Hyperbranched Core Research Articles

Amphiphilic Hyperbranched Fluoropolymers as Nanoscopic 19F Magnetic Resonance Imaging Agent Assemblies

Three hyperbranched fluoropolymers were synthesized and their micelles were constructed as potential (19)F MRI agents. A hyperbranched star-like core was first synthesized via atom transfer radical self-condensing vinyl (co)polymerization (ATR-SCVCP) of 4-chloromethyl styrene (CMS), lauryl acrylate (LA), and 1,1,1-tris(4'-(2''-bromoisobutyryloxy)phenyl)ethane (TBBPE). The polymerization gave a small core with M n of 5.5 kDa with PDI of 1.6, which served as a macroinitiator. Trifluoroethyl methacrylate (TFEMA) and tert-butyl acrylate (tBA) in different ratios were then "grafted" from the core to give three polymers with M(n) of about 120 kDa and PDI values of about 1.6-1.8. After acidolysis of the tert-butyl ester groups, amphiphilic, hyperbranched star-like polymers with M(n) of about 100 kDa were obtained. These structures were subjected to micelle formation in aqueous solution to give micelles having TEM-measured diameters ranging from 3-8 nm and DLS-measured hydrodynamic diameters from 20-30 nm. These micelles gave a narrow, single resonance by (19)F NMR spectroscopy, with a half-width of approximately 130 Hz. The T1/T2 parameters were about 500 and 50 ms, respectively, and were not significantly affected by the composition and sizes of the micelles. (19)F MRI phantom images of these fluorinated micelles were acquired, which demonstrated that these fluorinated micelles maybe useful as novel (19)F MRI agents for a variety of biomedical studies.

Preparation of star block copolymers with polystyrene‐block‐poly(ethylene oxide) as side chains on hyperbranched polyglycerol core by combination of ATRP with atom transfer nitroxide radical coupling reaction

AbstractThe star block copolymers with polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) as side chains and hyperbranched polyglycerol (HPG) as core were synthesized by combination of atom transfer radical polymerization (ATRP) with the “atom transfer nitroxide radical coupling” (“ATNRC”) reaction. The multiarm PS with bromide end groups originated from the HPG core (HPG‐g‐(PS‐Br)n) was synthesized by ATRP first, and the heterofunctional PEO with α‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy group and ω‐hydroxyl group (TEMPO‐PEO) was prepared by anionic polymerization separately using 4‐hydroxyl‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (HTEMPO) as parents compound. Then ATNRC reaction was conducted between the TEMPO groups in PEO and bromide groups in HPG‐g‐(PS‐Br)n in the presence of CuBr and pentamethyldiethylenetriamine (PMDETA). The obtained star block copolymers and intermediates were characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, fourier transform‐infrared in detail. Those results showed that the efficiency of ATNRC in the preparation of multiarm star polymers was satisfactory (>90%) even if the density of coupling cites on HPG was high. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6754–6761, 2008

AB2 + A Type Copolymerization Approach for the Preparation of Thermosensitive PEGylated Hyperbranched Polymers

Hyperbranched polyethers having poly(ethylene glycol) (PEG) segments at their molecular periphery were prepared by a simple procedure wherein an AB2 type monomer was melt-polycondensed with an A-type monomer, namely, heptaethylene glycol monomethyl ether. The presence of a large number of PEG units at the termini rendered a lower critical solution temperature (LCST) to these copolymers, above which they precipitated out of an aqueous solution. In an effort to understand the effect of various molecular structural parameters on their LCST, the length of the hydrophobic spacer segment within the hyperbranched core and the extent of PEGylation were varied. Additionally, linear analogues that incorporates pendant PEG segments were also prepared and comparison of their LCST with that of the hyperbranched analogue clearly revealed that hyperbranched topology leads to a substantial increase in the LCST, highlighting the importance of the peripheral placement of the PEG units.

Dendritic Polymers with a Core−Multishell Architecture: A Versatile Tool for the Stabilization of Nanoparticles

A core−multishell architecture based on a hyperbranched PEI core surrounded by a double layered shell of alkyl hydrophobic groups linked to a PEO chain was successfully used as stabilizer for the formation and the stabilization for hydrophilic and hydrophobic gold nanoparticles in a wide range of solvents.

