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     

Bulk properties of dendronized polymers with tailored end‐groups emanating from the same backbone

Dendronized polymers with a methacrylate backbone bearing pendant aliphatic polyester dendrons based on 2,2‐bis(methylol)propionic acid have been investigated by rheological measurements, differential scanning calorimetry (DSC), size exclusion chromatography (SEC), and ¹H NMR self‐diffusion techniques. The change in material properties due to the attachment of larger dendrons and/or different end‐groups to a backbone of the same length is investigated. Dendronized polymers of the second to fourth generation with hydroxyl, acetonide, or hexadecyl end‐group functionalities have been studied. DSC revealed that the glass transition temperature of the amorphous polymers increases with increasing size of the dendrons, and that the ability for the hexadecyl functional polymers to crystallize decreases with increasing size of dendrons. ¹H NMR self‐diffusion and longitudinal relaxation data are consistent with an elongated rod‐like model of the polymers in solution. Larger dendrons lead to a larger rod diameter that approximately double when increasing the generation of dendronized polymer from two to four. Rheological measurements demonstrated that the complex viscosity at low frequency increased with dendron size. Independently of the functionality, the second and third generation samples initially showed a Newtonian plateau, followed by a shear thinning region at higher frequencies. The fourth generation samples only showed shear thinning over the whole frequency region. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4496–4504, 2005     

Covalent functionalization of solid cellulose by divergent synthesis of chemically active dendrons

Covalent surface modification of solid cellulose with well‐defined and chemically reactive dendrons is introduced as a platform for cellulose grafting with functional materials. Surface functionalization with a first generation dendron is achieved by esterification employing bifunctional molecules based on 2,2‐bis(hydroxymethyl) propionic acid (bis‐MPA) under mild conditions and short reaction times. The activated cellulose surface displays hydrophobic properties and contains two reactive alkene end‐groups per graft, which are used for covalent binding to active agents, as demonstrated by selective functionalization of the modified cellulose with fluorescent dye via photopatterning. The number of active end‐groups on the surface of cellulose is multiplied by divergent solid‐state synthesis of second and third generation dendrons having four and eight reactive sites per dendron, respectively. The dendrons are assembled in only few hours by a sequence of thiol‐ene/esterification reactions. The ability to accurately control the number of binding sites on the surface of cellulose allows fine tuning of the surface properties, as shown by the attachment of hydrophobic small molecules to the dendronized cellulose. The first, second and third generation dendrons allow preparing surfaces with increasing hydrophobicities; second and third generation dendrons functionalized with small perfluoroalkyl molecule display superhydrophobic properties. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2103–2114     

两亲嵌段树枝状分子Gx-PBE-b-Gx-PMPA(OH)x2的合成及多重氢键作用

合成了1~3代的嵌段树枝状分子聚苄醚-聚脂肪酯(Gx-PBE-b-Gx-PMPA, x=1,2,3)和两亲嵌段树枝状分子聚苄醚-周边含羟基的聚脂肪酯[Gx-PBE-b-Gx-PMPA(OH)x2, x=1,2,3]. PMPA(OH)x2-树枝片(Dendron)段周边的羟基数目分别是2, 4和8. 通过1H NMR, 13C NMR, FTIR和基质辅助激光解吸附电离飞行时间质谱(MALDI-TOF)(或场解析电离质谱)技术表征了Gx-PBE-b-Gx-PMPA和Gx-PBE-b-Gx-PMPA(OH)x2的结构. 同时, 采用变温FTIR光谱研究了在两亲嵌段树枝状分子中形成的氢键模式. 结果表明, 随着树枝片代数的增加, 两亲嵌段树枝状分子内趋向于形成作用较弱的分子内氢键, 说明形成3代两亲嵌段树枝状分子的三维结构削弱了羟基形成分子间氢键的能力.     

