No description available.

Thin film composite membranes were prepared by coating the surface of polyethersulfone ultrafilnation membranes with dilute solutions of sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) polymer. Poly(2,6-dimethyl-1,4-phenylene oxide) was first sulfonated to different degrees, thus obtaining polymers of different ion exchange capacities, from which the coating solutions in methanol or methanol/chloroform mixtures were prepared. The reverse osmosis performance of the thin film composite membranes was studied using electrolyte solutes of different valences and ionic radii. The effect of the solvent used for the preparation of the polymer solution for surface coating was also investigated through testing the performance of the composite membranes in separating different electrolyte solutions as well as by micrographic techniques using a Scanning Electron Microscope and an Atomic Force Microscope. It was found that the preparation of thin film composite membranes with high selectivity and high flux was possible by adjusting properly the ion exchange capacity and the solvent used in making the coating solution. It was also found that the membrane performance was governed primarily by the ion exchange reaction between the solute cation and the proton in-SO$\sb3\sp{-}$H$\sp{+},$ as well as by the Donnan equilibrium. An attempt was also made to investigate the effect of changing the microporous substrate of the thin film composite membrane on the membrane permeation rate and selectivity. The porosity and the structure of the substrate play a significant role in determining the performance of the composit membrane.

A regenerable polystyrylboronic acid resin has been prepared for the selective functionalization of polyols. The resin reacts with a diol group of a polyol to form a resin-bound cyclic boronate. Both the coupling and cleavage steps are performed under very mild conditions (removal or addition of water) and the resin is regenerated directly by the cleavage step. Monoacyl derivatives of some acyclic polyols and some partially acylated carbohydrate derivatives have been prepared efficiently on the resin without the need for any purification of intermediates. In addition, the polystyrylboronic acid resin which exhibits a high selectivity for cis diol systems, can be used in the separation of cis and trans diol mixtures such as the cyclohexanediols by affinity chromatography.

Heat of polymerization. With the use of a Tian-Calvet microcalorimeter, the heats of polymerization of a number of monomers have been measured in aqueous emulsion systems; the emulsifying agent was cetyltrimethylammonium bromide, and initiation was by Fenton's reagent (Fe++ + H 2O2). The monomers employed were acrylic acid, methyl, ethyl and butyl acrylates, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methacrylic acid, and methyl, ethyl, butyl and hexyl methacrylates. The heats of polymerization lie in the range from 13 to 19 kcal per mole, the experimental standard deviation being 40 to 110 cal per mole. A steady increase was observed for acrylic acids and its CH3, C2H5 and C 4H9 esters, and for methacrylic acid and its CH3, C2H5, C4H9 C6H 13 esters. This change is attributed to a steady increase in the proportion of head to head, tail to tail polymers, leading to a decrease in steric hindrance in the polymer. Abnormally low heats observed with hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate are attributed to the solvation of the monomer, less solvation being possible in the polymer as a result of shielding. Kinetics of polymerization. The microcalorimeter has been used to obtain rates of polymerization of a number of monomers in emulsion systems. The rates with the acrylates are consistently higher than those with the methacrylates, and this is attributed to there being less steric hindrance in the acrylate polymerization. Low rates found with the monomers containing a hydroxyl groups are explained as due to solvation in the initial monomer state. In both the acrylates and methacrylates the rates go through a maximum as one goes up the series methyl: ethyl: butyl: hexyl. This is discussed in terms of inductive and steric effects. Heats of vaporization. Heats of vaporization of fourteen alcohols, having from one to five carbon atoms, have been determined in a Calvet microcalorimeter, using a special technique. The method consisted of allowing the alcohol to vaporize into a vacuum, the heat required for the vaporization being provided by passing a current through a resistance wire which was immersed in oil in a U-tube surrounded by the alcohol. The additivity scheme previously devised by Laidler for heats of formation and related properties was applied to the results, and the agreement with experiment was within a few tenth of a percent. Additivity. An empirical bond energy scheme has been derived and applied to several physico-chemical properties of several families of compounds. The scheme proposed is a modification of Tatevskii's scheme. It defines three types of C-H bonds and several types of C-C bonds depending on their multiplicity and their environment. Other functional groups (e.g. -CHO, -COH) have been considered as a group and have been treated as such. They are assigned group symbols and their contribution to the physico-chemical property is a group contribution. The scheme has been applied to alkanes, alkenes, dienes and cylic hydrocarbons for the following properties; molar volume, molar refraction, entropy of formation and heat of atomization, all at 25°C. Molar sound velocities and diamagnetic susceptibilities are two other properties treated for several families of compounds.

