The field of self-healing materials is growing dramatically due to the obvious in- centive of having structural materials with the ability to repair damage. Some polymers have demonstrated the ability to heal from damage autonomously[12, 26], when exposed to heat[1], or when punctured[5, 9]. The goal of this research is to develop a "proof-of-concept" polymer composite that has the ability to heal when exposed to an alternating magnetic field. Several types of magnetic particulate were inspected for use in the production of polymer composite test samples. The types of particulate used in sample production were two supplies of γ-Fe₂O₃, one supply of α-Fe₂O₃, and one supply of Ni-Zn Ferrite. Surlyn 8940 was selected as the bulk polymer due to its self-healing qualities[9]. A method for melt mixing the particulate with the polymer in various volume fractions was developed and an SEM was used to study the dispersion of the particulate. Once the polymer composite samples were made, various tests were conducted to characterize the samples in order to determine what effects the particulate had on the prop- erties of the bulk polymer. These tests included differential scanning calorimetry (DSC), rheology, conductivity, and magnetic response. Once the samples were characterized, tests were performed to study the composite polymers ability to heat and heal. These tests included healing microscopy, induction heating, and tensile testing. From this study, it was found that the addition of particulate to the bulk polymer does alter the properties by increasing viscosity and electrical conductivity. However, the addition of particulate does not change the melt temperature, but allows the magnetic hysteresis loop of each composite sample to be revealed through magnetic testing. Through healing microscopy and tensile testing, the polymer composites were found to heal when heated, but at a higher temperature than the pure bulk polymer samples. Each type of polymer composite also heated to varying degrees through magnetic induction. Due to the ability of the polymer composite to heal and heat, a "proof-of-concept" has been provided for a magnetically healing polymer composite. / Master of Science

One of the important dynamic parameter characterizing the properties of polymer nanocomposite is viscosity. It is a quantity of interest on macroscopic scale also. A thorough study of viscosity in case of polymer nanocomposite has not been carried out in the existing literature. In this work we used atomic force microscope, force-distance spectroscopy to experimentally measure the viscosity of polymer and polymer nanocomposite thin films. In particular we try to tune viscosity by changing the nature of interface of polymer grafted nanoparticle and polymer melt. The interface nature in varied by changing the miscibility parameter ( f ), defined as the ratio of grafted chain length to the matrix chain length. Using coarse-grained molecular dynamic simulations, dynamics at the nanoparticle-matrix interface is explored by calculating slip length and mobility at the interface. Equilibrium molecular dynamic simulation is employed to calculate the viscosity of nanocomposite. Chapter 1 We introduce some basic models for polymer chain conformation and dynamics. The known facts about the structural and dynamics of polymer grafted nanoparticle are also described. Chapter 2 We present our experiment method and results for various nanocomposite systems for two different volume fractions of nanoparticles and for two different thicknesses. We show that introduction of nanoparticles causes reduction in viscosity of thin film with respect to the neat polymer films. Further for the low volume fraction system (0:5%) the extent of reduction decreases with increasing f -value and almost matching the neat system at the highest f . At high volume fraction (1%), for lower f we observe a reduction in viscosity and for highest f surprisingly there is an increase in viscosity of nanocomposite with respect to the neat system with a cross-over for intermediate f . We attribute the effects to possible slip at the nanoparticle-matrix interface. A rough estimation of slip length from the measured value of viscosity of nanocomposite and pure polymer is provided which strongly supports our idea of slip at the interface Chapter 3 Briefly discusses some basic aspects of molecular dynamic simulation. Chapter 4 Using MD simulation we calculate the slip-length at the grafted nanoparticle-matrix interface for various systems with different f values. A spherical core grafted with atoms same as the matrix is kept fixed at the canter of simulation box. The particle is rotated for calculating slip length. We also look at the mobility variation of matrix chains as a function of radial distance from the centre of nanoparticle. From both slip-length and mobility calculation we observe that slip length as well as mobility is higher for lower f systems as compared to higher f thus supporting our assertion of slip as the most likely cause for our experimental observations. Chapter 5 Now instead of single grafted nanoparticle we have multiple nanoparticles which are free to move in the matrix. Using Green-Kubo formalism we calculate the equilibrium viscosity for pure polymer and nanocomposite systems from MD simulations. We observe increase in viscosity for nanocomposite system as compared to the pure polymer system. We also look at various structural and dynamical changes, that occurs in the filled system with respect to neat system, that leads to such increase in viscosity.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Various companies produce waxes, which are used extensively in various applications, either as produced or as chemically or physically modified value-added products. They are used in the traditional candle industry and applications including hot melt adhesives, inks, plastics, polishes and emulsions for rust prevention or fruit coating. Insight into the properties of these waxes is required to assist the applications chemist in understanding the role of the wax component in a specific formulation. Analytical techniques such as differential scanning calorimetry (DSC), thermogravimetry (TG), rheometry, gel permeation chromatography (GPC), high temperature gas chromatography (HTGC) and infra-red spectroscopy (IR) were used to characterise Fischer Tropsch, polyethylene, natural and petroleum waxes. Property profiles were formulated by integrating the results from the various techniques. The results of traditional wax analyses (e.g. congealing point, melting point, penetration, density and viscosity) were also correlated to relevant analytical results obtained from the instrumental techniques. Structure-property relationships have been proposed. / AFRIKAANSE OPSOMMING: Verskeie maatskappye vervaardig wasse, wat in menige toepassings gebruik word - of direk, of as chemies- of fisies- veranderde produkte van hoër waarde. Benewens die tradisionele kersbedryf, word die wasse in toepassings soos warmsmeltkleefmiddels, ink, plastiek, roeswerende- en vrugtebedekkings- emulsies en politoere gebruik. Wetenskaplikes betrokke by die formuleering van wasse vir verskillende toepassings sal baat vind by beter inligting van waseienskappe en die rol van waskomponente in formulasies. Tegnieke, bv. differensialeskandeerkalorimetrie (DSC), termogravimetrie (TG), reologie, gelpermeasiechromotografie (GPC), hoëtemperatuurgaschromatografie (HTGC) en infrarooispektroskopie (IR), is gebruik om Fischer Tropsch-, polietileen-, petroleum- en natuurlike wasse te karakteriseer. Profiele van waseienskappe is geformuleer deur die integrasie van die data verkry van die verskillende analitiese tegnieke. Die resultate van tradisionële wasanalises (bv. stolpunt, smeltpunt, penetrasie, digtheid, viskositieit en olie-inhoud) word ook in verband gebring met die resultate van die instrumentele analises. Verbande tussen struktuur en waseienskappe word ook voorgestel.

Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: In this study, the feasibility of the non-conjugated 1,5-hexadiene as monomer in metallocene catalised cyclopolymerizations was considered. Homopolymers and copolymers with ethylene, propylene, 1-pentene, 1-hexene and 2-methyl-1,5- hexadiene as comonomers were synthesised in the presence of Cp2ZrCh and rac-Et(lnd)2Zrh. The microstructure (stereoregularity and cyclisation) and number-average molecular weight were determined from NMR analysis. Crystalline oligomers with functional (eg -OH) and vinylidene end groups were obtained. / AFRIKAANSE OPSOMMING: Die studie behels die ondersoek rakende die gebruik van ongekonjugeerde 1,5- heksadieen as monomeer in metalloseengekataliseerde polimerisasies. Homopolimere, sowel as kopolimere van etlieen, propileen, 1-penteen, 1- hekseen en 2-metiel-1,5-heksadieen, is in die teenwoordigheid van Cp2ZrChen rac-Et(lnd)2ZrCI2 gepolimeriseer. Die mikrostruktuur (stereochemie en siklisering) en die getal-gemiddelde molekulêre gewig van die gesintetiseerde polimere is met behulp van KMR spektroskopie ondersoek. Die studie het getoon dat kristallyne oligomere met funksionele (bv -OH) en vinilideen endgroepe gesintetiseer is.

Due to the high crosslink density of cured epoxy resins they generally lack damage tolerance. A significant amount of research has been expended to improve the toughness of epoxies. Research into the area of thermoplastic epoxy modifiers has begun to overcome some of the limitations of early methods of epoxy toughening (i.e. lower modulus and thermal stability).;This study examines the physical and mechanical properties of random poly(arylene ether-co-imidazole) (PAE-co-Is) and the characterization of epoxies modified with poly(arylene ether-co-imidazole)s.;Poly(arylene ether-co-imidazole)s exhibited the highest solubility in N,N,N{dollar}\rm\sp\prime,N\sp\prime,{dollar}-tetraglycidyl- 4,4{dollar}\sp\prime{dollar} diaminodiphenyl methane (TGMDA) based resins. The high molecular weight polymers caused significant decreases in melt flow behavior of the modified systems. Modification of TGMDA resins with PAE-co-Is significantly decreased the tetrahydrofuran sensitivity of the cured system and did not significantly affect the moisture absorption properties. One system modified with 10% w/w polymer exhibited increases in fracture toughness 1.7 times that of the unmodified system.

