Robert A. Orwoll

Polymer–Solvent Interaction Parameter χ

14.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 14.2 Methods of Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 14.3 General Features and Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Thermal Pressure Coefficients and Specific Volumes of Cyanobiphenyls and their Transition Entropies at Constant Volume

Abstract Specific volumes and thermal pressure coefficients (∂p/∂T)v of 5CB, 7CB, 50CB, and 80CB were measured from temperatures near their crystalline melting points to above their nematic-isotropic transitions. At TNI, volume changes ΔV of 0.52, 0.67, 0.25, and 0.48 cm3 mol−1, respectively, were found. A discontinuity of 0.02 cm3 mol−1 in the volume of 80CB was observed at its smectic A-nematic transition. The entropy change at constant volume ΔSv was determined at TAN and TNI by subtracting the entropy of dilation (∂p/∂T)v ΔV from the entropy change at constant pressure. The latter quantity was obtained from the slope of the phase boundary curve according to the Clapeyron equation. This was judged to be a more reliable procedure than using transition heats from DSC. Values of ΔSv vary from 0.03Rto 0.10R for the nematic-isotropic transition, where R is the gas constant.

The effects of atomic oxygen on polymer films containing bis(triphenyltin) oxide

A tin-containing compound, bis(triphenyltin) oxide (BTO), was added to two polymeric materials in an effort to reduce the erosion of the materials in the presence of atomic oxygen. The BTO was added to a solution of a thermoplastic polyetherimide, and to the amic acid solution of a polyimide thermoset before curing. The films of these materials were tested in the laboratory by exposing them to atomic oxygen from a plasma generator. Subsequently, they were exposed to the Low Earth Orbit (LEO) on two Space Shuttle flights. In all cases, the BTO-containing materials exhibited significantly less mass loss than the corresponding pure polymer. Analysis by X-ray photoelectron spectroscopy showed that after exposure to atomic oxygen, the BTO-containing films had a predominance of tin oxide on their surfaces. This could serve as a barrier to resist further erosion.

Polyimide Nanocomposites Prepared with a Novel Aromatic Surfactant

Montmorillonite clays modified with 1,5-bis(3-aminophenoxy)-3-oxapentane dihydrochloride (BAOD) were used in the preparation of polyimide/organoclay hybrid films. Organoclays with varying surface charge based upon BAOD were prepared and examined for their dispersion behavior in the polymer matrix. Initial evaluation was performed by preparing high molecular weight poly(amide acid) solutions in the presence of the organoclays at a 3 wt% loading. Films were cast and subsequently heated to 300 °C to cause imidization. The resulting nanocomposite films were characterized by transmission electron microscopy and x-ray diffraction. It was found that the clays cation exchange capacity (CEC) played a key role in determining the extent of dispersion in the polyimide matrix. Considerable dispersion was observed in nanocomposite films prepared from organoclays possessing medium and high CECs. One organoclay that dispersed well was further evaluated in nanocomposite films at weight loadings of 5 and 8%. The nanocomposite films were characterized by transmission electron microscopy, x-ray diffraction, and thin-film tensile testing. High levels of clay dispersion were achieved even at the higher clay loadings. Mechanical testing of these films showed that the moduli of the materials increased with increasing clay concentration, but the strength and elongation were generally adversely affected.

The effects of UV radiation on several high-performance polyimide composites

Three high-performance polyimides were exposed at 177°C to ultraviolet radiation at three different intensities and for three different times so that the product of intensity and time was a constant. Intensities of 1, 2 and 3 suns, and times of 500, 250 and 167h were used. One sun is the power in space at one earth-sun distance and is 0.135J s -1 cm -2 . The polyimides were LARC-8515, PETI-5 and K3B. Samples were analysed by XPS, TGA, TMA and DMA. Thermal analyses by TGA, TMA and DMA, which measure bulk properties, showed essentially no difference between samples exposed to heat and UV radiation, and control samples. Surface analysis by XPS showed an apparent decrease in carbonyl on the surface of some exposed samples. This could be correlated for the PETI-5 and LARC-8515 samples to surface contamination by a silicone-containing material.