Abstract not available.

This thesis describes a variety of synthetic attempts to prepare dendrimer-metal complexes anchored to silica. The new complexes were obtained by immobilization of a tridentate diphosphinoaryl ligand (PCP-type) palladium(II) complex onto silica and silica supported dendrimers which combine the advantages of heterogeneous and homogeneous catalysts. They are thermally stable and they are also stable towards oxygen and moisture. These complexes show high catalytic activity for the Heck reaction of aryl iodides with styrene and n-butyl acrylate, resulting in high yields of stilbene and cinnamate ester. They are also active in the reactions of a variety of aryl bromides with n-butyl and methyl acrylate, providing para-substituted cinnamate esters in good yields. These complexes are also effective catalysts for the cyclocarbonylation reaction of 2-allylphenol yielding five- or seven-membered ring lactones in good selectivity and in high yields. In addition, these complexes can be recycled by simple filtration in air and reused with little to moderate loss of activity. In both kinds of reactions, the dendritic systems show higher activity compared to the non-dendritic systems.

Hybrid organic-inorganic materials represent a new class of materials having scientific and technological potential. In this thesis, Polyhedral Oligomeric Silsesquioxanes (POSS) are used as an inorganic building block which has been tethered to an organic polymer. POSS are silica precusors, having a well defined silsesquioxane cental core surrounded by an organic periphery which makes them compatible with monomers and possibly polymers. The objectives of this study are to (1) study the basic structures of POSS homopolymers, (2) to incorporate POSS building blocks by a bottom-up approach into polymer chains and study the resulting morphologies, and (3) to study the thin film behavior of POSS block copolymers. PMA and styryl POSS homopolymers of different peripheries were synthesized by ATRP and mass spectrometry studies were carried out by MALDI-TOF and ESI. PMA POSS chains undergo a number of fragmentations while styrly POSS chains have a relatively robust backbone. Poly(ethylene-butylene-b-MAPOSS), AB type copolymers and poly(MAPOSS-b-styrene-b-MAPOSS), ABA type copolymers were synthesized by a combination of anionic and ATRP polymerization. Spheres, inverse cylinders, lamellar and crystalline lamellar morphologies were observed for the poly(ethylene-butylene-b-MAPOSS) copolymers. In the poly(MAPOSS-b-styrene-b-MAPOSS) copolymers, cylindrical, lamellar and perforated lamellar morphologies were obtained. Beyond the interaction parameter (χ), total degree of polymerization (N) and volume fraction (f), the conformational asymmetry (ϵ) also plays an important role in determining the morphology of these block copolymer. Crystallization of the POSS phase and better thermal properties were observed in the both block copolymers. Thin film studies of poly(MAPOSS- b-styrene-b-MAPOSS) copolymers showed that the microdomains can be oriented either parallel or perpendicular to the substrate depending upon the film thickness, morphology and relative volume fractions of the connecting blocks. By removal of the organic phase, ordered mesoporous low dielectric constant silica films were obtained. These hybrid block copolymers are a potential candidate for nanopatterning applications.

Single polymer passage through geometrically confined regions is ubiquitous in biology. Recent technological advances have made the direct study of its dynamics possible. We studied the capture of DNA molecules by the electroosmotic flow of a nanopore induced by its surface charge under an applied electric field. We showed theoretically that the DNA molecules underwent coil-stretch transitions at a critical radius around the nanopore and the transition assisted the polymer passage through the pore. To understand how a polymer worms through a narrow channel, we investigated the translocation dynamics of a Gaussian chain between two compartments connected with a cylindrical channel. The number of segments inside the channel changed throughout the translocation process according to the overall free energy of the chain. We found a change in the entropic driving force near the end of the process due to the partitioning of the chain end into the channel rather than the initial compartment. We also developed a theory to account for the electrophoretic mobility of DNA molecules passing through periodic confined regions. We showed that the decrease in the translocation time with the molecular weight was due to the propensity of hairpin entries into the confined regions. To further explore the dynamics of polymer translocation through nanopores, we performed experimental studies of sodium polystyrene sulfonate translocation through α-hemolysin protein nanopores. By changing the polymer-pore interaction using different pH conditions, we identified the physical origins of the three most common event types. We showed that increasing the polymer-pore attraction increased the probability of successful translocation. Motivated by understanding the dynamics of a polymer in a crowded environment, we investigated the dynamics of a chain inside a one dimensional array of periodic cavities. In our theory, the chain occupied different number of cavities according to its confinement free energy which consisted of entropic and excluded volume parts. By assuming that the chain moved cooperatively, the diffusion constant exhibited Rouse dynamics. Finally, we performed computer simulations of a chain inside a spherical cavity. We found that the confinement effect was best described by the hard sphere chain model. We further studied the escape dynamics of the chain out of the cavity through a small hole. The equilibrium condition of the chain during the escape was discussed.