On the Synthesis and Selective Deprotection of Low‐Generation Dendrons with Orthogonally Protected Peripheral Amine Groups and a Possible Impact of the Deprotection Conditions on the Stability of Dendronized Polymers' Skeletons

The synthesis of first‐ and second‐generation dendrons with defined ratios of orthogonally protected amine groups in the periphery ((benzyloxy)carbonyl (Cbz) and (tert‐butoxy)carbonyl (Boc) protection) and the degree to which they can be selectively removed are described. The reaction conditions required for these deprotections were applied to methacrylic acid (= 2‐methylprop‐2‐enoic acid) based dendronized polymers carrying the same peripheral protecting groups to investigate whether they have any detrimental interference with the polymer skeleton. Specifically it was explored whether dendrons attached to the backbone could possibly be cleaved off as a whole (de‐dendronization). Finally it was investigated how de‐dendronizations can be used for quantifying both the dendron‐structure perfection and the polymer‐backbone configurations.     

Iterative synthesis of 1,3,5-polyphenylene dendrons via C-H activation

An iterative synthesis of 1,3,5-polyphenylene dendrons via C-H activation/Suzuki-Miyaura coupling up to a third generation dendron is described. C-H bonds at the focal points of the dendrons are selectively borylated via iridium-catalyzed borylation, eliminating the need for reactive protecting groups. Sequential additions of low catalyst loadings efficiently borylate higher-generation dendrons, whereas higher initial catalyst loadings are less efficient.     

Disassembly via an environmentally friendly and efficient fluorous phase constructed with dendritic architectures

Traditionally the fluorous phase is generated with perfluorinated alkyl groups that are usually perfluorooctyl or longer and are bioaccummulative and biopersistent and therefore, are considered environmentally unfriendly. Here we report a new concept for the construction of the fluorous phase. This concept is based on the amplification of the fluorous effect with the help of dendritic architectures containing very short semifluorinated groups on their periphery. This new concept was demonstrated by the convergent synthesis of the first and second generation AB₃ and AB₂ benzyl ether dendrons functionalized on their periphery via catalytic nucleophilic addition of their phenolates to perfluoropropyl vinyl ether. The resulting dendrons are liquids. Their fluorous phase affinity was analyzed and demonstrated that the dendritic architecture amplifies the fluorous phase at a specific generation by the number of functional groups on the dendron periphery, and at different generations by increasing their generation number. Therefore, this concept is very efficient for the design and synthesis of new fluorous materials. In addition, by contrast with dendrons containing perfluoroalkyl groups on their periphery, the current dendrons mediate the disassembly of their parent building blocks but do not mediate the self‐assembly in a supramolecular architecture. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2498–2508, 2010     

Layered Dendritic Block Copolymers

A star-shaped molecule and a layered structure are displayed by the title compound, where the layers consist of high molecular weight polymers. A core molecule that is functionalized by six hydroxyl groups acts as the initiator for the ring-opening polymerization of ε-caprolactone, leading to a six-arm star polymer. The second layer of the dendritic block copolymer with 12, 24, or 48 hydroxyl groups (depending on the dendron generation in use) is obtained by the linkage of chain ends with functionalized dendrons. These macromoleculse act as “macroinitiators” for the construction of a further layer of poly(ε-caprolatone), the third generation of dendritic block copolymers.     

Solid-phase synthesis of polyfunctional polylysine dendrons using aldehyde linkers

A straightforward method for the solid-phase synthesis of C-terminally modified polylysine dendrons has been developed by applying bisalkoxybenzaldehyde and trisalkoxybenzaldehyde linkers. The method has been used for the synthesis of polylysine dendrons with a variety of C-terminal ‘tail groups’ such as alkyl, propargyl, and dansyl to give dendrons in high crude purity. Furthermore, the method was successful for the synthesis of dendrons with multiple N-terminal pentapeptide groups together with C-terminal alkyl and propargyl tail groups. Finally, the method was shown to be well-suited for automated synthesis.     

Facile Synthesis of Second-Generation Dendrons with an Orthogonal Functional Group at the Focal Point

Facile synthesis of second-generation dendrons with an aldehyde, epoxy, or t-Boc group at the focal point and nine carboxylic acid groups at the periphery is reported. The scheme includes a coupling of the first-generation dendrons and a two-step, one-pot reaction that proceeds through a Boc deprotection and in situ conjugation at the focal point.     

