Jane C. Graper

Highly swollen hydrogels: vinyl pyrrolidone copolymers☆

Abstract The objective was to prepare hydrogels which, though highly swollen, would have sufficient strength to allow crosslinked poly(vinyl pyrrolidone). Inclusion of tetraethyleneglycol dimethacrylate resulted in only a low physical (hydrophobic) crosslinks. The most successful results were achieved by gamma-irradiation of aqueous solutions of vinyl pyrrolidone plus methyl acrylate. Glass transitions of xerogels were characterized by differential scanning calorimetry. It was deduced that the hydrophobic comonomer (methyl acrylate or methyl methacrylate) is concentrated in microphase domains embedded in a matrix of almost pure crosslinked poly(vinyl pyrrolidone). Inclusion of tetraethylene glycol dimethacrylate resulted in only a low crosslinking efficiency but, nevertheless, had a marked influence in preventing phase separation, which gives hydrogels of improved clarity and mechanical strength.

Mechanisms of Oxygen and Water Diffusion Through Multilayer Inorganic/Organic Coatings

Polyethyleneterephthalate substrates were coated with thin films of silicone oxide deposited by magnetically enhanced chemical vapor deposition. The rates of oxygen and water vapor transport through the coated and uncoated film systems were obtained as a function of temperature. Activated rate theory treatment of oxygen transmission rates revealed that silicone oxide coatings were imperfect; the apparent free energies of activation (ΔEp) for transport through film substrates which were coated on a single side were statistically identical to uncoated controls. However, multilayer coatings, consisting of two silicone oxide layers separated by an organic layer resulted in a dramatic increase in the ΔEp value. Similar effects were observed in polymer films coated on both sides with identical oxide layers. A simple empirical model for the change in transport mechanism is offered to explain this unanticipated results. Activated rate theory treatment of water vapor transmission rates for these same film systems showed no obvious change in transport mechanism. However, ΔEp values obtained for water vapor permeation through silicone oxide coated polyethyleneterephthalate, polystyrene, polypropylene, and polycarbonate substrates were identical within experimental error, suggesting attractive interaction between the oxide layer(s) and water.