Ester‐ and amide‐terminated dendrimers with alternating amide and ether generations

Ester‐terminated polyamide dendrimers up to the third generation and amide‐terminated polyamide dendrimers of the first generation were synthesized by convergent growth. The Williamson ether synthesis and diphenylphosphoryl azide (DPPA) coupling of amines to carboxylic acids were used for the construction of the dendrimers, having alternate ether and amide generations. The methyl ester‐ and N,N‐diethylamide‐terminated dendrimers were readily soluble in common organic solvents while the N‐methylamide‐ and N‐benzylamide‐terminated dendrimers were soluble only in DMF and DMSO. Both the end and internal amide groups of the N,N‐diethylamide‐terminated dendrimer were reduced by LiAlH₄ to form a polyamine dendrimer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1533–1543, 2000     

Photoresponsive nanocarriers based on PAMAM dendrimers with a o‐nitrobenzyl shell

Gn (n = 3, 4, and 5) poly(amidoamine) (PAMAM) dendrimers were synthesized and peripherally modified with photocleavable o‐nitrobenzyl (NB) groups by reacting o‐nitrobenzaldehyde with the terminal amine groups of PAMAM dendrimers, followed by reducing the imine to amine groups with NaBH₄. The NB‐modified dendrimers, Gn‐NB (n = 3, 4, and 5), were characterized by nuclear magnetic resonance and fourier transform infrared spectroscopy. The results showed that the NB groups were successfully attached on the periphery of the dendrimers with near 100% grafting efficiency. Such a photosensitive NB shell could be cut off on irradiation with 365 nm ultraviolet (UV) light. The encapsulation and release of guest molecules, that is, salicylic acid (SA) and adriamycin (ADR), by Gn‐NB were explored. The encapsulation capability of these dendrimers was found to increase as the guest molecular size was decreased and have dependence on the generation of dendrimers as well. For both of SA and ADR, the average encapsulation numbers per dendrimer decreased in the order of G4‐NB > G5‐NB > G3‐NB, indicating that the fourth generation dendrimer was a better container for the guest molecules. The rate of SA release was found to be greater with UV irradiation than that without, suggesting that the NB‐shelled PAMMAM dendrimers could function as a molecular container/box with photoresponsive characteristics. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 551–557, 2010     

Cinnamoyl shell‐modified poly(amidoamine) dendrimers

Poly(amidoamine)(PAMAM) dendrimers with a cinnamoyl shell were prepared by reacting full generation PAMAM dendrimers (G=3.0) with 2‐chloroethanol and cinnamoyl chloride, which resulted in densely packed polymerizable unsaturated groups on the periphery. The cinnamoyl shell of the dendrimers dimerized when irradiated under a UV light by using 5‐nitroacenaphthylene as an initiator in dilute dimethylformamide (DMF). FTIR, ¹H NMR, UV‐Vis, SEC, and a viscosity test certified that the photocycloaddition of the cinnamoyl shell of the dendrimers took place within the molecules with the disappearance of double bond signals in the FTIR. ¹H NMR spectra as well as the intrinsic viscosity and polydispersity value of the products both before and after irradiation showed no difference. It was further found that the cinnamoyl shell‐modified dendrimers possessed fluorescence property, and the fluorescence intensity became stronger when the shell was photocyclized under UV‐ irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4147–4153, 2000     

Self‐assembly of a new class of amphiphilic poly(amidoamine) dendrimers and their electrochemical properties

Amphiphilic poly(amidoamine) (PAMAM) dendrimers consisting of a hydrophilic dendrimer core and hydrophobic aromatic dansyl or 1‐(naphthalenyl)‐2‐phenyldiazene (NPD) shells have been synthesized. These amphiphilic dendrimers from the zero generation to the third generation self‐assemble into vesicular aggregates in water. The self‐assembly behavior of these dendrimers strongly depends on their generations. The generation dependence has been further investigated by an exploration of their electrochemical properties. For the PAMAM–NPD aggregates, the photoisomerization process leads to a change in the aggregate size. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5512–5519, 2005     

Thermal and X‐ray powder diffraction studies of aliphatic polyester dendrimers

The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004     

Facile synthesis of dendrimers combining aza‐Michael addition with Thiol‐yne click chemistry

We report a highly efficient approach to prepare dendrimers by taking advantage of the orthogonal characteristic of aza‐Michael addition and thiol‐yne reactions. A fifth generation dendrimer was synthesized within five steps without protection/activation procedures. The reactions proceed under benign conditions without byproducts, and the target products can be easily purified via extraction or precipitation without chromatography. The structure of each generation dendrimer was characterized using NMR spectroscopy, size exclusion chromatography, and mass spectrometry. The obtained dendrimers can have peripheral amine or alkyne groups. We demonstrated that these groups can be used for selective and specific conjugation with various functional groups. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of carbohydrate‐linked poly(polyoxometalate) poly(amido)amine dendrimers

