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Abstract

The present invention is directed to pure polyurethanes which are biocompatible. These pure polyurethanes comprise the reaction product of: a) a pre-adduct containing NCO groups and comprising the reaction product of i) a diisocyanate selected from the group consisting of aliphatic diisocyanates, cycloaliphatic diisocyanates, and mixtures thereof, with ii) a macrodiol having a molecular weight of from 500 to 10,000 wherein said components i) and ii) reacted at temperatures of from 90.degree.-150.degree. C.; with b) a chain extender having a molecular weight of from 62 to 400 and being selected from the group consisting of aliphatic diols, cycloaliphatic diols, and mixtures thereof, and optionally, c) additional diisocyanate selected from the group consisting of aliphatic diisocyanates, cycloaliphatic diisocyanates, and mixtures thereof, wherein said component c), when added, is added either simultaneously with component b) or separately from component b), the quantities of components a)i), a)ii), and c) being such that the molar ratio of diisocyanate to macrodiol is from 1.5:1 to 22:1, and the reaction of components a) and b) and optionally component c) is conducted at temperatures of from 90.degree. to 230.degree. C., with the proviso that the reaction conditions are maintained until said polyurethane has a melt viscosity of at least 2500 mPa.s at 120.degree. C.

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First Claim