Conformationally restricted linear polyurethanes from acetalized sugar-based monomers

Linear polyurethanes based on sugar monomers having D-gluco, galacto, and D-manno configurations and their secondary hydroxyl groups protected as bicyclic acetals, have been prepared by polyaddition reaction of these diol monomers to hexamethylene diisocyanate (HMDI) and 4,4'-methylene-bis(phenyl isocyanate) (MDI). The new polyurethanes seem to be amorphous materials, except that obtained from 2,3:4,5-di-O-methylene-galactitol and HMDI. Weight-average molecular weights, determined by GPC, were in the range 16,000115,200. TGA analyses indicated that the thermal stability of these bicyclic polyurethanes is comparable to those based on the isosorbide; both the onset and the maximum rate decomposition temperatures increased significantly with respect to the polyurethanes based on acyclic sugar monomers. The presence of the acetalized alditol units in the polyurethanes also increased the Tgs as compared with their acyclic analogs. Deacetalization of the polyurethanes containing di-O-isopropylidene-D-mannitol units yielded the polyhydroxylated polymers in good yields, without apparent degradation of the polymer chain. These hydroxylated polymers showed an enhanced hydrophilicity and degradability and lower Tgs and thermal stability than their parent acetalized polyurethanes. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012