The development of boron-containing polymeric materials for neutron shielding applications was undertaken. Three types of materials were characterized for physical and thermal properties: boron powder-filled epoxy composites, carborane polyamides having boron chemically bonded into the polymer, and boron-loaded polyimide thin films. Addition of amorphous submicron boron powder did not affect significantly the thermal performance of the epoxy. The 17% boron loading produced a 26% increase in compressive failure strength and a 68% increase in the compressive modulus. 0.125 inch thick specimens containing 17% boron absorbed 92% of incident neutrons from a 5-Curie Pu/Be source compared with {dollar}<{dollar}1% for the neat epoxy. Dispersion of the boron in the epoxy was improved with the addition of larger size crystalline boron powders. Carborane polyamides containing up to 35% boron were thermally stable up to 400{dollar}\sp\circ{dollar}C in air. The polymers had hydrogen/boron ratios from 2.0 to 3.8 and were soluble in several organic solvents. Polymer solutions were processed into clear, colored thin films. Boron-filled polyamic acid solutions of a PMDA-ODA polyimide containing up to 10% boron were processed into thin films. Neutron absorption of the opaque films measured in a 5-Curie Pu/Be neutron source was linear with boron concentration and film thickness. The fraction of neutrons absorbed varied linearly with boron concentration and film thickness. The applicability of boron-containing materials to the aerospace, nuclear power and accelerator industries was investigated.

The ability to process high performance polymers into useful adhesives and high quality composites has been significantly advanced by synthetic techniques in which oligomers terminated with reactive groups cure or crosslink at elevated temperature after the article has been fabricated. Several matrix resin systems of considerable interest to the aerospace community utilize phenylethynyl terminated imide (PETI) technology developed at the Langley Research Center to achieve this advantage. This work addresses the cure chemistry of PETI oligomers.;The thermal cure of selected oligomers and model compounds was studied using a variety of analytical techniques including differential scanning calorimetry, high pressure liquid chromatography, Fourier transform infrared, nuclear magnetic resonance, electron spin resonance and mass spectroscopies and liquid chromatography - mass spectroscopy. Model compound studies indicate that the cure is extremely complex. Many stable products were isolated and attempts at identification were made. Initial cure mechanisms have been proposed based on experimental results. The intent of this research is to provide fundamental insight into the molecular structure of these new engineering materials so that their performance and durability can be more adequately appreciated.

The objective of this research was to develop an in-situ sensing technique that monitors the molecular-level response of ions and dipoles to an applied electric field in order to characterize the changes in state of a polymer resin during chemical processing. This technique needs to be capable of monitoring the reaction progress not only in the laboratory setting but also in-situ in the processing tool or reaction environment. Frequency Dependent Electromagnetic Sensing (FDEMS) was selected for this task.;This dissertation investigates the applicability of FDEMS to monitoring two types of processing methods: reactive and batch reactor. The reactive processing system examined involves the processing of a high glass transition thermoplastic, either polyethylene ether or polyether imide blended with a thermoset, diglycidyl ether of bisphenol-A and 4,4'-methylene bis (3-chloro 2,6-diethylaniline]. The batch reactor processing systems examined involve the in-situ process control of an industrial batch reactor process involving five different systems: epoxy acrylic, polyester, latex, emulsion for lotions and surfactants.

