LCST and UCST Behavior of Poly(N-isopropylacrylamide) in DMSO/Water Mixed Solvents Studied by IR and Micro-Raman Spectroscopy

Abstract

Temperature-responsive phase separations of poly(N-isopropylacrylamide) (PNiPAm)/dimethylsulfoxide (DMSO)/water mixtures have been investigated by infrared and confocal micro-Raman spectroscopy. The ternary mixtures exhibited lower critical solution temperature (LCST) and upper critical solution temperature (UCST) phenomena at low and high DMSO concentrations, respectively. The amide I band of PNiPAm consists of two components; the intensity of the 1650 cm-1 component increased, and that of the 1625 cm-1 component decreased with increasing temperature during both LCST and UCST phase transitions. Gradual red shifts of the C-H stretching and the amide II bands with increasing temperature or increasing DMSO concentration indicate a removal of water molecules from the alkyl and N-H groups. Raman microscopic measurements showed that DMSO is excluded from the polymer-rich phases upon both LCST and UCST phase separation. On the basis of the experimental results and the quantum chemical calculations, a model that explains the solvation change of the polymer during phase transitions was proposed.

In Situ Characterization of Thermo‐Responsive Poly(N‐Isopropylacrylamide) Films with Sum‐Frequency Generation Spectroscopy

“…Table 1. IR [29] and Raman [30][31] showing that this vibrational band is most affected by the LCST. Negative cross peaks indicate that the band intensity of one conformation is increasing while the intensity for the other conformation is decreasing.…”

Effect of the Branching Pattern of Hydrophobic Dendrons on the Core Structure of Linear‐Dendritic Copolymer Micelles

“…[ 48 ] Furthermore, temperatureresponsive polymers are known to show LCST behavior in mixed solvent systems. [ 49,50 ] The PEG chains in the shell of our micellar aggregates are in a water-rich environment and may follow the same behavior. As PEG chains start to become dehydrated with increasing temperature, the interfacial area between hydrophobic dendron and bulk aqueous solvent increases.…”

Phase separation behavior and fluorescence properties of poly(N-isopropylacrylamide) with chalcone side groups in mixed solvents

“…Organic solutes such as hydroxybenzoic acids also decrease the transition temperature [9]. In particular, the addition of solvents affects the phase transition of an aqueous PNIPAM solution remarkably [11][12][13], and a wide variety of techniques and theories have been applied to understand and explain the essence of the phase transition of PNIPAM in watercononsolvent systems [14][15][16][17][18][19][20][21]. Moreover, the effects of organic solvents have a wide variety.…”

“…PNIPAM exhibits a single LCST-type phase separation behavior in water-cononsolvent systems such as water-methanol [11], water-acetone [13], water-tetrahydrofuran [12], and water-dioxane [12], and the addition of organic solvents initially decreases the transition temperature and a further addition increases it. However, in water-ethanol [13,14], water-propanol [13], water-N,Ndimethylformamide [13], and water-dimethylsulfoxide [13,20] systems, PNIPAM shows simultaneous LCST-type separation behavior in water-rich mixtures and an upper critical solution temperature-type (UCST-type) separation behavior in organic solvent-rich mixtures. The phase separation phenomenon of PNIPAM in water-solvent systems has been termed cononsolvency by Schild et al [12].…”