they have the advantage in particular of a relatively low viscosity low viscosities are particularly advantageous e g in the uses of u201c flexible packaging u201d or u201c reactive polyurethane hot melt adhesives u201d hotmelts u201c flexible packaging u201d is understood here as meaning the production of composite films by gluing with an adhesive based on polyurethane in this case the adhesive is typically applied in liquid form to a film and directly thereafter joined with a second film reactive polyurethane hot melt adhesives are understood as meaning adhesive systems which are in the form of a melt at elevated temperatures and are applied in liquid form at these temperatures after application and joining the still reactive adhesive cools and thereby rapidly builds up an initial strength the final strength is achieved after complete curing with moisture from the atmosphere the use of formamide based prepolymers polyisocyanates is also possible in combination with polyisocyanates and or prepolymers with urethane biuret carbodiimide isocyanurate allophanate iminooxadiazinedione uretdione ester polyester ether polyether carbonate or polycarbonate structural units the invention will now be described in further detail with reference to the following non limiting examples 222 g of formic acid ethyl ester are added dropwise at a maximum of 50 u00b0 c to 116 g of 1 6 hexamethylenediamine dissolved in 170 g of ethanol in the course of 4 hours and the mixture is subsequently stirred for 4 hours the excess formic acid ethyl ester and the ethanol formed and employed are then distilled off the formamide terminated defined compound formed is metered into 2 523 g of desmodur u00ae h.