Dendrimers and hyperbranched polymers as high-loading supports for organic synthesis

A composite of platelet-like orientated BiVO4 fused with MIL-125(Ti): Synthesis and characterization

The development of heterojunctions is the current focus of the scientific community as these materials are visible light active and the staggered positioning of their band edges combats electron-hole recombination which is the downside of most photocatalysts. In this work, a two- step hydrothermal synthesis protocol was utilized to fabricate a novel observable-light active material, composed of platelet-like BiVO4 and a titanium-based metal organic framework (MOF) called MIL-125(Ti). The tuning of specific morphologies, such as platelet-like in BiVO4, provides the exposure of most reactive facets which are more reactive towards photooxidation of organics in water, thus increasing their efficiency. The as-synthesized heterojunction was characterized by Transmission electron microscopy (TEM), scanning transmission microscopy (SEM), X-Ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), X-Ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectra. The formation of the heterojunction lead to a positive shift of the 3-2 Bi:Ti valence band (VB) (1.78 eV) when compared to 1.27 eV VB position of BiVO4. The PL and photoelectrochemical measurements revealed that the heterojunction photocatalyst designated 3-2 Bi-Ti demonstrated inhibited recombination rate (platelet-like BiVO4 > 3-2 Bi:Ti (PM) > MIL-125 > 1-1 Bi:Ti > 2-3 Bi:Ti > 3-2 Bi:Ti) and highly efficient interfacial charge shuttle between platelet-like BiVO4 and MIL-125(Ti) through the formed n-n junction.

Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

Two different commercial hyperbranched poly(ethyleneimine)s (HBPEI), with molecular weights (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, respectively, as well as the mixtures with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal analysis techniques (DSC, TGA), dielectric relaxation spectroscopy (DRS), and dynamic mechanical analysis (DMA). Only a single glass transition is observed in these mixtures by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The average activation energy for the γ-relaxation is similar for all HBPEIs and is associated with the motion of the terminal groups. The β-relaxation has the same average activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asymmetric peak with a shoulder on the high temperature side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixtures, the γ- and β-relaxations follow the behaviour of the epoxy resin alone, indicating that the epoxy resin dominates the molecular mobility. The α-relaxation by DRS is observed only as a shoulder, as a consequence of an overlap with conductivity effects, whereas by DMA, it is a clear peak.

Hollow polymer nanocapsules: synthesis, properties, and applications

Hollow polymer nanocapsules (HPNs) have gained tremendous interest in recent years due to their numerous desirable properties compared to their solid counterparts.

Synthesis of a sequence-controlled in-chain alkynyl/tertiary amino dual-functionalized terpolymer via living anionic polymerization

A dual-functionalized sequence-defined terpolymer was synthesized via living anionic polymerization; meanwhile its kinetic characteristics and sequence structure were investigated in detail via the in situ¹H NMR method.

Chiral dendrigraft polymer for asymmetric synthesis of isoquinuclidines

A copper complex of chiral modified dendrigraft amidoamine polymer with a pentaerythritol initiated polyepichlorohydrin core, PEN-G₂, on a solid resin support is employed in the synthesis of isoquinuclidines via aza Diels–Alder reaction between cyclohexenone and imines.

Silica-Supported Oligomeric Benzyl Phosphate (Si-OBP) and Triazole Phosphate (Si-OTP) Alkylating Reagents

The syntheses of silica-supported oligomeric benzyl phosphates (Si-OBP(n)) and triazole phosphates (Si-OTP(n)) using ring-opening metathesis polymerization (ROMP) for use as efficient alkylating reagents is reported. Ease of synthesis and grafting onto the surface of norbornenyl-tagged (Nb-tagged) silica particles has been demonstrated for benzyl phosphate and triazole phosphate monomers. It is shown that these silica polymer hybrid reagents, Si-OBP(n) and Si-OTP(n), can be used to carry out alkylation reactions with an array of different nucleophiles to afford the corresponding benzylated and (triazolyl)methylated products in good yield and high purity.

Synthesis of Aromatic Hyperbranched Polyester (HBPE) and its Use as a Nonmigrating Plasticiser

A series of aromatic hyperbranched polyesters (HBPEs) were synthesised through one-pot reaction of benzene-1,2,4-tricarboxylic anhydride, diethylene glycol, and methanol. The molecular structure of HBPEs was characterised by 1H-NMR, Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry (DSC), and thermogravimetric analysis. HBPE was used as plasticiser for poly(vinyl chloride) (PVC), and compared with traditional plasticiser bis(2-ethylhexyl) phthalate (DOP). When the plasticiser concentration in PVC was below 40 wt-%, HBPE showed better plasticisation efficiency than DOP, with enhanced impact strength and ultimate elongation. Volatility and extractability tests for PVC films indicated that there was no migration if HBPE was used as plasticiser, even under very harsh conditions, while the migration in PVC films plasticised by DOP was much greater, indicating that HBPE could be used as a substitution for DOP to lower the potential health risk from migrating phthalates during the use of PVC products.

