Reduced number of steps for the synthesis of dense and highly functionalized dendrimers

A series of densely functionalized dendrimers is synthesized using two branched monomers of type AB₂ and CD₂, in which the A function (NH₂) reacts with D (CHO) and the B function (Cl) reacts with C (OH). The reaction has been carried out up to the fourth generation possessing 96 end groups and has been obtained in only four steps.     

Accelerated methods of synthesis of phosphorus-containing dendrimers

In order to shorten the long and tedious synthesis of dendrimers, several improvements have been proposed. This paper is a review of the improved methods recently published concerning the synthesis of phosphorus-containing dendrimers. It describes first the synthesis of hyperbranched polymers and their comparison with real dendrimers obtained from the same monomer. Then, the influence of the modification of the core of dendrimers is shown. In a third part, the use of dendrons is illustrated by several examples; they allow for instance to built a generation 8 directly from a generation 3 dendrimer. The last part describes the use of branched monomers of types AB₂ and CD₂, in which A reacts only with D and B reacts only with C. These reactions do not need any protecting groups, and the only by-products are H₂O and N₂. Using these monomers, the 4th generation is obtained in only four steps, instead of 8 for classical methods. This method has been improved by using more branched monomers AB₅ and CD₅, built from the cyclotriphosphazene. In this case, a dendrimer having 750 end groups is obtained in only three steps. The A (NH₂), B (PPh₂), C (N₃) and D (CHO) functions are identical in all cases, and they allow a real “Lego” chemistry, as shown by the synthesis of CA₂ and DB₂ monomers, also used for the accelerated synthesis of dendrimers.     

Growth of first generation dendrons on SiO2: controlling chemisorption of transition metal coordination complexes

We have investigated the growth of first generation branched polyamidoamine dendrons on silicon dioxide as a way to tailor and control the subsequent chemisorption of transition metal coordination complexes. Beginning with straight-chain alkyl, amine-terminated self-assembled monolayers as anchors, we find that the efficiency of the dendritic branching step depends on the length of the anchor, it being nearly perfect on a 12-carbon chain anchor. The reaction of these layers, both the anchor layers and the first generation dendrons, with Ta[N(CH3)2]5 and Ti[N(CH3)2]4 have been examined in ultrahigh vacuum using X-ray photoelectron spectroscopy. We find that the saturation coverage increases with the density of terminal -NH2 groups; thus, the branching step has effectively amplified the chemisorptive capacity of the surface. Concerning the spatial extent of reaction we find that it depends on the thickness and structure of the organic layer. The thinnest layer cannot prevent penetration of the metal complex to the organic/SiO2 interface, where it can react with residual -OH, whereas, on the longer straight chain anchor, reaction occurs exclusively at the terminal -NH2 group. On the branched dendrons, the situation is more complex, and reaction occurs not only with the terminal -NH2 group but also likely with functional groups, such as -NH-(C=O)-, on the backbone of the branched dendron.     

One‐Step Synthesis of Dendritic Highly Branched Polystyrenes by Organotellurium‐Mediated Copolymerization of Styrene and a Dienyl Telluride Monomer

Dendritic highly branched polystyrenes (HB‐PSts) were prepared by a one‐step copolymerization of dienyl telluride 6 and St in the presence of organotellurium chain transfer agent 2 . The molecular weight (MW), dendritic generation, and branching density were easily controlled by the ratio of 2 to 6 to styrene (St) with maintaining monodispersity. The branching efficiency estimated by a deuterium‐labeling experiment showed that 6 quantitatively (>95 %) served as the branching point. The end group fidelity was high (ca. 90 %) as determined by the end group transformation to pyrene‐derivative. Intrinsic viscosity of the HP‐polystyrenes was significantly lower than that of linear polystyrenes and were easily tuned by the branching number and branching density. The method is compatible of various functional groups and chloro and acetoxy‐substituted styrenes were also used as a comonomer. A tadpole block copolymer was also synthesized starting from linear PSt as a macroinitiator.     

