Syntheses and self-assembly of poly(benzyl ether)-b-poly(N-isopropylacrylamide) dendritic-linear diblock copolymers

Janus-Like Single-Chain Polymer Nanoparticles as Two-in-One Emulsifiers for Aqueous and Nonaqueous Pickering Emulsions

The exploration of Pickering emulsions is very significant owing to their versatile and important applications in many scopes. In this study, synthesis of a novel kind of single-chain polymer nanoparticle (SCPN) and its stabilized Pickering emulsions were demonstrated. To this end, linear-dendritic diblock copolymers consisting of poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA) blocks and four-generation dendritic aliphatic polyester blocks (G₄) have been first synthesized by the combination of click chemistry and reversible addition-fragmentation chain transfer (RAFT) polymerization reaction. The subsequent intramolecular cross-linking of the PDMAEMA block of PDMAEMA-b-G₄ copolymers in DMF using 1,4-diiodobutane as cross-linkers afforded Janus-like SCPNs that exhibited a cross-linked PDMAEMA head tethered by a short dendritic tail. The molecular weight and distribution together with the structure of polymers were carefully characterized by GPC and NMR spectroscopy. By the employment of the as-synthesized Janus-like SCPNs as Pickering emulsifiers, aqueous and nonaqueous Pickering emulsions including water-in-oil and oil-in-oil as well as ionic liquid-in-oil were generated. Under the same conditions, it was found that the long-term stabilities of Pickering emulsions stabilized by Janus-like SCPNs were superior to those of Pickering emulsions stabilized by their linear quaternized PDMAEMA-b-G₄ by CH₃I analogous.

Thermoresponsive Poly(glycidyl ether) Brush Coatings on Various Tissue Culture Substrates-How Block Copolymer Design and Substrate Material Govern Self-Assembly and Phase Transition

Thermoresponsive poly(glycidyl ether) brushes can be grafted to applied tissue culture substrates and used for the fabrication of primary human cell sheets. The self-assembly of such brushes is achieved via the directed physical adsorption and subsequent UV immobilization of block copolymers equipped with a short, photo-reactive benzophenone-based anchor block. Depending on the chemistry and hydrophobicity of the benzophenone anchor, we demonstrate that such block copolymers exhibit distinct thermoresponsive properties and aggregation behaviors in water. Independent on the block copolymer composition, we developed a versatile grafting-to process which allows the fabrication of poly(glycidyl ether) brushes on various tissue culture substrates from dilute aqueous-ethanolic solution. The viability of this process crucially depends on the chemistry and hydrophobicity of, both, benzophenone-based anchor block and substrate material. Utilizing these insights, we were able to manufacture thermoresponsive poly(glycidyl ether) brushes on moderately hydrophobic polystyrene and polycarbonate as well as on rather hydrophilic polyethylene terephthalate and tissue culture-treated polystyrene substrates. We further show that the temperature-dependent switchability of the brush coatings is not only dependent on the cloud point temperature of the block copolymers, but also markedly governed by the hydrophobicity of the surface-bound benzophenone anchor and the subjacent substrate material. Our findings demonstrate that the design of amphiphilic thermoresponsive block copolymers is crucial for their phase transition characteristics in solution and on surfaces.

Linear-dendritic block copolymer for drug and gene delivery

Dendrimers as a new class of polymeric materials have a highly ordered branched structure, exact molecular weight, multivalency and available internal cavities, which make them extensively used in biology and drug-delivery. Concurrent with the development of dendrimers, much more attention is drawn to a novel block copolymer which combines linear chains with dendritic macromolecules, the linear-dendritic block copolymer (LDBC). Because of the different solubility of the contrasting regions, the amphiphilic LDBCs could self-assemble to form aggregates with special core-shell structures which exhibit excellent properties different from traditional micelles, such as lower critical micelle concentration, prolonged circulation in the bloodstream, better biocompatibility, and lower toxicity. The present review briefly describes the type of LDBC, the self-assembly behavior in solution, and the application in delivery system including the application as drug carriers and gene vectors. The interactions between block copolymers and drugs are also summarized to better understand the release mechanism of drugs from the linear-dendritic block copolymers.

