Gas-phase conformations of synthetic polymers: Poly(ethylene glycol), poly(propylene glycol), and poly(tetramethylene glycol)

被引:146
作者
Gidden, J
Wyttenbach, T
Jackson, AT
Scrivens, JH
Bowers, MT [1 ]
机构
[1] Univ Calif Santa Barbara, Dept Chem, Santa Barbara, CA 93106 USA
[2] ICI Res & Technol Ctr, Middlesbrough TS90 8JE, Cleveland, England
关键词
D O I
10.1021/ja993096+
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Effects of chain flexibility and cationizing agent on the gas-phase conformations of a series of polyethers were studied. Collision cross-sections of poly(propylene glycol) (PPG) and poly(tetramethylene glycol) (PTMEG) oligomers (from the 5-mer to 14-mer) cationized by sodium were measured using ion mobility methods and compared to earlier work on sodiated poly(ethylene glycol) (PEG). Molecular mechanics/dynamics calculations show that all three polyethers form a ring of oxygen atoms around Na+, coordinating additional oxygens to the cation from above and/or below this ring. However, the number and arrangement of these oxygens are system dependent. Up to 8 oxygens in PEG coordinate Na+, but that number drops to 7 for PPG and 6 for PTMEG. The difference is attributed to changes in the structural details of the ring as well as the position of the Na+ ion in that ring. Molecular mechanics/dynamics calculations were also used to investigate the structures of neutral PPG and PTMEG oligomers. In these cases, the oligomers are relatively compact below 200 K but they suddenly unfold into more extended structures between 200 and 300 K.
引用
收藏
页码:4692 / 4699
页数:8
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