Control of the solubility transition in novel temperature-responsive linear polymers comprising alpha-amino acid diamide derivatives

This paper enumerates the preparation and characterization of novel tempera ture-responsive linear polymers comprising N-acryloylamino amide derivative s. The lower critical solution temperature (LCST) at which aggregation star ts of a polymer derived from N-acryloyl-L-valine N'-methylamide through tel omerization was noted to be less than that of a poly(N-isopropylacrylamide) (PNIPAAm) solution. The alanine derivative critical temperature exceeded t hat of the valine derivative owing to its smaller hydrophobicity. The therm al transitions of the internal hydrophobicity and solubility were found to be controlled by the N-methylation of the C-terminal amide and that of the N-terminal amide in the polymer. Either process caused a decrease in LCST o f the polymers. These findings are discussed from the standpoint of changes in the hydrogen bonding between the amino acid diamide moieties in polymer s. Temperature-responsive polymers, such as PNIPAAm, form a hydrophobic env ironment about their residues, as indicated by a measurement of the interna l polarity with a fluorescence probe.