The superstructure of carbosilane dendrimers with perfluorinated end groups in bulk and in solution

Carbosilane dendrimers of generation 1 to 4 are functionalized with perfluorinated (-C₆F₁₃) end groups. Extending the spacer between the central Si and the first layer of branching points allows the synthesis of the 4^th generation. The superstructure of these systems in bulk observed with X-ray scattering is the result of the microphase separation between the carbosilane scaffold and the end groups. It varies with generation from a layered to a columnar structure. In dilute solution only the second generation dendrimer shows a tendency for aggregation. The others form compact particles consisting of single molecules with a core shell structure.     

基于环糊精的高度支化聚合物*

环糊精（CD）与高度支化聚合物都存在空腔结构,若将两者结合起来可构筑出含有两种不同疏水空腔且具有特异物理化学功能的高分子体系,并有望在分子包合与识别、药物控释、基因传输等领域得到新的应用。本文根据高度支化聚合物与环糊精结合方式的不同,从以环糊精为核的高度支化聚合物、外端悬挂环糊精的高度支化聚合物、高度支化聚合物的结构单元与环糊精包合、环糊精与客体分子包合后自组装成高度支化聚合物,以及用功能化的环糊精单体合成超支化聚合物等5个方面对其研究进展进行了总结和评述,并在此基础上展望了该类聚合物的研究方向和发展趋势。     

Facile synthesis of polyester dendrimer via combining thio‐bromo “Click” chemistry and ATNRC

This article reports on developing an efficient synthesis approach to aliphatic polyester dendrimer, poly(thioglycerol‐2‐propionate) (PTP), by combination of thio‐bromo “Click” chemistry with atom transfer nitroxide radical coupling (ATNRC). Through the one‐pot two‐step method, linear polystyrene with hydroxyl end groups (l‐PS‐2OH) was obtained by first atom transfer radical polymerization of styrene and following termination using 4‐(2,3‐dihydroxypropoxy)‐TEMPO (DHP‐TEMPO) to capture the PS macroradicals via ATNRC method. Using l‐PS‐2OH as support, the dendritic repeating units divergently were grown from the hydroxyl end groups via esterification and thio‐bromo “Click” reaction two‐step process. In every generation, the resulting intermediates l‐PS‐d‐PTP (G1‐G4) can be easily isolated from the excessive unreacted monomers by simple precipitation in ethanol without help of time, labor and solvent consuming column chromatographic purification. At last, cleavage of the alkoxyamine group between the PS support and dendrimer at elevated temperature (125 °C) provided the targeted polyester dendrimer PTP up to the fourth generation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1762–1768     

α-二亚胺镍/Cp*TiCl3复式催化剂制备双峰长支链聚乙烯

合成了一种后过渡金属镍化合物 [二 N ,N′ (α 萘基 ) 2 ,3 丁二亚胺镍二溴化物 ][C1 0 H7—NC(CH3)C(CH3)N—C1 0 H7]NiBr2 ,此化合物在MAO活化下催化乙烯聚合能得到含有末端双键的低分子量聚乙烯 ,即长链α 烯烃 .此化合物和一种单茂钛化合物五甲基环戊二烯基三氯化钛 (Cp TiCl3)所组成的复式催化剂 ,用MAO活化后两种主催化剂具有良好协同作用 ,能使单一乙烯聚合制备出双峰型长支链的聚乙烯 .1 3C NMR表明由此复式催化剂制得的聚乙烯不但含有甲基、乙基、丙基、丁基、戊基支链而且还含有相当多的长支链 (支链长度大于或等于 6 ) .催化剂的摩尔比 (Ni Ti)、Al(MAO) (Ni+Ti)摩尔比和聚合温度等聚合条件对催化活性及聚合物的结构与性能有明显影响 .GPC测试表明所得到的支化聚乙烯分子量呈双峰分布 .     

