Multiarm star-like polydimethylsiloxanes based on dendrimers of the sixth generation

A series of star-like 128-arm polydimethylsiloxanes was synthesized by the anionic polymerization of hexamethylcyclotrisiloxane using the polylithium initiator, which was obtained from the carbosilane dendrimer of the sixth generation. The measured values of molecular weights and intrinsic viscosity made it possible to characterize the samples prepared as dense globular macromolecules. The behavior of the synthesized multiarm stars at the water-air interface was studied, and the cross-section surface areas of the macromolecules were calculated. A comparison of the obtained sizes with the calculated values suggests some deformation of the dendrite core due to the interaction of the arms with the water surface.     

A modular approach toward functionalized three-dimensional macromolecules: from synthetic concepts to practical applications

A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction.     

Synthesis of 3-miktoarm stars and 1st generation mikto dendritic copolymers by "living" radical polymerization and "click" chemistry

The facile synthesis of 3-miktoarm star polymers and 1st generation mikto polymeric dendrimers using atom transfer radical polymerization (ATRP) and "click" chemistry is demonstrated. ATRP was used to synthesize near uniform polymers with Br chain ends, which were easily converted into azido groups. These polymer chains were then attached to a trifunctional alkyne molecule (tripropargylamine) using click reactions in a variety of ways to make the miktoarm stars and miktoarm polymeric dendrimers.     

Diphilic carbosilane dendrimers with different densities of the hydrophilic layer

A universal method for the synthesis of hydrophilic dendrimers was considered. The method is based on a combination of carbosilane dendrimers with different molecular organizations and hydrophilizing agents, viz., substituted hydride silanes containing one and three protected hydroxyl groups. The combination of a limited set of the mentioned reagents makes it possible to control the ratio of hydrophilic and hydrophobic moieties of the molecular structure in wide limits. A simple and convenient method for the removal of trimethylsilyl protection of hydroxyl groups in the surface layer of dendrimers was developed.     

From the discovery of sodiumoxyorganoalkoxysilanes to the organosilicon dendrimers and back

Upon being discovered 20 years ago, sodiumoxyorganoalkoxysilanes became the key to the world of organoelement dendrimers. Even considering the great variety of objects that had appeared in this area during the last 20 years, the organosilicon dendrimers are still one of the most actual objects in this class. Above all, this is fair concerning the carbosilane systems. The high reactivity of the functional groups, the well controlled chemistry of their transformations, and the inertness of the molecular skeleton are the reason for making these systems highly actual in two main regards: as model objects for the deep research of the dendrimers' properties and as polyfunctional matrixes for numerous derivatives. In this review, we were mainly focusing on the importance of the former part. In the conclusion, we showed the motivation for further development of this area both in regard of synthesis of new carbosilane systems and further development of siloxane dendrimers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4935–4948, 2008     

Structuring of star-like multiarm polydimethylsiloxanes

The in situ structuring of multiarm star-like polydimethylsiloxanes (PDMS) synthesized on the base of the high-generation carbosilane dendrimers was studied. It was shown that, in contrast to the structures with 12, 16, and 48 arms, 128-arm star-like polydimethylsiloxanes form a stable mesophase formed by the PDMS arms. The data from polarized optical microscopy and differential scanning calorimetry revealed for the first time the formation of extended liquid-crystalline domains for the diorganosiloxane chains with the methyl substituents at the silicon atom. This effect can be attributed to the influence of close packing of the PDMS chains at the dendritic branching site in the case of actually multiarm structures.     

Multiarm Star Polymers. Fundamental Aspects. A Review

Doklady Chemistry - The review is devoted to the analysis of the currently available data in the field of the molecular organization of multiarm stars, macromolecules-particles characterized by the...     

The Usefulness of Trivalent Phosphorus for the Synthesis of Dendrimers

Dendrimers are hyperbranched macromolecules, which are synthesized step-by-step by the repetition of a series of reactions. While many different types of dendrimers are known, this review focusses on the use of trivalent phosphorus derivatives (essentially phosphines and phosphoramidites) for the synthesis of dendrimers. The first part presents dendrimers constituted of phosphines at each branching point. The other parts display the use of trivalent phosphorus derivatives during the synthesis of dendrimers. Different types of reactions have been applied to phosphines. The very first examples of phosphorus-containing dendrimers were obtained by the alkylation of phosphines. Then, several families of dendrimers were elaborated by reaction of phosphoramidites. Such a type of reaction is the base of the solid phase synthesis of oligonucleotides; it has been applied in particular for the synthesis of dendrimers constituted of oligonucleotides. Finally, the Staudinger reaction between phosphines and azides afforded different families of dendrimers, and was at the origin of accelerated methods of synthesis of dendrimers. Besides, the reactivity of the P=N-P=S linkages created by this reaction led to very original dendritic structures.     

