Hyperbranched Macromolecule Research Articles

Aromatization of residue caused by group aggregation of hyperbranched ester macromolecule capped with benzene rings improved flame retardancy of epoxy resin

To investigate the effect of the distribution state of phosphophenanthrene groups within the branched structure on the flame retardant efficiency, the hyperbranched ester macromolecules Bz-DQMC-n (n = 1, 2, 3) capped with benzene rings were synthesized. The aggregation effect of phosphaphenanthrene groups in Bz-DQMC-n enhanced the flame retardancy of epoxy resins (EPs). At the same phosphorus contents of EPs, the Bz-DQMC-n/EP passed the V-0 rating, except for 2-(6-oxid-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)-1,4-benzenediol (DOPO-HQ)/EP without aggregated phosphaphenanthrene groups, which only reached the V-1 rating in UL 94 test. The Bz-DQMC-2 showed a better flame inhibition effect. The limiting oxygen index (LOI) value of the Bz-DQMC-2/EP reached to 39.3%, and the peak heat release rate (pk-HRR) value was 563 kW/m2, which decreased by 62.5% compared to neat EP. In addition, the total heat release (THR), and average effective heat of combustion (av-EHC) values of EP with Bz-DQMC-2 were also lower than that with Bz-DQMC-1 and Bz-DQMC-3 in the cone calorimetry test. The mechanism demonstrated that the aggregated phosphophenanthrene groups and benzene rings in Bz-DQMC-2 jointly promoted the formation of high-quality residue with more aromatic structures. Meanwhile, the concentrated release feature caused by group aggregation slightly enhanced the quenching effect in the gas phase. The aggregation effect of phosphophenanthrene groups in specific structures provides guidance for the development of high-efficiency DOPO-based flame retardants.

Ni nanoparticles Entrapped by a Functional Dendrimer as a Highly Efficient and Recyclable Catalyst for Suzuki‐Miyaura Cross‐Coupling Reactions

AbstractNi nanoparticles (NiNPs) were prepared by thermal decomposition of nickel acetylacetonate in the presence of a third generation polypyridylphenylene dendrimer (G3) which acts both as a coordinating ligand due to presence of pyridine groups and as a stabilizing agent due to highly branched architecture. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and X‐ray photoelectron spectroscopy (XPS) were used to extensively evaluate structure and morphology of the synthesized NiNPs@G3. The selected area electron diffraction (SAED) allowed us to conclude about fcc structure of NiNPs while STEM EDS analysis demonstrated a formation of core‐shell NiO@Ni NPs. Further, the catalyst was tested in selected Suzuki‐Miyaura cross‐coupling reactions at mild conditions and demonstrated a high efficiency at low Ni loading with negligible content of Ni0 on the NP surface. The functional hyperbranched dendrimer macromolecule provided an excellent stabilization for NiNPs@G3 while allowing an easy access for reactants to catalytic sites. The high activity of the catalyst in the recycling experiments was maintained by the absence of Ni leaching from the NiNPs@G3.

Graphene quantum dot reinforced hyperbranched polyamide proton exchange membrane for direct methanol fuel cell

The hyperbranched macromolecule (HBM) polyamide proton exchange membrane with uniform 3D matrix topology is beneficial to the enhancement of proton conductivity. In order to extend the application of HBM in direct methanol fuel cell (DMFC), graphene oxide (GO) and graphene quantum dot (GQD) are incorporated into HBM to enhance the proton/methanol selectivity of the membrane. The functional groups on GO and GQD surface would interact with –SO3H groups in HBM by the hydrogen-bond interaction and participate in the proton conductive channel construction. And the GO and GQD in the composite can effectively prevent the permeation of methanol molecules. Most important, the HBM membrane filled by GQD (GQD-HBM) can effectively avoid large scale phase separation which occurs in HBM membrane filled by GO (GO-HBM) due to the greater size of GO. Proton conductivity of GQD-HBM (0.30 S/cm) is 17% improved compared with the pristine HBM while methanol permeability is significantly reduced by ca. 50% due to the physical barrier of GQD. The proton/methanol selectivity is therefore enhanced by more than 80% and the DMFC performance is also significantly enhanced.

