Synthesis of a novel starch-derived AB-type polyurethane

Starting from 1,4:3,6-dianhydrosorbitol (DAS, 1), a five step monomer synthesis led to 2-deoxy-1,4:3,6-dianhydro-2-isocyanato-L-iditol, 9, which by catalytic polyaddition gave polyurethane 13. A second route required the synthesis of 2-azido-5-O-chloroformyl-2-deoxy-1,4:3,6-dianhydro-L-iditol, 11. During catalytic hydrogenation, the intermediate 2-aminochloroformyl derivative 12 underwent spontaneous polycondensation. The structure of 13 was characterized by 1H and 13C NMR, IR spectroscopy and elemental analyses. Gel-permeation chromatography showed M̄n = 8 000–12 000 corresponding to a degree of polymerisation up to 70. Differential scanning calorimetry revealed the polyadduct to be semicrystalline with a glass transition at Tg = 118°C and a melting range of 190–200°C. The polycondensation product was found to be crystalline with a melting range of 140–180°C.