Fangxing Li

Study on the synthesis of high elongation polyurethane

Abstract In this paper, polyurethane (PU) was synthesized in the following steps: first, polytetramethaneoxy glycol (PTMG) prepolymerizes with 4,4′-diphenylmethane diisocyanate (MDI) at a molar ratio of 1:2; then, the prepolymer continuously reacts with 1,4-butanediol (BD) or hexanedimine (HD) to extend the polymer chain. A series of PU samples could be synthesized by reducing the amount of chain extender. The change in extensibility of PU with the amount of chain extender was investigated. The results indicate that the extensibility of PU could be improved greatly with a reduction of the amount of chain extender. This could be ascribed to the fact that excessive NCO groups can react with the hydrogen atoms in NHCOO, and form branch chains. When the molecular weight of PTMG is 1684, with BD as the chain extender, the ultimate elongation of PU was 2280%; when HD was the chain extender, the ultimate elongation of PU was 1809%. The submicroscopic structure of the samples was found to be amorphous by the method of small angle laser light scattering, and these samples could dissolve in dimethyl formamide (DMF). The influence of DMF on the polymerization was also investigated.

The design, synthesis and characterization of polyurethane with super macromolecular size

Abstract In the synthesis of polyurethane (PU), utilizing the property that –NCO at chain end in prepolymer can react with the hydrogen in –NHCOO– [Solomon DH, editor. Step-growth polymerizations. New York: Marcel Dekker, 1972 [Chapter 3].], a reaction system with cross-linking tendency is designed. Due to the cross-linking tendency, molecular weight will increase unlimitedly, meanwhile, intramolecular reaction presenting in the system consumes –NCO groups and then the cross-linking reaction can be prevented finally. By this way, PU with extremely complex structures and super macromolecular size is synthesized. When the molecular weight of the soft segment is 900, and the amount of chain extender is reduced by 40%, the molecular size is 750 nm. Compared with the polystyrene, which has a molecular weight of 2×106, the molecular size is only 96 nm, it is undoubtedly a super macromolecule. Elongation and extensile strength at break of this PU sample are 1683% and 28,000 N/cm2, respectively. When the molecular weight of the soft segment is 1684, elongation and extensile strength at break are 2300% and 51,000 N/cm2, respectively.

A novel method for extraction and separation of total flavones and total astragalosides from Radix astragali

In this paper a novel method for extraction and separation of total flavones and total astragalosides from Radix astragali using a resin method is suggested. Ethanol is used as the extractant, the macroporous absorption resin modeled H-107 is used to enrich the astragalus extract, and the macroporous strong base anion resin D-280 is used to separate the total flavones and the total astragalosides. This method allows a good yield of total flavones of 600 mg/100 g Radix astragali, a purity of 94.2%, and a yield of total astragalosides of 28 mg/100 g Radix astragali.