Infrared spectroscopic study on LCST behavior of poly(N,N-bis(2-methoxyethyl)acrylamide)

The phase separation behavior and solvation of poly(N,N-bis(2-methoxyethyl)acrylamide) (PbMoEA) in water and alcohol/water mixtures were investigated by infrared (IR) spectroscopy. A critical change in IR spectrum informs that PbMoEA undergoes the phase separation at around 54 °C in water. The red shift of ν(Csingle bondH) band and the blue shift of amide carbonyl band during the phase separation indicate that its alkyl and amide groups are partially dehydrated. The transition temperature (Tp) monotonically increases with increasing concentration of methanol, whereas it draws a re-entrant curve in 1-propanol/water mixtures. The blue shift of amide carbonyl band and the red shifts of ν(Csingle bondH) bands with increasing alcohol concentration indicate decreases in the number of hydrogen bonds to the carbonyl groups and that of hydrophobically hydrating water molecules around the alkyl groups, respectively. The former effect destabilizes the solutions and lowers Tp whereas the latter raises Tp. The dominance of the former lowers the Tp of PbMoEA in 1-propanol/water mixtures at low alcohol concentrations, and the opposite is the case in methanol/water mixtures. The behavior of random copolymers of N-isopropylacrylamide (NiPAm) and N,N-bis(2-methoxyethyl)acrylamide (bMoEA) in methanol/water mixtures indicates that not only the comonomer content but also at least diad monomer sequence is important for Tp, in other words, the interaction between adjacent monomer units affects the Tp of copolymers.