The synthesis of water soluble star‐block copolypeptides and their encapsulation properties are described. The star‐block copolypeptides, obtained by ring‐opening polymerization of amino acid N‐carboxyanhydrides, consist of a PEI core, a hydrophobic polyphenylalanine or polyleucine inner shell, and a negatively charged polyglutamate outer shell. The encapsulation study showed that these water soluble, amphiphilic star‐block copolypeptides could simultaneously encapsulate versatile compounds ranging from hydrophobic to anionic and cationic hydrophilic guest molecules.
Four linear and four star equimolar terpolymers based on non‐ionic hydrophilic methoxy hexa(ethylene glycol) methacrylate, ionizable hydrophilic 2‐(dimethylamino)ethyl methacrylate and neutral hydrophobic methyl methacrylate were synthesized using group transfer polymerization and investigated in aqueous dilute solutions. It was found that the (ABC)n multi‐arm star terpolymers formed unimolecular micelles comprising three centrosymmetric compartments. The position of each compartment could be determined by the block sequence (ABC, ACB or BAC) at will. On the other hand, the ABC linear counterparts formed loose associates with very low aggregation numbers. It was shown that the polymer architecture (linear versus star) greatly affected the micellization phenomena of the terpolymers in selective media.
In this communication, β‐cyclodextrin modified quantum dots were used as a water‐soluble “supramolecular” cross‐linker (SCL) because of its surface's supramolecular activity. The guest monomer‐loaded SCL (mSCL) can be used to copolymerize with water‐soluble monomers leading to transparent hybrid supramolecular hydrogels. This simple and versatile method opens new venues for the preparation of hybrid supramolecular hydrogels and the host–guest chemistry of cyclodextrins.
The preparation of hairy core–shell nanoparticles including (crosslinked) micelles, unimolecular micelles such as star polymers with block structures in each arm and surface grafted nanoparticles such as inorganic particles via the RAFT process are discussed. The RAFT process is certainly a highly versatile process. However, it should not be forgotten that RAFT polymerization is a process, i.e., superimposed on a conventional free radical process. Furthermore, the livingness of the process is dependent on the accessibility of the RAFT group, which can be hampered in certain approaches such as star synthesis and surface grafting from nanoparticles. Nevertheless, the RAFT process is a versatile toolbox that offers good solutions to a range of problems in the preparation of hairy nanoparticles.
This work focused on the synthesis and aqueous self‐assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3‐ethyl‐3‐(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self‐assembly mechanism for the large multimolecular micelles generated from the solution self‐assembly of hyperbranched copolymers.
A close correllation between molecular‐level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β‐cyclodextrin (β‐CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host–guest complexation between β‐CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra‐ and intermolecular host–guest complexation are found to control poly(acrylate) isomeric inter‐strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.
It has been clarified that syndiotactic polystyrene (sPS) forms co‐crystalline structures with polyethylene glycol dimethyl ethers (PEGDMEs) with molecular weights ranging from 178 to 1 000 g · mol−1 through a guest exchange procedure assisted by a plasticizing agent. The PEGDME molecules are incorporated into the spaces between sPS polymer sheets consisting of (T2G2)2 helices. The results of X‐ray diffraction and gravimetric measurements suggest that one or less molecules are included per unit cell for PEGDME with average molecular weight of 1 000 g · mol−1, which indicates the possibility that longer polymeric molecules can be introduced into sPS lattices with multiple site occupation.
The synthesis of new star‐shaped polymers, prepared by atom transfer radical polymerization of methyl methacrylate with tris(dialkylaminostyryl‐2,2′‐bipyridine) zinc(II) and iron(II) metalloinitiators, is reported. Their thermal and optical (absorption and emission) properties are discussed.
A novel amphiphilic diblock copolymer composed of a hydrophilic poly(ethylene oxide) block and a hydrophobic block copolymerized by azobenzene‐containing methacrylate and N‐isopropylacrylamide was synthesized using ATRP. The polymer micelles showed dual responsiveness to heat and light. The size of the micelles was dependent on temperature and the encapsulated substance in the hydrophobic cores was released during heating and cooling processes. The hydrophobicity of the micellar cores appeared as a reversible change in response to light with neither disruption of the micelles nor leakage of the encapsulated substance while H‐aggregation of the azobenzene moieties was detected.
We report the first example of the synthesis and the “schizophrenic” micellization behavior of a multi‐responsive double hydrophilic ABC miktoarm star terpolymer. A well‐defined miktoarm star terpolymer consisting of poly(ethylene glycol), poly(2‐(diethylamino)ethyl methacrylate), and poly(N‐isopropylacrylamide) arms, PEG(‐b‐PDEA)‐b‐PNIPAM, was synthesized via the combination of atom transfer radical polymerization (ATRP) and click reaction. Containing pH‐responsive PDEA and thermo‐responsive PNIPAM arms, this novel type of miktoarm star terpolymer molecularly dissolves in aqueous solution at acidic pH and room temperature, but supramolecularly self‐assembles into PDEA‐core micelles at alkaline pH and room temperature, and PNIPAM‐core micelles at acidic pH and elevated temperatures. Most importantly, both types of micellar aggregates possess well‐solvated hybrid coronas.
