Self-organizable vesicular columns assembled from polymers dendronized with semifluorinated Janus dendrimers act as reverse thermal actuators

The synthesis and structural analysis of polymers dendronized with self-assembling Janus dendrimers containing one fluorinated and one hydrogenated dendrons are reported. Janus dendrimers were attached to the polymer backbone both from the hydrogenated and from the fluorinated parts of the Janus dendrimer. Structural analysis of these dendronized polymers and of their precursors by a combination of differential scanning calorimetry, X-ray diffraction experiments on powder and oriented fibers, and electron density maps have demonstrated that in both cases the dendronized polymer consists of a vesicular columnar structure containing fluorinated alkyl groups on its periphery. This vesicular columnar structure is generated by a mechanism that involves the intramolecular assembly of the Janus dendrimers into tapered dendrons followed by the intramolecular self-assembly of the resulting dendronized polymer in a vesicular column. By contrast with conventional polymers dendronized with self-assembling tapered dendrons this new class of dendronized polymers acts as thermal actuators that decrease the length of the supramolecular column when the temperature is increased and therefore, are called reverse thermal actuators. A mechanism for this reversed process was proposed.     

Rodlike macromolecules through spatial overlapping of thiophene dendrons

Two novel dendritic macromonomers 7 and 8 functionalized with electroactive conjugated thiophene oligomers were synthesized by stepwise cross‐coupling reactions and the introduction of a vinyl group at the focal point. Both macromonomers were polymerized into dendronized polymers 9 and 10 by using a radical polymerization method. The photophysical and redox behaviors of dendronized polymers 9 and 10 are significantly different from those of the corresponding macromonomers. This difference may result from the spatial overlapping of thiophene dendrons through π–π interactions when the dendrons are connected to a polymer backbone. The dendronized polymers can organize into large‐area two‐dimensional sheets with a thickness of 4.8 nm. Polymer 9 , which has all‐dendritic thiophene side chains, exhibited enhanced conductivity by partial doping with iodine or nitrosonium tetrafluoroborate (NOBF₄). The novel amphiphilic dendronized polymer 15 was synthesized by the atom‐transfer radical polymerization of macromonomer 7 from a poly(ethylene glycol) (PEG) macroinitiator and was found to have a self‐organized structure in water.     

Synthesis of porphyrin‐embedded dendronized polymers by Suzuki polycondensation

Porphyrin‐embedded high molecular weight dendronized polymers up to fourth generation have been synthesized by Suzuki polycondensation of Fréchet‐type dendritic dibromo macromonomers and porphyrin diboronic pinacol ester. Higher generation lateral dendritic wedges not only endow the dendronized polymers with good solubility in commonly used organic solvents, but also prevent planar porphyrins and conjugated polymer backbones from aggregating by their “site isolation” effect. This type of porphyrin‐embedded dendronized polymers can be used as saturated red light‐emitting materials. With the increase of the generation of the lateral dendrons, the quantum yields of the dendronized polymers also gradually increased. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4030–4037, 2008     

Synthesis and polymerization of functionalized dendritic macromonomers

The synthesis of dendritic building blocks (dendrons) of the first generation (G1) and the second generation, which carry differently protected amine groups in the periphery, is reported. The dendrons are used for the synthesis of the corresponding acrylic and methacrylic macromonomers. Their polymerization behavior under radical conditions is investigated. The G1 dendronized polymers are decorated at their peripheral amino groups, that is, with the chiral amino acid L -phenylalanine by the attach-to approach. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1940–1954, 2001     