Synthesis and solution properties of novel thermo- and pH-responsive poly(N-vinylcaprolactam)-based linear–dendritic block copolymers

This study describes the synthesis and solution properties of the novel linear–dendritic block copolymers (LDBCs) based on thermoresponsive poly(N-vinylcaprolactam) (PNVCL) chains and pH-responsive poly(benzyl ether) dendrons.

Synthesis, nanoprecipitation and pH sensitivity of amphiphilic linear-dendritic hybrid polymers and hyperbranched-polydendrons containing tertiary amine functional dendrons

The combination of linear polymers with dendritic chain-ends has led to numerous studies of linear-dendritic polymer hybrid materials. Interchain branching within the linear segment of these materials has recently extended this concept to the formation of soluble hyperbranched-polydendrons. Here, the introduction of amphiphilicity into hyperbranched-polydendrons has been achieved for the first time through the use of tertiary amine functional dendritic chain-ends and branched hydrophobic polymer segments. The synthesis and aqueous nanoprecipitation of these branched materials is compared with their linear-dendritic polymer analogues, showing that chain-end chemistry/generation, precipitation medium pH and polymer architecture are all capable of influencing the ability to generate nanoparticles, the resulting nanoparticle diameter and dispersity, and subsequent response to changes in pH.

Fabrication of a multi-charge generable poly(phenyl isocyanide)-block-poly(3-hexylthiophene) rod–rod conjugated copolymer

A facile construction of diverse polymeric nanostructures was reported by simple quaternization reaction and UV irradiation starting from the same rod-rod conjugated PPI(-DMAENBA)-b-P3HT) diblock copolymers, which were prepared by sequential living copolymerization of PI and 3HT in one-pot.

Cyclotetrasiloxane frameworks for the chemoenzymatic synthesis of oligoesters

The lipase-mediated synthesis of branched and polycyclic polyester systems based on a cyclotetrasiloxane core.

Responsive linear-dendritic block copolymers

The combination of dendritic and linear polymeric structures in the same macromolecule opens up new possibilities for the design of block copolymers and for applications of functional polymers that have self-assembly properties. There are three main strategies for the synthesis of linear-dendritic block copolymers (LDBCs) and, in particular, the emergence of click chemistry has made the coupling of preformed blocks one of the most efficient ways of obtaining libraries of LDBCs. In these materials, the periphery of the dendron can be precisely functionalised to obtain functional LDBCs with self-assembly properties of interest in different technological areas. The incorporation of stimuli-responsive moieties gives rise to smart materials that are generally processed as self-assemblies of amphiphilic LDBCs with a morphology that can be controlled by an external stimulus. Particular emphasis is placed on light-responsive LDBCs. Furthermore, a brief review of the biomedical or materials science applications of LDBCs is presented.

Temperature- and pH-sensitive Polymeric Micelles for Drug Encapsulation, Release and Targeting

More than 50% of the drugs in the market and 70% of the new candidates are poorly water soluble according to the Biopharmaceutic Classification System (BCS(. Poor aqueous solubility and physico-chemical stability of drugs in biological fluids remain key limitations in oral, parenteral and transdermal administration and contribute to an increase the drug attrition rate. Motivated by the outbreak of nanotechnology, different nanocarriers made of lipids and polymers have been designed and developed to address these limitations. Moreover, robust platforms were exploited to achieve the temporal and spatial release of drugs, thus constraining the systemic exposure to toxic agents and the appearance of severe adverse effects and improving the safety ratio. Owing to unique features such as (i( great chemical flexibility, (ii( capacity to host, solubilize and physico-chemically stabilize poorly water soluble drugs, (iii( ability to accumulate selectively in highly vascularized solid tumors and (iv( ability of single amphiphile molecules (unimers( to inhibit the activity of different pumps of the ATP-binding cassette superfamily (ABCs(, polymeric micelles have emerged as one of the most versatile nanotechnologies. Despite their diverse applications to improve the therapeutic outcomes, polymeric micelles remain clinically uncapitalized. The present chapter overviews the most recent applications of temperature- and pH-responsive polymeric micelles for the encapsulation, release and targeting of drugs and discusses the perspectives for these unique nanocarriers in the near future.

