NEW POLYURETHANES BASED ON DIPHENYLMETHANE DIISOCYANATE AND 1,4 3,6-DIANHYDROSORBITOL .1. MODEL KINETIC-STUDIES AND CHARACTERIZATION OF THEHARD 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) a nd with a diisocyanate (4,4'-diphenylmethane diisocyanate, MDI) were s tudied with the help of a chromatographic method (size exclusion chrom atography, SEC). When the condensation reaction is performed in tetrah ydrofuran (THF) solution, with dibutyltin dilaurate (SnDBDL) as cataly st, DAS exhibits two equireactive hydroxyl groups. The reaction rate c an be well described by a second-order equation modified to include ca talysis by the formed urethane functions. MDI and DAS were then conden sed using two different experimental procedures (bulk and solution pol ycondensation in THF, in the presence of SnDBDL), and the characterist ics of the resulting polyurethanes were compared. Bulk polycondensatio n led to an amorphous polymer, whereas the polyurethane prepared in so lution was semi-crystalline. In both cases, we obtained a very high gl ass transition temperature (approximate to 186 degrees C). The synthes is of samples with various polymerization degrees gave a better unders tanding of the molecular weight distribution of segmented polyurethane s based on MDI and DAS.