Thesis (M.Sc.)--City University of Hong Kong, 2004. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Aug. 31, 2006) Includes bibliographical references.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Dr. Uwe H. F. Bunz, Committee Chair ; Dr. Laren M. Tolbert, Committee Member ; Dr. Joseph Perry, Committee Member ; Dr. David M. Collard, Committee Member ; Dr. Anselm C. Griffin, Committee Member.

Abstract Synthetic routes were developed for the preparation of 2-alkoxy-4-hydroxybenzoic acids and 2-alkoxyhydroquinones, and a large-scale synthesis was developed for the preparation of 2-thioalkoxyhydroquinones. The 2-alkoxy-4-hydroxybenzoic acids, which contained alkyl side chains of different length, were used in the synthesis of new main chain liquid crystalline (LC) homo-, random, and block co-oligomers. In addition, oligomers of terephthaloyl chloride and 2-thioalkoxyhydroquinones and oligomers of terephthaloyl chloride and 2-alkoxyhydroquinones were produced. All the oligomers were blended with aliphatic polyamide 11 (PA 11). The effect of alkyl side chain length on the compatibility behavior of the LC oligomers towards the aliphatic polymer was characterized by DSC and FTIR, and the effect of side chain length on the flexural properties of the blends was investigated with a three-point bending test. The miscibility studies showed variable interfacial adhesion between the blended compounds. The strongest adhesion was achieved between PA 11 and the homo-oligomers of 2-alkoxy-4-hydroxybenzoic acids with short or medium long substituents (C4-C10), but the interactions between PA 11 and the oligomer with long aliphatic side chain (C18) were poor, as were those between PA 11 and the wholly aromatic oligomer of 4-hydroxybenzoic acid. The compatibility between PA 11 and the co-oligomers of 2-alkoxy-4-hydroxybenzoic acids was slightly lower than the compatibility of the corresponding homo-oligomers. DSC and FTIR analyses of the blends of oligomers of terephthaloyl chloride and 2-thioalkoxyhydroquinones and oligomers of terephthaloyl chloride and 2-alkoxyhydroquinones with PA 11 implied that the interactions between the blended compounds were poor. FTIR spectra and viscosity measurements confirmed that all the oligomeric structures could self-associate, with effect on the final mechanical properties of the polyamide. The strength of PA 11 in a three-point bending test was increased by the addition of only 1% of LC oligomers to the matrix. The results also showed that the strengthening ability of the oligomers is directly proportional to the total amount of aliphatic carbons. The best strengthening results were obtained with unsubstituted oligomers, random co-oligomers of 2-alkoxy-4-hydroxybenzoic acids, and homo-oligomer of 2-butoxy-4-hydroxybenzoic acid. DSC investigations of a ternary blend of the oligomer of 2-decanyloxy-4-hydroxybenzoic acid, PA 11, and wholly aromatic commercial LC polymer showed the promising compatibilizing effect of the oligomer.

In this study, crystalline poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-co-AAc) nanoparticle network in organic solvents was obtained by self assembling precursor particles in acetone/epichlorohydrin mixture at room temperature followed by inter-sphere crosslinking at ~98 °C. The crystals thus formed can endure solvent exchanges or large distortions under a temporary compressing force with the reoccurrence of crystalline structures. In acetone, the crystals were stable, independent of temperature, while in water crystals could change their colors upon heating or changing pH values. By passing a focused white light beam through the crystals, different colors were displayed at different observation angles, indicating typical Bragg diffraction. Shear moduli of the gel nanoparticle crystals were measured in the linear stress-yield ranges for the same gel crystals in both acetone and water. Syntheses of particles of different sizes and the relationship between particle size and the color of the gel nanoparticle networks at a constant solid content were also presented. Temperature- and pH- sensitive crystalline PNIPAm-co-AAc hydrogel was prepared using osmosis crosslinking method. Not only the typical Bragg diffraction phenomenon was observed for the hydrogel but also apparent temperature- and pH- sensitive properties were performed. The phase behavior of PNIPAm nanoparticles dispersed in water was also investigated using a thermodynamic perturbation theory combined with lightscattering and spectrometer measurements. It was shown how the volume transition of PNIPAM particles affected the interaction potential and determined a novel phase diagram that had not been observed in conventional colloids. Because both particle size and attractive potential depended on temperature, PNIPAM aqueous dispersion exhibited phase transitions at a fixed particle number density by either increasing or decreasing temperature. The phase transition of PNIPAm-co-AAc colloids was also studied. The results from the comparison between pure PNIPAm and charged PNIPAm colloids showed that the introducing of carboxyl (-COOH) group not only contributed to the synthesis of three-dimensional nanoparticle network but also effectively increased the crystallization temperature and concentration range. The phase transitions at both low and high temperatures were observed from the turbidity change by using UV-Vis spectrometer. Centrifugal vibration method was used to make crystalline PNIPAm-co-AAc dispersion at high concentration (8%). The turbidity test proved the formation of iridescent pattern.

