Temperature‐Induced Phase Separation and Hydration in Aqueous Polymer Solutions Studied by NMR and IR Spectroscopy: Comparison of Poly(N‐vinylcaprolactam) and Acrylamide‐Based Polymers

Abstract

SummaryUsing NMR and IR spectroscopy we compared the LCST behaviour of two types of thermoresponsive polymer systems, poly(N‐vinylcaprolactam) (PVCL) and acrylamide‐based polymers in aqueous solutions. We confirmed that during phase separation both PVCL and poly(N‐isopropylmethacrylamide) (PNIPMAm) chains undergo coil‐globule transition. At the same time some important differences were found for PVCL in comparison with PNIPMAm and poly(N‐isopropylacrylamide) (PNIPAm), especially a much lower level of dehydration of PVCL segments at temperatures above the phase transition. We assume that the origin of these differences can be in different structure of respective monomer units. From time dependences of ATR FTIR spectra it follows that the low degree of dehydration of PVCL segments is not changed with time. Small increase in the wavenumbers of the Amide I components of the hydrated PVCL carbonyl groups with time indicates that water released from PVCL mesoglobules with time, as revealed from NMR T2 measurements, might be mainly indirectly bound water.