Self-Assembly and Micellization of a Dual Thermoresponsive Supramolecular Pseudo-Block Copolymer

This paper reports the studies on self-assembly and thermosensitive micellization phenomena of a supramolecular polymeric host−guest system consisting of star-shaped poly(N-isopropylacrylamide) (PNIPAAm) with a β-cyclodextrin (β-CD) core (the host polymer) and bis(adamantyl)-terminated poly(propylene glycol) (PPG) (the guest polymer) in aqueous solution. This interesting host−guest system exhibited dual thermoresponse in aqueous solution because of the existence of two kinds of thermoresponsive segments, PPG and PNIPAAm, in the polymeric guest and host components, respectively. This unique thermoresponsive behavior was completely tunable by the ratio of host/guest up to 1.0. Beyond this range, the effect of the host was saturated, indicating that the host−guest system involved a 1:1 complexation between adamantyl moiety and β-CD core. In other words, this polymeric host−guest system was able to form ABA-type supramolecular pseudo-block copolymer via inclusion complexation in aqueous solution. This pseudo-block copolymer underwent a reversible temperature-induced transition from solution to micelle and further to aggregate under suitable conditions. However, different from conventional polymeric micelles, in the micelles formed from this pseudo-block copolymer, the shell (composed of host component) and the core (composed of guest component) were connected by physical interactions rather than chemical bonding. The micellization phenomena of the host−guest system were extensively studied by a combination of 1H NMR, fluorescence probe technique, dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The critical micelle temperature (CMT) for this thermoresponsive host−guest system was dependent on the composition and concentration of the components. The size of the resultant noncovalently connected micelle could be easily tuned not only by adjusting the temperature and the concentration of the components but also by the ratio of host/guest and the length of the PPG block in the guest polymer

A Well-Defined Ladder Polyphenylsilsesquioxane (Ph-LPSQ) Synthesized via a New Three-Step Approach: Monomer Self-Organization−Lyophilization—Surface-Confined Polycondensation

A high-molecular-weight and well-defined ladder polyphenylsilsesquioxane (Ph-LPSQ) was synthesized via a new three-step approach: monomer self-organization in solution, lyophilization, and surface-confined polycondensation. A ladder superstructure, which served as a template to direct the polycondensation, was self-assembled from the 1,3-diphenyl-tetrahydroxy-disiloxane monomer (M) in acetonitrile solution. Following that, it was lyophilized to form a thin layer on the inner surface of a flask. Subsequently, polycondensation of the ordered monomeric thin layer was performed under a triethylamine (TEA) atmosphere. This strategy increased the ladder regularity of the Ph-LPSQ by preventing common complications faced in solution polycondensation of silanol-containing monomers, such as cyclization and gelation side reactions. 29Si NMR analysis showed a very narrow peak (peak width at half-height, w1/2 = 2.5 ppm) at δ = –78.5 (corresponding to a Ph-SiO3/2unit), indicating a high degree of regularity of the polymer structure

Autonomous Chitosan-Based Self-Healing Hydrogel Formed through Noncovalent Interactions

A facile strategy was developed for the formation of an autonomous chitosan-based self-healing hydrogel. This hydrogel was fabricated using in situ free radical polymerization of acrylic acid (AA) and acrylamide (AM) in the presence of chitosan in dilute acetic acid aqueous solution under mild conditions. The in situ formed hydrogel is mainly composed of chitosan graft copolymers (CS-g-P­(AM-r-AA)) and a small amount of nongrafted copolymers (P­(AM-r-AA)), which interact with each other through a combination of multiple noncovalent interactions, including the interchain electrostatic complexation between −[AA]– segments and positively charged amino groups of chitosan, the H-bonding between −[AM]– segments, and the H-bonding between −[AM]– segments and the chitosan backbone. Owing to the cooperation of these noncovalent interactions and the reversible nature of the noncovalent network structure, the obtained hydrogel exhibits rapid network recovery, high stretchability, and efficient autonomous self-healing properties. The hydrogel can also dissolve completely in dilute acidic aqueous solution under mild conditions, visibly reflecting the unique network feature of this self-healing hydrogel system

Synthesis of Novel Biodegradable Thermoresponsive Triblock Copolymers Based on Poly[(<i>R</i>)-3-hydroxybutyrate] and Poly(<i>N</i>-isopropylacrylamide) and Their Formation of Thermoresponsive Micelles

Novel thermoresponsive amphiphilic triblock copolymers with two hydrophilic poly(N-isopropylacrylamide) blocks flanking a central hydrophobic poly[(R)-3-hydroxybutyrate] block were synthesized by atom transfer radical polymerization. The copolymers were characterized by gel permeation chromatography (GPC) and 1H and 13C NMR spectroscopy. The thermal stability of the copolymer was investigated by thermogravimetric analysis (TGA), and crystallization behavior was studied by differential scanning calorimetry (DSC). The water-soluble copolymers formed core−corona-type micelle aggregates in water. The critical micelle concentrations of the triblock copolymers were in the range of 1.5 to 41.1 mg/L, and the partition coefficients were in the range of (1.64−20.42) × 105. Transmission electron microscopy showed that the self-assembled micelle aggregates had well-defined spherical shape. The temperature sensitivity of the micelles was demonstrated by the phase transition of a 0.5 mg/mL aqueous polymer solution at the lower critical solution temperature (LCST). Preliminary cytotoxicity studies showed that these micelles were nontoxic and could be potential candidates for the encapsulation and release of therapeutic drugs in the biological system

Thermoresponsive Delivery of Paclitaxel by β‑Cyclodextrin-Based Poly(<i>N</i>‑isopropylacrylamide) Star Polymer via Inclusion Complexation