Ferrocenyl‐functionalized long chain branched polydienes

A convenient two‐step approach for the synthesis of ferrocenyl‐functionalized long chain branched polydienes, based on both butadiene and isoprene, respectively, is presented. Classical living anionic polymerization was used to synthesize different AB_n type poly(diene) macromonomers with moderate molecular weights between 1700 and 3200 g/mol and narrow polydispersity. Quantitative end‐capping with chlorodimethylsilane resulted in the desired AB_n macromonomer structures. In the ensuing Pt‐catalyzed hydrosilylation polyaddition, branched, functionalized polydienes were obtained by a concurrent AB_n + AR type of copolymerization with mono‐ and difunctional ferrocenyl silanes (fcSiMe₂H or fc₂SiMeH). Molecular weights of the branched polymers were in the range of 10,000 to 44,000 g/mol (SEC/MALLS). Because of the large number of functional end groups, high loading with ferrocene units up to 63 wt % of ferrocene was achieved. Detailed studies showed full conversion of the functional silanes and incorporation into the branched polymer. Further studies using DSC, TGA, and cyclovoltammetry (CV) measurements have been performed. Electrochemical studies demonstrated different electrochemical properties for fcSiMe₂‐ and fc₂SiMe‐units. The CVs of polymers modified with diferrocenylsilane units exhibit the pattern of communicating ferrocenyl sites with two distinct, separate oxidation waves. The polymers were also deposited on an electrode surface and the electrodes investigated via CV, showing formation of electroactive films with promising results for the use of the materials in biosensors. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2518–2529, 2009     

Divergent growth of coordination dendrimers on surfaces

Divergent growth of surface-initiated dendritic nanostructures on gold surfaces in a highly controlled, stepwise manner is demonstrated, using metal-organic coordination as the binding motif. The repeat unit for dendrimer growth was a branched, C3-symmetrical ligand building block bearing three bis-hydroxamate groups. The surface initiation sites for dendrimer growth were obtained by the formation of a mixed monolayer comprising isolated bis-hydroxamate disulfide anchor ligands and octanethiol (OT) at very low anchor/OT ratios. Following functionalization of the surface with spaced anchors, alternate immersion in solutions of Zr4+ ions and the branched ligand afforded surface-confined dendrimers of increasing generation, where the number of generations is conveniently controlled by the number of coordination binding sequences. The heights of different generation dendrimers are in excellent agreement with values predicted by molecular models, as well as with thicknesses of branched multilayers prepared by the same procedure on full anchor monolayers. At higher generation numbers, gradual dendrimer overlap and coalescence are observed, eventually resulting in a continuous overlayer and a transition from 3D to 1D growth. A mechanism for the development of dendritic coordination nanostructures on surfaces is discussed.     

Chain end analysis of bisphenol A polysulfone and its relation to molecular weight

The preparation of amine-terminated polysulfone by step polymerization of the monomers bisphenol A and dichlorodiphenyl sulfone in the presence of end-capping reagent 4-aminophenol was investigated. A persistent problem with end-capping strategy as applied to step polymerization is the presence of end groups other than those introduced by the end-capping reagent. These unintended end groups, which can persist in the polymer product even when 100% of the end-capping reagent has reacted, are associated with a proportionate decrease in polymer chain length. This situation renders quantitative analysis of a single type of end group invalid as a method for molecular weight determination. The presence of unintended end groups does not appear to correlate with a particular set of reaction conditions; unintended end groups were found to occur in polymerizations conducted under strong base conditions (NaOH), under weak base conditions (K₂CO₃), and with a wide range of monomer feed ratios. A scheme for unambiguous quantification of chain ends and molecular weight for end-capped polysulfone is described. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1309–1316, 1998     

α-二亚胺镍复式催化剂/MAO制备高支化的长支链聚乙烯

研究了由两种α-二亚胺镍催化剂[Cat1:α-萘基-丁二亚胺二溴化镍,Cat2:2,6-二异丙基苯基苊二亚胺二溴化镍]组成的复式镍催化剂在MAO活化下催化单一乙烯聚合.可制备得到支化度高达上百个支链(每1000个碳),长支链的比例占到30%左右的聚乙烯.13C-NMR、GPC、DSC、WAXD、DMA结果表明此复式催化剂催化乙烯聚合可得到分子量较高、分子量分布较窄的长支链聚乙烯弹性体.在合适的条件下,此复式催化体系还具有促进提高催化活性的良好协同作用,其聚合活性比两种单一催化剂都高(4·6×105g PE/mol Ni·h).     