Bushy-surface hybrid nanoparticles for developing epoxy superadhesives

Hydroxyl-rich halloysite nanotube (HNT)/silica nanosphere (SiO2) core/shell particles were functionalized with multi-arm hyperbranched polyethylenimine macromolecule to develop epoxy superadhesives for metal/polymer composite interfaces. A variety of techniques including FTIR, TGA, XRD, XPS, and TEM were employed to precisely monitor the surface and bulk chemistry of HNTs flecked with silica particles and subsequently with hyperbranched polymer. Amine groups of the functionalized core/shell nanoparticles were exchanged with imide ones through the reaction with pyromellitic acid dianhydride to make the system thermally stable. Incorporation of the developed reactive bushy-surface hybrid nanoparticles into epoxy resulted in a highly crosslinkable superadhesive with exceptional thermal and mechanical properties; so that addition of only 0.5 wt% of core/shell nanoparticles caused a rise of about 31 °C in glass transition temperature with respect to the blank epoxy, suggesting very high potential of particles to cure with epoxy. Cure of adhesives containing 2 wt% of bushy-surface hybrid nanoparticles via nonisothermal differential scanning calorimetry was indicative of facilitated crosslinking, as detected by a higher enthalpy of ca. 106 J/g at low heating rate of 5 °C min−1 in a narrower temperature interval of ca. 13 °C compared to blank epoxy, visualized by the Cure Index universal dimensionless criterion. From property standpoint, a rise of ca. 130% in lap shear strength was surprisingly observed for adhesives containing bushy-surface hybrid nanoparticles.

NMR relaxation in semiflexible Vicsek fractals

We consider the role of local orientational mobility for the NMR relaxation of hyperbranched macromolecules modeled in form of Vicsek fractals. The spectral density J(ω), that is relevant for the NMR relaxation, is studied for labeled segments of flexible and semiflexible Vicsek fractals. We show that the semiflexibility leads to strong effects. For flexible Vicsek fractals the function ωJ(ω) has a single maximum, whose position is determined by the local-scale modes and therefore independent of the location of the labeled segments. For the labeled segments of a semiflexible Vicsek fractal, we observe a broad spectral density. It is characterized by the overall relaxation of the branch that originates from the labeled segment and by the overall relaxation of the subbranches that build this branch. In this way, going from the periphery to the inner part of the macromolecule, the labeled segments display a broader spectral density. However, this effect saturates when the labeled segments get closer to the core of the hyperbranched macromolecule, so that they do not feel their remoteness from the periphery anymore.

PH-Dependent Conformations for Hyperbranched Poly(ethylenimine) from All-Atom Molecular Dynamics

Hyperbranched poly(ethylene imine) (PEI) with its high amino content is a versatile functional polymer that is widely used as a gene delivery vector in biological applications and as a ligand and precursor for ion exchange resins and membranes in water purification and metal recovery. We report here the first fully atomistic model of a 25 kDa hyperbranched PEI macromolecule. We utilized this model to carry out molecular dynamics (MD) simulations with explicit water molecules and chloride ions to study pH-dependent conformational changes. We find that growing the PEI macromolecule sequentially from the monomers yields atomistic structures whose sizes (radius of gyration) are in good agreement with the small angle neutron scattering experiments. Our analysis of the structural properties from MD simulations shows that conformations of the hyperbranched PEI exhibit oblate ellipsoidal elongation at low pH compared to high or neutral pH but with no significant changes in the corresponding sizes. This fully atom...

Controllable synthesis of silver nanoparticles in hyperbranched macromolecule templates for printed flexible electronics

A facile approach was successfully developed to synthesize uniform and monodisperse silver nanoparticles with hyperbranched macromolecules as templates. This strategy would have enormous potential for flexible electronics and biosensors.