Paclitaxel (PTX), a hydrophobic anticancer drug, is facing several clinical limitations such as low bioavailability and drug resistance. To solve the problems, a well-defined β-cyclodextrin-poly­(<i>N</i>-isopropylacrylamide) star polymer was synthesized and used as a nanocarrier to improve the water solubility and aim to thermoresponsive delivery of PTX to cancer cells. The star polymer was able to form supramolecular self-assembled inclusion complex with PTX via host–guest interaction at room temperature, which is below the low critical solution temperature (LCST) of the star polymer, significantly improving the solubilization of PTX. At body temperature (above LCST), the phase transition of poly­(<i>N</i>-isopropylacrylamide) segments induced the formation of nanoparticles, which greatly enhanced the cellular uptake of the polymer-drug complex, resulting in efficient thermoresponsive delivery of PTX. In particular, the polymer–drug complex exhibited better antitumor effects than the commercial formulation of PTX in overcoming the multi-drug resistance in AT3B-1 cells

A Calix[4]arene Carceplex with Four Rh₂⁴⁺ Fasteners

It is shown that a spheroidal carceplex can be assembled by linking two bowl-shaped calix[4]arenes via four dimetal units, (DAniF)2Rh2 (DAniF = N,N‘-di-p-anisylformamidinate), with a molecule (diethyl ether) or a cation (tetraethylammonium ion) trapped inside. The tetraethylammonium carceplex, 1b, has been characterized by X-ray crystallography, 1H NMR, IR, and mass spectrometry. The tetraethylammonium ion fits snugly in the interior of the spheroidal carceplex. A two-fold axis of the tetrahedral cation coincides with the idealized four-fold axis of the cage, and the cation is disordered over two rotational orientations. Only one axial position on each dirhodium unit is occupied by a ligand, CH3CN or H2O. The carceplex is very stable, and the axial ligands can be exchanged in single crystals without disrupting the crystallinity of the samples. In this way, a red crystal of the complex with all axial positions occupied by acetonitrile can be transformed to a green crystal of the complex with two axial positions having acetonitrile and the other two having water by simply putting the crystal in contact with distilled water. The calix[4]arene used to make the carciplex structure is 25,26,27,28-tetra-n-propoxycalix[4]arene-5,11,17,23-tetracarboxylic acid. By employing 25,26,27,28-tetrapropoxy-5,17-dibromo-calix[4]arene-11,23-dicarboxylic acid, two 1:1 dimetal:calixarene compounds have also been made and characterized:  2, cis-Rh2(DAniF)2(calix)(CH3OH), and 3, cis-Mo2(DAniF)2(calix). The Rh−Rh distances in 1b are in the range of 2.410(2)−2.428(2) Å, that in 2 is 2.4383(4) Å, and the Mo−Mo distance in 3 is 2.0931(4) Å

Pseudo-Block Copolymer Based on Star-Shaped Poly(<i>N</i>-isopropylacrylamide) with a β-Cyclodextrin Core and Guest-Bearing PEG: Controlling Thermoresponsivity through Supramolecular Self-Assembly

Pseudo-Block Copolymer Based on Star-Shaped Poly(N-isopropylacrylamide) with a β-Cyclodextrin Core and Guest-Bearing PEG: Controlling Thermoresponsivity through Supramolecular Self-Assembl

A Calix[4]arene Carceplex with Four Rh₂⁴⁺ Fasteners

It is shown that a spheroidal carceplex can be assembled by linking two bowl-shaped calix[4]arenes via four dimetal units, (DAniF)2Rh2 (DAniF = N,N‘-di-p-anisylformamidinate), with a molecule (diethyl ether) or a cation (tetraethylammonium ion) trapped inside. The tetraethylammonium carceplex, 1b, has been characterized by X-ray crystallography, 1H NMR, IR, and mass spectrometry. The tetraethylammonium ion fits snugly in the interior of the spheroidal carceplex. A two-fold axis of the tetrahedral cation coincides with the idealized four-fold axis of the cage, and the cation is disordered over two rotational orientations. Only one axial position on each dirhodium unit is occupied by a ligand, CH3CN or H2O. The carceplex is very stable, and the axial ligands can be exchanged in single crystals without disrupting the crystallinity of the samples. In this way, a red crystal of the complex with all axial positions occupied by acetonitrile can be transformed to a green crystal of the complex with two axial positions having acetonitrile and the other two having water by simply putting the crystal in contact with distilled water. The calix[4]arene used to make the carciplex structure is 25,26,27,28-tetra-n-propoxycalix[4]arene-5,11,17,23-tetracarboxylic acid. By employing 25,26,27,28-tetrapropoxy-5,17-dibromo-calix[4]arene-11,23-dicarboxylic acid, two 1:1 dimetal:calixarene compounds have also been made and characterized:  2, cis-Rh2(DAniF)2(calix)(CH3OH), and 3, cis-Mo2(DAniF)2(calix). The Rh−Rh distances in 1b are in the range of 2.410(2)−2.428(2) Å, that in 2 is 2.4383(4) Å, and the Mo−Mo distance in 3 is 2.0931(4) Å

A Chiral Luminescent Au₁₆ Ring Self-Assembled from Achiral Components

A luminescent supramolecular chiral Au16 ring with 4.822 nm perimeter that self-assembled from a tetrameric array of achiral Au2 units is described. Intra- and intermolecular Au···Au interactions play an important role in directing its chiral self-assembly

A Chiral Luminescent Au₁₆ Ring Self-Assembled from Achiral Components

A luminescent supramolecular chiral Au16 ring with 4.822 nm perimeter that self-assembled from a tetrameric array of achiral Au2 units is described. Intra- and intermolecular Au···Au interactions play an important role in directing its chiral self-assembly