allyl amine hydrochloride) (PAH) and poly(sodium styrene sulfonate) (PSS), and polyaniline (PAn) and PSS, were self-assembled onto the PMP-COOH surface. The stratification and the thickness of the layers were determined with surface-sensitive analytical techniques. The polyelectrolyte molecules were shown to be packed into the PAH/PSS multilayers in a dense and rigid manner giving improved gas barrier properties. The PAn/PSS multilayers were shown to be stratified in a similar fashion to PAH/PSS, but the molecules were bound in a loose network resulting in no changes in the gas permeability properties of the composite membranes.

In 1844 Charles Goodyear obtained U.S. Patent #3,633 for his “Gum Elastic Composition”. In a published circular, which describes his patent for the sulfur vulcanization of gum elastic composition, he stated: “No degree of heat, without blaze, can melt it (rubber)… It resists the most powerful chemical reagents. Aquafortis (nitric acid), sulphuric acid, essential and common oils, turpentine and other solvents… …” Goodyear's sulfur vulcanization of rubber fueled much of the industrial revolution and made transportation possible, as it exists today. In doing so, Goodyear created one of the most difficult materials to recycle. Rubber will not melt, dissolve, or lend itself to the usual methods of chemical decomposition. Ironically, Goodyear recognized this problem and in 1853 he patented the process of adding ground rubber to virgin material, now currently known as regrind blending. Today, scrap tires represent one of the most serious sources of pollution in the world. Studies estimate that there are roughly 2 billion scrap tires in U.S. landfills and more are being added at a rate of over 273 million tires per year. Current methods of recycling waste tires are crude, ineffective, and use rubber powder as a low cost filler instead of a new rubber. The groundwork for a very simple and effective method of producing high-quality rubber goods using 100% scrap rubber was discovered in 1944 by A. V. Tobolsky et al. This application, however, was not recognized until recently in our laboratory. The process as studied to date represents a method of creating quality, high-value added rubber goods with nothing other than heat and pressure. High pressure is required to obtain a void-free compaction of the rubber particles by forcing all of the free surfaces into intimate contact. High temperature then activates the chemical rearrangement, scission, and reformation of the chemical bonds thus providing new bridges between the once fractured interfaces. This occurs both within and between particles. The technique of high-pressure high-temperature sintering has worked on all types of thermoset materials. Typical mechanical properties for sintered SBR powder rubber are as follows: 1.3 MPa 100% Modulus, 12.0 MPa Tensile Strength and 300% Elongation at Break. The goal of this research is two-fold. First, to gain an understanding of the variables that control the process of high-pressure high-temperature sintering. Second, to study the factors governing the mechanism of fusion with the hope of controlling and exploiting this process so that tires can be recycled to produce high quality and high-value added products.

Liquid crystalline polymers (LCPs) are a new class of high strength materials. Their rheological behavior is different from that of ordinary isotropic polymers because they are inherently anisotropic in the melt state. Crystallization in rigid-rod mesogenic systems in the nematic melt and super-cooled states has been studied by small amplitude oscillatory shear, which has been found to be in some ways more sensitive than conventional techniques like DSC or X-ray scattering (in that changes are measured by orders of magnitude instead of merely on a linear scale). A scheme of preheating is suggested for unsubstituted, rigid-rod polymers whereby a metastable nematic melt can be achieved, effectively suppressing crystallization and enabling a thorough rheological characterization. For example, an excellent agreement has been obtained for the stress relaxation modulus between experimental values and those calculated from dynamic oscillatory measurements, thereby confirming the existence of a linear viscoelastic range for the LCP. Non-linear creep studies illustrate how rheological properties are strongly affected by structural changes upon deformation. Structure in unsubstituted rigid-rod nematic systems is hypothesized to exist at two levels--Non-Periodic Layer (NPL) Crystallites and Domains/Disclination Network. Another aspect of research concerns a comparative study of the phase behavior of liquid crystalline components in closely related blends and copolymers.