Synthesis of non-cytotoxic poly(ester-amine) dendrimers as potential solubility enhancers for drugs: methotrexate as a case study

This study describes the synthesis of two new families of dendrimers based on the esterification of N-alkylated 3-amine-1-propanol with two different cores, adipic acid (1st and 2nd generations) and ethylenediamine (generation 1.5), both with carboxylic acid end groups, offering a wide variety of further modifications at the periphery. According to the cytotoxic evaluation of the dendrimers and their possible degradation products within cell lines, these materials could be considered as innocuous. In preliminary studies, the synthesized dendrimers proved to be potential enhancers of solubility of highly hydrophobic drugs, like methotrexate, widely used in chemotherapy.     

Static and dynamic properties of computer simulated melts of multiarm polymer stars

Cooperative motion algorithm (CMA) is applied to simulate properties of polymer stars in dense systems which are considered as representations of polymer melts. Effects of arm number and arm length of stars on static and dynamic properties of model systems are analysed. Static properties are characterised by star sizes and their spatial correlations. Dynamic properties describing arm orientation relaxation and translational motion of stars are presented. Results indicate strong ordering effects for multiarm stars in the melt and suggest that the terminal relaxation of star melts can alternatively be controlled by arm orientation relaxation or by cooperative star translations depending in the two parameters of star structure i.e. arm length and arm number.     

Facile synthesis of poly-(l-lysine) dendrimers with a pentaaminecobalt(III) complex at the core

The synthesis of second and third generation dendrimers based on poly-(l-lysine) with a pentaamine cobalt(III) metal complex at the core is described. The synthesis and purification of these dendrimers were facilitated by using the metal complex as the C-terminal protecting group.     

Synthesis of polyglutamine conjugates of lysine dendrimers in solution and polymer gel

The synthesis of polyglutamine conjugates of lysine dendrimers, in which carboxyl groups of polyglutamine chains are linked via one point to the amino groups of N-terminal lysine fragments of dendrimers, is studied. Lysine dendrimers of third, fourth, and fifth generations are preliminarily prepared via the solid-phase synthesis on a polymer support, crosslinked p-methylbenzohydrylaminopolystyrene. The first approach to the synthesis of polyglutamine conjugates of dendrimers consisted in that, after the synthesis of lysine dendrimers, their removal from the polymer support, their full unblocking, and their purification, γ-benzyl glutamate N-carboxyadhydride is involved in solution polymerization at the amino groups of lysine of the outer sphere of dendrimers. The second approach includes the polymerization of γ-benzyl glutamate N-carboxyadhydride on the amino groups of N-terminal lysine residues of lysine dendrimers performed before dendrimer removal from the polymer support. The structural study of star-shaped conjugate of lysine dendrimers makes it possible to for the first time estimate the similarities and differences in these two approaches to the synthesis of polyglutamine conjugates of lysine dendrimers.     

Dynamic-covalent macromolecular stars with boronic ester linkages

Macromolecular stars containing reversible boronic ester linkages were prepared by an arm-first approach by reacting well-defined boronic acid-containing block copolymers with multifunctional 1,2/1,3-diols. Homopolymers of 3-acrylamidophenylboronic acid (APBA) formed macroscopic dynamic-covalent networks when cross-linked with multifunctional diols. On the other hand, adding the diol cross-linkers to block copolymers of poly(N,N-dimethylacrylamide (PDMA))-b-poly(APBA) led to nanosized multiarm stars with boronic ester cores and PDMA coronas. The assembly of the stars under a variety of conditions was considered. The dynamic-covalent nature of the boronic ester cross-links allowed the stars to reconfigure their covalent structure in the presence of monofunctional diols that competed for bonding with the boronic acid component. Therefore, the stars could be induced to dissociate via competitive exchange reactions. The star formation-dissociation process was shown to be repeatable over multiple cycles.     

Dendrimers and miktoarm polymers based multivalent nanocarriers for efficient and targeted drug delivery

The delivery of biologically active agents to the desired site in the body and intracellular organelles is still a big challenge despite efforts made for more than five decades. With the elaboration of synthetic methodologies to branched and hyperbranched macromolecules such as miktoarm stars and dendrimers, the focus has shifted to nanocarriers able to release and direct drug molecules to a desired location in a controlled manner. We present here recent developments in the field of targeted drug delivery with a focus on two specific macromolecular nanocarriers, dendrimers and miktoarm stars, and provide examples of these nanocarriers tested in different biological systems. A particular attraction of miktoarm stars is their versatility in achieving superior drug loading within their self-assembled structures. Advantages of dendrimers over linear polymers are that the former provide a platform for development of multivalent and multifunctional nanoconjugates, in addition to their ability to accommodate a large number of molecules inside, or at their surfaces.     

Polyelectrolyte stars in planar confinement

We employ monomer-resolved molecular dynamics simulations and theoretical considerations to analyze the conformations of multiarm polyelectrolyte stars close to planar, uncharged walls. We identify three mechanisms that contribute to the emergence of a repulsive star-wall force, namely, the confinement of the counterions that are trapped in the star interior, the increase in electrostatic energy due to confinement as well as a novel mechanism arising from the compression of the stiff polyelectrolyte rods approaching the wall. The latter is not present in the case of interaction between two polyelectrolyte stars and is a direct consequence of the impenetrable character of the planar wall.     

