Synthesis and Characterization of Sugar-Derived [n]-Polyurethanes

VARELA, OSCAR; GOMEZ, ROMINA V.; ARCE, SILVINA M.; KOLENDER, ADRIANA A.

Oslo, Noruega

Simposio; 24th International Carbohydrate Symposium; 2008

Natural regrowing resources are increasingly employed for the chemical synthesis of polymers. Particularly, carbohydrates are considered inexpensive and readily available precursors, with great stereochemical diversity. Carbohydrate-derived polyurethanes are usually biodegradable and biocompatible materials that find interesting biomedical applications. However, few examples of linear sugar-based [m,n]-polyurethanes are described and, as far as we know, no [n]-polyurethane analogues have been reported. In this communication we describe alternative procedures for the synthesis of selectively protected amino deoxy alditols monomers and their polycondensation to [n]-polyurethanes. DGalactono- 1,4-lactone (1) or D-glucamine (4) have been employed as starting materials for the synthesis of monomers 3 and 6, via the respective intermediates 2 and 5.For polycondensation reactions, di-tert-butyltricarbonate (DTBTC) was employed as coupling reagent; the reaction proceeds via isocyanate intermediates. The conditions for the polymerization of both 3 and 6 were optimized (solvent, catalyst) to obtain the respective polyurethanes 7 and 9, and to prevent the formation of N-substituted ureas as by-products. Thus, the polycondensation of 3 using DTBTC in tetrahydrofuran and in the presence of a zirconium catalyst [Zr(acac)4] afforded the linear polyurethane 7 with high molecular weight (Mw = 20,170). Under similar reaction conditions the monomer 6 gave the linear polymer 9 together with cyclic oligomers. On the other hand, removal of the isopropylidene protecting groups of 7 by smooth acid hydrolysis led to the polyhydroxypolyurethane 8, without degradation of the polymer chain. The varied type and polarity of the functionalities present in polyurethanes 7, 8 and 9 allow the control of their solubilities and other physical properties.