Synthesis of new cores and their use in the preparation of polyester dendrimers

Six dendrimer and dendron cores terminated by hydroxyl groups that are neither phenolic nor cleavable by hydrogenolysis have been prepared in a consistent one-pot manner from terminal allyl groups by reduction of the product of reductive ozonolysis. Some of the terminal allyl derivatives are new and others have been prepared by new methods. The well-known O-benzylidene derivative of 2,2′-bis(hydroxymethyl)propanoic acid was shown to be the cis-stereoisomer. A new AB₃-type anhydride, tris(benzyloxymethyl)acetic anhydride has been prepared. It was demonstrated that these cores and dendrons could be assembled into first and second generation homo- and mixed polyester dendrimers.     

Effect of pH and generation of dendron on single‐step synthesis of gold nanoparticles using PEGylated polyamidoamine dendron in aqueous medium

Three types of PEGylated polyamidoamine (PAMAM) dendrons were synthesized through PEGylation of primary amines at the periphery of second, third, and fourth generation dendrons. Au(III) precursors and the synthesized PEGylated PAMAM dendrons were mixed at various pHs to evaluate the effect of pH on gold nanoparticle (Au NP) synthesis by monitoring the change in surface plasmon resonance. The Au NP synthesis reaction was controlled by pH through the balance between protonated and deprotonated tertiary amines and the reactivity of Au(III) precursors. By using PEGylated PAMAM dendrons with higher generation, the obtained Au NPs had narrow size distribution with small average size because of the limitation of intermolecular space among PEGylated PAMAM dendrons for the growth to Au NP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1391–1398, 2010     

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.     

Convergent synthesis of platinum-acetylide dendrimers

An efficient convergent route to the main chain type of organometallic dendrimers, in which platinum moieties are linked by 1,3,5-triethynylbenzene, has been developed. The synthesis of platinum-acetylide dendrons involved the use of two types of trialkylsilyl groups for protection of the terminal acetylene. The platinum-acetylide dendrimers were prepared up to the third generation by reacting dendrons with a triplatinum core and a tetraplatinum core. Spectroscopic characterization and trace experiments by gel permeation chromatography indicated that the dendrimer molecules have no structural defects. Although a pi-conjugated system was used as the bridging ligand, electronic and fluorescence spectra suggested that the interaction among the platinum-acetylide moieties in the dendrimers was small.     

A convergent approach to biocompatible polyglycerol "click" dendrons for the synthesis of modular core-shell architectures and their transport behavior

Dendrimers are an important class of polymeric materials for a broad range of applications in which monodispersity and multivalency are of interest. Here we report on a highly efficient synthetic route towards bifunctional polyglycerol dendrons on a multigram scale. Commercially available triglycerol (1), which is highly biocompatible, was used as starting material. By applying Williamson ether synthesis followed by an ozonolysis/reduction procedure, glycerol-based dendrons up to the fourth generation were prepared. The obtained products have a reactive core, which was further functionalized to the corresponding monoazido derivatives. By applying copper(I)-catalyzed 1,3-dipolar cycloaddition, so-called "click" coupling, a library of core-shell architectures was prepared. After removal of the 1,2-diol protecting groups, water-soluble core-shell architectures 24-27 of different generations were obtained in high yields. In the structure-transport relationship with Nile red we observe a clear dependence on core size and generation of the polyglycerol dendrons.     

