Hyperbranched polymers with maleic functional groups as radical crosslinkers

The crosslinking performance of the unsaturated hyperbranched polyester poly(allyloxy maleic acid‐co‐maleic anhydride) (MAHP) was investigated with copolymerizations of three different monomers: styrene, vinyl acetate, and methyl methacrylate. Both styrene and vinyl acetate afforded interpenetrating‐polymer‐network copolymer gels. The gels exhibited crosslink density gradients through the polymer matrices on a macroscopic level, and density maximums were concentrated around the MAHP moieties. The heterogeneity of the gels is briefly discussed in terms of a modified two‐phase model, where one phase consists of an elastic part of low crosslinking density and the other phase consists of an inelastic dendritic part with a highly condensed bond density. Unlike the two‐phase model developed by Choquet and Rietsch, the modified two‐phase model takes into account that both phases swell in good solvents. Unlike copolymerizations employing styrene or vinyl acetate, the copolymerization of MAHP with methyl methacrylate afforded noncrosslinked starbranched copolymers that consisted of a MAHP core from which long poly(methyl methacrylate) branches were protruding. The different behaviors of the copolymerizations of the three monomers used in this study can rationally be explained by their different reactivity ratios with maleic end groups of MAHP. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 964–972, 2001     

Hyperbranched polymers as delivery vectors for oligonucleotides

We report on the synthesis and characterization of hyperbranched dimethylaminoethyl methacrylate (DMAEMA) polymers using reversible addition fragmentation chain transfer polymerization. These polymers are unimolecular and globular and hence interact differently with DNA than conventional DMAEMA or block copolymers. The polymers were shown to effectively bind and condense oligonucleotides (ODNs); visualization of the bound complexes was achieved using atomic force microscopy, whereas isothermal titration calorimetry described the thermodynamics of binding. The ODNs were effectively protected from enzymatic degradation (DNAses) when condensed by all the polycations studied. However, internalization of the complexes into HeLa cells was less effective when the polycation was chain extended with polyethyleneglycol monomethylether methacrylate. Conjugation of folic acid to the periphery of the polycation facilitated much enhanced uptake of the oligomeric DNA into the HeLa cells due to overexpression of folate receptors on the surface of HeLa cells. Although significant cytotoxicity was observed at high polymer concentrations, this could be alleviated by shielding of the polycation using poly(ethyleneglycol monomethylether methacrylate). These results suggest that hyperbranched polymers formed in this way exhibit interesting complexation behavior with ODNs and thus are promising models to study as gene delivery vectors. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Fluorescent dendritic polymers and nanostructured coatings for the detection of chemical warfare agents and other analytes

Polyamidoamine (PAMAM) dendrimers of generations zero (G0) to four (G4), and a hyperbranched polyurea (HB‐PU), were functionalized with 1,5‐dansyl (1,5‐D), 2,5‐dansyl (2,5‐D), 2,6‐dansyl (2,6‐D) and nitrobenzofurazan (NBD) fluorophores that change their fluorescence emission wavelength in response to chemical environment, and the resulting dendritic polymers were characterized by MALDI‐TOF mass spectrometry, ¹H NMR, ¹³C NMR, and fluorescence spectroscopy. Fluorophore‐functionalized dendritic polymers were then reacted further with 3‐acryloxypropyldimethoxymethylsilane (AOP‐DMOMS) at various fluorophore to DMOMS substitution ratios. The resulting materials were cast onto glass slides, and cured into robust nanostructured coatings. Coatings with 50% fluorophore–50% DMOMS substitution showed the strongest fluorescence and the best physical properties. Coated coupons were tested against a wide range of analytes including the chemical warfare agent simulants dimethyl methylphosphonate (DMMP) and chloroethylethylsulfide (CEES), and the water‐methanol‐ethanol series. It was found that the ability of the coatings to distinguish between analytes decreased with increasing cross‐link density for both dendrimer and hyperbranched polymer‐based coatings. It was also found that the percent fluorophore substitution and the type of dendritic polymer carrying the fluorophore had no significant effect upon fluorescence emission wavelength, but fluorescence emission wavelength became less dependent upon solvent with increasing dendrimer generation and molecular mass. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5101–5115, 2009     

Hyperbranched aryl polycarbonates derived from A2B monomers versus AB2 monomers

Hyperbranched aryl polycarbonates were prepared via the polymerizations of A₂B and AB₂ monomers, which involved the condensation of chloroformate (A) functionalities with tert‐butyldimethylsilyl‐protected phenols (B), facilitated by reactions with silver fluoride. The polymerization of the A₂B monomer gave hyperbranched polycarbonates bearing fluoroformate chain ends, which were hydrolyzed to phenolic chain‐end moieties and further elaborated to tert‐butyldimethylsilyl ether groups. The polymerization of the AB₂ monomer gave tert‐butyldimethylsilyl ether‐terminated hyperbranched polycarbonates. The polymerizations were conducted at 23–70 °C in 20% acetonitrile/tetrahydrofuran in the presence of a stoichiometric excess of silver fluoride for 20–40 h to afford hyperbranched polycarbonates with weight‐average molecular weights exceeding 100,000 Da and polydispersity indices of typically 2–3. The degrees of branching were determined by a reductive degradation procedure followed by high‐performance liquid chromatography. Alternatively, the degrees of branching were measurable by solution‐state ¹H NMR analyses and agreed with the statistical 50% branching expected for the polymerization of A₂B and AB₂ monomers not experiencing constructive or destructive electronic effects on the reactivity of the multiple functional groups. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 823–835, 2002; DOI 10.1002/pola.10167     

