Thermoresponsive Reversible Unimer Micelles of Amphiphilic Fluorinated Copolymers

Amphiphilic fluorinated copolymers PEGMAx-co-FAy and TEGMAx-co-FAy are prepared by activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP). All polymers present a reversible thermoresponsive lower critical solution temperature-type behavior, and a cloud point temperature (T_c) in the range of 30–60 °C strictly dependent on the length of the oxyethylene side chain, the content of the hydrophobic counits, and the concentration of the solution. Combined small angle X-ray scattering (SAXS) and dynamic light scattering measurements are used to study the self-assembly behavior in water, organic solvents (tetrahydrofuran [THF] and dimethylformamide [DMF]), and a fluorinated solvent (hexafluorobenzene [HFB]). SAXS confirms the formation of compact-globular single-chain self-folded unimer micelles in water below T_c, which generally presents small hydrodynamic diameters (D_h ≤ 8 nm) as a result of the folding of the hydrophobic perfluorohexylethyl acrylate counits. The copolymers are also able to form reverse unimer micelle in HFB. The copolymers are not able to self-assemble in unimer micelles in THF or DMF solutions, in which they adopt conventional random coil conformations.     

具有高临界相转变温度的热敏性高分子材料

介绍了一类具有高临界相转变温度(UCST)的热敏性高分子材料,并对其相转变机理、热敏性影响因素及表征方法做了讨论。UCST类高分子材料的热敏性受到相对分子质量、疏水基团、溶液中的质子受体/给体、电解质等多种因素的影响。当UCST类高分子材料与具有最低临界相转变温度(LCST)的高分子材料共聚后,可得兼具UCST和LCST特点的新型功能材料,拓展了热敏高分子材料的应用领域。     

AGET ATRP of Methyl Methacrylate Based on Thermoregulated Phase Transfer Catalysis in Organic/Aqueous Biphasic System: Facile and Highly Efficient In Situ Catalyst/Ligand Separation and Recycling

A novel polymerization system with activators generated by electron transfer for atom transfer radical polymerization (ATRP) for sustainable catalyst/ligand separation and recycling in situ is developed based on thermoregulated phase transfer catalysis in organic/aqueous biphasic system. Herein, a typical iniferter agent 1‐cyano‐1‐methylethyldiethyldithiocarbamte is used as the initiator, and CuBr₂, monomethoxy poly(ethylene glycol)‐350‐supported substituted dipicolylamine (L₃₅₀), ascorbic acid, and methyl methacrylate are employed as the catalyst, thermoresponsive ligand, reducing agent, and the model monomer, respectively. The “living” nature of the system is confirmed by polymerization kinetics with recycled catalyst complex aqueous solution and chain‐extension experiments via iniferter and ATRP mechanism, respectively. In addition, the catalyst residue in polymers is less than 2 ppm and the recycling efficiency of catalyst complex in water kept more than 95% even after 5 times of recovery experiments while keeping narrow molecular weight distribution (M_w/M_n < 1.33).

     

Block Copolymer Micelles with an Intermediate Star‐/Flower‐Like Structure Studied by 1H NMR Relaxometry

¹H NMR relaxation is used to study the self‐assembly of a double thermoresponsive diblock copolymer in dilute aqueous solution. Above the first transition temperature, at which aggregation into micellar structures is observed, the trimethylsilyl (TMS)‐labeled end group attached to the shell‐forming block shows a biphasic T₂ relaxation. The slow contribution reflects the TMS groups located at the periphery of the hydrophilic shell, in agreement with a star‐like micelle. The fast T₂ contribution corresponds to the TMS groups, which fold back toward the hydrophobic core, reflecting a flower‐like micelle. These results confirm the formation of block copolymer micelles of an intermediate nature (i.e., of partial flower‐like and star‐like character), in which a part of the TMS end groups folds back to the core due to hydrophobic interactions.

     

Temperature‐Responsive Electrophoretic Deposition of Sulfone‐Containing Nonionic Poly(N‐isopropylacrylamide)

Recently, it has been found that nonionic aliphatic and aromatic poly(ester sulfone)s show anode selective electrophoretic behavior, and it is shown that the electrophoresis is induced by a partial charge separation of the protic solvent at the dispersion interface. In this paper, the first example of temperature‐responsive electrophoretic deposition (EPD) is reported. Electrophoresis of a nonionic sulfone‐containing poly(N‐isopropylacrylamide) [poly(NIPAM)] is performed above the lower critical solution temperature. The poly(NIPAM) is prepared via reversible addition–fragmentation chain transfer radical copolymerization of NIPAM with a sulfone‐containing methacrylate. After EPD, adhesion of human umbilical vein endothelial cells on the deposited surfaces is also demonstrated, aiming at the subsequent temperature‐sensitive detachment.     

