NEW POLYURETHANES BASED ON DIPHENYLMETHANE DIISOCYANATE AND 1,4/3,6-DIANHYDROSORBITOL .1. MODEL KINETIC-STUDIES AND CHARACTERIZATION OF THE HARD SEGMENT

1,4:3,6-Dianhydrosorbitol (DAS) seems to be an interesting reagent for the synthesis of polyurethanes. In the present work, the kinetics of the reaction of DAS with a monoisocyanate (p-tolyl isocyanate, p-TI) and with a diisocyanate (4,4'-diphenylmethane diisocyanate, MDI) were studied with the help of a chromatographic method (size exclusion chromatography, SEC). When the condensation reaction is performed in tetrahydrofuran (THF) solution, with dibutyltin dilaurate (SnDBDL) as catalyst, DAS exhibits two equireactive hydroxyl groups. The reaction rate can be well described by a second-order equation modified to include catalysis by the formed urethane functions. MDI and DAS were then condensed using two different experimental procedures (bulk and solution polycondensation in THF, in the presence of SnDBDL), and the characteristics of the resulting polyurethanes were compared. Bulk polycondensation led to an amorphous polymer, whereas the polyurethane prepared in solution was semi-crystalline. In both cases, we obtained a very high glass transition temperature (approximate to 186 degrees C). The synthesis of samples with various polymerization degrees gave a better understanding of the molecular weight distribution of segmented polyurethanes based on MDI and DAS.