Models for the Dynamics of Hyperbranched Macromolecules

Summary: We focus on the motion of hyperbranched macromolecules in solution, paying particular attention to the relation between underlying topological structure and dynamics; we consider especially the mechanical moduli. Under the prominent representatives of hyperbranched polymers are both regular structures (such as the dendrimers) as well as disordered structures (such as irregular Cayley-trees). Evidently, batch-prepared hyperbranched macromolecules are closer to the latter. In order to theoretically determine their mechanical moduli we employ the method of generalized Gaussian structures (GGS), which allows us to study the situation including or excluding the hydrodynamic interactions (HI). Disordered hyperbranched structures display a complex dynamics; here we recall several analytical and numerical schemes for determining it and compare our theoretical results to the experimental data.     

无机和金属有机多核分子树络合物

本文介绍近年来国外无机和金属有机多核分子树络合物的研究进展, 主要侧重于这类分子树络合物的设计合成、物化特性、催化反应及其应用前景。     

新型超支化聚芳烃的合成与性能研究

3,6-二乙炔基-9-(三苯胺基)-咔唑、4,4′-二乙炔基-4″-(咔唑基)-三苯胺双炔和1-辛炔单炔在CpCo(CO)2-hν催化的条件下合成了新型超支化聚芳烃.所得的聚合物都溶于普通溶剂(甲苯、THF、氯仿、二氯甲烷等).在光激发的条件下,聚合物在428 nm左右发射蓝光,其荧光量子效率达到62%.所有超支化聚合物都表现出优异的热稳定性,它们的起始分解温度高达484℃.     

Linear‐Hyperbranched Amphiphilic AB Diblock Copolymers Based on Polystyrene and Hyperbranched Polyglycerol

Summary: A convenient three‐step strategy has been developed for the preparation of well‐defined amphiphilic, linear‐hyperbranched block copolymers by hypergrafting. The synthetic procedure is based on a combination of carbanionic polymerization with the alkoxide‐based, controlled ring‐opening multibranching polymerization of glycidol. A linear AB diblock copolymer polystyrene‐block‐polybutadiene (PS‐b‐PB) with narrow polydispersity was obtained by anionic copolymerization. Subsequent hydroxylation by hydroboration led to PS₅₀₈‐b‐(PB‐OH)₅₆, used as macroinitiator for the polymerization of glycidol under slow monomer addition conditions.

Structure of the linear‐hyperbranched amphiphilic AB diblock copolymer PS₅₀₈‐b‐(PB₅₆‐hg‐PG_x) and an AFM micrograph of its micellar core–shell structure observed after solution casting.     

Hyperbranched polymers as a novel class of pigment dispersants

Hyperbranched polymers form a novel class of materials that are employed as components of resin formulations. They are appreciated for their low intrinsic viscosities, which is ascribed to their spherical shape. It was envisaged to devise pigment dispersants with hyperbranched moieties as structural elements. Commercially available hyperbranched polymers with polyester, polyesteramide and polyethylene imine backbones were chemically modified to develop a range of disperants with core- and shell-type pigment anchoring mechanisms. Both the shell- and core-type anchoring principles generally can be used for pigment dispersion and stabilisation at a low viscosity level.     

Rapid Hyperbranched Polythioether Synthesis Through Thiol-Michael Addition Reaction

In this study, two types of hyperbranched (HB) polythioether could readily be achieved in a short time at ambient temperature through a thiol-Michael addition reaction. Dimethyl acetylenedicarboxylate (DMADC) or methyl propiolate (A₂) and trimethylolpropane tris(3-mercaptopropionate) (B₃) monomers were reacted using an organobase 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a catalyst in chloroform at room temperature to provide subsequent HB polythioethers. The effect of TBD concentration on the polymerization was studied for the DMDAC case monitoring the molecular weight evolution against time. HB polythioethers were characterized using spectroscopic (nuclear magnetic resonance) and chromatographic (gel permeation chromatography with refractive index and light-scattering detectors) techniques. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 824–830     

Enzyme‐Catalyzed Synthesis of Hyperbranched Aliphatic Polyesters

Hyperbranched aliphatic copolyesters have been prepared by copolymerization of ε‐caprolactone with 2,2‐bis(hydroxymethyl)butyric acid, catalyzed by immobilized Lipase B from Candida antarctica (Novozyme 435) under mild conditions. Via this novel combination of ring‐opening AB polymerization and AB₂ polycondensation, the degree of branching (DB) and, consequently, the density of functional end groups can be controlled by the comonomer ratio in the feed (0 < DB < 0.33).     