Dendrimers are perfectly branched, well-defined macromolecules with a layered structure and a large amount of peripheral end groups. The high functionality in combination with the possibility of dendrimers to adopt a globular shape at high molecular weights, gives them very unique properties.In this work dendrimers up to fifth generation based on 2,2-bis(methylol)propionic acid (bis-MPA) were synthesized with different core structures. The core moieties were chosen in aspects of functionality and flexibility and the impact of the core on the physical and rheological properties was studied. By using the divergent growth approach dendrimers with acetonide, hydroxyl, allyl ether and methacrylate end groups were obtained.The bulk properties of the acetonide- and hydroxyl- terminated dendrimers were investigated with a rheometer. Temperature sweep tests were performed on the acetonide protected dendrimers in a temperature range of -50 up to 120°C at a constant frequency of 1 Hz. It was observed that the glass transition temperature (Tg) increased with increasing generation and that the modulus dropped without a trace of rubbery plateau for lower generations. This lack of rubbery plateau is due to the absence of entanglements between dendrimers. Interestingly, a small rubbery plateau was visible for generation five which implies enhanced interactions between the dendrimers. This behaviour suggests to be strongly influenced by the structural collapse at higher generations. Further, frequency sweep tests were performed on hydroxyl functional dendrimers at different temperatures. The results revealed Newtonian properties for lower generations and shear-thinning behaviour for higher generations at high frequency.Furthermore, this research involves the creation of well-defined thiol-ene networks by incorporation of allyl ether or methacrylate functional dendrimers in thermosets. This was accomplished by using two trithiols of different molecular weights and react them with the enes under UV irradiation. The thiol-methacrylate crosslinking reaction resulted in inhomogeneous films with and residual unsaturations. The thiol-ene films based on allyl ether dendrimers, on the contrary, resulted in homogeneous films with intermolecular couplings between the ene and the thiol being the dominant mode of polymerization. / Dendrimerer är perfekt grenade, väldefinierade molekyler med en struktur indelad i lager och med ett stort antal ändgrupper. Dendrimerer har, på grund av sina många funktionella grupper och sin förmåga att vid höga molekylvikter anta en mer sfärisk struktur, väldigt speciella egenskaper. Dendrimerer upp till femte generation, baserade på 2,2-dimetylolpropan syra (bis-MPA), har syntetiserats med olika typer av kärnstrukturer. Kärnorna valdes med avseende på funktionalitet och flexibilitet, och strukturens påverkan på dendrimerernas fysikaliska och reologiska egenskaper undersöktes. Dendrimerer med acetonid-, hydroxyl-, allyleter- samt metakrylatändgrupper syntetiserades genom att använda en divergent syntesmetod. De hydroxyl- och acetonidfunktionella dendrimerernas reologiska egenskaper i bulk karakteriserades med en reometer. De acetonidskyddade dendrimererna karakteriserades med temperatursvep i ett intervall mellan -50 °C och 120°C och med en konstant frekvens på 1 Hz. Analyserna visade att glastransitionstemperaturen (Tg) ökade med ökande generation och att dendrimerer av lägre generation inte uppvisade någon gummiplatå. Anledningen till detta är att det inte förekommer några kedjeintrasslingar mellan dendrimerer. Dock uppvisar femte generationens dendrimerer liten gummiplatå vilket pekar på ökade interaktioner mellan dem. Detta beteende påverkas av att dendrimerna kollapsar vid höga generationer och att förändringen i strukturen tydligt påverkar interaktionerna. Hydroxylfunktionella dendrimererna karaktäriserades med frekvessvep vid olika temperaturer. Det visade sig att lägre generationer uppvisar Newtonskt beteende medan högre generationer visar sig vara skjuvförtunnande vid höga frekvenser. Som en ytterligare del i detta projekt skapades väldefinierade tiol-en nätverk genom att reagera allyleter och metakrylat-funktionella dendrimerer med två trifunktionella tioler av olika molekylvikt. Reaktionerna initierades med UV-ljus. Tiol-metakrylat filmerna visade på en hög andel homopolymerisation vilket resulterade i inhomogent tvärbundna nätverk med ett stort antal oreagerade grupper. Tiol-allyleter filmerna visade uppvisade däremot homogena nätverk med en liten andel homopolymerisation. / QC 20100831

The construction of nanoscale polymeric objects with complex, well-defined structures and regiochemical functionalities is of great importance, because it enables the fabrication of soft materials with tunable properties. Direct polymerization of macromonomers through covalent bond formation and self-assembly of block copolymers via non-covalent interactions are two typical strategies to afford nanoscopic structures. Molecular brush polymers are composed of densely-grafted side chains along a polymeric backbone. Due to the significant steric repulsion from the side chains, they tend to adopt bottle-brush like conformations, as opposed to linear polymers. "Grafting through" synthesis of molecular brush polymers can provide precise control over the dimensions and functionalities of brush polymers. Shell crosslinked knedel-like nanoparticles (SCKs) are constructed by assembling from amphiphilic block copolymers into micelles, followed by covalent shell crosslinking to further stabilize the nanoparticles and introduce additional functional moieties. SCKs are attractive nanocarriers because of their variable morphologies, compositions and functionalities, which allow for the development of platforms for therapeutic or diagnostic purposes. By utilizing the orthogonal reactivity of the norbornene group and methacrylate group, two distinctly different reactive well-defined linear polymers, and a facile, one-pot synthesis of well-defined molecular brush polymers were studied by selective, orthogonal controlled radical polymerizations (CRPs) and ring-opening metathesis polymerization (ROMP). The living and high efficient characteristics of "grafting-through" strategy were further investigated for the preparation of topology-controlled brush polymers with tunable dimensions of both backbone and side chain lengths. Apart from the fundamental investigation of molecular brush polymers, a series of poly(carboxybetaine) (PCB)- and poly(ethylene glycol) (PEG)-grafted degradable SCKs were developed to evaluate their in vivo pharmacokinetics and biodistributions, aiming to achieve novel therapeutic and diagnostic platforms that may surpass the performance of the conventional PEGylated analogs.