Zong Minhua

Synthesis of Hyperbranched Polyester by Combination of Prepolymerization with Enzymatic Condensation Polymerization and Its Characterization

A new route for hyperbranched aliphatic polyester by the prepolymerization of comonomers followed by the enzymatic condensation polymerization in organic media was developed using glycerol, 1,6-hexanediol, and adipic acid as comonomers and using immobilized lipase Novozym 435 as a biocatalyst. The organic solvents, such as isooctane, toluene, tert-butanol, tetrahydrofuran, and acetone, were used as the reaction medium for enzymatic condensation polymerization. The effects of reaction medium and reaction temperature on the enzymatic condensation polymerization were investigated. The molecular mass and the structure of the prepared polyesters were characterized by gel permeation chromatography and NMR. The results indicated that the hyperbranched aliphatic polyester could be successfully synthesized under the mild conditions by the combination of prepolymerization of comonomers with enzymatic condensation polymerization in organic media. Toluene was the best reaction medium among the examined ones, and the lipase Novozym 435 exhibited the highest activity at 70 degrees C within the temperature range from 50 to 90 degrees C. The polyester prepared by prepolymerization and the enzymatic condensation polymerization in toluene at 70 degrees C possessed the maximal molecular mass of up to 1.31x10(4) and the branching degree of about 0.27.

Formation of reverse micelles in supercritical carbon dioxide and its thermodynamics

The solubilization behavior of methyl orange as a solvation probe in multiple systems composed of supercritical carbon dioxide, surfactants and co-solvents, is studied. It is concluded that some surfactants, such as sodium bis-(2-ethylhexyl) sulfosuccinate (AOT) and isooctyl phenol polyethoxylate (TX-10), could form reverse micelles in supercritical carbon dioxide under the action of butanol. The formation of reverse micelles is a spontaneous process thermodynamically. Specifically for the nonionic surfactant TX-10, the formation of reverse micelles is dependent on the entropy increase in the system, while for the anionic surfactant AOT, the micellization is mainly dominated by the increase in enthalpy at higher temperatures, but by the increase in entropy at lower temperatures.