含光敏剂184结构的超支化碱溶性感光聚合物的合成及性能

以季戊四醇为“中心核”,通过与偏苯三酸酐,环氧氯丙烷反应合成超支化聚酯,利用合成聚合物分子外围的羧基与含环氧基的1-羟基环己基苯基酮、甲基丙烯酸缩水甘油酯反应合成分子末端含光敏剂结构的超支化碱溶性感光聚合物。聚合反应转化率在1 h内可达80%以上;合成聚合物的玻璃化转变温度为200℃,200℃以内无失重,200~300℃之间有轻微失重,其粘度表现为超支化聚合物的粘度特性,并且在碱性水溶液中溶解性好,无需外加光敏剂,在紫外光照射下便可固化、交联,具有较小的凝胶曝光能量E0(1×10-3~1×10-2J/cm2)和较好的光敏性。     

Hyperbranched polymers—All problems solved after 15 years of research?

Fifteen years of research on hyperbranched polymers in the group of Brigitte Voit are described, with a focus first on hyperbranched polyester synthesis and then on the addition and cycloaddition reactions used for the preparation of the hyperbranched structure. The characterization of structural details and bulk, solution, and thin‐film properties is highlighted, and steps toward the elucidation of a general property profile of hyperbranched polymers are discussed. Some effects of hyperbranched polymers in reactive formulations and blends and in thin films are addressed that can lead to applications in coatings, as additives, and in microelectronics or sensorics. The great progress possible in the last years is shown, but open questions and unsolved problems are also pointed out. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2679–2699, 2005     

Synthesis of hyperbranched polymers with precise conjugation length

A set of AB₂ type monodisperse conjugated oligomers carrying two bromo functional groups and one boronic ester functional group were prepared by iterative deprotection and Sonogashira cross‐coupling reactions. Suzuki polycondensation of these AB₂ type monodisperse oligomers afforded hyperbranched polymers. The hyperbranched conjugated polymers we prepared possess not only precisely controlled conjugation length like monodisperse conjugated oligomers but also the structural feature of hyperbranched polymers. Optical property investigation demonstrated that the maximum absorption and emission wavelength red‐shifted along with the increasing of the conjugation length between the two branching points and the hyperbranched structure could effectively reduce the aggregation of the conjugated polymer chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1084–1092, 2007     

端基对超支化高分子性质影响的研究

对端羟基脂肪族超支化高分子的端基进行了乙酰化和硅烷化改性，研究了不同端基对超支化高分子的玻璃化温度，折光指数增量以及特性粘度的影响。结果表明，端基的极性减小使超支化高分子的玻璃化温度降低，不同端基的超支化高分子的折光指数增量也有很大差异，而强极性的端基使超支化高分子在溶液中易产生团聚作用。由于端基在超支化高分子中所占比重较大，端基是影响超支化高分子性质的重要因素。     

Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution

Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo‐dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high‐generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1–G4) pseudo‐dendrimers strongly resembles the behavior of dendrimers in higher generations (G5–G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano‐sphere with a smooth surface even in the first generation.     

Dynamics of hyperbranched polymers and dendrimers: theoretical models

Chemical reactions depend in many ways on the dynamics of the underlying reactants, and an important aspect is the distance covered by the reactants before the reaction act occurs. Hence, even diffusion-limited reactions between point particles in confined geometries and in low-dimensional systems display decay forms which are very different from those obtained from simple chemical kinetics. Clearly, even more complex decay forms hold for macromolecules, given their internal degrees of freedom. Here we discuss how the dynamics of macromolecules in solution relates to their topological structure and focus on the motion of macromolecular segments (monomers) under the influence of external fields. After a general survey of the method of generalized Gaussian structures (GGS) we recall the wealth of forms which are observed, depending on the topology and on the microscopic dynamics involved. Paradigmatic are the findings for the class of hyperbranched macromolecules; to these belong the dendrimers. While the dendrimers do not show a typical scaling behavior, as found, say, for linear chains, the situation is different for particular classes of regular hyperbranched polymers which are fractal. We end by discussing their pattern of motion in the GGS-Rouse-Zimm picture.     

Nanoimprint Lithography with UV-Curable Hyperbranched Polymer Nanocomposites

Nano-scale patterns were produced with UV-curable acrylated hyperbranched polymer nanocomposites using nanoimprint lithography with a glass master in a rapid, low-pressure process. The pattern of the glass master was replicated with composites containing up to 25 vol% SiO₂ with a shape fidelity better than 98%. Photo-rheology, interferometry and atomic force microscopy were used to analyze the material behavior. Attention was paid to the relationship between composition, nanoparticle dispersion, kinetics of photo-polymerisation, shrinkage, pressure and shape fidelity of nano-gratings. It was shown that the gel-point of the nanocomposite was an important factor that determined the stability as well as the dimensions of the imprinted structure. Dimensional accuracy also strongly depended on the level of internal stress, which in fact increased with the amount of silica. A resin rich layer on the surface of the composite accounted for the good surface quality of the nano-pattern.