Solubility (S) and diffusion (D) of water in low-density polyethylene have been studied by means of desorption experiments. The dependence of S and D on the state of oxidation of the polymers has been measured. A model has been developed to describe the bound-oxygen dependence of S and D. Physically the oxygen groups act as traps that are strong enough to bind the water but not so deep as to remove the water from the diffusion process. Hydroxyl, hydroperoxide, and carboxylic acid groups form the strongest traps, ketone groups are weaker, and ester groups exhibit negligible trapping. Permeation is unaffected by bound oxygen. Trap volumes deduced from the analysis lie in the range of a few cubic angstroms. Some restriction of rotational motion of the trapped water is required by the analysis, and independent NMR evidence is presented to support this result.

he Brabender Plasti-Corder torque rheometer has T been widely used to study the rheological behavior of polymer melts under processing conditions (1, 2, 3 ) . This instrument, however, imparts a very complex shearing motion to the polymer; consequently the manner in which data taken with the Brabender may be related to specific processing operations, such as extrusion or milling, is unknown.The Brabender rheometer, depicted in Figure 1 , consists of a heated sample chamber which fits over two irregularly-shaped rollers. A quantity of polymer which will just fill the sample chamber is charged and melted.The total torque required to turn the rollers in the melt ASSEMBLY VIEW -TOP SAMPLE CHAMBER . ROLLER ASSEMBLY VIEW -FRONT Figure 1. Brabender torque rheometer.

Photopolymers are attractive candidates for high-density holographic data storage because of their high sensitivity and refractive index contrast. We have incorporated several high-index organic monomers into high optical quality acrylate oligomer-based formulations. Using reactivity ratios, reaction kinetics, and component refractive indices as guidelines, a 6-fold increase in Δn has been achieved compared to an initial all-acrylate formulation. Samples prepared from these formulations have been used to write and read >200 high-quality holograms in a given volume of material. This is the first time a photopolymeric medium has successfully been used to multiplex this number of holograms. Using these resins, a protocol for the evaluation of photopolymers as holographic media has been developed.

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The capillary flow instability resulting in extrudate distortion has been studied for ethylene polymer melts using a molecular structure approach. It is found that the instability initiates at a critical value of elastic strain energy independent of (average) molecular weight for linear polyethylene. Once the flow breaks down, a slip interface within the melt is formed near the capillary wall, causing an abrupt increase in volumetric throughput. The velocity gradient within the melt remains continuous through the instability, however. Low molecular weight species present in the molecular weight distribution of linear polyethylene tend to suppress slip. Blends of linear and branched polyethylene exhibit instability behavior characteristic of both components throughout the entire range of composition. Results are discussed in terms of specific molecular mechanisms.