Homopolypeptide bearing azobenzene and triethylene glycol spacers, and 1-butylimidazolium pendants, namely P(Azo-OEG 3 -ImX) (X = Cl, I, BF 4 ) are prepared by 1,3-dipolar cycloaddition and subsequent ion-exchange reaction. Both 1 H NMR and FTIR confirm the polymer structures and reveal a high grafting efficiency (97%). P(Azo-OEG 3 -ImI) shows reversible upper critical solution temperature (UCST)-type thermoresponsive property in ethanol while P(Azo-OEG 3 -ImI/BF 4 ) shows a UCST in ethanol/water solvent mixtures. P(Azo-OEG 3 -ImI) shows UCST-type phase transitions in ethanol or ethanol/water solvent mixtures. After UV irradiation, the UCST-type cloud point temperature ( T cp ) 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-OEG 3 -ImCl/I) shows NaI-induced UCST in water. The T cp of the P(Azo-OEG 3 -ImCl/I) aqueous solution is highly related to the polymer/salt concentration and nature of counteranions. P(Azo-OEG 3 -ImCl) also shows reversible light-responsive properties in NaI aqueous solutions. Higher NaI concentration is needed to induce a UCST for P(Azo-OEG 3 -ImCl) after UV irradiation. Moreover, ciprofloxacin-loaded hydrogel containing P(Azo-OEG 3 -ImCl) shows more efficient drug release while the UV irradiation leads to slightly low drug release.
The simple and straightforward construction of multi-responsive systems with tunable LCST and UCST dual phase transitions is a great challenge. This study affords an efficient route to tune cloud points via control over the chemical composition of hydroxyl and diethylamino bearing poly(amido thioether)s which were prepared by one-pot thiol–amine–acrylate polyaddition. Owing to the balance of inter/intrachain interactions, various copolymers could exhibit LCST (fOH < 0.84), LCST–UCST (fOH = 0.84–0.89) and UCST (fOH > 0.89) behaviors relying on the hydroxyl fraction in comonomer units. Meanwhile, the thermoresponsive behaviors of copolymer solutions could be efficiently tuned via switching the solvent and solution pH, applying CO2/N2 bubbling, and oxidation. The success of this study further paves the way for the robust synthesis and practical applications of smart polymers with double thermoresponsivity.
Aqueous dispersion polymerization is an environmentally friendly and low-energy method for the preparation of micron polymer microspheres. Crosslinked polymer microspheres could be obtained by aqueous dispersion polymerization via methods such as controlled radical polymerization. However, most of these commonly used cross-linking methods are complicated and the product is toxic. Herein, we provided a facile approach for the preparation of temperature-responsive crosslinked polymer microspheres (c-PMAD) by aqueous dispersion polymerization. Chain transfer reaction of 2-(dimethylamino) ethyl methacrylate (DMAEMA) instead of traditional crosslinkers was used to achieve the crosslinking. It is found that the microsphere is a spherical material with uniform surface, which has an average particle size of 5.21 μm in deionized water at 25 °C. It has a relatively high thermal stability. The microsphere has the upper critical solution temperature transition (UCST) behavior at 66.5 °C. The particle size of c-PMAD could increase with increasing temperature and decrease with increasing dosage of NaCl. Moreover, diameter of c-PMAD could decrease to original size with decreasing temperature, which endows it the feature of reusing. The UCST behavior of c-PMAD could be kept in 8 wt% NaCl solution. In addition, the effect of process conditions of preparation on the particle size of microspheres were studied in this paper. Micron-sized microspheres could be obtained at 45–65 °C. Microspheres size decreased with increasing initiator dosage, decreasing monomers concentration, increasing of acrylamide dosage and increasing of crosslinker dosage.
Chao Xing,Zhekun Shi,Jiliang Tian,Jing Sun,Zhibo Li
Stimuli-responsive polymers have received increasing interest for a variety of applications. Here, we report a series of unique charge-determined thermoresponsive polypeptoids synthesized by a combination of ring-opening polymerization and click chemistry. The LCST-type and UCST-type behavior is mainly dominated by the charge state on the side chain. Further, the phase transition temperature highly depends on the degree of polymerization, the side-chain architecture, the pH value, and so on. The obtained polypeptoid solutions exhibit good stability against temperature and salt concentration. To our knowledge, this report presents the first charge-determined LCST/UCST-type polymer from identical homopolymer backbone that displays a wide range of tunable cloudy points in aqueous media. We propose the hydrogen-bonding interaction plays a critical part on the solution behavior. These features make polypeptoids ideal candidates for highly designable stimuli-responsive polymeric materials.
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