Highly stable “pore-filling” tubular composite membrane by self-crosslinkable hyperbranched polymers for toluene/n-heptane separation

The stability of membrane is a key issue for pervaporation separation of aromatic/aliphatic hydrocarbon mixtures. In this study, in order to enhance the stability, composite membrane with “pore-filling” structure was formed on porous ceramic tubular substrate. A simple self-crosslinking strategy based on the unique hyperbranched macromolecule, Boltorn W3000, was utilized in the preparation procedure. The hydroxyl and carboxyl groups on Boltorn W3000 molecules reacted at intramolecular and intermolecular during thermal cross-linking process, and then hyperbranched polymers were assembled onto the top layer and sublayer of the ceramic substrate. The morphologies and structures of “pore-filling” composite membrane were characterized by FTIR, SEM, and Nano Indenter. Moreover, “non-pore-filling” membrane was also prepared by the same method with an additional “plugging-holes” step. Both of these two composite membranes were used for separating toluene/n-heptane mixtures. The results indicated that the “pore-filling” membrane showed more stable separation performance, due to its excellent anti-swelling properties. This work thus not only illustrated a new approach for the preparation of “pore-filling” membrane, but also produced a potentially useful organic/inorganic composite membrane for aromatic/aliphatic hydrocarbon mixtures separation.

Growing Hyperbranched Polymers Using Natural Sunlight

In nature, a sapling can grow into a big tree under irradiation of sunlight. In chemistry, a similar concept that a small molecule only exposing to sunlight grows into a hyperbranched macromolecule has not been realized by now. The achievement of the concept will be fascinating and valuable for polymer synthesis wherein sunlight is inexpensive, abundant, renewable, and nonpolluting. Herein, we report a new strategy in which small monomers can directly grow into big hyperbranched macromolecule under irradiation of sunlight without any catalyst.

Reversible and Multisensitive Quantum Dot Gels

Functional fluorescent semiconductor quantum dot (QD) based gels prepared via immobilizing QDs in organic matrices have shown promising properties, but the compatibility of QDs and organic matrix is not good, and the interactions of the ligands on the surface of QDs with organic matrix are weak, which lead to poor dispersion of QDs in the formed gel and decrease of photoluminescence after gelation in some cases. In this work, we report a hyperbranched macromolecule that can not only act as an excellent ligand to stabilize QD but also act as a good gelator that can gel QD solution to form a reversible and multiresponsive fluorescent gel. This hyperbranched macromolecule-capped QD is stable, and the sol–gel switching can be easily realized via heating and ultrasonicating. Most important, the formed QD gel shows stronger fluorescence than that of the corresponding solution. This novel QD-hyperbranched macromolecule inorganic/organic hybrid network shows great promise in fields such as imaging, sensors, drug ...

Red blood cell membrane grafting of multi-functional hyperbranched polyglycerols

The covalent attachment of hydrophilic polymers or biopharmaceuticals to the surface of red blood cells (RBCs) has previously been shown as a relatively compatible and effective method for a range of applications. Here, the first example of cell-surface grafting with a hyperbranched and multi-functional macromolecule is described. A range (3 kDa–101 kDa) of dense, globular, and blood compatible hyperbranched polyglycerols (HPG) were synthesized and functionalized with cell-surface reactive, succinimidyl succinate groups (1–12 groups per polymer). Subsequently, HPG was grafted to the RBCs, which were analyzed using physical characterization techniques such as aqueous two-phase partitioning and particle electrophoresis. It was found that the extent of grafting was enhanced by increasing HPG molecular weight, the number of reactive groups per HPG, HPG concentration, and reaction time. Good in vitro cell viability – as measured by lipid peroxidation, hemoglobin oxidation, cell lysis, osmotic fragility, stability in fresh serum and aggregation behavior – was observed for grafting concentrations up to 4.8 m m. The multi-functional aspect of HPG is highlighted by the following observations: using fluorescein-labeled Anti-D (monoclonal) antibody and flow cytometry, the detection of cell-surface Rhesus (RhD) antigens were significantly reduced upon HPG grafting. Secondly, the potential for using HPG as a multi-functional, delivery agent was demonstrated by attaching fluorescent markers to the HPG via degradable linkages prior to grafting.

