Infrared Spectroscopic Insight into Hydration Behavior of Poly(N-vinylcaprolactam) in Water

Abstract

IR spectroscopy in combination with two-dimensional correlation spectroscopy (2DCOS) and the perturbation correlation moving window (PCMW) technique is employed to illustrate the dynamic hydration behavior of poly(N-vinylcaprolactam) (PVCL) in water, which exhibits a typical type I continuous lower critical solution temperature (LCST) behavior. PCMW easily determined the transition temperature to be ca. 43.5 °C during heating and ca. 42.5 °C during cooling and the transition temperature range to be 39.5-45 °C. On the other hand, 2DCOS was used to discern the sequence order of different species in PVCL and concluded that hydrogen bonding transformation predominates at the first stage below LCST while hydrophobic interaction predominates at the second stage above LCST. In combination with molecular dynamics simulation results, we find that there exists a distribution gradient of water molecules in PVCL mesoglobules ranging from a hydrophobic core to a hydrophilic surface. Due to the absence of self-associated hydrogen bonds and topological constraints, PVCL mesoglobules would form a "sponge-like" structure which can further continuously expel water molecules upon increasing temperature, while poly(N-isopropylacrylamide) (PNIPAM) with self-associated hydrogen bonds forms mesoglobules with a "cotton-ball-like" structure without an apparent distribution gradient of water molecules and does not change much upon increasing temperature.

Synthesis and characterization of “Living” star‐shaped poly(N‐vinylcaprolactam) with four arms and carboxylic acid end groups

“…The C@O groups are interacting with a small amount of water by hydrogen bonding, and this is further evident in the broad band appearing at 3436 cm 21 which can be attributed to water of hydration. 46 By using CTA-1 as an RAFT agent, the polymerization of NVCL in p-dioxane at 65 8C could be controlled. To prepare star-shaped PNVCL polymers of different M n , polymerizations were performed using fixed concentrations of monomer and initiator and varying concentrations of the multifunctional CTA-1.…”

“…The PNVCL COOH/water system corresponds to polymers of type I with a Flory-Huggins behavior, in which the LCST value of polymers decreases with increasing polymers chain length and is based on the changes in the polymer-solvent interaction. [46][47][48] The decrease of the M n of PNVCL-COOH from 66,300 to 10,000 g mol 21 lead to the increase of the LCST from 33 to 43 8C [ Fig. 9(b)].…”

Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers

“…Although the fundamental mechanisms and grounds of the "responsive" behaviour are comparable, properties such as water affinity, degree of chain contraction and dehydration, and the structure of the mesoglobules may differ signicantly depending on the polymer architecture. 40,51,52 We, therefore, anticipated that static light scattering (SLS) studies could provide additional insight into the association/aggregation behaviour of these labelled chains below and above their LCST, which could assist in explaining the observed uorescence characteristics. Table 3 summarizes the values of R g , M w,app , r, and the aggregation number (N agg ¼ M w,app /M w ) for all polymers at three different temperatures deduced from SLS studies.…”

Effect of the molecular architecture on the thermosensitive properties of chitosan-g-poly(N-vinylcaprolactam)

“…This polymer exhibits a "classical" Flory-Huggins thermoresponsive phase behavior in water (Type I systems) and therefore, the value of its LCST is strongly dependent on molecular weight and concentration (Beija, Marty, & Destarac, 2011;Meeussen et al, 2000). The LCST of PVCL is also affected by the molecular dispersity or the nature of end groups (Maeda, Nakamura, & Ikeda, 2002;Sun & Wu, 2011).…”