Dual Thermoresponsive and pH-Responsive Poly(vinyl alcohol) Derivatives: Synthesis, Phase Transition Study, and Functional Applications

Abstract

Novel poly­(vinyl alcohols) (PVA) functionalized with pendant thermo- and pH-responsive groups were prepared by carbonyl­diimidazole (CDI)-mediated couplings of N 1,N 1-diethylethane-1,2-diamine (DEEDA) with controllable modification degree. Nuclear magnetic response (NMR) and IR have verified the successful modification of PVA. The macro- and microscopic phase transition behavior of the obtained PVA-DEEDA-t (t = 10, 30, 70, and 90 h) was thoroughly characterized using various techniques, including turbidity measurement, NMR, and dynamic light scattering (DLS). PVA-DEEDA-t is demonstrated to possess tunable lower critical solution temperature (LCST) between 58 and 24 °C. LCST is dependent on solution pH and degree of PVA modification (14.1–20.9%). By combining DLS and DOSY characterizations, it can be concluded that both coil-to-globule transition and aggregation occurred to PVA-DEEDA-t during phase transition, while only coil-to-globule transition can be detected for the pristine PVA. 2D NOESY proved that the −NH– segment on PVA-DEEDA-t is in close (<5 Å) proximity to the main chain of PVA, as evidenced by the appearance of NOE signal between −NH– on DEEDA and −CH2–CH– chain of PVA when the temperature increased above LCST. To exploit the functional applications, the PVA-DEEDA-90 h was transformed into gel and film forms. PVA-DEEDA-90 h gel obtained by adding borax enabled controlled drug (e.g., RhB) release due to its temperature- and pH-dependent permeability. The PVA-DEEDA-90 h film was also casted on ITO glass, creating a smart surface with tunable wettability and interfacial ion transportation with high sensitivity toward the pH and temperature.

Backbone‐Based LCST‐Type Hyperbranched Poly(oligo(ethylene glycol)) with CO2‐Reversible Iminoboronate Linkers

“…[6][7][8][9] Adjustment and control of the phase transition temperature of LCST-type polymers are essential for their applications. [1][2][3][4][5] For this purpose, controlled copolymerization of OEG-based acrylic esters with other stimuli-responsive monomers and various block, graft, or hyperbranched polymers of poly(ethylene glycol) have been carried out to tune their thermo-responsive behaviors. [10][11][12] Obviously, hyperbranched poly(ethylene glycol) (hPEGs) have several superiorities contrasted to the linear polyethers for use in controlled delivery system due to their globule shapes with abundant terminal functional groups and programmable internal cavities available to encapsulate guest molecules.…”

“…In recent years, water‐soluble polymers exhibiting a soluble–insoluble phase transition at the lower critical solution temperature (LCST) in water have been actively studied for their potential use in controlled drug delivery, biomedical soft materials, etc . Perhaps the ethylene glycol‐based polymers, such as poly(ethylene glycol) (PEG) or oligo(ethylene glycol) (OEG) functionalized polymers, are the most promising thermo‐responsive polymers due to their outstanding biocompatibility .…”

pH and reduction dual‐stimuli‐responsive PEGDA/PAMAM injectable network hydrogels via aza‐michael addition for anticancer drug delivery

“…poly( N ‐isopropylacrylamide)‐ co‐poly(acrylic acid) revealing the hydrogel's potential applications as carriers in drug delivery and cell therapy systems . Additionally, a series thermo‐ and pH‐responsive PVA‐derivatives (PVA‐DEEDA‐ t ) were synthesized by Gao et al by coupling N 1, N 1 ‐diethylethane‐1,2‐diamine (DEEDA) with PVA via carbamate linkage . The carbamate linkages were mainly responsible for the thermo‐responsive behavior, whereas amino‐groups provide pH‐dependent responses due to protonation.…”

“…The carbamate linkages were mainly responsible for the thermo‐responsive behavior, whereas amino‐groups provide pH‐dependent responses due to protonation. These PVA‐derivatives with high degree of modification was successfully transformed into gels on addition of borax which showed controlled drug release kinetics …”

Temperature and pH dual stimuli responsive PCL-b-PNIPAAm block copolymer assemblies and the cargo release studies

“…These polymers find potential applications in drug delivery, emulsification, sensing or detection, catalysis, self‐healing, and so forth. The response of these smart polymers to stimuli such as pH, temperature, redox, magnetic field, light (ultra‐violet or visible), and so forth in macromolecular architectures such as block, graft, star, cyclic, and crosslinked/hyperbranched polymers has been extensively studied. The combination of controlled/living polymerization methods such as nitroxide‐mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition‐fragmentation chain transfer polymerization (RAFT), ring opening polymerization (ROP), and so forth with click reactions have been widely explored to obtain such stimuli‐responsive smart macromolecular architectures.…”