Partitioning, Fractionation, and Conformations of Star Poly(ethylene glycol) in Isobutyric Acid and Water
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- 作者：Alexander I. Norman ; Derek L. Ho ; Sandra C. Greer
- 刊名：Macromolecules
- 出版年：2007
- 出版时间：December 25, 2007
- 年：2007
- 卷：40
- 期：26
- 页码：9628 - 9639
- 全文大小：308K
- 年卷期：v.40,no.26(December 25, 2007)
- ISSN：1520-5835
文摘
We investigate the partitioning, fractionation, and conformations of star poly(ethylene glycol) (PEG)in coexisting liquid phases of isobutyric acid and water. Star PEG does partition: 98% in the upper isobutyricacid phase, versus 80-90% for linear PEG. There is no significant fractionation of the star PEG for molecularmasses less than or equal to 10 kg/mol, but fractionation may occur at higher molecular masses. Small angleneutron scattering shows that the arms of the star PEG molecules form coils in D2O but form stiff rods in deuteratedisobutyric acid. At higher average molecular masses (>4 kg/mol) and higher temperatures (60 C), some armsare coils and some are rods in isobutyric acid. Polarimetry studies indicate that these "rodlike" arms are actuallyhelical conformations. At a star molecular mass of 2 kg/mol, the helical arms persist above 70 C, but at largermolecular masses, the helical arms revert to coils at temperatures around 75 C. The addition of PEG to isobutyricacid and H2O increases the critical temperature of the solvent mixture, and the increase is less as the star branchingincreases.