Morphological transformations in a dually thermoresponsive coil-rod-coil bioconjugate

We report the conformational and assembly behavior of a thermoresponsive triblock biohybrid conjugate under aqueous conditions. The triblock comprises of poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA) conjugated to the ends of a triple-helix forming collagen-like peptide. The circular dichroism (CD) experiment confirms the ability of the collagen-like peptide middle block to assemble as a triple helix in the hybrid conjugate. Above the LCST (~35 °C), the collapse of the thermoresponsive PDEGMEMA polymer at the ends of the peptide domain resulted in a concomitant increase in the conformational stability of the peptide domain towards thermal denaturation. Upon cooling back, the kinetic conformational refolding behavior was still observed for the peptide domain in the hybrid conjugate. Static light scattering (SLS) experiments suggested the formation of supramolecular structures upon increasing solution temperatures to above the LCST. The scattering intensity increased with increasing temperature, until at 75 °C then it was found to decrease. Cryogenic scanning electron microscopy and regular transmission electron microscopy suggested the formation of spherical aggregates that increased in size with increasing temperature up to 65 °C and a morphological transformation into fibrils was also observed at 75 °C. The synergistic effect of dual thermoresponsive behavior from the peptide and the polymer block in the triblock hybrid is suggested for the observed conformational and assembly behaviors.

How switching the substituent of a pyrene derivative from a methyl to a butyl affects the fluorescence response of polystyrene randomly labeled with pyrene

A series of polystyrenes randomly labeled with 1-pyrenebutanol were prepared by copolymerizing styrene and 1-pyrenebutylacrylate yielding the CoBuE–PS series. Solutions of CoBuE–PS were prepared in nine organic solvents having viscosities ranging from 0.36 to 5.5 mPa·s and the fluorescence spectra and pyrene monomer and excimer fluorescence decays were acquired. Analysis of the fluorescence spectra yielded the IE/IM ratio, whereas analysis of the fluorescence decays with the fluorescence blob model (FBM) yielded the parameters N blobo , <kblob × Nblob> , and k blobo . These parameters were compared to those obtained with two other series of pyrene-labeled polystyrenes, which had been studied earlier, namely CoA–PS and CoE–PS where pyrene was attached to the polymer backbone via a methylamide and benzyl methylether linker, respectively. Although the parameters IE/IM, N blobo , <kblob × Nblob>, and k blobo took different values according to the specific nature of the linker connecting pyrene to the polystyrene backbone, they exhibited trends that were quite similar for all the pyrene-labeled polystyrene constructs. The excellent agreement between the parameters retrieved for the three different types of pyrene-labeled polystyrenes suggests that the FBM accounts satisfyingly for differences in the nature of the label used, while still retrieving information pertinent to the polymer of interest.

Orderly arranged NLO materials based on chromophore-containing dendrons on exfoliated layered templates

Three chromophore-containing dendrons were intercalated into montmorillonite layered silicates via an ion-exchange process. Enlarged d spacings ranging from 50 to 126 A were achieved for these novel organoclays. After the organoclays were blended with a polyimide, the steric bulkiness of the dendrons and the interaction between dendron and polyimide resulted in an ordered morphology. The orderly arranged nanocomposites were characterized by a UV-visible spectrophotometer, a variable-temperature infrared spectrometer, and electro-optical modulation. The dendrons in layered silicates were capable of undergoing a critical conformational change into an ordered structure, indicated by the drastic changes of interlayer distances at certain packing densities. Electro-optical coefficients increased sharply from 0 to 6 pm/V while the conformational change occurred. Furthermore, the addition of a polyimide capable of interaction-induced orientation was found to exert an enhancing effect on the degree of the noncentrosymmetric alignment.