Mannose‐functionalized and ethoxyethanol‐functionalized poly(amido)amine dendrimers bound multiple vanadate‐substituted polyoxotungstate Wells–Dawson‐type polyoxometalates (POMs). Dendrimers incorporating 10–30 POMs were characterized with NMR, transmission electron microscopy, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry techniques. The number of metal clusters per dendrimer molecule varied according to the dendrimer generation and the nature of the surface functional groups. Efforts aimed at using the poly(polyoxometalate) dendrimers as oxidation catalysts are also described. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3059–3066, 2005     

Synthesis of dendrimers through divergent iterative thio‐bromo “Click” chemistry

The development of a novel nucleophilic thio‐bromo “Click” reaction, specifically base‐mediated thioetherification of thioglycerol with α‐bromoesters, is reported. Combination of this thio‐bromo click reaction with subsequent acylation with 2‐bromopropionyl bromide provides an iterative two‐step divergent growth approach to the synthesis of a new class of poly(thioglycerol‐2‐propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high‐structural fidelity. The isolated G1–G4 bromide‐terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star‐polymers via SET‐LRP. Additionally, the intermediate hydroxy‐terminated dendrimers are analogs of other water‐soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009     

End‐capped carbosilane dendrimers with benzoxazole,quinoline, and pyrone derivatives

Dendritic carbosilanes containing benzoxazole, quinoline, and pyrone derivatives on the periphery were prepared. The parent dendrimers in the inner shell were prepared by the use of iterative hydrosilation and alkenylation cycles. The end generations were obtained by the reaction of terminal Si? Cl groups on each periphery with HOR [HOR = 2‐(2‐hydroxyphenyl)‐benzoxazole, 8‐hydroxyquinoline, and 3‐hydroxy‐2‐methyl‐4‐pyrone] in the presence of amine. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2308–2314, 2001     

Synthesis of double‐layered dendritic carbosilanes used on allyloxy and phenylethynyl groups

Double‐layered dendritic carbosilanes were prepared containing phenylethynyl groups on the peripheral layer as well as propyleneoxy and ethenyl groups in the inner shell. The preparation of the allyloxy group containing dendrimers was made by the reaction of chlorosilylated dendrimers with allylalcohol in the presence of TMED. The dendrimers with ethynyl groups on each terminal arm were obtained by the reaction of the chlorosilyl group containing generations with lithium phenylethynyl. Subsequently, by iterative reactions such as hydrosilation and alkynylation as well as alcoholysis, dendritic macromolecules were generated to the fourth generation with 64 phenylethynyl groups on the peripheral layer. Different branching layers such as propyleneoxy and phenylethenyl groups constructed the inner shell of the fourth generation of the prepared dendrimers. The dendrimers were characterized by the use of nuclear magnetic resonance, infrared, size exclusion chromatography, differential scanning calorimetry, ultraviolet, and elemental analysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 764–774, 2000     

Thiophene‐cored 2,2‐bis(methylol)propionic acid dendrimers for optical‐power‐limiting applications

The synthesis and characterization of dendron‐coated 2,5‐bis(phenylethynyl)thiophene chromophores are described. The dendrimers were grown divergently on the arylthiophene core with the versatile anhydride of 2,2‐bis(methylol)propionic acid. The arylthiophene core was synthesized with Sonogashira coupling reactions. Structurally well‐defined dendrimers up to the fourth generation were grown, as confirmed by size exclusion chromatography, NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight analysis. The different dendritic substitution did not influence the absorption spectra of the compounds in or near the visible region. Solutions of arylthiophenes had good transparency at wavelengths greater than 400 nm. The dendritic thiophenes exhibited an optical‐power limit at the laser wavelength of 532 nm. However, the magnitude of the optical‐power limit of these compounds was slightly lower than that of a nondendritic arylthiophene with n‐pentyl substituents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1177–1187, 2005     

Light harvesting and energy transfer within coumarin‐labeled polymers

Linear copolymers that have pendant coumarin‐2 and coumarin‐343 chromophores were prepared as analogues to previously synthesized light‐harvesting dendrimers. The chromophore ratios within these polymers were maintained similar to those of the various generation dendrimers to investigate the effect of polymer architecture on the energy‐transfer efficiency between the coumarin‐2 donors and coumarin‐343 acceptors. Both physical and photophysical properties of these polymers were analyzed and compared to those of the analogous dendrimers. Energy‐transfer efficiencies were relatively high in the polymers; however, deleterious excimer formation between the coumarin‐343 chromophores diminished the quantum yield of fluorescence of the polymers when compared to the analogous dendrimers. Overall, it was found that the ultimate performance of the dendritic light‐harvesting antennae was superior to that of the polymeric analogues, but the polymers were more practical in terms of synthetic accessibility. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1366–1373, 2001     

