PROCESS FOR LINEARIZING CROSS-LINKED ISOCYANATE POLYADDITION PRODUCTS WITH POLYISOCYANATES

摘要

1422884 Polyurethanes BAYER AG 3 Aug 1973 [5 Aug 1972] 36958/73 Heading C3R Polyurethanes which are cross-linked via allophanate and/or bivret and/or uretone imine groups may be linearized by reaction with an organic polyisocyanate in the presence of a polar solvent and at a temperature of 90‹ to 200‹ C. The resulting products are macropolyisocyanates which retain the urethane and optionally urea groups of the starting polyurethane. These macropolyisocyanates may be modified by reaction with aminoalkyl alkoxysilanes and the modified products so produced reacted with atmospheric moisture to introduce siloxane bridges into the molecule. The process may be applied to polyurethane waste, e.g. in the form of elastomers, foams, films, microporous foils and elastomer threads. Suitably the polyisocyanate is used in amounts of 0À8 to 10% by weight based on the polyurethane to be linearized. Solvents for the process include dimethylformamide, diethylformamide, dimethylacetamide, tetramethyl urea, dimethyl sulphoxide, N-methylpyrrolidone, ethylene glycol carbonate, caprolactone and butyrolactone. The aminoalkyl alkoxysiloxane may be monofunctional or bifunctional with respect to isocyanate groups. In a typical example (1) a polyurethane elastomer derived from a polyester, 4,41-diphenylmethane diisocyanate and butane - 1,4 - diol at an NCO/OH ratio of 1À066 is linearized with isophorone diisocyanate in dimethylformamide at a temperature of 130‹ C. The resulting macropolyisocyanate is reacted with a silane of the formula to form a product which is cross-linked by atmospheric moisture by way of siloxane groups.