The underlying mechanism regarding the driving force of thermo-sensitive behavior for poly(N-methacryloyl-L--isopropylasparagine)

shorted as PA48

was investigated by the combination of UV-Vis turbid experiments

dynamic light scattering (DLS)

circular dichroism (CD)

temperature-dependant 1H-NMR analyses and solvent isotopic effect.Turbid experiments showed that the PA48 polymer at acidic solution exhibited a reversible LCST-type thermo-sensitivity.For example

at pH 1 it had a cloud point (CP) of 39.9℃ with a hysteresis of 0.9 K in the cooling circle.CD spectra revealed that the absorption wavelength did not change with temperature variation.Meanwhile

the PA48 polymer showed a dramatic solvent isotopic effect

e.g.

the CP of PA48 was 6 K lower in D2O than in H2O.DLS demonstrated that the PA48 was mono-molecular soluble in water under CP while formed aggregates near the CP

and further heating led to the dehydration and phase separation.Temperature-dependent 1H-NMR spectra indicated the dehydration process occured subsequently from hydrophobic backbones to hydrophilic aspartic acid side-chains.Based on these data

the thermo-sensitivity of PA 48 was concluded to be driven by hydrophobic association and followed with dehydration and phase separation from water.