Bulk morphologies and microphase separation behavior were studied as a function of composition and temperature for two-component (AB) diblock copolymers and as a function of composition and processing conditions for two-component segmented block copolymers. For the diblock study, well characterized, low molecular weight poly(styrene-isoprene) diblock copolymers (polystyrene volume fractions: 0.21-0.76) were examined with small angle X-ray scattering (SAXS) as a function of temperature to investigate the nature of order-order and order-disorder transitions near the microphase separation transition (MST). Data from these samples was used to develop a comprehensive morphology diagram, near the MST, as a function of $\sb{\chi}$N and composition. These results are compared with MST theories of Leibler and of Fredrickson and Helfand to provide a critical test of their predictions. Near a volume fraction of 0.5, both theories are shown to be relatively accurate, but at compositions far from 0.5 experimental results show that the two blocks are considerably less compatible than has been predicted. The absence of predicted order-order transitions near the MST indicates that composition fluctuation effects are important for low molecular weight diblocks. Further from the MST, an order-order transition was observed in a single sample as a function of temperature. The second study was an investigation of the effect of composition and processing conditions on microphase separation of segmented polyurea block copolymers used for reaction injection molding (RIM). Polyurea block copolymers polymerized in a RIM system were compared with solvent-cast solution polymerized polyureas of the same compositions (hard segment weight fractions: 0.11-0.66) to examine the effect of processing conditions. The Debye correlation function model, which assumes a random two-phase structure with no long or short range order and randomly shaped domains, was found to fit the SAXS data for the entire series of polyureas very well. Except at the highest hard segment content, the degree of phase separation, measured from the SAXS invariant, was higher for the RIM materials than the solution polymerized polyureas. This higher degree of phase separation correlates well with the better mechanical properties of the RIM samples.

Radiation crosslinked samples of poly(vinylidene fluoride) (PVF$\sb2$) were obtained from the Raychem Company, heated to above their crystalline melting point, stretched and isothermally recrystallized at 100$\sp\circ$C. The crystalline and amorphous orientation functions were studied as a function of crosslink density and extension ratio by X-ray diffraction and birefringence. The crystalline phase orients with its c-axis parallel to the deformation direction and the amorphous phase orients perpendicular to the deformation direction. The degree of orientation increases with both the crosslink density and the extension ratio. Values of both the crystalline and amorphous intrinsic birefringences of PVF$\sb2$ are offered. The intrinsic birefringence of the amorphous phase, calculated from bond polarizabilities and birefringence measurements using rubber elasticity theory, equals 0.098 $\pm$ 0.017. The intrinsic birefringence of the alpha crystalline phase is calculated from bond polarizabilities using the differentiated Lorentz-Lorenz equation and is equal to 0.145 $\pm$ 0.002. Each of the samples are characterized in terms of their polymorphic form by wide angle X-ray diffraction, their molecular weight using Flory-Rehner theory, and their degree of crystallinity from density measurements. In addition a value of 0.15 is offered for the polymer-solvent interaction parameter in N,N-dimethylacetamide. Finally, attempts at drawing a correlation between the amorphous orientation functions of molten PVF$\sb2$ samples and the orientation functions of these same samples after crystallization indicate that the crystalline orientation functions indeed depend upon the amorphous orientation functions of the deformed molten network rather than upon the crosslink density or extension ratio of the samples taken separately.

