Abstract: Low molecular weight N- and O-substituted diurethanes and/or polyurethanes are prepared by reacting a diamine and/or polyamine containing a primary amino group with an N-aryl-0-alkyl urethane in the presence of at least one high boiling alcohol. This reaction may be carried out at a temperature of from 180.degree. to 350.degree. C. and a pressure of approximately 0.1 to 1,500 mbar. The arylamine corresponding to the N-ary-0-alkyl urethane which forms during this reaction is continuously removed from the reaction mixture.

Abstract: Polyisocyanates are prepared by thermally splitting a carbamate corresponding to the formula:R.sup.1 (NH--CO--O--R.sup.2).sub.nin which R.sup.1, R.sup.2 and n are as defined herein into the corresponding isocyanate and alcohol. The splitting reaction is carried out at a temperature of from 150.degree. to 350.degree. C., at a pressure of from 0.001 to 20 bar and in the presence of an auxiliary agent. Suitable auxiliary agents are hydrogen chloride, organic acid chlorides, compounds having an alkylating effect and organotin (IV) chlorides. Inert solvents and catalysts may also be employed in the splitting products. The thus-produced isocyanate and alcohol are then separated, if necessary.