Polyurethanes hydrolytic degradation

Abrasion-resistant duties may involve abrasion in an aqueous phase or abrasion by dry particulate materials. The selection of the polyurethane type is most important to obtain the best results. Polyester-based polyurethanes perform best in dry abrasion due to their low hysteresis properties and excellent resistance to cut initiation and propagation. However, polyester polyurethanes are susceptible to hydrolytic degradation, and therefore polyether polyurethanes are normally used for aqueous abrasion duties. 

In dentistry, silicones are primarily used as dental-impression materials where chemical- and bioinertness are critical, and, thus, thoroughly evaluated.546 The development of a method for the detection of antibodies to silicones has been reviewed,547 as the search for novel silicone biomaterials continues. Thus, aromatic polyamide-silicone resins have been reviewed as a new class of biomaterials.548 In a short review, the comparison of silicones with their major competitor in biomaterials, polyurethanes, has been conducted.549 But silicones are also used in the modification of polyurethanes and other polymers via co-polymerization, formation of IPNs, blending, or functionalization by grafting, affecting both bulk and surface characteristics of the materials, as discussed in the recent reviews.550-552 A number of papers deal specifically with surface modification of silicones for medical applications, as described in a recent reference.555 The role of silicones in biodegradable polyurethane co-polymers,554 and in other hydrolytically degradable co-polymers,555 was recently studied. 

The polyurethanes based on the 0-benzyl protected 6, 11, and 12 yielded partially debenzylated products with Tg values ranging between 20 and 30°C. Fully benzylated polyurethanes showed high resistance to hydrolytic degradation, whereas polyurethanes with free hydroxyl side groups degraded significantly in saline buffer at pH 10 and 37°C [113, 114]. 

Autoclave sterilization is one of the most difficult common sterilization environments for a medical adhesive, and it is commonly used in hospitals and health care facilities for reusable devices. Autoclaves sterilize with high-pressure steam. Temperatures inside the sterilization chamber typically can reach 130°C with pressures above ambient. Certain adhesive systems, such as polyurethanes, may show hydrolytic degradation in such environments especially after multiple cycles. Epoxies perform the best under multiple autoclave exposures. However, on certain substrates, light-cured acrylics and cyanoacrylates will also perform fairly well. 

Tang, Y.W., Santerre, J.P., Labow, R.S. and Taylor, D.G. 1997a. Application of macromo-lecular additives to reduce the hydrolytic degradation of polyurethanes by lysosomal enzymes. Biomaterials 18 37-45. 

Special methods are necessary for the production of polyurethane dispersions because of the thermodynamically unstable nature of these two-phase systems. A simple application of the emulsion polymerization techniques for isocyanate polyaddition reactions is not possible, due to the reactivity of the NCO group with water. The extreme water sensitivity of all polyurethane preparation procedures which calls for the complete absence of water is obviously a major problem to be overcome in their preparation. It is surprising, given the basic hydrolytic degradability of polyurethane elastomers, to find that polyurethane latex has good long-term stability when it is a two-phase system. This is in contrast to the situation that applies when it is present in a one-phase system. 

One symptom by which acute hydrolytic degradation is observed in a polyurethane elastomer is the development of cracks, usually deep random... 

Brown D, Lowry R, Smith L. Hydrolytic degradation of polyester polyurethanes containing carbodiimides. Macromolecules 1982 15(2) 453-8. 

Takahara A, Hergenrother RW, Corny AJ, Cooper SL. Effect of soft segment chemistry on the biostabihty of segmented polyurethanes. II. In vitro hydrolytic degradation and hpid sorption. J Biomed Mater Res 1992 26(6) 801-18. 

Polyols are multifunctional alcohols with a polyether, polyester, or polycarbonate backbone. They are typically viscous liquids with molecular weights ranging from 200 to 5000g/mol. The polyol component of the polyurethane significantly affects the degradation rate of the final cured polyurethane. Typically, the rate of hydrolytic degradation of polyols observes the order polycarbonate[Pg.482]

Polyurethane oil seals failed due to hydrolytic degradation which happened because over time the oil became contaminated with water. All polyurethanes are prone to hydrolysis and oil absorbs water during use. If testing had been done in used oil the problem would have been obvious. Eventually the material was changed to EPDM. 

T. Takamoto, H. Shirasaka, H. Uyama and S. Kobayashi, Lipase-catatyzed hydrolytic degradation of polyurethane in organic solvent, Chem. Lett, (6) 492-493,2001. 

Polyurethanes obtained from renewable resources, such as carbohydrates, have attracted much attention in recent years [110,111]. This new interest results from great biomass access and their potential as replacements for some petroleum-based polymer precursors. The polymers obtained from natural products are expected to be biodegradable and non-toxic. The inclusion of hydrophilic monomers, such as carbohydrates, into the polymer chain facilitates water attack, increasing the hydrolytic degradation. 

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