| abstract |
The present invention relates to pure polyurethanes containing aliphatic and / or cycloaliphatic diisocyanates, macrodiols from MW 500 to 10,000 and chain extenders from MG 62 to 400, obtainable by reacting aliphatic and / or cycloaliphatic diisocyanates with a macrodiol to form a pre-adduct containing NCO groups, wherein 1.5 to 22 moles of diisocyanate are used per mole of macrodiol, and the chain extension of the pre-adduct is carried out with low-molecular aliphatic and / or cycloaliphatic diols, optionally further diisocyanate - while maintaining the above NCO / OH ratio - as a chain extender, that the pre-adduct formation is carried out at 90-150 ° C and the chain extension is carried out at temperatures of 120-230 ° C, with the proviso that the reaction conditions mentioned are maintained at least as long until a melt viscosity of at least 2500 mPas, measured at 120 ° C., has been reached and the polyaddition may then end at any time, if appropriate at an elevated temperature of up to 240 ° C.n n n The polyurethanes are preferably used in medical technology. |