Dendritic Polyethylene Research Articles

Synthesis and Thermoreversible Gelation of Coil-Rod Copolymers with a Dendritic Polyethylene Core and Multiple Helical Poly(γ-benzyl-L-glutamate) Arms.

Coil-rod copolymers with a dendritic polyethylene (DPE) core and multiple helical poly(γ-benzyl-L-glutamate) (PBLG) arms (DPE-(PBLG)n) were prepared by palladium-catalyzed copolymerization in tandem with ring-opening polymerization (ROP). Macroinitiator (DPE-(NH2)11) was firstly prepared by the group transformation of DPE-(OH)11 generated from palladium-catalyzed copolymerization of ethylene and acrylate comonomer. Coil-helical DPE-(PBLG)11 copolymers were prepared by ROP of γ-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA). These DPE-(PBLG)11 copolymers could form thermoreversible gels in toluene solvent, and the dendritic topology of the DPE core increased the critical gelation concentrations. The self-assembled nanostructure of gels was fully characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD), and the morphology of the fibrous structure was a twisted flat ribbon through a self-assembled nanoribbon mechanism. The self-assembled fibers formed by DPE-(PBLG45)11 are more heterogeneous and ramified than previously observed fibers formed by PBLG homopolymer and block copolymers.

Dendritic polyethylene glycol-modified folate–nickel nanotubes as an efficient antitumor nano-metal medicine

Metal-containing nanomaterials have attracted substantial research efforts due to their rich compositional and structural diversity as well as the broad possible applications. However, the most metal-containing nanomaterials are normally only used as new delivery vehicles in the field of biomedicine but do not possess biological activity by itself. Herein, we modified dendritic polyethylene glycol on one folate–nickel nanotube to fabricate a new-type of metal-containing nanotube PEG-FA-Ni NTs. We found PEG-FA-Ni NTs have exhibited excellent in vitro and in vivo antitumor activity comparable to the positive drugs doxorubicin and cisplatin. Meanwhile, this study indicates that the PEG-FA-Ni NTs may achieve more optimal antitumor effects by damaging DNA, blocking cell cycle, and ultimately inducing apoptosis. All the results showed that PEG-FA-Ni NTs could be a potent nanomedicine for the further development and application on cancer therapy.

Synthesis of amphiphilic copolymers based on dendritic polyethylene grafted by polyhydroxyethylmethacrylate and polyhydroxypropylmethacrylate and their use for construction of nanoparticles

By grafting from approach amphiphilic grafted copolymers with a hydrophobic core based on dendritic polyethylene and hydrophilic grafts of polyhydroxyethylmethacrylate (PHEMA) and polyhydroxypropylmethacrylate (PHPMA) were synthesized by tandem chain walking copolymerization and ATRP. Copolymers with molar mass 160–1400 kg/mol and ∼50–90% of hydrophilic grafts were obtained. Core-shell nanoparticles with very narrow size distribution were prepared from the copolymers by solvent displacement method. Particles diameter was efficiently regulated by molar mass of the copolymers in the range of 60–180 nm. We demonstrated that these nanoparticles can act as nanocontainers for hydrophobic Nile red dye, achieving up to 25% encapsulation efficiency. Dendritic polyethylene (dPE) nanoparticles with biocompatible polar PHEMA and PHPMA shell can find application in nanocatalysis and cargo delivery.

Synthesis of Dendritic Polyethylene Brushes with Polysiloxane as the Main Chain

A new synthetic procedure is described for the preparation of dendritic polyethylene brushes with polysiloxane as the main chain, describing for the first time that it is possible to simply and efficiently prepare highly branched architectures for this type of polymer. Furthermore, as a result of the polymer brush architecture, polyethylene acts as the side chains and SiOSi as the backbone. The number average molecular weight (Mn) of the polyethylene brushes, which is determined using a multiple angle laser light scattering detector, increases from 5946 to 27 684 g mol−1 while retaining relatively narrow polydispersities (1.5–2.4). The polymer brushes are characterized by solid 29Si NMR and high-temperature 1H NMR spectra. In addition, X-ray photoelectron spectroscopy and gel permeation chromatography were used to confirm the structure.

