Trees with the minimum Wiener number

The Wiener number (𝒲) of a connected graph is the sum of distances for all pairs of vertices. As a graphical invariant, it has been found extensive application in chemistry. Considering the family of trees with n vertices and a fixed maximum vertex degree, we derive some methods that can strictly reduce 𝒲 by shifting leaves. And then, by a process, we prove that the dendrimer on n vertices is the unique graph reaching the minimum Wiener number. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 331–340, 2000     

Carbosilane dendrimers based on siloxane polymer

A method for synthesizing growth ring‐type dendritic macromolecules starting from siloxane polymer with Si H bonds [Me₃SiO(MeSiOH)_nSiMe₃] as the core and dichlorovinylsilane, dichloromethylsilane, lithium phenylacethylide, and allylmagnesium bromide as the building blocks is described. The siloxane polymer was produced to the second dendritic generation by the repetition of hydrosilation and alkenylation as well as by an alkynylation process. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 724–729, 2000     

有机硅树枝状化合物-硅胶键合固定相的制备及其在色谱中的应用

采用发散式合成法合成了末端为烯丙基的第一代（G1）与第二代（G2）硅碳烷树枝状大分子,通过硅氢加成反应使其进一步与球形硅胶反应,将硅碳烷树枝状大分子的两代分子分别键合于硅胶上,制备了有机硅树枝状大分子．硅胶键合固定相,对其进行了物理化学性能的表征及色谱性能的初步评价．G2-硅胶键合固定相的分离性能优于G1-硅胶键合固定相,对醇类,烷基取代苯类,N-取代苯类,甲基丙烯酸酯类,邻苯二甲酸酯类等具有良好的分离效果．     

Controlling surfaces and interfaces with functional polymers: Preparation and functionalization of dendritic–linear block copolymers via metal catalyzed “living” free radical polymerization

The preparation and chemical modification of dendritic–linear block copolymers with surface functionalized dendritic components are presented. Isophthalate ester-functionalized dendrons featuring benzylic halide groups at their focal points have been used for the metal catalyzed “living” radical polymerization of styrene. The molecular weight of the dendritic–linear block copolymers determined by MALDI-TOF and Size Exclusion Chromatography was found to be accurately controlled up to molecular weights of ca. 30,000 a.m.u., with polydispersities less than 1.2. Subsequent functional group modifications of the peripheral ethyl ester groups of the dendritic block have been successfully carried out leading to carboxylic acids, butyl amides, benzyl alcohols, benzyl halides, and also accelerated generation growth via transesterification with a first generation dendritic alcohol. Several of these new dendritic–linear block copolymers exhibit interesting aggregation characteristics as evidenced by ¹H-NMR spectroscopic studies. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1–10, 1998     

A SAXS study of the internal structure of dendritic polymer systems

Small-angle x-ray scattering was used to characterize the single-particle scattering factors produced by poly(amidoamine) dendrimers, poly(propleneimine) dendrimers, and polyol hyperbranched polymers in dilute solutions with methanol as solvent. Fits from electron density modeling reveal similar overall densities of the dendrimers as a function of dendrimer generation. The seventh through tenth generation poly(amidoamine) dendrimers exhibit higher order scattering features that require nearly monodisperse, spherical particles with essentially uniform internal segment densities. Dilute hyperbranched polymer solutions exhibit scattering more indicative of the inherent irregularity of internal segment densities and overall sizes to be expected within these systems. Radii of gyration estimated from electron density modeling agree reasonably well with those estimated by standard Guinier methods used in previous studies. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2913–2924, 1997     

Molecular relaxations in ester‐terminated,amide‐based dendrimers

This study utilized Matrix Assisted Laser Desorption/Ionization Time‐of‐Flight Mass Spectrometry, Thermogravimetric Analysis, Differential Scanning Calorimetry, X‐Ray Diffraction, and Dielectric Analysis to assess the viscoelastic and structural properties of three generations of tert‐butyl and methyl ester, amide‐based dendrimers. The effect of generation number and functionality on glass‐transition temperatures and corresponding apparent activation energies, obtained via adherence to WLF behavior, were determined. Both were found to increase with increasing generation number and bulkiness of terminal functionalities. WLF constants, C₁ and C₂, allowed the determination of free volume, and thermal expansion coefficients, respectively. Secondary transitions, conforming to Arrhenius behavior, were also characterized and increased in temperature with generation number. The apparent activation energy was greater when the matrix was crystalline. Dielectric relaxation responses were analyzed to yield dielectric strengths of the molecular relaxations which increased with generation number and were comparable for both tert‐butyl and methyl esters in the glass‐transition region. Electrical properties of the dendrimers were dominated by ionic conductivity in the high temperature region. In order to unmask the glass transition, the data were treated in terms of the electric modulus. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2025–2038, 1999     

