|
In this work, the two-step synthesis method was utilized to synthesize a series of polyether type star polyurethanes. First, the prepolymers with different molecular weights were prepared by change the reacting equivalent ratio of ether-type glycol(PTMO) of molecular weight 2000 with aromatic diisocyanate(MDI). Second, 1/20 equivalent of multi-hydroxy cores with different functionahties (including 3, 4 hydroxy groups) as chain extenders were put to react with the prepared polymers. Finally, the remaining free NCO groups were terminated by reacting with the di-n-butyl amine and the raw star polymers were fractionated by adding the nonsolvent, methanoi. The desired star polymer, its chemical structure, molecular weight and distribution, and physical properties were analyzed and studied.
In chemical structure, the IR and NMR spectra of star polyurethane were almost the same as their corresponding linear polyurethane. The analysis of GPC result indicated that the obtained star polyurethanes were imperfect, not only the attacted branches but also the length of branches had broad polydisperse values. The themial (DSC) and dynamic mechanical (DMA) properties of star polyurethanes were mainly dependent on the soft segment concentration of their corresponding linear polyurethane(side chain). However, the effect of branches would destroy the structure of polymer chain and decrease the crystalhzation. In dilute solution properties, the intrinsic viscosity of star polymer was lower than the linear one at the same molecular weight, whatever the solvent temperatures were changed. And in concentrated solution, because of the entanglements formed were not enough tested here, the zero-shear viscosity of star polymer was still lower than the linear one at the same molecular weight.
|