Novel phenolic antioxidant-functionalized dendritic polyethylene: Synthesis by tailor-made nickel(II) α-diimine-catalyzed copolymerization and its characteristics as non-releasing additive

This work describes a simple one-pot and controlled synthetic method to generate migration-resistant bio-friendly tailor-made antioxidants through ethylene–sterically hindered phenolic antioxidant (SHPA) copolymerization by coordination polymerization using MAO-activated nickel(II)-α-diimine catalyst. The antioxidant tethering into the polymer chain by chain walking catalysts leads to adjustable copolymer architectures possessing different thermal features. It was found that oxidation induction time could be fine-tuned (from 2 to 36min) by appropriate SHPA content selection and PE altering (from 10 to 0.5bar of gage). Furthermore, the chemical composition analysis of DPE–SHPA copolymer shows 0.6wt% SHPA incorporation (approximately 80% conversion) besides a dendritic architecture, containing 123 branches per 1000 carbon atoms and AFM images resembling semi-spherical topology. The migration resistance of the synthesized copolymers and their application as non-releasing additives are also investigated.

Anomalous Rheological Behavior of Dendritic Nanoparticle/Linear Polymer Nanocomposites

We investigated the effects of soft dendritic polyethylene (dPE) nanoparticles on the rheological properties of a linear polystyrene (PS) matrix. The viscosity of PS–dPE nanocomposites is found to exhibit nonmonotonic dependence on the dPE concentration. In particular, with the addition of 1% dPE nanoparticles, we already observe more than 1 order of magnitude reduction in viscosity. The minimum viscosity was observed at 5% nanoparticles. At dPE concentrations higher than 5%, nanocomposite viscosity increases by addition of nanoparticles, yet it remains below the viscosity of PS. Addition of nanoparticles not only influences the terminal relaxation times of the nanocomposites but also affects their whole relaxation spectra. The viscosity of PS–dPE nanocomposites at high temperature is found to reversibly evolve with time, which proves the existence of supramolecular interactions between the PS matrix and the nanoparticles. Atomic force microscopy confirms that dPE nanoparticles are well distributed in the PS matrix, though each component of the nanocomposite exhibits its own glass transition. While the origin of viscosity reduction remains unknown, it cannot be attributed to confinement, free volume effect, change of entanglement density, surface slippage, shear banding, or particle induced shear thinning.

Blends of Pegylated Polyoctahedralsilsesquioxanes (POSS-PEG) and Methyl Cellulose as Solid Polymer Electrolytes for Lithium Batteries

Solid polymer electrolytes (SPEs) were prepared by blending LiClO4, methyl cellulose (MC) and an oligometric dendritic polyethylene glycol (PEG), formed from polyoctahedralsilsesquioxane functionalized with ∼ 8 PEG side chains (POSS-PEG) on the SiO1.5 core. Compositions with 80/20, 70/30 and 60/40 POSS-PEG/MC, and LiClO4 (O/Li=16/1) were investigated for their electrochemical, mechanical and morphological properties, where O/Li indicates the molar ratio of ether oxygens from POSS-PEG to Li+ ions. Since compatible blends can be made over a range of compositions, ranging from “tacky” with low amounts of MC, to “hard” with high percentages of MC, this system is a paradigm for preparing batteries with continuous interfaces from the electrodes to the SPE. SEM and TEM images indicate that POSS-PEG/LiClO4(O/Li=16/1)/MC form microporous structures in which the pore walls are microphase separated. In these microphase separated blends, the LiClO4 partitions into the POSS-PEG phase and is amorphous between −100°C and its decomposition temperature, Td ∼ 300°C, as evidenced by an increased glass transition temperature (Tg) for the POSS-PEG/LiClO4 phase, while the MC phase is semicrystalline, as evidenced by x-ray diffraction data, showing the persistance of crystalline regions of MC in the blends. At temperatures below the glass transition temperature (Tg) of POSS-PEG/LiClO4(O/Li=16/1) the moduli of the blends increase with increasing POSS-PEG content, indicating that the POSS-PEG component behaves like high molar mass polyethylene oxide (PEO) reinforced with SiO1.5. At temperatures T>Tg (POSS-PEG/LiClO4), where POSS-PEG/LiClO4 is highly viscous (does not flow under its own weight) but not a true solid, the moduli of the blends increase with MC content, consistent with the high modulus MC forming cross-link sites to the dominant POSS-PEG/LiClO4 phase. It is proposed that these crosslink sites are due to residual primary OH groups from MC that form hydrogen bonds with ether oxygens of POSS-PEG/LiClO4 and result in a rubbery morphology (32 - 156MPa) at room temperature, with the Li+ ions preferentially binding to the ether oxygens in the interior of the microphase separated regions. Conductivities of 1.6×10−5 and 1.1×10−6 S/cm were measured at 30°C and 0°C, respectively, for the 80/20 POSS-PEG/LiClO4 (O/Li=16/1)/MC blend. Stability and reversibility of the blends at 50°C were observed in the range 1.5 to 4.2V.

