Patent ID: 6930163

Claim:
A continuous process for the preparation of thermoplastic, homogeneous polyurethane having improved softening properties comprising reacting substantially to completion, in a tubular reactor equipped with a stirrer at least one diisocyanate (A) with a mixture (B) containing B1) 1 to 85 equivalent %, based on the isocyanate groups in (A) of at least one compound having on average at least 1.8 and at most 2.2 Zerewitinoff-active hydrogen atoms per molecule and a number average molecular weight of 450 to 5000 glmol, and B2) 15 to 99 equivalent %, based on the isocyanate groups in (A) of at least one chain lengthening agent having on average at least 1.8 and at most 2.2 Zerewitinoff-active hydrogen atoms per molecule and a molecular weight of 60 to 400 g/mol, wherein (A) and (B) are employed in an NCO:OH ratio of 0.9:1 to 1.1:1, said tubular reactor characterized in the absence of positively controlled conveyance therefrom and in that the ratio between the circumferential speed of said stirrer expressed in terms of meter/second and the throughput expressed in terms of g/second is greater than 0.03 meter/g , said reacting substantially to completion amounting to conversion greater than 90%, based on starting component (A) the said absence of positively controlled conveyance restricting said stirrer to a monoaxially rotating stirrer having as mixing elements a member selected from the group consisting of beams, rods, anchors, grids, blades and propellers.