The incorporation of a small amount of ionic groups on a hydrocarbon polymer backbone profoundly alters its thermal, rheological and electrical properties. During this study, the effects of ionic content, neutralization level and processing history on ionic group mobility have been clarified. Randomly sulfonated polystyrenes (SPS) along with their sodium and zinc salts were prepared and carefully characterized via element analysis, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). These techniques all indicate a reduction in polymer chain mobility by enhanced glass transition temperatures (T$\sb{\rm g}$) and rubbery plateau moduli and decreased dielectric relaxation strength with increasing sulfonation and neutralization levels. In addition, the importance of processing history was observed through increased rubbery plateau moduli and ionic transition temperatures with increasing molding temperature. A secondary relaxation mechanism associated with ionic domains was revealed by the failure of the Williams-Landel-Ferry (WLF) equation to describe frequency plane shifts of DMTA and DETA data. These results are consistent with a model of ionomer morphology in which polar groups phase separate into thermally labile ionic crosslinks of high functionality with trapped hydrocarbon inclusions. For comparison with recent theories on relaxations of semi-crystalline polymers, a series of ethylene-methyacrylic acid(E-MAA) copolymers and their sodium salts were prepared and characterized by infra-red(IR) spectroscopy, DSC and DMTA. All E-MAA samples exhibited mechanical relaxations similar to low density polyethylene (LDPE). In the acid form, typical copolymer behavior was observed where the alpha transition temperature (T$\sb{\alpha}$) associated with the crystalline phase decreased and the beta transition temperature (T$\sb{\beta}$) or T$\sb{\rm g}$ increased with increasing MAA content. The gamma transition (T$\sb{\gamma}$) associated with local methylene segment motions remained independent of MAA content. The sodium neutralized samples displayed characteristics of a phase separated system in which T$\sb{\beta}$ was independent of MAA content, but about 5$\sp\circ$C higher than LDPE,and T$\sb{\gamma}$ decreased slightly with increasing MAA. The ionic transition temperature of E-MAA materials was found to be about 100$\sp\circ$C lower than the equivalent SPS material, indicating the weaker clustering behavior of carboxylate compared to sulfonate ionomers and the greater flexibility of ethylene- than styrene-based copolymers. Preliminary experiments probing ionic group and cation mobility in E-MAA samples on a molecular scale were undertaken using $\sp{23}$Na nuclear magnetic resonance (NMR) spectroscopy and DETA. The results indicated a broad step increase in the spin-spin relaxation time (T$\sb2$) with increasing temperature in ethylene glycol and water saturated materials. This increase was correlated with a broad dielectric "water relaxation" peak.

Tremendous advances in the synthesis and functionalization of nanoparticles over the past twenty years have resulted in remarkable discoveries in the field of nanotechnology. One such development is found in quantum dots, semiconductor nanoparticles that exhibit unique optical and electronic properties not found in the bulk. Research efforts associated with the combination of quantum dots and polymers center on uniting the mechanical or processing properties of the polymer with the optical properties of the quantum dot. Simply blending polymers with nanoparticles typically leads to nanoparticle aggregation, which negates the inherent advantageous properties of the quantum dots. The development of organic and polymer ligands for nanoparticle surface modification enables the preparation of dispersed nanocomposites that retain, or even enhance, the original nanoparticle properties. Presented here is the synthesis of functionalized nanoparticles that are tailored for the growth of polymers directly from the particle surface. Initial studies focused on the preparation of nanoparticle-polymer hybrid materials where the nanoparticles were evenly dispersed throughout the polymer. A method was developed to cross-link polymers grafted from the nanoparticle in an encapsulating shell, with the goal of minimizing nanoparticle degradation. In addition, polymerization chemistry from quantum dot surfaces was modified and optimized to produce conjugated polymer-quantum dot composites. The coupling of these two electronically active components gave composite materials with very unique optical properties that hold potential as displays, sensors, and light-emitting materials.