Synthesis of dendritic–linear block copolymers by living ring-opening polymerization of lactones and lactides using dendritic initiators

Polyether dendrons have been successfully used as macroinitiators for the living ring-opening polymerization (ROP) of lactones and lactides. A hydroxyl group located at the focal point of dendrimers of different generations was transformed into diethyl aluminum alkoxides by reaction with triethyl aluminum. The dendritic aluminum alkoxides proved to be efficient macroinitiators for the living ROP of ε-caprolactone (εCL), 1,4,8-trioxa(4,6)spiro[9]undecanone (TOSUO), D ,L - and L ,L -lactide. Formation of these block copolymers of unusual macromolecular architecture was supported by size exclusion chromatography and spectroscopy. The versatility of this synthetic approach allowed ω-functional dendrimer block-polyesters, such as macromonomer, and macromolecules with novel architectures, to be prepared. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1923–1930, 1999     

Fluorescence Investigations of Oxygen‐Doped Simple Amine Compared with Fluorescent PAMAM Dendrimer

Blue emission of oxygen‐doped tertiary amine (triethylamine), a key unit of fluorescent poly(amido amine) dendrimer, was demonstrated. It was found that the fluorescence intensity could be further enhanced if the tertiary amines locate densely in the dendrimer interior as the branching sites. Moreover, a solvatochromic phenol blue, instead of oxygen, is able to induce the blue fluorescence of the tertiary amino‐branching sites based on a guaranteed host‐guest complexation of phenol blue molecules and dendrimer interior.

     

A Fast and Convenient Synthesis of New Water-Soluble,Polyanionic Dendrimers

Reasonably simple, efficient, and possessing aspects of generality, the methodology for the synthesis of new, water-soluble, dendrimeric polyesters with great potential applications as antiviral drugs in their own right is described. The essential aspect of the presented approach is a quite unique, immediate access to the polyanionic material at each generation during divergent synthesis. Six target polyanionic dendrimers (generations 1, 2, and 3) have been synthesized. The key monomers applied in this project were 1,3,5-benzenetricarboxylic acid derivatives, which also worked as direct precursors of the charged dendrimer surface.     

Effect of solvent-controlled aggregation on the intrinsic emission properties of PAMAM dendrimers

Solvent-induced aggregation and its effect on the intrinsic emission properties of amine, hydroxy and carboxylate terminated, poly(amidoamine) (PAMAM) dendrimers have been investigated in glycerol, ethylene glycol, methanol, ethylene diamine and water. Altering the solvent medium induces remarkable changes in the intrinsic emission properties of the PAMAM dendrimers at identical concentration. Upon excitation at 370 nm, amine terminated PAMAM dendrimer exhibits an intense emission at 470 nm in glycerol, ethylene glycol as well as glycerol-water mixtures. Conversely, weak luminescence is observed for hydroxy and carboxylate terminated PAMAM dendrimers in the same solvent systems. When the solvent is changed to ethylene diamine, hydroxy terminated PAMAM exhibits intense blue emission at 425 nm. While the emission intensity is varied when the solvent milieu is changed, excited state lifetime values of PAMAM dendrimers remain independent of the solvent used. UV-visible absorption and dynamic light scattering (DLS) experiments confirm the formation of solvent-controlled dendrimer aggregates in the systems. Comparison of the fluorescence and DLS data reveals that the size distribution of the dendrimer aggregates in each solvent system is distinct, which control the intrinsic emission intensity from PAMAM dendrimers. The experimental results suggest that intrinsic emission intensity from PAMAM dendrimers can be regulated by proper selection of solvents at neutral conditions and room temperature.