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Vestopal is a copolymer between a polyester of maleic and fumaric acids, esterified with di- and tri- hydroxyalcohols and styrene. In Vestopal, as supplied, styrene is mainly present as the monomer although some copolymer with the polyester is usually present. Vestopal "monomer" may be stored at -15°C. For several months without noticeable change.
Because this plastic is not miscible with water, biological specimens must be thoroughly dehydrated before infiltration with Vestopal. Dehydration may be carried out with acetone, dioxane, or glycol methacrylate.
The following procedure illustrates a typical use of Vestopal.
The hardness of the blocks, as already mentioned, is controlled by the amount of t-butyl perbenzoate in the final embedding mixture. It is also possible to produce softer blocks by the addition of dibutyl phthalate.
It is possible to polymerize Vestopal with ultraviolet light. Cobalt naphthenate may be omitted from mixture IV if UV polymerization is desired. Depending on the UV source, polymerization usually takes 2 - 4 hours.
One additional modification of the above procedure may be of interest: Rather than transferring specimens through several Vestopal-acetone mixtures (step 2), the specimen may be placed in a solution of 25% Vestopal in Acetone. The acetone is then allowed to gradually evaporate (usually overnight). This procedure results in complete infiltration of the specimen. Care should be taken, however, that moisture does not condense on the plastic as it is cooled by the evaporating acetone. The plastic will acquire a slightly white appearance should water vapor condense on it.
Cobalt naphthenate included in our kit is a 6% solution. Immediately prior to use, it should be diluted to a 3% solution by mixing with an equal volume of styrene.
DO NOT MIX COBALT NAPHTHENATE AND t-BUTYL PERBENZOATE DIRECTLY TOGETHER, AS THIS COMBINATION MAY BE EXPLOSIVE. ALWAYS ADD THESE REAGENTS TO THE VESTOPAL MIXTURE.
Kellenberger, Ryter, and Sechaud, J. Biophys., Biochem., Cytol 4:671, (1958).
Ryter, A. And Kellenberger, E., J. Ultrastruct. Res. 2:200 (1958)