Novel Dendritic alpha-Sialosides: Synthesis of Glycodendrimers Based on a 3,3'-Iminobis(propylamine) Core

The cluster or multivalent effect has been recognized as an effective means by which to increase binding interactions between carbohydrates and proteins. In fact, it has been demonstrated that sialylated multibranched L-lysine dendrimers were potent inhibitors of hemagglutination of human erythrocytes by Influenza viruses. In a continuation of these studies, the synthesis of novel glycodendrimers with even valencies from 2 to 16 and ending with equidistant thiosialoside residues is described. These symmetrical dendrimers were more readily characterized by standard NMR spectral techniques than previously reported nonsymmetrical dendrimers of this general type. The synthesis of the dendritic core was based on the regioselective protection of the primary amines of 3,3'-iminobis(propylamine) (4) using benzyl cyanoformate. The resulting secondary amine 5 was alkylated with tert-butyl bromoacetate to provide divalent core structure 6 with Cbz protected amines and acid protected tert-butyl ester. Sequential deprotection by trifluoroacetolysis or hydrogenation afforded acid 7 or diamine 8 as key precursors, respectively. The two fragments were coupled using HOBt/DIC strategy to provide Cbz-protected dendrimers with valencies of 2, 4, 8, and 16 in the first, second, third, and fourth generations, respectively, in reasonable to good yields (42-82%). Cbz-protected precursors were efficiently transformed into N-chloroacetylated dendrimers by hydrogenolysis and treatment of the resulting amines with chloroacetic anhydride (82-91%). N-Chloroacetylated dendrimers were then treated with an excess of 2-thiosialic acid derivative 3 to give fully protected sialodendrimers in 76-96% yields. Deprotection of sialodendrimers under Zemplén conditions followed by methyl ester saponification and purification by gel permeation chromatography afforded symmetrical dendritic alpha-thiosialosides 21, 23, 25, and 27 in fair yields (47-58%). These novel sialodendrimers, in keeping with their design, are currently being evaluated as inhibitors of human erythrocyte hemagglutination by Influenza viruses.     

季戊四醇及其衍生物在树状大分子合成中的应用

含多羟基官能团的季戊四醇在树状大分子合成中具有重要作用,以季戊四醇及其衍生物为核的树状大分子的对称结构与独特性能已引起广泛关注.综述了季戊四醇及其衍生物在树状大分子合成中的应用.     

含硅的树枝状大分子的研究进展

树枝状大分子是一类具有规则的、高度支化的三维结构的高分子 ,含硅的树枝状大分子是以硅原子作为两代之间的支化点的树枝状大分子。本文主要综述了硅氧烷型、碳硅烷型、硅烷型树枝状大分子的合成方法及含硅的树状金属络合物的研究进展。     

Multiarm star polymers with a thermally cleavable core: A “grafting‐from” approach paves the way

Thermally cleavable multiarm star polymers containing thermo‐reversible furan–maleimide cycloadduct‐based core were synthesized using dendritic macroinitiators. Peripheries of dendritic macroinitiators were modified with bromine containing free radical initiators to obtain multiarm polymers by utilizing atom transfer radical polymerization (ATRP). Cleavage of thus obtained multiarm polymers was achieved via the retro Diels–Alder cycloreversion reaction of the furan–maleimide core at elevated temperatures. As an alternative approach, combination of multiarm polymers containing a furan and maleimide functional group at their core was attempted to realize that the steric bulk does not allow their formation. Hence the “grafting‐from” route using a thermally fragmentable trigger containing multiarm initiators provides a plausible methodology for fabrication of such thermally cleavable multiarm polymeric materials. Syntheses of dendritic initiators, formation of star polymers as well as their fragmentation were followed by proton nuclear magnetic resonance spectroscopy and size exclusion chromatography. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 885–893     

Structure,Dynamics and Properties of Materials with Polymers Having Complex Architectures

Various non-linear highly branched polymers such as multiarm stars, block copolymer micelles and bottlebrush-like polymers have been studied in order to analyze their intramolecular structure and effects of spatial ordering resulting from their specific macromolecular architecture. These polymers constitute a class of compact macromolecules which, due to the high intramolecular density, interact strongly, excluding each other in space. Investigations of the structure and dynamics in such systems, using various experimental methods as well as computer simulations, have been performed. Small angle X-ray scattering is used to characterize the structure and mechanical spectroscopy is used for the detection of the dynamic behavior of the systems. Simulations have been performed using the cooperative motion algorithm with lattice polymers equivalent to the considered macromolecules. Results of both experiments and the simulation seem to support the concept of slow structural cooperative rearrangements controlling the flow in such systems. The effects are analogous to those related to flow in low molecular liquids but take place on another size scale. The new slow relaxation processes creates new super soft-states which are characterized by shear modulus plateau lower than 10⁴ Pa.