A series of monodisperse six‐arm benzene‐cored star oligofluorenes are prepared by a divergent/convergent strategy, starting from the repetitive divergent synthesis of symmetrical ethynyl‐bridged oligofluorenes to the convergent Co‐catalyzed alkyne cyclotrimerization. The structures of these six‐arm molecules are fully characterized. The diameter of the largest molecule SF3 reaches ca. 3 nm. These highly substituted star‐shaped oligomers exhibit extremely high fluorescent quantum yields in solution and unexpected red‐shifted and broadened emission with fine structure in the film as a result of the formation of stable aggregates.
Supramolecular self‐assembly of block copolymers in aqueous solution has received ever‐increasing interest over the past few decades due to diverse biological and technological applications in drug delivery, imaging, sensing and catalysis. In addition to relative block lengths, molecular weights and solution conditions, chain architectures of block copolymers can also dramatically affect their self‐assembling properties in selective solvents. This feature article mainly focuses on recent developments in the field of supramolecular self‐assembly of amphiphilic and double hydrophilic block copolymers (DHBCs) possessing nonlinear chain topologies, including miktoarm star polymers, dendritic–linear block copolymers, cyclic block copolymers and comb‐shaped copolymer brushes.
Two kinds of cyclodextrin/peptide (CD/peptide) hybrids bearing ZnII‐cyclen or cyclen, dansyl and β‐cyclodextrin (β‐CD) units have been synthesized as chemosensors for organic anionic molecules. ZnII‐cyclen serves as a ligand site and β‐CD is a receptor site for guest molecules, while the dansyl unit acts as a fluorescent probe. Examination of the fluorescence behaviors of these CD/peptides suggest that the hybrid containing Zn2+ has larger binding constants with respect to anionic molecules than that without Zn2+.
Summary: Dissipative particle dynamics simulation was performed to study the formation of multicompartment micelles from ABC star triblock copolymers in water. The study revealed some new morphologies that had not been observed before and also provided a direct visualization of the evolution of wormlike multicompartment micelles that follows the fusion process. Thus, this work provides molecular understanding of multicompartment micelles which will be useful for the future rational synthesis of novel micelles.
Multicompartment micelles formed from ABC star triblock copolymers in water by DPD simulations. 相似文献
Summary: A series of novel mesogen‐jacketed liquid crystal miktoarm star rod‐coil block copolymers were synthesized via atom transfer radical polymerization (ATRP). Their architectures {coil conformation of styrene segment and rigid rod conformation of {2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (MPCS) segment} were confirmed by GPC, 1H NMR, and MALDI‐TOF studies. The liquid crystalline behaviors of the synthesized copolymers are evidenced from POM observation. The liquid crystalline phase depends on the molecular weights of the rigid rod arm of miktoarm star copolymers.
A novel pH‐switchable macroscopic assembly is reported using alginate‐based hydrogels functionalized with host (α‐cyclodextrin, αCD) and guest (diethylenetriamine, DETA) moieties. Since the interaction of αCD and DETA is pH sensitive, the host hydrogel and guest hydrogel could adhere together when the pH is 11.5 and separate when the pH is 7.0. Furthermore, this pH‐controlled adhesion and dissociation shows a good reversibility. The host and guest polymers have good biocompatibility; therefore, this pH‐sensitive macroscopic assembly shows great potential in biotechnological and biomedical applications.
Blue emission of oxygen‐doped tertiary amine (triethylamine), a key unit of fluorescent poly(amido amine) dendrimer, was demonstrated. It was found that the fluorescence intensity could be further enhanced if the tertiary amines locate densely in the dendrimer interior as the branching sites. Moreover, a solvatochromic phenol blue, instead of oxygen, is able to induce the blue fluorescence of the tertiary amino‐branching sites based on a guaranteed host‐guest complexation of phenol blue molecules and dendrimer interior.
The morphology of a H‐shaped block copolymer (poly(ethylene glycol) backbone and polystyrene branches (PS)2PEG(PS)2) in a thin film has been investigated. A peculiar square lamella that has a phase‐separated microdomain at its surface is obtained after spin coating. The experimental temperature plays a critical role in the lamellar formation. The copolymer first self‐assembles into square lamellar micelles with an incomplete crystalline core due to the crystallizability of PEG. In the subsequent process of solvent evaporation, phase separation between PS and non‐crystalline PEG attached at the chain‐folded PEG surface takes place, which results in phase‐separated microdomains being formed at the lamellar surface.
We report a combined experimental and theoretical study of micellization of block copolymer with hydrophilic nonionic corona‐forming blocks and weak polyelectrolyte (wPE) core‐forming blocks with pH‐triggered solubility in aqueous solutions. We demonstrate that in addition to micelles with neutral cores, there exist two other types of micelles with PE‐ or ionomer‐like cores, in which monovalent counterions are released or condensed on core wPE block, respectively. The transition between the two types of micelles occurred upon changes in ionization of the PE core block and resulted in nonmonotonous changes of aggregation number as a function of pH. Such micelles with stimulus responsive cores represent promising nanocarriers for controlled delivery applications.