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An A-B monomer containing an ether group, 4(4-acetoxyphenoxy) benzoic acid (PAPBA) was successfully synthesized via a new route using 4-methoxyphenol and 4-chlorobenzonitrile as starting materials. Another ether containing monomer, 4(2-acetoxy-6-naphthoxy) benzoic acid (PANBA), which appears to be a novel monomer, was also prepared in high yields from 6-methoxy-2-bromonaphthalene and ethyl-4-hydroxybenzoate via the Ullmann condensation reaction. These monomers were found to be useful for synthesizing LCP copolymers and segmented copolymers. A variety of polyarylates based on 5-tertiary butylisophthalic acid were synthesized via melt acidolysis techniques. The resulting high molecular weight polyarylates were amorphous polymers and the t-butyl groups along the polymer backbones were found to be thermoxidatively stable. Thermotropic liquid crystalline polyesters (LCPs) are well known for their thermoxidative stability, ductility, solvent resistance and the potential of generating extremely strong, stiff molecular chains. In this dissertation research, several novel liquid crystalline aromatic polyether-ester copolymers were synthesized by the incorporation of an A-B monomer, either PAPBA or PANBA, into the polymer main chain. The corresponding copolymers were thermoxidatively stable and melt processable over a wide compositional range. Novel carboxyl terminated oligomers of an amorphous engineering polymer, poly(arylene ether ketone)(PEK) were successfully synthesized. The synthetic method was somewhat similar to that of carboxyl terminated poly(arylene ether sulfone) oligomers. The PEKCOOH oligomers were quantitatively endcapped and their molecular weights could be controlled. Thermogravimetric analysis revealed that the PEKCOOH oligomers were thermoxidatively stable and therefore suitable for high temperature post-reactions. In general, thermotropic liquid crystalline polymers show excellent properties in the longitudinal direction. Nevertheless, to improve the transverse mechanical properties of liquid crystalline polymers, novel poly(arylene ether ketone)-LCP segmented copolymers were synthesized via melt acidolysis techniques. Chemically bonding an isotropic engineering thermoplastic into a potentially liquid crystalline anisotropic polyester affords segmented copolymers which may possess a balance of mechanical properties in both the longitudinal and transverse directions. In the case of PEK-poly(oxybenzoate)(PEK-POB), a limited amount of POB (~25 wt %) could be incorporated so as to produce segmented copolymers which would yield coherent films. On the other hand, when PEK-POB was modified by adding PAPBA to form PEK-POB-POPB segmented copolymers, a series of the segmented copolymers with various compositions was realized. The liquid crystalline behavior was found to be retained in the segmented copolymers, depending on the degree of the LCP content. The structural analysis of the A-B monomers mentioned earlier was performed by elemental analysis, mass spectroscopy, proton NMR and FT-IR. All the polymers synthesized were characterized by thermal analysis (DSC and TGA). The molecular weight of the carboxyl terminated PEK oligomers was determined by an automatic titration method, and indirectly, by intrinsic viscosity measurements. The latter method was also used to assess the molecular weight of the amorphous polyarylates. For liquid crystalline polyether-ester copolymers and PEK-LCP segmented copolymers, DSC and hot stage optical microscopy were utilized to investigate their thermotropic liquid crystalline behavior. DMTA was used to determine the high temperature properties of the polymers and tensile tests, i.e. stress-strain data, were employed to obtain information on their mechanical properties. / Ph. D.

The superior material properties of polymer/clay nanocomposites have attracted much research interests in the past years. The hypothesis of polymer stiffening in the vicinity of the nano-c1ay described using the "core-shell" model has not been fully investigated yet. The investigation of the interfacial region by atomic force microscopy (AFM) has provided us with details of the physical state of this region. It was found that the polymer stiffening region could extend as far as 200nm and 100nm from the face and the edge of a nano-clay respectively. Two different degrees of polymer stiffening have been observed from AFM micrographs with the help of amplitude and phase contrasting techniques. The temperature dependant property of the stiffened polymer has been studied using a heating stage, which showed the stiffened polymer was softened with increasing temperature between the studied range, 60°C and 91°C. The relative polymer crystallinity derived from the X-ray diffraction (XRD) data showed a general trend that increases with the clay content, regardless of the clay modification. However, an exception has been observed with the set of bi-axially drawn specimens, of which the highest polymer crystallinity was found to be the neat polymer when compared with the nanocomposites counterpart. It is believed that the presence of nano-c1ay particles restricted the reorientation of the polymer chains upon stress. From the in situ isothermal investigation of polymer crystal growth, it has been found the crystal grown from a nano-clay particle is larger than that from the bulk. This indicated that the crystallisation began at a lower temperature. The nano-clay and polymer crystal orientations have been further studied with X-ray texture analysis. It was found that the polymer chains were not completely aligned alone the extrusion direction as expected. Also, from the annealed specimens it was found that the orientation of the nano-clay particles had been influenced by the relaxation of the polymer chains.

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Thesis (Ph. D.)--Michigan State University. Chemical Engineering, 2008. / Title from PDF t.p. (viewed on Mar. 30, 2009). Includes bibliographical references. Also issued in print.