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Permeability of low molecular weight compounds in polymeric matrices greatly
varies with the molecular structure of the polymer matrix. Membranes used in a
medical environment, i.e. oxygenators (heart-lung machines) and foils in the
packaging industry (PVC and PVDC) show impressive differences in the permeability
of gases and vapours. Structural parameters governing the kinetics of
diffusion are well established. Thus, oxygen diffusion through soft contact
lenses is greatly improved by incorporating bulky side groups in the backbones
of a very slightly crosslinked polyacrylate. Polymer systems may even accommodate
considerable amounts of chemicals having molecular weights mounting
up to 1000 daltons. Thus, swollen hydrogels of scarcely crosslinked polyhydroxyethyl
acrylates have been extensively studied as controlled release
devices of drugs in vitro and both animal and human biophases. From these
studies the role of the degree of crosslinking on the rate of diffusion and the
amount of foreign material accommodated in polymeric systems have been
firmly established [1-4].
EBC-acrylate coated laboratory benchtop material is presently marketed as
TRESPAToplab+ and sold to satisfy a: number of specific needs in various
laboratory environments: large seamless surfaces that are easy to decontamina-
te and to desinfect in a biological or clinical environment and chemical resistancy.
The coatings on these panels have a layered structure comprising a pigmented
base coating and a clear protective top coating. Although EBC-acrylates are
surprisingly resistant to a wide range of chemicals and, due to their cross-linked
structure, do not dissolve or even swell considerably in powerful organic sol-
vents, we were incidently faced with problems due to the diffusion of coloured
compounds into the coating. The main cause of this'staining turned out to be
due to diffusion and not to a direct chemical attack of the EBC-polymer. This
prompted us to investigate and improve the diffusion behaviourof chemicals in
EBC-acrylate coatings and the application of silica to inhibit diffusion in EBCfilms.
Incorporation of silica organosols [5] in polymeric material to improve
abrasion resistance is now well established [6]. However, the use of these
inorganic additives to monitor the diffusion characteristics of low molecular
weight compounds in polymer films is now about to be. explored. Optically
transparent silica deposits with a thickness of a few microns on polyester and
polypropylene films impose gas diffusion barriers comparable to PVDC films and
even aluminium foil and have been proposed [7-9] for 'packaging purposes.
However, incorporation of silica organosols in polymer films to retard permeation
of low-molecular weight compounds has, to the best of our knowledge, not
yet been reported.
