(720a) Comparing the Phase Behavior of Linear and Hyperbranched Polyglycerols

Hyperbranched Polymers (HPBs) have recently attracted much interest due to their physical, thermal and chemical properties. In contrast to dendrimers with their highly uniform and monodisperse structures [1], HBPs are randomly branched, polydisperse polymers and can easily be synthesized via economically favourable one-step reactions. Recently it has been suggested that HBPs can be used as process solvents or additive in separations based on absorption or extraction to increase separation performance [2-4]. However, the experimental data for these systems is rare and not much is known about the influence of the highly branched structure on the phase behaviour of their mixtures.

To evaluate the influence of the hyperbranched structure and compare the phase behavior of linear and hyperbranched polymers, the phase envelopes of the ternary system linear polyglycerol + methanol + carbon dioxide were determined for polymers of varying molar mass. Phase changes were detected by a static synthetic method using the Cailletet setup for temperatures between 331K and 421K and pressures up to 13.1MPa. The experimental results are similar to systems with hyperbranched polymers [4]. For the systems with linear polymers, however, the bubble-point pressures show no significant dependence on the polymer molar mass. In contrast, it was shown that the bubble-point pressures for mixtures of hyperbranched polyglycerol + methanol + carbon dioxide changes significantly with the polymer molar mass. Further, the polymer concentration at the lower critical solution temperature is remarkably high when the polymers have a hyperbranched structure.

References

 [1] J.M.J. Frechet, D.A. Tomalia, Dendrimers and other dendritic polymers   (2001) John Wiley&Sons, West Sussex, UK.

[2] M. Seiler, Fluid Phase Equilib. 241 (2006) 155-174.

[3] J. Rolker et al., Ind. Eng. Chem. Res. 46 (2007) 6572-6583.

[4] M.K. Kozlowska et al., J. Phys. Chem. B, 113 (2009) 1022-1029.