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2113584 
Journal Article 
Folding and unfolding of polymer helices in solution 
Norman, AI; Fei, Y; Ho, DL; Greer, SC 
2007 
1 
Macromolecules
ISSN: 0024-9297
EISSN: 1520-5835 
40 
7 
2559-2567 
WOS:000245208400035 
Poly(ethylene glycol) (PEG) has previously been shown to assume a helical conformation in isobutyric acid. In this work, it was shown that the formation of helices by PEG in isobutyric acid required the presence of a trace amount of water. The helices could be made to coil and uncoil by adding or removing traces of water to/from the solvent. Poly(ethylene imine) (PEI) formed helices in isobutyric acid and PEG formed helices in isopentanoic and n-propanoic acids but not in isobutanol or n-butanol. PEI (number-average molecular weight = 21.8 kg/mol) formed only helices in isobutyric acid, whereas PEG (number-average molecular weight = 21.0 kg/mol) formed a mixture of helices and coils. Helical PEI showed a helix-to-coil transition when the temperature was increased to about 50 deg.C whereas PEG showed this transition at 40-45 deg.C. When the trace water in the solution was deuterium oxide, the helix-to-coil transition for PEG moved to a higher temperature (about 56 deg.C), possibly because of stronger hydrogen bonding. 46 refs. 
OPTICAL PROPERTIES; MOLECULAR STRUCTURE; HELICAL; TRANSITION TEMP.; ETHYLENIMINE POLYMER; THERMOPLASTIC; TABLES; PROPERTIES; TEMPERATURE; GRAPH; MECHANISM; ETHYLENE GLYCOL POLYMER; MOLECULAR CONFORMATION; NEUTRON SCATTERING; HELIX; CHEMICAL STRUCTURE; HYDROGEN BONDING; SOLVENT; OPTICAL ROTATION; COMPANY; SMALL ANGLE NEUTRON SCATTERING; THERMALLY INDUCED; DIAGRAM; POLYETHYLENE GLYCOL; POLYETHYLENIMINE; HELIX-COIL TRANSITION; COIL; DATA; INSTITUTION; POLYETHYLENE IMINE; PLASTIC; FOLDING; MOLECULAR CONFIGURATION; TECHNICAL; CONFORMATIONAL TRANSITION; COMPANIES; NUMBER-AVERAGE MOLECULAR WEIGHT; TRANSITION TEMPERATURE; POLYETHYLENEIMINE; MOLECULAR WEIGHT