Functionalization of cationic poly(p-phenylene ethynylene) with dendritic polyethylene enables efficient DNAzyme delivery for imaging Pb2+ in living cells.

We report here an effective Pb2+-dependent DNAzyme (8-17 DNAzyme) delivery system based on the water-soluble dendritic polyethylene-cationic poly(p-phenylene ethynylene) for successfully imaging Pb2+ in living cells. For utilizing the 8-17 DNAzyme and its unique ability to catalyze a phosphodiester bond cleavage reaction in the presence of Pb2+, the distinctive conjugated polymer-based polyvalent nanocarrier design manages to load and transport 8-17 DNAzyme across cell membranes, and to realize the fluorescence imaging of Pb2+ in living cells. As shown by the confocal microscopy and flow cytometry observations, the fluorescence of Cy5.5 is obviously activated under the conditions of incubation with Pb2+, compared with the absence of Pb2+. Taken together, the study demonstrates the combination of the molecular-wire effect with "dendrimer effects" on their effective DNAzyme delivery and their cellular imaging Pb2+.

Elongation flow-triggered morphology transitions of dendritic polyethylene amphiphilic assemblies: host-guest implications.

The assemblies and transformations of dendritic polyethylene (DPE)-poly(oligo(ethyleneglycol) methacrylate) (POEGMA) amphiphilic micelles have been demonstrated by cryo-TEM and DLS techniques under elongation flow stimuli. The flow rate-dependence of the dissymmetry ratio suggests the possibility that a combination of shear and elongation could also be responsible for the transitions of DPE-POEGMAs, but it is obvious that the exposure of elongation flow is essential and plays a key role in the assembly and fusion of the DPE-POEGMA micelles. Fluorescence resonance energy transfer (FRET) is used to provide insight into the assembly and fusion of DPE-POEGMA under elongation flow. The FRET results show that a shorter separation distance of DiO-DiI with higher elongation rate can result in higher FRET efficiency. Furthermore, DPE-POEGMAs can display the responsive switching ability of the elongation flow-triggered FRET.

Microfluidic‐Assisted Self‐Assembly of Complex Dendritic Polyethylene Drug Delivery Nanocapsules

Microfluidic platform for the synthesis of complex nanocapsules is presented via a controlled self-assembly. The monodisperse nanocapsules in the range of 50-200 nm consist of a dendritic polyethylene core and a Pluronic copolymer shell. The resultant nanocarriers encapsulate large amount of hydrophobic anticancer drug like paclitaxel while providing a low complement activation as well as sustained release profile with high tunability.