Density Functional Theory Study of the Mechanisms of Iron‐Catalyzed Regioselective Anti‐Markovnikov Addition of C‐H Bonds in Aromatic Ketones to Alkenes

The mechanisms of iron‐catalyzed regioselective anti‐Markovnikov addition of C‐H bonds in the aromatic ketones to alkenes are studied using Density Functional Theory (DFT) calculations with the B3LYP‐D3 method. Our results show that the overall catalytic cycle includes the initial generation of aromatic ketone C‐H activation, the coordination and insertion of a styrene, and finally C‐C reductive elimination. Two different alkylation products are obtained through the linear or branched formation via several different paths. The formation of the linear product is energetically favorable over that of the branched product, which is in agreement with the experimental observation. The rate‐limiting step for the whole catalytic cycle to obtain the main linear product is the reductive elimination step where the Gibbs free energy in solvent THF ΔG_sol is 13.5 kcal/mol computed using the SMD method.     

Functionalization of poly(ethylene terephthalate) in the melt state: Chemical and rheological aspects

This article deals with a new way of improving the melt viscosity of linear poly(ethylene terephthalate) (PET) chains through the reaction of the PET end groups (alcohol and acid) with new chain extenders, 3‐(triethoxysilyl)propylsuccinic anhydride (ASSI) and 3‐glycidoxypropyltrimethoxysilane, during the melt processing of PET. The reactions, investigated with model compounds monomethylterephthalate and triethylene glycol monomethylether for PET? COOH and ? OH end groups, respectively, by multinuclear NMR spectroscopy (¹H, ¹³C, and ²⁹Si), provided evidence of well‐known acid–epoxide and alcohol–anhydride reactions, respectively. In addition, numerous other species appeared because of the presence of alkoxysilane groups, such as alcohol–alkoxysilane exchange reactions, acyloxysilane formation, and hydrolysis–condensation reactions of alkoxysilane. All these reactions led to the formation of branched chains when transposed to PET melt modification. A size exclusion chromatography analysis and the rheological behavior confirmed the presence of branched structures embedded in shorter linear PET chains. The rheological behavior of this blend was drastically modified in comparison with that of neat PET; consequently, there was an important increase in the zero‐shear viscosity, with a maximum concentration of branched structures of about 17 vol % obtained with an ASSI/PET molar ratio of 4. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2207–2223, 2005     

Polyphosphazene Based Star‐Branched and Dendritic Molecular Brushes

A new synthetic procedure is described for the preparation of poly(organo)phosphazenes with star‐branched and star dendritic molecular brush type structures, thus describing the first time it has been possible to prepare controlled, highly branched architectures for this type of polymer. Furthermore, as a result of the extremely high‐arm density generated by the phosphazene repeat unit, the second‐generation structures represent quite unique architectures for any type of polymer. Using two relativity straight forward iterative syntheses it is possible to prepare globular highly branched polymers with up to 30 000 functional end groups, while keeping relatively narrow polydispersities (1.2–1.6). Phosphine mediated polymerization of chlorophosphoranimine is first used to prepare three‐arm star polymers. Subsequent substitution with diphenylphosphine moieties gives poly(organo)phosphazenes to function as multifunctional macroinitiators for the growth of a second generation of polyphosphazene arms. Macrosubstitution with Jeffamine oligomers gives a series of large, water soluble branched macromolecules with high‐arm density and hydrodynamic diameters between 10 and 70 nm.

     

Context-dependent photodimerization in isolated thymine-thymine steps in DNA

The effect of 280 nm irradiation on a family of synthetic DNA hairpins possessing an alkane linker connecting a six-base pair stem having a single T-T step located at different positions within the hairpin has been investigated. A single adduct assigned to the product of 2+2 dimerization is obtained except in the case of a T-T step located adjacent to the linker, in which case both 2+2 and 6-4 adducts are obtained. The efficiency of dimerization is similar for three hairpins having a T-T step located within the duplex interior. Lower efficiency is observed for a T-T step located at the open end of the hairpin and in T overhangs, whereas higher efficiency is observed for the T-T step adjacent to the linker and in a single T bulge. The context-dependence of dimerization efficiency is discussed.     