Theoretical and experimental characterization of amino‐PEG‐phosphonate‐terminated Polyphosphorhydrazone dendrimers: Influence of size and PEG capping on cytotoxicity profiles

The synthesis of new series of PPH (poly(phosphorhydrazone)) dendrimers with amino‐PEG phosphonates or the corresponding amino‐PEG phosphonic acids as terminal groups is presented, from generations 1–3. The size of PEG‐terminated dendrimers is experimentally measured by diffusional NMR, and by means of dynamic light scattering. Classical molecular dynamics and well‐tempered metadynamics simulations are used to assess or confirm the formation of aggregates in some cases. The influence of PEG capping on the cytotoxicity profiles of the dendrimers is evaluated on human peripheral blood mononuclear cells by means of LIVE/DEAD assays, and confirms the importance of PEG capping to ensure low cytotoxicity. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 761–774     

Synthesis and thiol–ene photopolymerization of allyl‐ether functionalized dendrimers

Well‐defined, allyl‐ether functional, first‐generation dendrimers have been synthesized. The convergent growth approach was utilized, using the anhydride of the allyl‐ether terminated building block. Three different core moieties were used: trimethylolpropane, trisphenol, and ditrimethylolpropane. The coupling reactions proceeded in good yields and all compounds were characterized by NMR, MALDI‐TOF, and SEC. The allyl‐terminated dendrimers were crosslinked by thiol–ene chemistry, using a multifunctional thiol, TriThiol, to give clear and smooth films. The photopolymerization was conducted in the presence of a photoinitiator, Irgacure 651, and no traces of either allyl‐ether groups or thiols were observed by FT‐Raman after cure. All crosslinked films were characterized with respect to mechanical (DMA) and thermal (DSC) properties. It was found that homogeneous networks were formed and that the core functionality and structure had little effect on the network properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1339–1348, 2008     

A versatile preparation of azobenzene‐dye functionalized colored polymer nanoparticles by surface modification

A series of stable and translucent colored nanolatex, that is, colloidal aqueous suspensions of dye‐tagged polymer nanoparticles (NPs) in the 15‐ to 20‐nm diameter range, have been prepared by covalent attachment of azobenzene chromophores to the surface of reactive NPs. Primary crosslinked NPs bearing chlorobenzyl groups were produced by microemulsion copolymerization of styrene and vinylbenzylchloride. Amine‐functionalized NPs were obtained after a second functionalization step with polyamines (cyclam and polypropyleneimine dendrimers of first and third generations). Dye‐doped particles were obtained by reacting pyridylazo‐dimethylaminobenzene (PADA) with chlorobenzyl‐NPs and by reacting amine‐reactive dimethylaminoazobenzene dyes (DABsyl, DAB‐ITC) as well as Disperse Red 1 acrylate with polyamine‐coated NPs. Regardless the dye solubility, the grafting readily proceeded in aqueous suspensions at room temperature in the presence of a cationic surfactant without added solvent. Purple, red, and orange suspensions (maximum absorption around 550, 500, 430 nm), with dye loads ranging from 0.3 to 1.2 mmol/g, corresponding to 400–1800 azobenzene residues per NP, are obtained. The reported results indicate that functional polymer NPs, with remarkably accessible multiple anchoring sites, are useful building blocks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3375–3386, 2008     

Synthesis of anionic carbosilane dendrimers via “click chemistry” and their antiviral properties against HIV

The synthesis and characterization of four families of anionic carbosilane dendrimers bearing carboxylate, phosphonate, naphthylsulfonate, and sulfate terminal groups prepared by cycloaddition of azide–alkyne catalyzed by copper (CuAAC) are presented here. For the preparation of these anionic carbosilane dendrimers, two strategies starting from azide‐terminated carbosilane dendrimers were followed: (i) click coupling of neutral alkynes followed by derivatization into anionic moieties or (ii) click coupling of anionic alkynes. Both strategies require different reaction conditions in order to accommodate the different substrate polarities. These anionic dendrimers, in general, do not present cell toxicity in vitro until concentration up to 20 µM. Therefore, they can be used in inhibition experiments in concentrations below this limit. We have observed that dendrimers bearing phosphonate groups possess poor anti‐HIV capabilities in vitro in PBMCs, while carboxylate dendrimers can reduce HIV infection levels moderately. On the other hand, sulfate and naphthylsulfonate dendrimers are powerful anti‐HIV agents and their antiviral activity is generation and concentration dependent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1099–1112     