Synthesis of narrow‐polydispersity degradable dendronized aliphatic polyesters

The divergent dendronization of an ?‐caprolactone‐based polymer has been performed to provide access to dendronized polymers with sufficient biocompatibility and degradability for use as drug‐delivery scaffolds. The synthesis was performed through the tin(II) 2‐ethylhexanoate‐catalyzed polymerization of a γ‐functionalized ?‐caprolactone monomer, followed by the divergent growth of pendant polyester dendrons at each repeat unit. The resulting dendronized polymers were obtained up to the fourth generation with molecular weights as high as 80,000 Da and with polydispersities between 1.11 and 1.22. The fourth‐generation hydroxyl‐terminated dendronized polymer was degradable under a variety of aqueous conditions. A comparison of the dendronization approach with a procedure involving the ring‐opening polymerization of a second‐generation dendritic macromonomer reveals that the former procedure is best suited for the preparation of this family of dendronized polyesters because it requires shorter reaction times and affords materials with higher degrees of polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3563–3578, 2004     

Supramolecular Organogels Based on Dendrons and Dendrimers

Dendrons and dendrimers have well‐defined, discrete structures that can be precisely controlled at the molecular lever. Owing to their unique architectures and multiple functionalities, dendritic molecules have shown intensive self‐assembly behavior and functional performance. In particular, they have been shown to be promising candidates for applications in the assembly of gel‐phase materials. Furthermore, the introduction of suitable functional moieties into the core, the branches, and/or the periphery of the dendritic gelators enables the construction of smart and functional supramolecular gel materials. Over the past decade, a number of dendritic organogelators that are based on poly(amino acid), poly(amide), and poly(aryl ether) dendrons, or together with multiple alkyl chains on the periphery, have been reported. This review describes the important developments in dendritic organogelators, with an emphasis on new strategies for the molecular design of dendritic gelators, understanding of driving forces for gel formation, and their evolution for potential applications in smart soft materials.     

Nanoscopic assemblies between supramolecular redox active metallodendrons and gold nanoparticles: synthesis,characterization, and selective recognition of H2PO4-, HSO4-, and adenosine-5'-triphosphate (ATP2-) anions

Tri- and nonaferrocenyl thiol dendrons have been synthesized and used to assemble dendronized gold nanoparticles either by the ligand-substitution method from dodecanethiolate-gold nanoparticles (AB(3) units) or Brust-type direct synthesis from a 1:1 mixture of dodecanethiol and dendronized thiol (AB(9) units). The dendronized colloids are a new type of dendrimers with a gold colloidal core. Two colloids containing a nonasilylferrocenyl dendron have been made; they bear respectively 180 and 360 ferrocenyl units at the periphery. These colloids selectively recognize the anions H(2)PO(4)(-) and adenosine-5'-triphosphate (ATP(2)(-)) with a positive dendritic effect and can be used to titrate these anions because of the shift of the CV wave even in the presence of other anions such as Cl(-) and HSO(4)(-). Recognition is monitored by the appearance of a new wave at a less positive potential in cyclic voltammetry (CV). The anion HSO(4)(-) is also recognized and titrated by the dendronized colloid containing the tris-amidoferrocenyl units, because of the progressive shift of the CV wave until the equivalence point. These dendronized colloids can form robust modified electrodes by dipping the naked Pt electrode into a CH(2)Cl(2) solution containing the colloids. The robustness is all the better as the dendron is larger. These modified electrodes can recognize H(2)PO(4)(-), ATP(2)(-) and HSO(4)(-), be washed with minimal loss of adsorbed colloid, and be reused.     

Highly congested liquid crystal structures: dendrimers, dendrons, dendronized and hyperbranched polymers

In this tutorial review we describe some studies concerning liquid crystal dendritic polymers. We have chosen to present several representative examples that illustrate the diverse kinds of LC dendritic structures, namely: dendrimers, dendrons, dendronized polymers and hyperbranched polymers. We review their synthesis, mesogenic properties and the way that they are arranged to form supramolecular liquid crystal assemblies.     