The overall objectives of the projects which constitute this Ph.D. thesis are a preparation of two-component polymer nanorods using anodic alumina membranes as templates and an investigation of their structures as well as a possibility for a preparation of composite nanorods. Anodic alumina membranes with various pore size prepared by the anodization of aluminum in electrochemical cell are used as well as commercial membrane (Chapter 2). Diblock copolymer nanorods are prepared using these membranes and their microphase-separated structures inside the membrane pores are investigated (Chapter 3 and 4). Semicrystalline polymer nanorods are prepared using these membranes and their composites are prepared by polymerizing second monomer inside these nanorods (polymer/polymer composite nanorods) or depositing metal clusters inside these nanorods (polymer/metal composite nanorods) (Chapter 5). Microphase-separated structures of diblock copolymers inside the cylindrical membrane pores are affected by the relationship between the size of pores and the repeat period of the block copolymers (commensurability). Polystyrene- b-polybutadiene (PS-b-PBD) confined inside the membrane pores show novel structures that cannot be accessed by any other method, caused by the commensurability and large curvature of the templates. The interaction between each block of diblock copolymer and the alumina surface is another factor for the micro-phase separated structures of diblock copolymers inside alumina membrane pores. Surface modification of alumina membrane pores using octyltrimethoxysilane (OTMS) inverted the multi-barrel structure of symmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA) and asymmetric PS-b-PMMA at large D/L 0, by changing the polarity of the templates. Asymmetric PS- b-PMMA at small D/L0 does not show this inversion. Poly(4-methyl-1-pentene) (PMP) nanorods are prepared using commercial alumina membranes. PMP/polynorbornene nanorods are prepared by polymerizing norbornene inside PMP nanorods using liquid CO2 as reaction medium. This also provides a way to observe the structures of these semicrystalline polymer nanorods. PMP/Pt nanorods are prepared by introducing Pt precursors, dimethyl(cyclooctadiene)platinum(II) (CODPtMe2), clusters using supercritical CO2 as a medium and reducing it with H2 to form Pt clusters inside PMP nanorods.

Emphasizing on the effect of molecular structure, the issues surrounding the thermal stability amorphous and crystalline states of poly(lactic acid), or PLA, are explored. Enthalpic relaxation, which correlates with physical aging, is investigated for PLA of different tacticities, and we find that a decreased number of configurational defects in the polymer backbone leads to a smaller Kohlrausch-Williams-Watts exponent. On the other hand, specific volume, or equivalently density, does not relate simply to enthalpic stability when comparing the α and stereocomplex forms of PLA crystals. Although the a crystal has the higher density, molecular interactions, as inferred from vibrational spectroscopy and molecular modeling, are stronger in the stereocomplex, a trend consistent with a higher enthalpy of fusion. The methyl-methyl and carbonyl-carbonyl interactions are the main contributors to the α crystal thermal stability, whereas the methyl-methyl and carbonyl-to-α-hydrogen interactions are the important interactions for the thermal stability of the stereocomplex. In addition, good correlation between the post-Tg exotherm and fiber shrinkage can be explained using spectroscopic and calorimetric means. We find that fiber thermal stability is not achieved when crystallizable chains remain largely uncrystallized. During processing, if crystallization is not completed before vitrification sets in, fiber shrinkage will take place, followed by crystallization enhanced due to pre-existing crystallites from processing.

Thesis. / Includes vita. Includes bibliographical references (leaves 148-152)

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 242-269.