Solid-supercritical fluid (S-SCF) and liquid-vapor equilibria (cloud-point pressures) for iPP/propane systems were determined. Liquid-vapor equilibria below S-SCF equilibria temperatures for iPP/propane were obtained by studying the atactic polypropylene (aPP)/propane system. Modeling of these systems by the Sanchez-Lacombe lattice fluid theory required empirical adjustment of mixing parameters. Cloud-point pressures for polyolefins of increasing branch length and some poly(ethylene-co-octene) copolymers in propane were also determined. They decrease with increasing percentage of carbon in the branches. Crystallization of iPP from single phase systems was achieved by controlling temperature and pressure. Under most conditions, crystallizations of unnucleated iPP resulted in large (100+ $\mu$m) microspheres having poor mechanical coherency. A highly effective nucleating agent, dibenzylidene-d-sorbitol (DBS), was added to promote nucleation and coherence, but requires a cosolvent for solubilization. S-SCF equilibria for DBS in propane/1-propanol mixtures were determined as well as changes in the phase behavior of aPP/propane with the addition of an alcohol and is summarized in terms of changes in critical behavior. Surface areas and pore size distributions (PSD) in the mesopore range (20 to $\sim$500 A) were determined by analysis of nitrogen adsorption-desorption isotherms. Surface areas ranged from 120-180 m$\sp2$/g with most probable pore sizes, based on a cylindrical pore model, of between 100-200 A. This pore size is supported by small angle x-ray scattering data analyzed by a model which treats the pores as a distribution of spherical aggregates. A more specific model is proposed in which the microsphere contains a dense core defined by a radius beyond which fibrillation and gas adsorption sets in. The high surface area of porous iPP is attributed to as yet unknown details of the organization of iPP lamellae on the nanoscale.

O polietileno linear de baixa densidade (LLDPE) com comonômeros 1-buteno e 1-octeno apresenta fácil processabilidade e baixo custo. Por outro lado, as poliolefinas em geral possuem baixa reatividade, dificultando a adesão com outros substratos e limitando suas aplicações. Por esta razão tratamentos foram desenvolvidos para minimizar essa característica, sendo conhecidos como processos de enxertia ou funcionalização. Este trabalho teve por finalidade avaliar a influência do tamanho dos comonômeros buteno e octeno e dos dois tipos de agentes funcionalizantes anidrido maléico (AM) e anidrido tetrahidroftálico (ATF) no processo de funcionalização via úmida das poliolefinas. Para se avaliar a significância estatística de quatro variáveis dos experimentos: porcentagem do agente funcionalizante (AM ou ATF), porcentagem do iniciador peróxido de benzoíla (BPO), tipo de comonômero (buteno e octeno) e o tempo de reação, usou-se as ferramentas estatísticas conhecidas como planejamento fatorial fracionário e planejamento fatorial composto central. O grau de funcionalização das poliolefinas modificadas foi determinado por espectroscopia vibracional no infravermelho (IR). Os efeitos do grau de funcionalização e do tipo de anidrido sobre o grau de cristalinidade das amostras foram obtidos por difração de raios-X e calorimetria exploratória diferencial (DSC). A molhabilidade das poliolefinas foi determinada, antes e depois da funcionalização, por medidas de ângulo de contato, utilizando-se gotas de água como líquido. Observamos que (1) a funcionalização das poliolefinas modificadas com AM se mostrou mais eficiente do que com ATF, porque as moléculas de ATF são mais reativas, o que as torna mais suscetíveis a reações paralelas como a homopolimerização e/ou reticulação; (2) a modificação das poliolefinas com AM apresentou significância estatística só nas