| abstract |
1479344 Microporous polyurethanes BAYER AG 5 Sept 1974 [7 Sept 1973] 38791/74 Heading C3R Microporous polyurethane sheets are prepared by coagulating a hygroscopic polyurethane or polyurethane urea solution which may contain ionic polyurethane or polyurethane urea dispersions and which solution contains a polyurethane - polysiloxane or polyurethanep olysiloxane-urea containing structural units of the formula wherein n is at least 2, Z is an alkyl, aryl, siloxyl, siloxanyl or -R-Y-CO-NH- group R represents an alkylene group which may contain hetero atoms and Y represents -NH-, -O- or -S-. Most preferably the total quantity of siloxane units in the sheet is from 0À1 to 20% by weight. The solution to be coagulated is prepared by adding to a solution of a palyurethane free from siloxane groups, a p ilyurethane containing siloxane units which is either in the form of a solution or an aqueous dispersion. The solutions may be applied to porous or non-porous substrates and coagulated by the addition of non-solvent, preferably water. |