A general strategy has been developed to synthesize biologically monodisperse polypeptides with the major repeat unit 1. These polymers are derivatives of poly($\alpha$,L-glutamic acid) (PLGA).$$- \rm Glu\sb{17}Asp-\qquad{\bf 1}$$ Such polymers should adopt an $\alpha$-helical structure when the side chain carboxylate groups are protonated, since Glu has the highest helix forming propensity (P$\sb\alpha$ = 1.59) of all twenty natural amino acids. Polymer 2 was synthesized as a fusion protein with glutathione S-transferase (GST) in a bacterial host, and was liberated from the GST fragment by CNBr cleavage.$$\rm GluAsp(Glu\sb{17}Asp)\sb4GluGlu\qquad{\bf 2}$$ DNA sequencing and amino acid analysis confirmed the composition of 2. Polymer 2 undergoes a conformational transition in aqueous solution from a random coil to an $\alpha$-helix as indicated by circular dichroism measurements. The $\alpha$-helical structure persists when the solvent is removed as demonstrated by Fourier transform infrared (FTIR) spectroscopy. Electrophoresis shows that polymer 2 is much more homogeneous in terms of molecular weight than chemically synthesized PLGAs of comparable molecular weight. A method was adopted to make the monodisperse rodlike molecule 3, a derivative of poly($\gamma$-benzyl $\alpha$,L-glutamate) (PBLG), by reacting 2 with phenyl diazomethane. Quantitative conversion was indicated by nuclear magnetic resonance spectroscopy. In helicogenic solvents for PBLG, 3 also assumes an $\alpha$-helical structure and transforms into a random coil when trifluoroacetic acid is added to the solution. Polymer 3 self-assembles into $\alpha$-helical structure when cast as a film from tetrahydrofuran solution. Gel permeation chromatography shows that 3 has a much narrower molecular weight distribution than chemically synthesized PBLG of comparable molecular weight.$$\eqalign{\rm Glu(OBzl)Asp(OBzl)&\{\lbrack(\rm Glu(OBzl)\rbrack\sb{17} Asp\cr&\qquad(\rm OBzl)\}\sb4Glu(OBzl)Glu(OBzl)\qquad{\bf 3}\cr}$$where OBzl denotes a benzyl ester. High molecular weight PLGA was chemically synthesized from $\gamma$-benzyl $\alpha$,L-glutamate N-carboxy anhydride. This polymer was modified with 8 mol % or 15 mol % hexylamine. The modified polymers can disrupt dilauroylphosphatidylcholine multilamellar vesicles and egg yolk phosphatidylcholine small unilamellar vesicles in a manner which is dependent on the solution pH. Fluorescent probes, specifically pyrene and S-anilino-naphthalene-1-sulfonic acid, ammonium salt, indicate that the modified polymers associate in a pH-dependent fashion and provide hydrophobic domains to solubilize lipid membrane vesicles.

Genetic engineering of protein-based polymers offers distinct advantages over conventional synthesis of polymers. Microorganisms can synthesize high molecular weight materials, in relatively large quantities, that are inherently stereoregular, monodisperse, and of controlled sequence. In addition, specific secondary and higher order structures are determined by this protein sequence. As a result, scientists can design polymers to have unique structural features found in natural protein materials and functional properties that are inherent in certain peptide sequences. For this reason, genetic engineering principles were used to create a set of artificial genes that encode twelve macromolecules having both $\alpha$-helical and disordered coil protein sequences with the last amino acid being cysteine (cys) or tryptophan (trp). Triblock copolymer sequences having coiled-coil protein ends, A or B, where A and B represent $\alpha$-helical acidic and basic leucine zipper proteins, separated by a water soluble flexible spacer coil protein, C, where C represents ((AG)$\sb3$PEG) $\sb{\rm n}$ (n = 10 or 28), showed reversible physical gelation behavior. This behavior is believed to result from the aggregation of two or more helices that form physical crosslinks with the disordered coil domain retaining solvent and preventing precipitation of the chain. Diffising wave spectroscopy was used to investigate the gelation behavior of AC$\sb{10}$Acys in buffer when environmental conditions such as pH, temperature, and concentration were varied. The dynamic intensity autocorrelation function recorded over time for 5% (w/v) AC$\sb{10}$Acys showed that the protein behaved as a gel at pH 6.7-8.0 and that the melting point was between 40$\sp\circ$C and 48$\sp\circ$C. In addition to the triblock results, the incorporation of 5$\sp\prime$,5$\sp\prime$,5$\sp\prime$-trifluoroleucine (Tfl) in place of leucine (Leu) in the A and B blocks was accomplished by synthesizing proteins in bacterial hosts auxotrophic for Leu. The substitution of Tfl for Leu in A and B was confirmed by electrospray mass spectrometry. Amino acid analyses performed on purified Tfl A and Tfl B populations suggested 66% and 38% levels of Tfl substitution, respectively. Thermal denaturation temperatures measured by circular dichroism of the Tfl containing helices were higher than those of the corresponding Leu containing helices by 8$\sp\circ$C and 13$\sp\circ$C for A and B respectively.