variáveis: porcentagem de BPO e porcentagem de AM; (3) as, poliolefinas modificadas com ATF apresentaram duas variáveis significativas, o tempo da reação e a interação existente entre o tempo de reação e a porcentagem de ATF; (4) as poliolefinas modificadas com AM e ATF apresentaram uma redução na temperatura de fusão de até 3,3°C e 4,3°C respectivamente, evidenciando alterações na estrutura cristalina do polímero; (5) ensaios de difração de raios-X corroboram com os valores obtidos por calorimetria exploratória diferencial (DSC), uma vez que não ocorreu deslocamento dos máximos de difração e tampouco do halo amorfo; mas houve uma diminuição acentuada nos picos de difração (diminuição da altura e aumento da largura), reflexo da desestruturação causada pelo agente funcionalizante nos domínios cristalinos; (6) observou-se que o aumento no GF promoveu uma maior molhabilidade da superfície, indicando uma maior interação dos grupos polares enxertados com a água. Os valores altos de Li8 indicam alta rugosidade e ou heterogeneidade química da superfície; (7) não houve variação significativa no grau de funcionalização quando utilizado poliolefinas com diferentes comonômeros; (8) o aumento na concentração de poliolefina promove uma maior funcionalização. (9) o método de funcionalização desenvolvido levou à reticulação mínima da poliolefinas. / Linear low-density polyethylene with comonomer 1-butene and 1-octene presents the advantages of easy processing and low cost. On the other hand, polyolefins are inert materials with very low surface energy, impeaching the adhesion to other materials. In order to improve the adhesion to other materials, grafting or functionalization processes have been developed. This work evaluates the influence of the comonomers butene and octene and of two types of anhydride, maleic anhydride (MA) and tetrahydrophthalic anhydride (THA), on the functionalization of polyolefins by means of chemical reactions in solution. In order to evaluate the statistic meaning of four variables (content of anhydride, content of benzoyl peroxide, type of comonomer, and time of reaction) in the functionalization process the fractional factorial design and the central composite experimental design were used. The degree of functionalization (DF) was determined by means of infrared spectroscopy (IR). The effects of (DF) and of the type of anhydride on the crystallinity of the modified samples were obtained from X-ray diffraction and differential scanning calorimetry (DSC). The wettability of polyolefins was determinated before and after of the functionalization by means of contact angle measurements using water drops like liquid. We observe that ( 1) the functionalization of polyolefins modified with MA are more efficient than the polyolefins modified with THA because the THA molecules are more reactive than the MA molecules, favoring side reactions as homopolymerization and cross-linking; (2) the modification of the polyolefins with MA shows statistic meaning only in the following variables: contents of BPO and MA percentage; (3) the polyolefins modified with THA show significative variables: the time of reaction and the interaction between the time of reaction and the THA content; (4) the polyolefins modified with MA and THA show a reduction in the melt temperature of 3,3°C and 4,3°C respectively, indicating changes in the crystalline structure of polymer; (5) X-ray diffractograms confirmed the results obtained by differential scanning calorimetry (DSC), since the diffraction peaks turned smaller; (6) the increase in the DF improved the surface wettability; (7) the size of comonomer has no influence on the DF; (8) the DF depends on the polyolefin concentration; (9) the polyolefins modification by chemical reactions in solution presented very low cross-linking degree.

