| PurSil® AL is a family of aliphatic, thermoplastic silicone polyether urethane copolymers. These polymers are formed by the incorporation of silicone in the polymer backbone together with polyether soft segments, and the use of Surface-Modifying End Groups™ (SME) to terminate the polymer chain. The biocompatibility of conventional silicones has been combined with the processability and toughness of thermoplastic polyurethanes. In related aromatic polyether urethanes the covalently bonded silicone seems to protect the polyether soft segment from oxidative degradation in vivo. Although less than 1% silicone can give silicone-like surface properties, higher silicone contents are useful in obtaining silicone-like bulk properties such as gas permeability or reduced water absorption. In the PurSil® AL family there are three currently available polymers with different silicone contents: 5%, 10% and 20% by weight. Depending on silicone content, modulus can be as low as that of natural rubber. The range of silicone content provides the device developer with the opportunity to select a particular formulation for a specific application. Optical transparency is possible over the range of silicone contents. These polymers have an unusual combination of high strength and high elongation with very low modulus values. This makes them attractive as high-performance thermoplastic silicone-polyurethanes that are potential alternatives to conventional thermo-set silicone rubber in both disposable and short term implantable biomedical devices. They are also used in applications that require good stability with exposure to visible light*. |
