Synthesis and Properties of UCST‐Type Thermo‐ and Light‐Responsive Homopolypeptides with Azobenzene Spacers and Imidazolium Pendants

Abstract

Homopolypeptide bearing azobenzene and triethylene glycol spacers, and 1‐butylimidazolium pendants, namely P(Azo‐OEG3‐ImX) (X = Cl, I, BF4) are prepared by 1,3‐dipolar cycloaddition and subsequent ion‐exchange reaction. Both 1H NMR and FTIR confirm the polymer structures and reveal a high grafting efficiency (97%). P(Azo‐OEG3‐ImI) shows reversible upper critical solution temperature (UCST)‐type thermoresponsive property in ethanol while P(Azo‐OEG3‐ImI/BF4) shows a UCST in ethanol/water solvent mixtures. P(Azo‐OEG3‐ImI) shows UCST‐type phase transitions in ethanol or ethanol/water solvent mixtures. After UV irradiation, the UCST‐type cloud point temperature (Tcp) remains constant in ethanol. However, it decreases after UV irradiation and increases after visible light irradiation in ethanol/water solvent mixtures due to the trans–cis isomerization of azobenzene moieties. P(Azo‐OEG3‐ImCl/I) shows NaI‐induced UCST in water. The Tcp of the P(Azo‐OEG3‐ImCl/I) aqueous solution is highly related to the polymer/salt concentration and nature of counteranions. P(Azo‐OEG3‐ImCl) also shows reversible light‐responsive properties in NaI aqueous solutions. Higher NaI concentration is needed to induce a UCST for P(Azo‐OEG3‐ImCl) after UV irradiation. Moreover, ciprofloxacin‐loaded hydrogel containing P(Azo‐OEG3‐ImCl) shows more efficient drug release while the UV irradiation leads to slightly low drug release.

Molecular Mass Affects the Phase Separation of Aqueous PEG–Polycation Block Copolymer

“…18 Other cationically derivatized polymers include poly(propylene glycol) (PPG), 19 poly(γ-propyl- l -glutamate) (PPLG), 20 poly(γ-2-ethoxyethyl- l -glutamate) (PEELG), 21 and poly(γ-3-azidopropyl- l -glutamate) (PAPLG). 22 The changes in the phase separation processes induced by the cationic units may be profound and the system may even change from a LCST to an UCST one.…”

“…The phase separation of copolymers consisting of nonionic and cationic repeating units has been intensely explored, good examples being poly­( N -isopropylacrylamide) (PNIPAM) copolymers, − poly­(2-hydroxyethyl methacrylate) (PHEMA), poly­(oligo­(ethylene glycol) methacrylate) (POEGMA), poly­(ethylene glycol) (PEG), , and poly­[oligo­(2-ethyl-2-oxazoline)­acrylate] P­(OEtOxA) . Other cationically derivatized polymers include poly­(propylene glycol) (PPG), poly­(γ-propyl- l -glutamate) (PPLG), poly­(γ-2-ethoxyethyl- l -glutamate) (PEELG), and poly­(γ-3-azidopropyl- l -glutamate) (PAPLG) . The changes in the phase separation processes induced by the cationic units may be profound and the system may even change from a LCST to an UCST one.…”

Thermoresponsive polymers in non-aqueous solutions

“…9). 105 As in the case of methanol, polypeptides containing 1-butyl, 1-hexyl, or 1-dodecyl side-chains showed a UCST-type behaviour in EtOH. 91 For polymers having similar main chain length, a decrease in the T CP from 71.1 to 56.9 °C was observed with the increase in the alkyl side-chain length from 4 to 12 carbon atoms.…”

“…9 Chemical structure of the homopolypeptide P(Azo-OEG 3 -ImI). 105 Polymer Chemistry Review hydrophobic interactions and entanglement between polymer chains. Glycopolymers also displayed thermoresponsive behaviour in EtOH.…”

Recent advances in poly(ionic liquid)s for biomedical application

“…The simultaneous presence of multiple stimulus signals makes it difficult for delivery systems that respond to a single 190 Homopolypeptides with azobenzene, triethylene glycol spacers, and 1-butylimidazolium pendant exhibit reversible UCST characteristics in ethanol, and their phase transition behaviour will change under UV irradiation. 191 Their application in a drug delivery system can achieve differential release at varying temperatures and under ultraviolet radiation, which can achieve smart drug delivery.…”