Photoinduced energy transfer in bichromophoric co-assemblies based on amphiphilic poly(amidoamine) dendrons

Spherical co-assemblies were generated from an equivalent-molar-ratio mixture of amphiphilic poly(amidoamine) dendrons that were modified with focal carbazole and/or pyrene chromophores from the first to the third generation (DnCz I and DnPy, where n=1, 2, 3 denotes the generation of dendrons) in water at a concentration of 3.0 x 10(-6) M, lower than the individual critical aggregation concentrations (CAC) of either DnCz I or DnPy. UV-vis absorption and fluorescence emission spectra indicated that fluorescence resonance energy transfer (FRET) from carbazole to pyrene units occurred efficiently within the co-assemblies. Further study implied that part of the carbazole and/or pyrene units stacked homogeneously in the co-assemblies via pi-pi stacking and the dendritic branches served as connectors due to the hydrogen-bonding interaction.     

Thermoresponsive dendronized copolymers for protein recognitions based on biotin-avidin interaction

Thermoresponsive biotinylated dendronized copolymers carrying dendritic oligoethylene glycol(OEG) pendants were prepared via free radical polymerization,and their protein recognitions based on biotin-avidin interaction investigated.Both first(PG1)and second generation(PG2)dendronized copolymers were designed to examine possible thickness effects on the interaction between biotin and avidin.Inherited from the outstanding thermoresponsive properties from OEG dendrons,these biotinylated cylindrical copolymers show characteristic thermoresponsive behavior which provides an envelope to capture avidin through switching temperatures above or below their phase transition temperatures(T_cps).Thus,the recognition of polymer-supported biotin with avidin was investigated with UV/vis spectroscopy and dynamic laser light scattering.In contrast to the case for PG1,the increased thickness for copolymer PG2 hinders partially and inhibits the recognition of biotin moieties with avidin either below or above its T_cp.This demonstrates the significant architecture effects from dendronized polymers on the biotin moieties to shift onto periphery of the collapsed aggregates,which should be a prerequisite for protein recognition.These kinds of novel thermoresponsive copolymers may pave a way for the interesting biological applications in areas such as reversible activity control of enzyme or proteins,and for controlled delivery of drugs or genes.     

PAMAM-containing semiconducting polymers: Effect of dendritic side chains on optoelectronic and solid-state properties

Dendronized polymers are a particularly interesting platform for the preparation of advanced semiconductors given their high degree of functionalization, monodispersity, and bulkiness. Despite advantageous features, the incorporation of dendritic moieties in semiconducting polymers is still relatively underexplored, and the impact on the optoelectronic, thermomechanical, and solid-state properties are difficult to predict. This work focuses on the incorporation of polyamidoamine (PAMAM) dendritic side chains to semicrystalline polymers based on diketopyrrolopyrrole. Using a versatile synthetic strategy based on the azide-alkyne Huisgen 1,3-dipolar cycloaddition, dendronized semiconducting polymers were prepared and the effect of the dendritic side chains on different properties were carefully characterized using different techniques. The dendritic side chains were found to reduce aggregation and crystallinity of the polymers in thin films. PAMAM-containing semiconducting polymers were also shown to have good charge transport properties in organic field-effect transistors, within the same order of magnitude to that of diketopyrrolopyrrole-based polymers bearing branched alkyl chains. This new design approach is particularly interesting to develop advanced semiconducting polymers given its synthetic versatility and the structural diversity of the dendronized moieties. Furthermore, the utilization of dendritic moieties in semiconducting polymers is a promising approach to fine-tune the thermomechanical properties toward semiconducting polymers for next-generation organic electronics.     

Supramolecular Self-Associations of Amphiphilic Dendrons and Their Properties

This review presents precisely defined amphiphilic dendrons, their self-association properties, and their different uses. Dendrons, also named dendritic wedges, are composed of a core having two different types of functions, of which one type is used for growing or grafting branched arms, generally multiplied by 2 at each layer by using 1→2 branching motifs. A large diversity of structures has been already synthesized. In practically all cases, their synthesis is based on the synthesis of known dendrimers, such as poly(aryl ether), poly(amidoamine) (in particular PAMAM), poly(amide) (in particular poly(L-lysine)), 1→3 branching motifs (instead of 1→2), poly(alkyl ether) (poly(glycerol) and poly(ethylene glycol)), poly(ester), and those containing main group elements (poly(carbosilane) and poly(phosphorhydrazone)). In most cases, the hydrophilic functions are on the surface of the dendrons, whereas one or two hydrophobic tails are linked to the core. Depending on the structure of the dendrons, and on the experimental conditions used, the amphiphilic dendrons can self-associate at the air-water interface, or form micelles (eventually tubular, but most generally spherical), or form vesicles. These associated dendrons are suitable for the encapsulation of low-molecular or macromolecular bioactive entities to be delivered in cells. This review is organized depending on the nature of the internal structure of the amphiphilic dendrons (aryl ether, amidoamine, amide, quaternary carbon atom, alkyl ether, ester, main group element). The properties issued from their self-associations are described all along the review.     