Chiral {bis[N,N′-(2-ethyl-6-methylphenyl)imino]-1,2-dimethylethane}dibromonickel bearing sec-phenethyl groups: Synthesis, characterization and application in synthesis of nanosized dendritic polyethylene

A series of {bis[N,N’N′-(2-ethyl-6-methylphenyl)imino]-1,2-dimethylethane}dibromonickels have been synthesized and characterized. The crystal structures of representative chiral ligand, bis[N,N’N′-(2-ethyl-6-methyl-4-s-phenethylphenyl)imino]-1,2-dimethylethane (S,R)–2a and its chiral complex, {bis[N,N’N′-(2-ethyl-6-methyl-4-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel (S,R)–3a, have been confirmed by X-ray crystallographic analysis. The asymmetric unit of chiral (S,R)–2a contains one half-molecule which exhibits a crystallographically imposed center of symmetry. The single C-–C bond in 1,4-diazabutadiene fragment is trans-configured and situated on an inversion center. However, the trans-configured ligand can be transformed into cis-configured ligand in order to facilitate the formation of chiral complex (S,R)–3a. Complex (S,R)–3a has pseudo-tetrahedral geometry about the nickel center. Complex (S,R)–3a bearing one ethyl and one methyl in the ortho-aryl position and an electron-donating sec-phenethyl groups in the para-aryl position, activated by diethylaluminum chloride (DEAC), shows highly catalytic activity for the polymerization of ethylene [3.22×106 106g gPE/(mol Ni.h.bar)]. Interestingly, complex 3b bearing one ethyl and one methyl groups in the ortho-aryl position and a strong electron-withdrawing Cl substituent group in the para-aryl position produced the more dendritic polyethylenes (branching degree: 92, 114 and 139 branches/1000 C at 20, 40 and 60 60(°C, respectively) under low ethylene pressure. The dendritic polyethylene particle size can be controlled in the 1–20nm range, and could be expected to become the nano-targeted drug carrier after modified with water-soluble oligo(ethylene glycol) (OEG).

Highly active ortho-phenyl substituted α-diimine Nickel(II) catalysts for “chain walking polymerization” of ethylene: Synthesis of the nanosized dendritic polyethylene

Three new α-diimine Ni(II) complexes {bis[N,N′-(4-fluoro-2,6-diphenylphenyl)imino]acenaphthene}dibromonickel 4a, {bis[N,N′-(4-chloro-2,6-diphenylphenyl)imino]acenaphthene}dibromonickel 4b, and {bis[N,N′-(4-methyl-2,6-diphenylphenyl)imino]acenaphthene}dibromonickel 4c, were synthesized and characterized. The crystal structure of the complex 4a was determined by X-ray crystallography. Complex 4a has pseudo-tetrahedral geometry about the nickel center, showing C2v molecular symmetry. These complexes, activated by diethylaluminum chloride (DEAC) were tested in the polymerization of ethylene under mild conditions. Complex 4a bearing 2,6-diphenyl and strong electron-withdrawing 4-fluorine groups, activated by diethylaluminum chloride (DEAC) shows highly catalytic activity for the polymerization of ethylene [4.95×106gPE/(molNihbar)] and produced dendritic polyethylene (153.3branches/1000C). The dendritic polyethylene particle size obtained by 4a/DEAC can be controlled in the 1–20nm under 0.2bar ethylene pressure, and could be expected to become a nano-targeted drug carrier after modified with water-soluble oligo(ethylene glycol) (OEG).

Nickel(II)-α-diimine complexes containing naphthyl substituents for ethylene polymerization under low ethylene pressure

Two new α-diimine containing Ni(II) complexes, {bis[N,N′-(2,6-dimethyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3a and {bis[N,N′-(2-methyl-4-naphthylphenyl)imino]-1,2-dimethylethane}dibromonickel 3b were synthesized and characterized. The crystal structures of representative ligand 2a and its complex 3a were determined by X-ray crystallography. Complex 3a bearing 2,6-dimethyl and 4-naphthyl groups, activated by diethylaluminum chloride (DEAC), shows high catalytic activity for the polymerization of ethylene [4.43 × 106 g PE/(mol Ni h bar)]. Interestingly, complexes 3a and 3b bearing the naphthyl substituent in the para-aryl position produced dendritic polyethylenes (branching degree, 3a: 112, 118, and 147; 3b: 113, 127, and 151 branches/1,000 C at 20, 40, and 60 °C, respectively). The dendritic polyethylene particle size obtained by 3a and 3b/DEAC can be controlled in the 1–20 nm range under low ethylene pressure (diameter, 3a: 18.31, 14.44, and 11.09; 3b: 12.29, 8.98 and 6.27 nm at 20, 40, and 60 °C, respectively) and could be expected to produce a nano-targeted drug carrier after modification with water-soluble oligo(ethylene glycol).

