D.H. Weinkauf

Characterization of polyisoprene - clay nanocomposites prepared by solution blending

The effects of clay dispersion and the interactions between clays and polymer chains on the viscoelastic properties of polymer/clay nanocomposites are investigated using oscillatory shear rheology, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Four different montmorillonite silicates of natural clays, plasma-treated clays, and organically modified clays (OCs) have been used in this study. For the polyisoprene (PI)/clay nanocomposites, the exfoliation of the OC dispersed in the PI matrix is confirmed with XRD and SAXS although TEM images show both exfoliated and non-exfoliated nanoclay sheets. In contrast aggregation or intercalation is obtained for the other PI/clay composites studied here. Additionally, the effective maximum volume packing fraction of OC for the exfoliated nanocomposites is determined from the overlapping of dynamic viscosity at low frequency regime, in which the effective maximum volume packing fraction is larger than the percolation threshold determined from the storage modulus of the nanocomposites.

Characterization of gas transport in selected rubbery amorphous polyphosphazene membranes

Gas permeabilities for six different gases have been evaluated for a series of closely related polyphosphazenes. Polyphosphazenes are attractive polymers for use as gas separation membranes due to their inherent chemical, thermal, and radiation stability. Additionally, polyphosphazenes may be tailored for specific chemical affinities. In this report, polyphosphazenes with three different pendant groups with varied hydrophilicity were characterized for gas permeation. All polymers were characterized as having modest permeabilities for methane, oxygen, nitrogen, helium, and hydrogen. These gases were not observed to have a significant interaction with the polymer structure and transport is attributed to segmental chain motion. Carbon dioxide was found to have a significant intermolecular interaction with the polymer and the permeability was observed to be proportional to the percentage of hydrophilic 2-(2-methoxyethoxy)ethanol on the backbone. Thus, we report a promising method for the development of CO2 selective membranes.

Vapor sorption in plasma polymerized vinyl acetate and methyl methacrylate thin films

Abstract Vapor sorption isotherms of vinyl acetate (VAc) and methyl methacrylate (MMA) plasma polymer thin films are measured and compared with those for cast films of the conventionally polymerized analogs. Sorption isotherms are collected for methanol, acetone, hexane, and water at 30°C using a Quartz Crystal Microbalance (QCM). The isotherms are analyzed using both Dual-Mode and Flory–Huggins sorption models. In general, plasma polymer sorption isotherms approximate those of the conventional polymer analogs, but exhibit an enhanced Langmuir-type sorption component at low activity. Accordingly, Dual-Mode model parameters show roughly equivalent Henrys Law solubility coefficients with the Langmuir-type capacity parameters (CH′) being 5–20-fold higher than those for the conventional polymer materials.

Pervaporation of water-dye, alcohol-dye, and water-alcohol mixtures using a polyphosphazene membrane

A novel phosphazene heteropolymer (HPP) was synthesized that contained three differing pendant groups: 2-(2-methoxyethoxy)ethanol (MEE), 4-methoxyphenol, and 2-allylphenol. The resulting polymer is an amorphous elastomer with good film forming properties where MEE and 4-methoxyphenol pendant groups influenced the hydrophilicity and the solvent compatibility of the polymer. Sorption studies were performed to characterize the polymer in terms of Hansen solubility parameters. Additionally, group contributions were used to predict the Hansen parameters for the polymer and these data compared favorably with the observed solubility behavior with 15 solvents that ranged from hydrocarbons to water. Homopolymers synthesized from MEE and 4-methoxyphenol were also studied for solubility revealing different behaviors with each representing a limit in hydrophilicity; MEE formed a water-soluble hydrophilic polymer and 4-methoxyphenol yielded a hydrophobic polymer. Membranes formed from HPP were characterized for use as pervaporation membranse using five different feeds: water–dye, methanol–dye, 2-propanol–dye, water–2-propanol, and water–methanol. Fluxes of methanol and isopropanol were greater than for water. For the alcohol–water separations, the alcohol was the favored permeate in all cases with higher fluxes observed for higher alcohol feed concentrations, however, separation factors declined.

Gas Transport in Liquid Crystalline Polymers

ABSTRACT The gas transport characteristics of main chain liquid crystalline polymers have been examined in order to understand the nature of the mesophase and what opportunities these materials offer for useful membranes or barriers. Is the liquid crystalline state more like a liquid (or amorphous glass) or a crystal? Experimental investigations of commercial aromatic polyamide and polyester liquid crystalline materials are reviewed. All of these materials prove to be exceptional barriers to permeation. For the polyesters, this is largely due to an extraordinarily low gas solubility. Analyses in terms of two phase and free volume models suggest that most of the transport may be occurring in a small volume fraction of a less dense boundary phase. The polyamides do not show the unusually low solubility; thus, a different physical model must be imagined for these materials.