O polietileno linear de baixa densidade (LLDPE) com comonômeros 1-buteno e 1-octeno apresenta fácil processabilidade e baixo custo. Por outro lado, as poliolefinas em geral possuem baixa reatividade, dificultando a adesão com outros substratos e limitando suas aplicações. Por esta razão tratamentos foram desenvolvidos para minimizar essa característica, sendo conhecidos como processos de enxertia ou funcionalização. Este trabalho teve por finalidade avaliar a influência do tamanho dos comonômeros buteno e octeno e dos dois tipos de agentes funcionalizantes anidrido maléico (AM) e anidrido tetrahidroftálico (ATF) no processo de funcionalização via úmida das poliolefinas. Para se avaliar a significância estatística de quatro variáveis dos experimentos: porcentagem do agente funcionalizante (AM ou ATF), porcentagem do iniciador peróxido de benzoíla (BPO), tipo de comonômero (buteno e octeno) e o tempo de reação, usou-se as ferramentas estatísticas conhecidas como planejamento fatorial fracionário e planejamento fatorial composto central. O grau de funcionalização das poliolefinas modificadas foi determinado por espectroscopia vibracional no infravermelho (IR). Os efeitos do grau de funcionalização e do tipo de anidrido sobre o grau de cristalinidade das amostras foram obtidos por difração de raios-X e calorimetria exploratória diferencial (DSC). A molhabilidade das poliolefinas foi determinada, antes e depois da funcionalização, por medidas de ângulo de contato, utilizando-se gotas de água como líquido. Observamos que (1) a funcionalização das poliolefinas modificadas com AM se mostrou mais eficiente do que com ATF, porque as moléculas de ATF são mais reativas, o que as torna mais suscetíveis a reações paralelas como a homopolimerização e/ou reticulação; (2) a modificação das poliolefinas com AM apresentou significância estatística só nas variáveis: porcentagem de BPO e porcentagem de AM; (3) as, poliolefinas modificadas com ATF apresentaram duas variáveis significativas, o tempo da reação e a interação existente entre o tempo de reação e a porcentagem de ATF; (4) as poliolefinas modificadas com AM e ATF apresentaram uma redução na temperatura de fusão de até 3,3°C e 4,3°C respectivamente, evidenciando alterações na estrutura cristalina do polímero; (5) ensaios de difração de raios-X corroboram com os valores obtidos por calorimetria exploratória diferencial (DSC), uma vez que não ocorreu deslocamento dos máximos de difração e tampouco do halo amorfo; mas houve uma diminuição acentuada nos picos de difração (diminuição da altura e aumento da largura), reflexo da desestruturação causada pelo agente funcionalizante nos domínios cristalinos; (6) observou-se que o aumento no GF promoveu uma maior molhabilidade da superfície, indicando uma maior interação dos grupos polares enxertados com a água. Os valores altos de Li8 indicam alta rugosidade e ou heterogeneidade química da superfície; (7) não houve variação significativa no grau de funcionalização quando utilizado poliolefinas com diferentes comonômeros; (8) o aumento na concentração de poliolefina promove uma maior funcionalização. (9) o método de funcionalização desenvolvido levou à reticulação mínima da poliolefinas. / Linear low-density polyethylene with comonomer 1-butene and 1-octene presents the advantages of easy processing and low cost. On the other hand, polyolefins are inert materials with very low surface energy, impeaching the adhesion to other materials. In order to improve the adhesion to other materials, grafting or functionalization processes have been developed. This work evaluates the influence of the comonomers butene and octene and of two types of anhydride, maleic anhydride (MA) and tetrahydrophthalic anhydride (THA), on the functionalization of polyolefins by means of chemical reactions in solution. In order to evaluate the statistic meaning of four variables (content of anhydride, content of benzoyl peroxide, type of comonomer, and time of reaction) in the functionalization process the fractional factorial design and the central composite experimental design were used. The degree of functionalization (DF) was determined by means of infrared spectroscopy (IR). The effects of (DF) and of the type of anhydride on the crystallinity of the modified samples were obtained from X-ray diffraction and differential scanning calorimetry (DSC). The wettability of polyolefins was determinated before and after of the functionalization by means of contact angle measurements using water drops like liquid. We observe that ( 1) the functionalization of polyolefins modified with MA are more efficient than the polyolefins modified with THA because the THA molecules are more reactive than the MA molecules, favoring side reactions as homopolymerization and cross-linking; (2) the modification of the polyolefins with MA shows statistic meaning only in the following variables: contents of BPO and MA percentage; (3) the polyolefins modified with THA show significative variables: the time of reaction and the interaction between the time of reaction and the THA content; (4) the polyolefins modified with MA and THA show a reduction in the melt temperature of 3,3°C and 4,3°C respectively, indicating changes in the crystalline structure of polymer; (5) X-ray diffractograms confirmed the results obtained by differential scanning calorimetry (DSC), since the diffraction peaks turned smaller; (6) the increase in the DF improved the surface wettability; (7) the size of comonomer has no influence on the DF; (8) the DF depends on the polyolefin concentration; (9) the polyolefins modification by chemical reactions in solution presented very low cross-linking degree.