Facile Synthesis of Multi-Branched Gold Nanostructures through a TBAB-Assisted Route in Aqueous Solution and Their SERS Property

Facile synthesis of multi‐branched gold nanostructures by using the tetrabutyl ammonium bromide (TBAB) as a capping agent is described. The reaction is carried out in a one‐step process at mild temperature. Gold nanostructures with more than six sharp branches ranging from 70 to 130 nm in length are synthesized in high yield. It is proposed that the relative weak adsorption capacity of TBAB leads to the incompletely covered gold surface and the growth of nanoparticles occurs on the uncovered gold surface, and therefore short branches appear consequently. Then positively charged TBAB layers on the gold surfaces prevent the branches from aggregating with each other which stimulates the branch growth. The prepared branched gold nanoparticles show efficient surface‐enhanced Raman scattering (SERS) properties. Low temperature (4°C) is unfavorable to the formation of multi‐branched gold nanostructures, and only thin small irregular plate‐like nanoparticles are produced. The addition of SDS in TBAB aqueous solution results in forming SDS micelles at much lower concentration of SDS (0.4 mmol/L) as compared to that in pure water, and short branched gold nanoparticles are obtained in the SDS‐TBAB system.     

Synthesis of branched polyimides based on 9,9-bis(4-aminophenyl)fluorene and an oligomeric trianhydride,a 1,3,5-triaminotoluene derivative

A new three-arm reactive oligomer (A3) with three end anhydride groups is prepared via the high-temperature cyclocondensation of 1,3,5-triaminotoluene disulfate with excess 2,2-propylidene-bis(phenyl-4-oxyphthalic acid) dianhydride in molten benzoic acid at 140°C in the presence of [2.2.2]-diazobicyclooctane. A branched polyimide is synthesized via the one-step high-temperature catalytic polycondensation of oligomer A3 with 9,9-bis(4-aminophenyl)fluorene in benzoic acid at 140°C via scheme (A3 + B2) and characterized.     

Synthesis of High‐Molar Mass Arborescent‐Branched Polyglycidol via Sequential Grafting

A multiple grafting technique was used to synthesize arborescent‐branched high‐molecular mass poly(2,3‐epoxypropan‐1‐ol). In the first step, linear polyglycidol (M̄_n = 10 300) was obtained. Some of the hydroxyl groups were transformed into alcoholate anions in a reaction with potassium tert‐butoxide, and the obtained polyanion was used to initiate the polymerization of 1‐ethoxyethyl glycidyl ether, the glycidol having a protected hydroxyl group. Removing the protecting groups yielded polyglycidol‐graft‐polyglycidol. This procedure was repeated twice to give three generations of comb‐burst branched polyglycidol chains with M̄_n of 8.2×10⁴, 7.4×10⁵ and 1.8×10⁶.     

Branching generation during the free radical copolymerization of p-vinyl benzene sulfonyl chloride with styrene

The branching generation during the free radical copolymerization of chain transfer monomer p-vinyl benzene sulfonyl chloride (VBSC) with styrene was investigated by a simple mathematic model. Chain transfer constant of VBSC was determined to be around 0.3 by fitting the ¹H-NMR monitored experimental results with a mathematic model. According to the theoretical analysis, the obtained poly(VBSC) and its copolymers were substantiated to have a grafting-like main chain with residual pendent sulfonyl chloride groups after consuming most of the vinyl groups. The copolymerization results of VBSC with styrene at varied feed ratios demonstrated that conversion of sulfonyl chloride groups was lower than that of the monomer, which was in agreement with the theoretical results. The glass transition temperature, number average molecular weight and distribution of those obtained polymers were primarily investigated. Comparing with other chain transfer monomers, VBSC has a chain transfer constant much closer to unity therefore a more branched polymer is expected. Additionally, the branched polystyrene with residual sulfonyl chloride groups is hopefully to be further used as ATRP macroinitiators or reactive intermediates to synthesize functional polymers with complex structure.