Hollow spherical supramolecular dendrimers

The synthesis of a library containing 12 conical dendrons that self-assemble into hollow spherical supramolecular dendrimers is reported. The design principles for this library were accessed by development of a method that allows the identification of hollow spheres, followed by structural and retrostructural analysis of their Pm3n cubic lattice. The first hollow spherical supramolecular dendrimer was made by replacing the tapered dendron, from the previously reported tapered dendritic dipeptide that self-assembled into helical pores, with its constitutional isomeric conical dendron. This strategy generated a conical dendritic dipeptide that self-assembled into a hollow spherical supramolecular dendrimer that self-organizes in a Pm3n cubic lattice. Other examples of hollow spheres were assembled from conical dendrons without a dipeptide at their apex. These are conical dendrons originated from tapered dendrons containing additional benzyl ether groups at their apex. The inner part of the hollow sphere assembled from the dipeptide resembles the path of a spherical helix or loxodrome and, therefore, is chiral. The spheres assembled from other conical dendrons are nonhelical, even when they contain stereocenters on the alkyl groups from their periphery. Functionalization of the apex of the conical dendrons with diethylene glycol allowed the encapsulation of LiOTf and RbOTf in the center of the hollow sphere. These experiments showed that hollow spheres function as supramolecular dendritic capsules and therefore are expected to display functions complementary to those of other related molecular and supramolecular structures.     

Polyfunctional MDI oligomers through dendrimerization

An accessible pathway to synthesize dendronized MDI oligomers was studied. Two dendrons bearing -CN and -t-butyl functional groups on the periphery were obtained following the synthetic strategy proposed by Newkome et al. Dendrons with one focal point were converted from nitro into amino precursors and used as modifiers in the preparation of new functionalized materials. The coupling reaction of dendrons on oligomers with isocyanate groups was carried out through an easy and quick procedure. The dendronized oligomers showed conformation changes according to the polarity of the solvents, allowing a prediction of a “stimuli-responsive” behavior.     

Synthesis and energy-transfer properties of poly(amidoamine) dendrons modified with naphthyl and dansyl groups

Poly(amidoamine) dendrons of 1-3 generations with naphthyl groups at the periphery and a dansyl group at the focal point were synthesized and carefully characterized. Intramolecular energy-transfer properties of these flexible aliphatic-scaffold light-harvesting dendrons were investigated by UV-vis absorption and fluorescence spectroscopy. Efficient energy transfer from the naphthyl groups to the dansyl group occurred for both the first and the second generation dendrons (the energy-transfer efficiency was 94.3% and 76.9%, respectively), whereas the third generation dendron exhibited a low energy-transfer efficiency of 17.8%. The average donor-acceptor distances between the naphthyl and dansyl groups were calculated for different generation dendrons. Different degrees of the backfolding of dendritic branches were used to interpret the different donor-acceptor distances.     

Synthesis and Characterization of Dendronized Polymers

Summary: This research aims at the synthesis of several dendrons with different functional groups on their surface, and their use as functionalizing agents of synthetic polymers. Two principal products were synthesized and characterized: dendronized MDI oligomers and dendronized PMMI. The results of the characterization studies of dendronized polymers demonstrated the influence of the polarity of dendrons and the dendronization pathway on the properties of the final products.     