Deep‐red light‐emitting phosphorescent dendrimer encapsulated tris‐[2‐benzo[b]thiophen‐2‐yl‐pyridyl] iridium (III) core for light‐emitting device applications

New deep‐red light‐emitting phosphorescent dendrimers with hole‐transporting carbazole dendrons were synthesized by reacting tris(2‐benzo[b]thiophen‐2‐yl‐pyridyl) iridium (III) complex with carbazolyl dendrons by DCC‐catalyzed esterification. The resulting first‐, second‐, and third‐generation dendrimers were found to be highly efficient as solution‐processable emitting materials and for use in host‐free electrophosphorescent light‐emitting diodes. We fabricated a host‐free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/Alq₃ (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m² at 383.4 mA/cm² (12 V) for 15 , 1302 cd/m² at 321.3 mA/cm² (14 V) for 16 , and 422 cd/m² at 94.4 mA/cm² (18 V) for 17 . The third‐generation dendrimer, 17 (η_ext = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light‐harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep‐red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable materials for dendrimer light‐emitting diode (DLED) applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7517–7533, 2008     

Polyamido amine dendrimers functionalized with poly(phenylenevinylene) dendrons at their periphery

A series of polyamido amine (PAMAM) dendrimers (Generations 2, 3, 4, and 6) fully functionalized at their periphery with first‐ and second‐generation poly (phenylenevinylene) (PPV) dendrons have been efficiently prepared. MALDI‐TOF mass spectrometry proved to be particularly useful for the characterization of the new hybrid dendrimers as well as for the estimation of the average number of PPV dendrons attached to the surface. The optical absorption and emission properties of these systems were studied. The materials display extremely high molar extinction coefficients and emit blue light with only slightly lower fluorescence quantum yields than the corresponding free dendrons. Self‐quenching interactions between PPV units were not observed in THF. However, the luminescence properties underwent a dramatic change when toluene was used as the solvent. The lower polarity of toluene caused shrinkage of the PAMAM structure and brought the PPV chromophores closer together, leading to self‐quenching interactions and excimer formation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6409–6419, 2009     

A mechanistic investigation of a three‐component radical photoinitiator system comprising methylene blue,N‐methyldiethanolamine,and diphenyliodonium chloride

Three‐component systems, which contain a light‐absorbing species (typically a dye), an electron donor (typically an amine), and a third component (usually an iodonium salt), have emerged as efficient, visible‐light‐sensitive photoinitiators. Although three‐component systems have been consistently found to be faster and more efficient than their two‐component counterparts, these systems are not well understood and a number of distinct mechanisms have been reported in the literature. In this contribution, photodifferential scanning calorimetry and in situ, time‐resolved, laser‐induced, steady‐state fluorescence spectroscopy were used to study the initiation mechanism of the three‐component system methylene blue, N‐methyldiethanolamine and diphenyliodonium chloride. Kinetic studies based upon photodifferential scanning calorimetry reveal a significant increase in polymerization rate with increasing concentration of either the amine or the iodonium salt. However, the laser‐induced fluorescence experiments show that while increasing the amine concentration dramatically increases the rate of dye fluorescence decay, increasing the DPI concentration actually slows consumption of the dye. We concluded that the primary photochemical reaction involves electron transfer from the amine to the dye. We suggest that the iodonium salt reacts with the resulting dye‐based radical (which is active only for termination) to regenerate the original dye and simultaneously produce a phenyl radical (active in initiation) derived from the diphenyliodonium salt. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2057–2066, 2000     

Synthesis of an oligo(ethylene glycol)‐based third‐generation thermoresponsive dendronized polymer

An improved strategy to synthesize oligo(ethylene glycol)‐based secondary generation (G2) dendron is presented. The overall synthesis efficiency increased by 50% when comparing to the previous method, and the product purification by column chromatography becomes much easier. Based on this approach, the synthesis of the third‐generation (G3) dendrons and the corresponding methacrylate‐based G3 macromonomer becomes feasible. Because of the oil characteristics of this macromonomer, its polymerization was able to be conducted in bulk with AIBN as the initiator. The polymerization degree of the third‐generation dendronized polymer ( PG3 ) was found to be around 16 based on GPC measurement. The thermally induced dehydration processes of this polymer were monitored by temperature‐varied proton NMR spectroscopy, and its thermoresponsive behaviors were investigated with turbidity measurements using UV–vis spectroscopy. Similar to the lower generation counterparts, this threefold branched dendronized polymer also shows characteristic fast and sharp phase transitions around its apparent lower critical solution temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6630–6640, 2009