A bifunctional nanocarrier based on amphiphilic hyperbranched polyglycerol derivatives

We here report on the synthesis of a bifunctional nanocarrier system based on amphiphilic hyperbranched polyglycerol (hPG), which is modified by introducing hydrophobic aromatic groups to the core and retaining hydrophilic groups in the shell. "Selective chemical differentiation" and chemo-enzymatic reaction strategies were used to synthesize this new core-shell type nanocarrier. The system shows an innovative bifunctional carrier capacity with both polymeric and unimolecular micelle-like transport properties. Hydrophobic guest molecules such as pyrene were encapsulated into the hydrophobic core of modified hPG via hydrophobic interactions as well as π-π stacking, analogous to a unimolecular micelle system. A second guest molecule, which has a high affinity to the shell like nile red, was solubilized in the outer shell of the host molecule, thus connecting the nanocarrier molecules to form aggregates. This model is confirmed by UV-Vis, fluorescence, atomic force microscopy, and dynamic light scattering, as well as release studies triggered by pH-changes and enzymes. Encapsulated guest molecules, respectively in the core and in the shell, present different controlled release profiles. The bifunctional nanocarrier system is a promising candidate for simultaneous delivery of different hydrophobic drugs for a combination therapy, e.g., in tumor treatment.

A Facile Route to Functional Hyperbranched Polymers by Combining Reversible Addition-Fragmentation Chain Transfer Polymerization, Thiol-Yne Chemistry, and Postpolymerization Modification Strategies

This contribution reports on the preparation of functional hyperbranched polystyrene-based materials via a combination of reversible addition-fragmentation chain transfer (RAFT) polymerization, thiol-yne chemistry, and postpolymerization modification reactions. The thiol-yne approach allows the rapid preparation of hyperbranched polymers under mild reaction conditions from polymeric chains bearing a thiol group at one chain end and an alkyne moiety at the other. Postpolymerization modifications of the focal thiol and peripheral alkyne functionalities present within the hyperbranched structures were conducted using two highly efficient strategies, i.e., phosphine-catalyzed thiol-ene reaction and copper-catalyzed azide-alkyne cycloaddition (CuAAC), respectively. In addition to introducing functionalities by postpolymerization modification onto the periphery of the hyperbranched polymers, the interior of the globular structure could also be functionalized by taking advantage of the isocyanate chemical handle of a poly(styrene-co-3-isopropenyl-α,α-dimethylbenzyl isocyanate) (P(S-co-TMI)) copolymer. The combination of these strategies provides an elegant tool for the elaboration of a wide variety of multifunctional hyperbranched structures.

"Click"-capture, ring-opening metathesis polymerization (ROMP), release: facile triazolation utilizing ROMP-derived oligomeric phosphates

Soluble, high-load ring-opening metathesis polymerization (ROMP)-derived oligomeric triazole phosphates (OTP) are reported for application as efficient triazolating reagents of nucleophilic species. Utilizing a "Click"-capture, ROMP, release protocol, the efficient and purification-free, direct triazolation of N-, O-, and S-nucleophilic species was successfully achieved. A variety of OTP derivatives were rapidly synthesized as free-flowing solids on a multigram scale from commercially available materials.

Dendritic polyglycerols with oligoamine shells show low toxicity and high siRNA transfection efficiency in vitro

RNA interference provides great opportunities for treating diseases from genetic disorders, infection, and cancer. The successful application of small interference RNA (siRNA) in cells with high transfection efficiency and low cytotoxicity is, however, a major challenge in gene-mediated therapy. Several pH-responsive core shell architectures have been designed that contain a nitrogen shell motif and a polyglycerol core, which has been prepared by a two-step protocol involving the activation of primary and secondary hydroxyl groups by phenyl chloroformate and amine substitution. Each polymer was analyzed by particle size and ζ potential measurements, whereas the respective polyplex formation was determined by ethidium bromide displacement assay, atomic force microscopy (AFM), and surface charge analysis. The in vitro gene silencing properties of the different polymers were evaluated by using a human epithelial carcinoma cell (HeLaS3) line with different proteins (Lamin, CDC2, MAPK2). Polyplexes yielded similar knockdown efficiencies as HiPerFect controls, with comparably low cytotoxicity. Therefore, these efficient and highly biocompatible dendritic polyamines are promising candidates for siRNA delivery in vivo.

ROMP-derived oligomeric phosphates for application in facile benzylation

The development of new ROMP-based oligomeric benzyl phosphates (OBP(n)) is reported for use as soluble, stable benzylating reagents. These oligomeric reagents are readily synthesized from commercially available materials and conveniently polymerized and purified in a one-pot process, affording bench-stable, pure white, free-flowing solids on multigram scale. Utilization in benzylation reactions with a variety of nucleophiles is reported.

Supramolecular aggregates of water soluble dendritic polyglycerol architectures for the solubilization of hydrophobic compounds

Dendritic core-shell architectures which are based on hyperbranched polyglycerol for the solubilization of hydrophobic drugs have been synthesized and characterized. The core of hyperbranched polyglycerol has been modified with hydrophobic biphenyl groups or perfluorinated chains to increase the core hydrophobicity of the macromolecules. These amphiphilic core-shell type architectures were then used to solubilize pyrene, nile red, and a perfluoro tagged diazo dye, as well as the drug nimodipine in water. Specific host-guest interactions such as fluorous-fluorous interactions could be tailored by this flexible core design and determined by UV spectroscopy. The transport capacity increased 450-fold for nile red, 47-fold for nimodipine, and 37-fold for pyrene at a polymer concentration of only 0.1 wt.-%. Surface tension measurements and scanning force microscopy (SFM) were used to reveal the aggregation properties of these complexes. The formation of supramolecular aggregates with diameters of ≈20 nm and critical aggregate concentrations of 2 × 10(-6)  mol · L(-1) have been observed. This indicates the controlled self-assembly of the presented amphiphilic dendritic core-shell type architectures.