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Silicones and polyethers and silicones and polycarbonates
Release time:
2023-09-26
Silicone polymers have a long history of use in biomedical applications, particularly in the cardiovascular field. In general, pure silicone polymers have good haemocompatibility and relative nonthrombotic properties; however, they lack mechanical integrity and physical properties such as tear and cut growth extensibility, as well as the higher modulus required for some critical applications. Silicone-containing polyurethanes have been developed to improve not only the physical properties of silicone polymers, but also the surface and bulk properties of silicone-free polyurethanes. (Purchase Silicone Polyurethane Copolymers; Silicone Polycarbonate Polyurethane Copolymers; Contact Fulin Plastics Now)
Useful soft chain segment combinations include polyalkylene carbonate + polydimethylsiloxane or polyepoxane + polydimethylsiloxane. Increased silicone content improves biostability and (oxygen) permeability, but rapidly reduces toughness. Polyurethanes with these mixed soft chain segments can be optimised by soft chain segment composition, e.g. for biostability and/or permeability, while maximising the physico-mechanical properties. Figure 16 shows the effect of silicone content on the oxygen permeability of nine polymers, including polymers made from blended PTMO+PSX soft chain segment combinations. When extrapolating the graph to a "hypothetical polyurethane" containing 100% silicone, documented values for oxygen permeability are obtained for pure PSX, and in the case of non-porous polyurethanes (ureas) with two soft segments, one of which is hydrophilic, the permeability can be precisely controlled. Here, increasing the polyethylene oxide (PEO) content in PEO + PTMO (polytetramethylene oxide) polyether urethanes improves the "inverted cup" moisture vapour transmission rate (MVTR) as measured according to the ASTM E 96-BW standard for film thicknesses of 0.001 inch. MVTR values vary by five orders of magnitude among polymers. Hydrophilic polyurethanes are among the best known high-strength polymers for moisture permeability, and their applications include films, wound dressings, and (biodegradable) films used to prevent post-surgical adhesions. Tailored glucose permeability (measured in diffusion cells) is also possible, as shown on the right. In this family of polymers, the glucose permeability coefficient is not measurable at PEO levels below 10%, but increases rapidly at PEO levels above that concentration.
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