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types, such as polacrilin potassium (Amberlite IRP 88, sulfonated polystyrene resin) are used as tablet disintegrants because of the high degree of swelling the dry resins undergo on interaction with water.

8.5.3 Silicone oligomers and polymers

The silicones are examples of hydrophobic liquid polymers, although in high molecular weight they exist as waxes and resins. Silicones are polymers with a structure containing alternate atoms of Si and O; the dimethicones are fluid polymers with the general formula XIX in which each unit has two methyl groups and an oxygen atom attached to the silicon atom in the chain. The viscosity range extends from 0.65 cS to 3 x 106cS. The dimethicones 20, 200, 350 and 1000 (the number representing the average viscosity in centistokes at 25°C) have rheological properties which allow them to be used in ophthalmology and in rheumatoid arthritis. Dimethicone 200 has been used as a lubricant for artificial eyes and to replace

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