Synthesis and Mesogenic Properties of a Novel Hyperbranched Triphenylene-Based Discotic Liquid Crystal

A novel triphenylene-based hyper-branched macromolecule was synthesized from the functional compound-2, 6, 10-trihydroxy-3, 7, 11–tris (pentyloxy) triphenylene serving as core, using α,ω-dibromodecane as spacer and 1-bromopentane as terminal group for end capping by using a very simple synthesis method, one-pot reaction. The structure of the hyperbranched macromolecule was determined by FTIR and 1HNMR. The molecule weight and the molecular weight distribution were measured by GPC. Mesophase and their structural orders were determined using a polarized optical microscope and a differential scanning calorimeter.

Observation of disorder effects on charged carrier mobility in triphenylene-based discotic materials

A discotic 2,6,10-trihydroxy-3,7,11-tripentyloxytriphenylene material and a triphenylene-based hyperbranched macromolecule were synthesized, in which the latter was prepared from AB m molecules in a one-pot reaction. Adipic chloride and butyryl chloride were chosen as terminal groups to the 2,6,10-trihydroxy-3,7,11-tripentyloxytriphenylene. Mesophase and their structural orders were determined using a polarized optical microscope and a differential scanning calorimeter. Carrier mobilities of the pure and composite materials were measured via a time-of-flight method. A change in carrier mobility on the morphology of the materials was further discussed. It was found that degree of crystallization was the key for a discotic triphenylene material to possess charge-transporting properties, no matter it is ordered or disordered.

Energy transfer and trapping in regular hyperbranched macromolecules

Fluorescence depolarization under dipolar quasiresonant energy transfer allows to monitor the presence of the excitation on the originally excited chromophore. However, parallel to the radiative energy decay, there is also the possibility of loss due to energy trapping. Here we focus on the situation when the transfer occurs over a fractal hyperbranched macromolecule, whose center is a trap. Remarkably, the eigenvalues needed for the determination of the decay can be obtained through an iterative procedure, a fact which allows to study very large systems.

Synthesis of hyperbranched carbosiloxane macromolecule with triallyloxysilane and applications to the dendritic core

A hyperbranched carbosiloxane macromolecule (AB 3-type with Si–O bonds) was prepared by the self-hydrosilation of triallyloxysilane (H–Si(OCH 2CH=CH 2) 3) in the presence of a platinum catalyst. The prepared AB 3-type hyperbranched carbosilane was used for the carbosilane dendrimer as the core, which was progressed until the second generation by the use of iterative controlled methods such as hydrosilation and alcoholysis. NMR, MALDI mass and GPC identified the triallyloxysilane-based hyperbranched carbosilanes and dendrimers. To cite this article: C. Kim, H. Kim, C. R. Chimie 7 (2004) .

Synthesis of hyperbranched carbosiloxane macromolecule with triallyloxysilane and applications to the dendritic core

Synthesis of hyperbranched carbosiloxane macromolecule with triallyloxysilane and applications to the dendritic core

Pattern formation in a dendrimer model

A dendrimer is a hyperbranched macromolecule that is grown from a central core generation by generation. We demonstrate through Monte Carlo simulations of a dendrimer model in two dimensions that when the terminal monomers and the interior monomers interact through an effective Flory-Huggins parameter \ensuremath{\chi}, an angularly dependent domain structure forms in the molecule for sufficiently large \ensuremath{\chi}. Based on the simulation data, we further show that the formation of the domain pattern is a smooth crossover, not a phase transition, from a mixed structure.