Design,Preparation, and Characterization of Thermoresponsive Hybrid Nanogels Using a Novel Ulvan‐Acrylate Crosslinker as Potential Carriers for Protein Encapsulation

The aim of the present study is the design and development of thermoresponsive nanogels based on ulvan, a sulphated heteropolysaccharide of algal origins with unique biological and chemical properties. Hybrid nanogels are successfully synthesized by means of UV‐initiated radical copolymerization of N‐vinylcaprolactam with an ulvan derivate as a novel crosslinker. In nanogels, the ulvan‐grafted poly(N‐vinylcaprolactam) chains represent the thermoresponsive component. The most promising candidates, selected after a thorough physical–chemical characterization of nanogels in terms of size and responsivity to thermal variation at physiological conditions, are loaded with bovine serum albumin (BSA) as model bioactive compound. The developed nanogels display BAS loading efficiency values similar to those obtained by using synthetic crosslinkers, and thus indicating the suitability of the developed ulvan‐acrylate to act as novel macromolecular crosslinker for thermoresponsive nanogels preparation.     

Dendronized Hyperbranched Polyethyleneimines with Switchable Thermoresponsiveness and Encapsulation

Hyperbranched polyethyleneimines (PEIs) with multiple layered structures and high density of terminal amino groups have shown great potential for applications in biomedicine, sensors, and catalysis. In this work, a kind of dendronized hyperbranched PEIs (DHPs) is synthesized by modification of PEIs with dendritic oligoethylene glycols (OEGs). These DHPs not only inherit the characteristic thermoresponsive behavior from the OEG dendrons, but also show low cytotoxicity and switchable encapsulation capacities. Their thermoresponsive behavior is found to be mainly dependent on the coverage and amphiphilicity of dendritic OEGs, solution pH, and NaCl concentration. Moreover, DHPs exhibit advantages in thermally-switchable complexation with guest molecules because of their adjustable crowding effect from the densely packed OEG chains. In addition, these DHPs can also be used as nanoreactors, which can reduce metal ions into metal nanoparticles in a convenient way. In virtue of these peculiarities, it is believed that these dendronized hyperbranched PEIs with smart properties can be used as promising scaffolds in drug-controlled release and nanoreactors.     

Nanoengineered Thermoresponsive Magnetic Nanoparticles for Drug Controlled Release

Magnetic core–shell nanoparticles are one of the most interesting nanocarriers. Smart polymers can be attached to nanoparticles as a suitable shell. Cancer tissues, with higher temperature than normal one, are one of the best targets for these systems in which the polymeric shell shrinks and thus drugs are released. The aim of this research is to synthesize such a smart nanocarrier with a thermoresponsive shell. Magnetic nanoparticles are coated with poly(N‐isopropylacrylamide). Afterward, the as prepared nanoparticles are analyzed through different characterization methods (scanning electron microscope, Fourier‐transform infrared spectroscopy, carbon–hydrogen–nitrogen–sulfur elemental analysis, energy‐dispersive X‐ray spectroscopy) and their response to the temperature is investigated in different temperatures (37 and 40 °C). Results demonstrate that a biocompatible nanocarrier with the average size of about 35 nm and 83% entrapment efficiency for curcumin is successfully synthesized. The drug release process shows a controlled behavior over temperature. It has an increasing trend by increasing the temperature from 4 to 37 °C and then to 40 °C. Moreover, the cytotoxicity of drug loaded nanocarrier is obviously increased at 40 °C compared to 37 °C. It can be concluded that this new smart nanotheranostics agent can be successfully applied for cancer treatment.     

Effect of Block Order of ABA‐ and BAB‐Type NIPAAm/HEMA Triblock Copolymers on Thermoresponsive Behavior of Solutions

ABA and BAB triblock thermoresponsive copolymers (A = N‐isopropylacrylamide, B = 2‐hydroxyethyl methacrylate) have been synthesized by atom transfer radical polymerization (ATRP). BAB is shown to exhibit a higher transition temperature and a good solubility in water compared to ABA with the same composition and concentration. The differences are attributed to the distinct micellar structure, which is regulated by the block order of the copolymers. It is speculated that ABA and BAB copolymers separately form branch and flower micelles in water, which mainly influence the course of phase transition. The moduli of the ABA copolymer solution are higher than those of the BAB above gel point. In terms of hypothesized micelle models, it is proposed that the ‘branch’ micelles of the ABA solution preferably form more physical interconnections.

     

Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T _cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T _cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.