Synthesis of amphiphilic copolymers with a dendritic polyethylene core and poly(ethylene oxide) arms and their self-assembled nanostructures

A tandem synthetic strategy combining chain walking polymerization and azide–alkyne click chemistry was successfully used to prepare amphiphilic copolymers with a dendritic polyethylene core and poly(ethylene oxide) (PEO) arms. Dendritic polyethylene (DPE) tethered with multi-reactive hydroxyl groups (DPE-(OH)11) was synthesized by copolymerization of ethylene and trimethylsilyl-protected 2-hydroxyethyl acrylate using an α-diimine palladium catalyst under low ethylene pressure of 0.1 atm. Alkynyl-terminated DPE (DPE-()11) was quantitatively obtained by esterification reaction of DPE-(OH)11 with pentynoic acid. Using a “grafting to” technique, PEO precursors with a terminated azido group were introduced to the DPE core with high efficiency by azide–alkyne click coupling reaction. The self-assembly behaviors of the obtained core–shell amphiphiles in selective solvents including water and hexane were studied by TEM, AFM and fluorescence. Supramolecular vesicles, unimolecular micelles, and multi-molecular micelles were observed, which is dependent on selective solvent as well as number and chain length of PEO arm.

Functionalization of dendritic polyethylene with cationic poly(p-phenylene ethynylene) enables efficient siRNA delivery for gene silencing.

A novel system based on a dendritic polyethylene-cationic poly(p-phenylene ethynylene) polyvalent nanocarrier was developed for siRNA delivery. By using the combination of a molecular wire and a "dendritic effects" strategy, this design provides the nanocarrier system with low cytotoxicity, cellular imaging and high siRNA delivery efficiency, allowing it to exhibit remarkable gene knockdown abilities as well as real-time monitoring of the siRNA delivery process.

Tandem Coordination, Ring-Opening, Hyperbranched Polymerization for the Synthesis of Water-Soluble Core-Shell Unimolecular Transporters.

A water-soluble molecular transporter with a dendritic core-shell nanostructure has been prepared by a tandem coordination, ring-opening, hyperbranched polymerization process. Consisting of hydrophilic hyperbranched polyglycerol shell grafted from hydrophobic dendritic polyethylene core, the transporter has a molecular weight of 951 kg/mol and a hydrodynamic diameter of 17.5 ± 0.9 nm, as determined by static and dynamic light scattering, respectively. Based on evidence from fluorescence spectroscopy, light scattering, and electron microscopy, the core-shell copolymer transports the hydrophobic guests pyrene and Nile red by a unimolecular transport mechanism. Furthermore, it was shown that the core-shell copolymer effectively transports the hydrophobic dye Nile red into living cells under extremely high and biologically relevant dilution conditions, which is in sharp contrast to a small molecule amphiphile. These results suggest potential applicability of such core-shell molecular transporters in the administration of poorly water-soluble drugs.

