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

This paper enumerates the preparation and characterization of novel temperature-responsive linear polymers comprising N-acryloylamino amide derivatives. The lower critical solution temperature (LCST) at which aggregation starts of a polymer derived from N-acryloyl-L-valine N'-methylamide through telomerization was noted to be less than that of a poly(N-isopropylacrylamide) (PNIPAAm) solution. The alanine derivative critical temperature exceeded that of the valine derivative owing to its smaller hydrophobicity. The thermal 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 of the polymers. These findings are discussed from the standpoint of changes in the hydrogen bonding between the amino acid diamide moieties in polymers. Temperature-responsive polymers, such as PNIPAAm, form a hydrophobic environment about their residues, as indicated by a measurement of the internal polarity with a fluorescence probe.