Polyurethane networks bearing dendritic wedges: Synthesis and some properties

Polyurethane networks bearing dendritic wedges of the second, third and fou rth generation were prepared by polymerization of dendritic diols of the co rresponding generation with a commercially available triisocyanate (Desmodu r RFE). The formation of a three-dimensional network was greatly influenced by the shielding effect especially of dendritic wedges of generation four. This phenomenon led to an increase of the sol fraction with rising generat ion number. The swelling behavior of polyurethane networks was studied by m eans of molecular dynamics simulations and the results were compared, in a qualitative sense, with experimental data. As opposed to the theoretical da ta for perfect networks. the experimental swelling ratio increased as a fun ction of generation number. The discrepancy between molecular simulations a nd experimental data was attributed to the imperfect character, i.e., the p resence of defects, of synthesized networks comprising dendritic wedges of higher generations. Since the crosslinker Desmodur RFE contains phosphorus, P-31 NMR was applied to reveal the effect of dendritic wedges on the mobil ity of junction points. Both the line widths and T-1 relaxation data proved to be sensitive to the effect of the generation number on the mobility of network junctions.