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History of Silicone-Polyurethane
Release time:
2023-09-26
Although the use of silicone polymers as biomaterials predates polyurethanes by several years, researchers have long recognised the potential advantages of combining silicones and polyurethanes in a single biomaterial. Since about 1968, combinations of coatings, blends, interpenetrating networks, surface-modifying additives for polyurethane-based polymers, and, more recently, high-strength "structured" copolymers of silicones and polyurethanes have been prepared.
Prior to 1970, polyether-based polyurethanes doped with polytetramethylene oxide (PTMO) soft chain segments were known to be inherently hydrolytically stable and to have excellent flexural lifetimes.2 The late 1970s saw the continued development of the production of block thermoplastic copolymers with two or more of these soft chain segments in the polymer backbone. The use of more than one soft chain segment allowed the polymer properties to be optimised by controlling the concentration of each soft chain segment and the overall ratio of soft chain segments to hard chain segments. A range of polymers derived from thermodynamically compatible blends of poly(epoxidised) PTMO and PEO are highly permeable to water, gases and solutes, depending on the ratio of hydrophilic PEO to hydrophobic PTMO. These are currently used as films and occlusive dressings. As films or coatings, they have high moisture permeability as well as liquid and microbial barrier properties.
In polyurethane-silicone copolymers, silicones can be present along the polymer backbone and/or as covalently bonded end groups or grafts. Due to the surface activity of the silicone in the organic base polymer (even when copolymerised), silicone-like surface properties are relatively easy to obtain on polyurethanes at very low silicone content. This is especially true when the silicone is present as a mobile in the copolymer. The end groups can easily "self-assemble" on the copolymer surface. The challenge is to achieve some of the other desirable silicone properties, such as biostability or low modulus, while retaining the overall properties of the polyurethane, such as optical clarity, thermoplastic processability and very high toughness.
Structures of thermoplastic silicone-polycarbonate-polyurethane copolymers with silicone surface-modified end groups. Silicone content, hard chain segment concentration, and end group chemistry can be readily varied during synthesis to produce a wide range of surface and native properties. For example, fluorocarbon end groups can be used.
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