| 摘要 |
The degree of polymerization of polyvinyl alcohol is reduced, e.g. from above 15,000 to 500-10,000, by heating in aqueous solution in a pressure vessel at 170-250 DEG C. Preferably air is excluded by heating in an atmosphere of steam or nitrogen, using solutions containing less than 20 per cent of polyvinyl alcohol. The low molecular weight polyvinyl alcohol may be recovered from the solution by concentration under reduced pressure, followed by precipitation with a water-soluble organic liquid such as acetone, methanol, ethanol, or dioxane either in bulk or fractionally, and drying the fibrous product in vacuo. The finished product may be used as an ointment base, an emulsifying agent, or a vehicle for therapeutic agents. |