The majority of this dissertation focuses on proton conducting materials that could be used at high operating temperatures. Higher operating temperatures are desirable as they will increase fuel cell efficiency, reduce cost, and simplify the heat management system. The factors governing proton conduction including segmental mobility, protogenic group identity, and charge carrier density were investigated on a variety of polymers containing 1H -1,2,3-triazole moieties. Proton conductivity measurements were made using AC impedance spectroscopy. Random copolymers and terpolymers of triazole-containing acrylates and poly(ethylene glycol)methyl ether acrylate (PEGMEA) have been synthesized. Conductivity increased with increasing degree of PEG incorporation until reaching a maximum at 30% mole PEGMEA. In comparison to benzimidazole-functionalized polyacrylate with 35% mole PEGMEA, the triazole analog showed a higher proton conductivity, and a less pronounced conductivity temperature dependence. Further increases in conductivity was achieved through the addition of trifluoroacetic acid. To study the effect of charge carrier density on proton conduction, polyacrylates containing a different number of triazole groups per repeat unit were synthesized. The result showed that introduction of more than one triazole per repeat unit did not result in an increase in conductivity as there was an accompanying increase in Tg. To improve the thermal and mechanical properties, triazole groups were tethered to a higher T g backbone polymer, polynorbornene. Introduction of polyhedral oligomeric silsesquioxane (POSS) into triazole-functionalized polynorbornene was also investigated. In a parallel set of investigations, poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, and copolymers of DMAEMA and methyl methacrylate (PDMAEMA-co-PMMA) were synthesized via atom transfer radical polymerization (ATRP). Fluorescently-labeled PDMAEMAs were synthesized using fluorescent ATRP initiators to ensure the presence of one dye molecule on every polymer chain. PDMAEMAs and PDMAEMA-co-PMMA with different molecular weights have been deposited onto a negatively-charged silica surface via controlled flow deposition. The results show that the polymer deposition rate depends on molecular weight, and is inversely proportional to molecular weight. A preliminary adhesion study of 1-ìm negatively charged silica spheres onto these functionalized surfaces indicates that by varying the molecular weight, the adhesion threshold can be changed. System modeling is being conducted to support experimental observations.

Ionic liquids (ILs), neoteric salts with Tm < 100°C, have garnered vast interest due to a number of unique properties including vanishingly low volatility, non-toxicity and property tunability. Many polymers were found to dissolve in ILs, and polymer solution properties were measured using the room temperature IL 1-ethyl-3-methylimidiazolium ethylsulfate, [EMIM][EtSO 4], as a model IL. Polyethylene glycol (PEG) dissolves in [EMIM][EtSO 4] above ∼60°C, the neat polymer's melting temperature, and if concentration and molecular weight are high enough, the solution transforms into a semi-transparent gel at lower temperature. Thermoreversible gelation is traced to kinetically frustrated polymer crystallization, a mechanism established previously for many pairings of crystallizable polymer with aqueous or organic solvent. Negatively and positively charged polymers dissolve in [EMIM][EtSO 4], typically over long time periods, and solution chain properties are measured using common physiochemical techniques. Electrostatic interactions of sodium poly(styrene sulfonate) are screened without the need of added salt due to the presence of the charged solvent and size-molecular weight relationships indicate sodium poly(styrene sulfonate) assumes a coiled conformation in solution. Lysozyme dissolves in [EMIM][EtSO4] assuming an expanded conformation with compromised secondary structure, the unfolded structure stabilized by the IL. Preferential solvation of dissolved lysozyme in mixed [EMIM][EtSO 4]/H2O solvents prevents lysozyme aggregation above its denaturation temperature.