99 5 0 5 sorbitane trioleate5 97 0 3 0 polyoxyethylene monostearate______________________________________ sheeting 0 3 mm thick was poured from these solutions containing the fatty acid esters in a cleanroom subject to dust free conditions the sheets were transparent and smooth surfaced their blood compatibility was tested by the method described by fischer et al and was better in every case than that of the starting polyurethane prepared as described with reference to example 1 calcification was tested by the method described by glasmacher et al and was better in every case than that of the starting polyurethane prepared as described with reference to example 1 the starting polyurethane solution prepared as described in example 1 was treated with various fatty acid esters and cross linking agents as described in the following table __________________________________________________________________________ spu 1ex wt fatty acid ester wt cross linking agent wt __________________________________________________________________________6 96 0 3 isopropyl palmitate 1 0 u03b3 aminopropyl tris ethoxysilane7 96 5 3 polyoxyethylene sorbitane monooleate 0 5 n aminoethyl aminopropyl trimethoxysilane8 93 0 5 ethyl laurate 2 0 34 triaminosilane 34 h sub 2 n ch sub 2 ch sub 2 nh ch sub 2 ch sub 2 nh ch sub 2 ch sub 2 ch sub 2 si och sub 3 sub 3 __________________________________________________________________________ sheeting was also poured from these solutions in a cleanroom subject to dust free conditions once the solvent had been evaporated from the sheets they were left in deionized water at 60 u00b0 c for 24 hours and dried they were then tested for cross linkage by treating them with dimethyl acetamide and vibrating them in a shaker for 24 hours all of these sheets were insoluble whereas those poured as described with reference to examples 2 through 5 were soluble when.