关键词: 超临界流体, 丙烷, 聚苯乙烯, 分级, 模型

Abstract: Polystyrene can be fractionated with supercritical propane.The main advantage of supercritical fluid fractionation is that large polymer fractions with a narrow molecular mass distribution can be obtained without using hazardous organic solvent.Isothermal fractionation was performed using increasing pressure profiling that provided milligram-size fractions with M_w distribution of 1.0—2.0 as compared to parent polymer with polydispersity 4.225.At the same time,isobaric fractionation was performed using increasing temperature profiling that provided fractions with M_w distribution of 1.3—2.0 from the same parent polymer.The molecular mass of fraction increases with increasing operating pressure and temperature as the solvent power of SCF increases.The major benefit of SCF solvent relative to a liquid solvent is that the solvent power of SCF can be finely tuned by controlling operating conditions.It is recommended that pressure should be controlled to tune the solvent power of SCF effectively.With a SCF solvent, the solubility of a polymer drops to essentially zero if the pressure is reduced to near ambient condition,thus facilitating the recovery of a solvent-free polymer fraction.
A model relating the molecular mass of fraction to operating variables was deduced on the basis of the theory of polymer solution.The model parameters were estimated by using experimental data.The average relative deviation was below 18%.

Key words: 超临界流体, 丙烷, 聚苯乙烯, 分级, 模型