Fluorescent water-soluble probes based on dendritic PEG substituted perylene bisimides: synthesis, photophysical properties, and live cell images

Water-soluble dyes based on dendritic polyethylene glycol (PEG)-substituted perylene bisimides were designed and synthesised. According to the distribution of hydrophilic dendritic PEGs, these dyes can be divided into two classes: (I) head–tail structured dyes, in which the hydrophobic perylene bisimides are the heads of the dyes and the hydrophilic dendritic PEG are used as the tails; (II) core–shell structured dyes, in which the hydrophobic perylene bisimides are encapsulated by the hydrophilic dendritic PEG. The aggregation behaviour and optical properties of these dyes were investigated. The two classes of water-soluble perylene bisimides show similar aggregation behaviour, optical and cytocompatibility properties. With increased dendron PEG generation, the aggregation of the PBI in an aqueous solution is completely suppressed by the hydrophilic bulky dendritic PEG groups, and the fluorescence quantum yield increases from 4% to 93%. These dendritic PEG-substituted perylene bisimides have good cytocompatibility. The head–tail structured dyes show a limited cellular uptake process. By contrast, the core–shell structured dyes are efficiently internalised by cells and accumulated in the cytoplasm.

Local Polarity and Microviscosity of the Interior of Dendritic Polyethylene Amphiphiles

From the temperature dependent steady-state and time-resolved fluorescence studies of coumarin 153 (C153) in dendritic polyethylene (DPE)–poly(oligo(ethylene gylcol) methacrylate) (POEGMA) unimolecular micelles, the polarity and microviscosity of the microenvironments of DPE–POEGMA were obtained. The analysis of the steady-state emission suggested that C153 sensed a more polar microenvironment in dendrimer polyethylene (dPE)–POEGMA than that in hyperbranched polyethylene (hPE)–POEGMA. It is found that the microviscosity around C153 in DPE–POEGMA micelle could be predicted from the measured reorientational time, which was observed to decrease with increasing temperature, and that local friction experienced by C153 in dPE–POEGMA decreases faster than in hPE–POEGMA with the increase of temperature, although both have similar local friction ranges.

Synthesis and Investigation of Core−Shell Dendritic Nanoparticles with Tunable Thermosensitivity

A tandem polymerization strategy has been applied to the synthesis of novel core−shell soft nanoparticles having tunable thermosensitivity. These nanoparticles have amphiphilic dendritic core−shell structures, containing dendritic polyethylene (PE) as the hydrophobic core and a layer of poly(oligo((ethylene glycol) methacrylate)s (poly(OEGMA)s) as the hydrophilic shell. The dendritic PE core was first synthesized by chain walking polymerization, which was subsequently grafted with multiple poly(OEGMA) arms by atom transfer radical polymerization (ATRP) of OEGMAs. By varying the composition of the poly(OEGMA) grafts, the thermosensitivity of the core−shell nanoparticles can be tuned with the lower critical solution temperature (LCST) temperature ranging from 20 to 60 °C. Taking advantage of the thermosensitivity and amphiphilicity, the synthesized core−shell nanoparticles show interesting thermosensitive encapsulation of hydrophobic small molecules, which can be utilized for efficient separation of hydrophobic compounds from aqueous solution. This unique type of core−shell nanoparticles may find potential applications in drug formulation and delivery, water treatment, and other nanotechnology applications.

Temperature-Sensitive Phase Transition of Dendritic Polyethylene Amphiphiles with Core−Shell Architecture Revealed by a Rayleigh Scattering Technique

The phase-transition behavior of unimolecular dendritic polyethylene amphiphiles with core-shell architecture aqueous solutions was investigated by a Rayleigh scattering (RS) technique. Dendritic polyethylene (DPE)-poly(oligo(ethylenegylcol) methacrylate) (POEGMA) with a DPE hydrophobic core and a POEGMA hydrophilic shell was synthesized by the atom-transfer radical polymerization (ATRP) of OEGMA using DPE terminated by the bromine group as a macroinitiator. The fluorescence measurements implied that DPE-POEGMA molecules in aqueous solutions existed as the unimolecular micelles. To understand the phase-transition behavior of dendritic polyethylene amphiphilic unimolecular micelles in aqueous solutions, the temperature dependence of the RS spectra of DPE-POEGMA aqueous solutions under the heating-and-cooling cycle indicated that the heating and cooling processes were reversible but hysteresis existed. The phase transition of DPE-POEGMA aqueous solutions decelerated with increasing levels of PEGylation. DPE-POEGMA exhibited a lower phase-transition temperature in D(2)O than in water.