Thermoresponsive dendronized polymeric sensors

The first (G1) and second generation (G2) of dendronized copolymers carrying solvatochromic dyes were synthesized, and their thermoresponsive properties investigated. These copolymers were constituted with oligoethylene glycol (OEG)‐based dendrons to afford the thermoresponsiveness and disperse red 1 to act as the dye probe. The possible architecture and structure effects on sensoring were investigated by changing dendron generation from G1 to G2, and the interior structures of G2 polymers from hydrophilic OEG into hydrophobic alkyl chain. The sensoring ability of these copolymers to temperature and solution pH was examined with UV/Vis spectroscopy. Combined with the supports from fluorescence spectroscopy, remarkable thickness effects of dendronized polymers were discovered on the transitions of the dye moieties during the thermally‐induced aggregation process. This work enriches the field of thermoresponsive colorimetric polymeric sensors, and provides an in‐depth understanding of state changes of the dye probe during the thermally‐induced phase transitions within these bulky dendronized polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1706–1713     

Synthesis and self-assembly of supramolecular dendritic "Bow-Ties": effect of peripheral functionality on association constants

Self-assembled polyester dendritic bow-ties with various peripheral groups were prepared, and their association constants were measured by (1)H NMR in CDCl(3). The two complementary dendrons were prepared by attachment of either a bis(adamantylurea) or a glycinylurea to the focal point of the dendron. The parent self-assembled system with benzylidene acetals on one periphery and isopropylidene acetals on the other had an association constant of 520 M(-)(1). Upon deprotection of one dendron, the association constant is increased by more than an order of magnitude as the solubility of the hydroxyl-terminated dendron in CDCl(3) is decreased. In contrast, attachment of tri(ethylene oxide) units to the periphery of one dendron lowers the association constant by almost an order of magnitude. The causes of these relatively large changes in complex strength are discussed in terms of solubility, steric effects, competitive hydrogen bonding, and the structure of the dendritic scaffold.     

Poly(oxanorbornenedicarboximide)s dendronized with amphiphilic poly(alkyl ether) dendrons

Attaching dendritically branched side chains to each repeat unit of a linear polymer produces molecular building blocks of nanometer‐sized dimensions called dendronized polymers. The structure of these complex molecular architectures is highly tunable and, therefore, of interest for a wide range of potential applications. The first examples of dendronized polymers prepared by living ring‐opening metathesis polymerization of oxanorbornenedicarboximide macromonomers with poly(alkyl ether) dendrons are reported. Small‐angle X‐ray scattering experiments on bulk samples confirm that the diameter of the individual cylindrical polymers can be tailored by the choice of dendron generation or the length of the hydrocarbon peripheral group. Analysis of the SAXS data based on a core‐shell model indicates that although the diameter of the cylinder increases with generation, the size of the core does not change; this suggests that these dendrons only loosely encapsulate the polymer backbone. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3221–3239     

Synthesis and characterization of poly(fluorene‐co‐alt‐phenylene) containing 1,3,4‐oxadiazole dendritic pendants

A series of poly(fluorene‐co‐alt‐phenylene)s containing various generations of dendritic oxadiazole (OXD) pendent wedges were synthesized by the Suzuki polycondensation of OXD‐functionalized 1,4‐dibromophenylene with 9,9‐dihexylfluorene‐2,7‐diboronic ester. The obtained polymers possessed excellent solubility in common solvents and good thermal stability. Photophysical studies showed that the dendronized polymers appended with higher generations of OXD dendrons exhibited enhanced photoluminescence efficiencies and narrower values of the full width at half‐maximum. This was attributed to the shielding effect induced by the bulky dendritic OXD side chains, which prevented self‐quenching and suppressed the formation of aggregates/excimers. The energy transfer from the OXD dendrons to the polymer backbones was very efficient when excitation of the peripheral OXD dendrons resulted mainly in the polymer backbone emission alone. In particular, the photoluminescence emission intensities by the sensitized excitations of OXD dendrons in solid films of the polymers were all stronger than those by the direct excitations of their polymer conjugated backbones. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6765–6774, 2006