Thermoresponsive behavior of an LCST-type polymer based on a pyrrolidone structure in aqueous solution†
Abstract
Poly(3-ethyl-N-vinyl-2-pyrrolidone) (C2PVP) is a new type of thermoresponsive O peak shape is observed in the conventional IR spectra of tertiary-
O groups (C
O⋯2D2O and C
O⋯D2O) mainly coexist at the initial heating, and they change to the other two C
O groups involving the free C
O and C
O⋯DOD⋯O
C after heating, with the latter predominant above the LCST. A slight hysteresis is observed in the cooling process attributed to the existence of a weak “crosslinking” point originating from the structure of C
O⋯DOD⋯O
C. Based on 2Dcos results, the dehydration process of different groups could be described in the following order: ethyl groups > C
O groups > CH2 groups in ring (“>” means prior to), and the reversible sequence is observed during hydration process. In PNIPAM system, CH2 groups usually change prior to C
O groups, while for C2PVP the dehydrated rate of CH2 groups (in ring) lags behind that of C
O groups because of the steric hindrance of pyrrolidone structures. It is worth noting that cononsolvency of C2PVP can be found in