Synthesis of nanoparticle-cored dendrimers by convergent dendritic functionalization of monolayer-protected nanoparticles

This article presents a synthesis method for nanoparticle-cored dendrimers (NCDs), which have dendritic architectures around a monolayer-protected gold nanoparticle. The synthesis method is based on a strategy in which the synthesis of monolayer-protected nanoparticles is followed by adding dendrons on functionalized nanoparticles by a single coupling reaction. NMR spectroscopy, IR spectroscopy, and thermogravimetric analysis (TGA) characterizations confirmed the successful coupling reaction between dendrons with different generations ([G1], [G2], and [G3]) and COOH-functionalized nanoparticles ( approximately Au201L71). The dendrimer wedge density also could be controlled by reacting nanoparticles having different loading of COOH groups ( approximately 60 and approximately 10% COOH of the 71 ligands per gold nanoparticle) with functionalized dendrons. Transmission electron microscope results showed that this synthesis strategy maintains the average size of the nanoparticle core during dendron coupling reactions. This control over the composition and core size makes the systematic study of NCDs with different generations possible. The chemical stability of NCDs was found to be affected by dendron generation around the nanoparticle core. The current-potential response of NCD films on microelectrode arrays exhibited better electrical conductivity for NCDs with lower dendron generation.     

Globular Polymer Grafts Require a Critical Size for Efficient Molecular Sieving of Enzyme Substrates

A series of 2,2‐bis(hydroxymethyl)propionic acid dendrons of generation 2 through 8 having a strained cyclooctyne at the core and hydroxy groups at the periphery were prepared by a divergent method and used to functionalize azide‐decorated α‐chymotrypsin. The ability of the appended dendrons to selectively block enzyme activity (through a molecular sieving effect) was investigated using a small molecule substrate (benzoyl‐l ‐tyrosine p‐nitroanilide), as well as two proteins of different size (casein and bovine serum albumin). Additionally, the ability of dendrons to block complexation with a chymotrypsin antagonist, α‐antichymotrypsin, was investigated, and it was found that the dendron coating effectively prevented inhibition by this antagonist. We found that a critical generation is required to achieve efficient sieving with bis‐MPA dendrons, which illustrates the importance of macromolecular architecture and size in the shielding of proteins.     

Self-assembled structures in organogels of amphiphilic diblock codendrimers

Amphiphilic diblock codendrimers consisting of dendrons of hydroxyl-containing poly(methallyl dichloride) (PMDC) and long alkyl-containing poly(urethane amide) (PUA) were synthesized in different generations. These codendrimers were found to self-assemble into ribbonlike aggregates in organic solvent and further formed three-dimensional networks and behaved macroscopically as gels. The width of the self-assembled ribbons decreases with the generation of both dendritic blocks. Multiple intermolecular hydrogen bonds between amide and hydroxyl groups were found to be the main driving force to form these self-assembled gels.     

Divergent synthesis and self‐assembly of amphiphilic polymeric dendrons with selective degradable linkages

Enhancing the structural complexity and functionality of the building blocks allows the construction of supramolecular assemblies. In this work, we demonstrate a strategy for the design and synthesis of complex macromolecular architectures. We use atom transfer radical polymerization to produce well‐defined polymers with telechelic end‐group functionality, and “click” them together to form functional 3rd generation dendrons, and incorporated degradable linkages and certain functionality at the polymer chain‐ends of each generation. The 3rd generation polymeric dendrons consisted of homopolymer polystyrene (PSTY) with either four solketals or eight alcohols, diblock PSTY and poly(t‐butyl acrylate), and amphiphilic diblock. The peripheral ends consisting of alcohols create functionalization points for further chemical modification or chemical coupling and the cleavable linkages between the 2nd and 3rd generations all provide the first steps toward smart nanostructures. Importantly, we can synthesize these dendrons in pure form. The self‐assembly of the amphiphilic dendrons (the inner and outer generations consisting of PSTY and polyacrylic acid, respectively) in water produced micelles of uniform size with an aggregation number of 43 dendrons per micelle. The size of the micelles was small (D_H =20.7 nm) and comparable to the size found by transmission electron microscopy (14–18 nm). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1533–1547, 2008     

Preparation of novel polythioether dendrons on a solid support

A synthetic scheme for the solid-phase synthesis of unprecedented polythioether dendrons has been established, the dendrons prepared up to the fourth generation, and the applicability of the dendronized resins for supported catalysis has been demonstrated.