Investigations on the thermoresponsive behavior of copoly(2-oxazoline)s in water

• Published in: Polymer (Guilford) Vol. 175; pp. 294 - 301
• Main Authors: Hijazi, Montasser, Schmidt, Martin, Xia, Hekai, Storkmann, Jorena, Plothe, Ramona, Santos, Denise Dos, Bednarzick, Ulf, Krumm, Christian, Tiller, Joerg C.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 26-06-2019; Elsevier BV
• Subjects: Copoly(2-oxazoline); Copolymerization; Copolymers; Critical point; Hydrogels; Hydrophobicity; Investigations; LCST; Phase diagram; Phase diagrams; Phase transitions; Polymers; Smart materials; Temperature dependence; Temperature effects; Phase diagram; Copoly(2-oxazoline); LCST
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2019.05.040

Polymers with a lower critical point solution temperature (LCST) are widely investigated responsive materials and are already in use for smart materials applications, e.g., for medicinal purposes. Hydrogels prepared from these polymers usually exhibit a shrinking behavior over a broad temperature range, rather than an expected sharp phase transition. One reason for this is their cloud point temperature (Tcp) dependence on the concentration in water. Here, we investigate this behavior on the example of copolymers prepared by copolymerization of 2-ethyl-2-oxazoline (EtOx) with the respective heptyl (HepOx), butyl (BuOx), and isopropyl (iPrOx) derivatives, respectively. The resulting copolymers show greatly different dependencies of their TCP on concentration. While P(EtOx-stat-HepOx)s show a strong linear increase of Tcp on polymer concentration, the Tcp of P(EtOx-stat-BuOx)s is only slightly raising at higher concentration. P(EtOx-stat-iPrOx)s have two plateau regions in their water/polymer phase diagram. In general, copolymers with less strong differences in their hydrophobicity might be best suited for discretely thermo-switchable hydrogels, because they show the lowest dependence of Tcp on polymer concentration.
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•The phase diagrams of LCST Copoly(2-oxazoline)s are investigated.•P(EtOx-stat-HepOx) changes its LCST but not its phase diagram with varying composition.•Tcp of P(EtOx-stat-BuOx) is less dependent on concentration with higher BuOx content.•P(EtOx-stat-iPrOx)s have two non-zero points in the phase diagram.