Boron Containing Polyimides for Aerospace Radiation Shielding

In interplanetary travel and high altitude flight, humans will be exposed to high energy charged particles from solar flares and galactic cosmic rays. These particles lose energy in a material by Coulomb interactions and nuclear collisions. In nuclear collisions, large amounts of energy are transferred and secondary particles are formed from both the projectile and the struck nucleus. A significant portion of these particles are neutrons which can only lose energy by collisions or reactions with a nucleus. Hydrogen-containing materials, such as polymers, are most effective in reducing the neutron energy. When reduced to very low energies, neutrons have a high probability of reacting with a nucleus. Such reactions are dangerous in the human body, and can cause electronic equipment failure. Low energy neutrons react particularly well with a stable isotope of boron, 10 B. To test structural materials which contain both hydrogen to reduce the energy of neutrons and boron to absorb neutrons of reduced energy, samples of two polyimides were made which contained varying amounts of either amorphous boron powder or boron carbide whiskers. The polymers used were a thermoset, PETI-5 from Imitec, and a thermoplastic, K3B from Fiberite. Both materials were made in pure form and with up to 20% by weight of the boron additives. The addition of boron in either form did not change the thermal properties of these materials significantly. However, the compressive yield strength and the tensile strength were both affected by the addition of the boron materials. A neutron absorption test using a PuBe thermal neutron source showed that a 0.5 cm thick sample of K3B containing 15% amorphous boron powder absorbed over 90% of the incident neutrons.

Molecular Imprinting by 4-Hydroxybenzoic Acid: A Two-Site Model

4-Hydroxybenzoic acid (4HBA) imprinted polymer was synthesized with the functional monomer, acrylamide, and the crosslinking agent, ethylene glycol dimethacrylate, in acetonitrile. Hydrogen bonding between the template and the monomer not only controls the template molecules in and out of the binding sites, but also contributes to special binding sites in the resulting polymer resin. Batch analyses showed that the 4HBA-imprinted polymer has a special affinity for the para-substituted hydroxybenzoic acid, but not for its meta-substituted isomer (3HBA), nor for benzoic acid (BA). The binding behavior of 4HBA can be interpreted with a simple two-site model with one kind of site in the resin being special for 4HBA and the other kind being general with similar affinities for 4HBA, 3HBA, and BA. These general binding sites found in both the imprinted resin and the non-imprinted reference resin have greater affinity, but are less numerous than the sites unique to the imprinted resin.

Molecular Imprinting of 3-Hydroxybenzoic Acid: Special and General Binding Sites

A resin, imprinted with 3-hydroxybenzoic acid (3HBA), was synthesized from acrylamide (AA, the functional monomer) and ethylene glycol dimethacrylate (EGDMA, the crosslinking agent). Batch analyses showed that the imprinted polymer has a special affinity for the meta -substituted 3HBA, but not for its para -substituted isomer (4HBA) nor for benzoic acid (BA). These results are consistent with the principle that an imprinted resins ability to recognize is dependent on the targets size, shape, and functionality. Another resin, prepared from AA and EGDMA but in the absence of a template, had similar affinities for 3HBA, 4HBA, and BA; and thus it could not differentiate among the three. The results can be interpreted with a simple two-binding-site model with one site special for 3HBA and the other being more general with similar affinities for 3HBA, 4HBA and BA. The binding of 3HBA to the imprinted resin is characterized by an association constant and the density of each kind of site using a two-site Scatchard equation. The binding sites common to both the imprinted resin and the non-imprinted reference resin were found to have greater affinity but are less numerous than the sites unique to the imprinted resin.

Synthesis and characterization of poly(arylene ether)s and poly(arylene ether imidazole)s

Poly(arylene ether)s, poly(arylene ether imidazole)s and poly(arylene ether coimidazole)s are under investigation as part of a structure/property relationship study. The objective of this study is to identify polymers or copolymers with an attractive combination of properties for use as toughening agents for epoxies. The copolymers are being studied as possible toughness modifiers for epoxy resins because of their high glass transition temperatures, their high toughness and the ability of the active hydrogen on the imidazole moiety to react with the oxirane ring of epoxies. Homopolymers and copolymers were characterized by differential scanning calorimetry, thermal gravimetric analysis, thin-film tensile properties and neat resin flexural and toughness properties.

Modification of a high performance epoxy matrix with poly(arylene ether-co-imidazole)s

Abstract In an effort to improve toughness N,N,N′,N′ -tetraglycidyl-4,4′ diaminodiphenyl methane (TGMDA) was modified with poly(arylene ether- co -imidazole)s (PAE- co -Is). The PAE- co -Is contain imidazole units distributed randomly along the backbone which react with the epoxies upon curing. A system modified with 10% w/w high molecular weight polymer exhibited increases in fracture toughness of 1.7 times that of the unmodified system; however, controlled molecular weight PAE- co -Is were required to retain processablility. Modification also resulted in significant decreases in the tetrahydrofuran sensitivity. Scanning electron photomicrographs of the fractured surface showed stress whitening with no clear phase separation whereas poly(arylene ether)s without imidazole groups exhibited gross phase separation.