Synthesis and Characterization of UV-curable Hyperbranched Urethane Acrylate

The UV-curable hyperbranched urethane acrylate (HBUA) with a multi-hydroxyl functional hyperbranched polyester core was synthesized via a two-step procedure. The products were characterized by size exclusion chromatography, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and thermogravimetric analysis. The mechanical properties of UV-cured HBUA films were also investigated. The polydispersity index of HBUA is 2.31 and the endcapped degree of acrylation is 79.8%. The viscosity of HBUA is relatively low in favor of mixing and spreading. The UV-cured films exhibit high hardness and good flexibility.

Development of pH-responsive core–shell nanocarriers for delivery of therapeutic and diagnostic agents

In this paper new dendritic core–shell architectures with pH-labile linkers based on hyperbranched polyglycerol cores and biocompatible poly(ethylene glycol) shells were synthesized which encapsulate the anticancer agent doxorubicin and a dye for near-infrared imaging, an indotricarbocyanine. Acid-sensitive properties of the new nanocarriers and in vitro cytotoxicity of the doxorubicin-nanocarrier are presented as well as preliminary data regarding their toxicity and tumor targeting potential in nude mice.

Preparation of star polymers of hyperbranched polyglycerol core with multiarms of PS‐b‐PtBA and PS‐b‐PAA

AbstractAtom transfer radical polymerization (ATRP) was applied to synthesize a new kind of star polymers of hyperbranched polyglycerol (HPG) core with multiarms of PS‐b‐PtBA and PS‐b‐PAA by using the “core first” technique. The HPG core was obtained by anionic polymerization of glycerol first, and then the pendant hydroxyl groups of HPG were esterified with 2‐bromoisobutyryl bromide to yield the HPG‐g‐Br, which was used as macroinitiator for ATRP of the first monomer (St) and then second monomer (tBA). After hydrolysis of the PtBA block, poly(acrylic acid) (PAA) side chains were formed. The final products and intermediates were characterized by GPC, NMR, and FTIR in detail. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and supramolecular self‐assembly of thermosensitive amphiphilic star copolymers based on a hyperbranched polyether core

AbstractA novel amphiphilic thermosensitive star copolymer with a hydrophobic hyperbranched poly (3‐ethyl‐3‐(hydroxymethyl)oxetane) (HBPO) core and many hydrophilic poly(2‐(dimethylamino) ethyl methacrylate) (PDMAEMA) arms was synthesized and used as the precursor for the aqueous solution self‐assembly. All the copolymers directly aggregated into core–shell unimolecular micelles (around 10 nm) and size‐controllable large multimolecular micelles (around 100 nm) in water at room temperature, according to pyrene probe fluorescence spectrometry and 1H NMR, TEM, and DLS measurements. The star copolymers also underwent sharp, thermosensitive phase transitions at a lower critical solution temperature (LCST), which were proved to be originated from the secondary aggregation of the large micelles driven by increasing hydrophobic interaction due to the dehydration of PDMAEMA shells on heating. A quantitative variable temperature NMR analysis method was designed by using potassium hydrogen phthalate as an external standard and displayed great potential to evaluate the LCST transition at the molecular level. The drug loading and temperature‐dependent release properties of HBPO‐star‐PDMAEMA micelles were also investigated by using indomethacin as a model drug. The indomethacin‐loaded micelles displayed a rapid drug release at a temperature around LCST. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 668–681, 2008

Chain Walking Ethylene Copolymerization with an ATRP Inimer for One‐Pot Synthesis of Hyperbranched Polyethylenes Tethered with ATRP Initiating Sites

AbstractA one‐pot procedure for the synthesis of hyperbranched polyethylenes tethered with ATRP initiating sites by chain walking ethylene copolymerization with an acrylate‐type ATRP inimer, 2‐(2‐bromoisobutyryloxy) ethyl acrylate (BIEA) is reported. Because of its ability to incorporate acrylate‐type comonomers and tolerance toward the α‐bromoester group, the chain walking Pd‐diimine catalyst, [(ArNC(Me)(Me)CNAr)Pd(CH3)(NCMe)]SbF6 (Ar = 2,6‐(iPr)2C6H3), allowed the successful synthesis of a series of hyperbranched copolymers tethered with 2‐bromoisobutyryl groups at different densities. These copolymers may serve as polyfunctional macroinitiators for the ATRP of functional monomers to further synthesize core‐shell structured functionalized copolymers with a hyperbranched polyethylene core grafted with side chains of the functional monomers.magnified image

Water‐Soluble pH‐Responsive Dendritic Core‐Shell Nanocarriers for Polar Dyes Based on Poly(ethylene imine)

A simple general synthetic concept to build dendritic core-shell architectures with pH-labile linkers based on hyperbranched PEI cores and biocompatible PEG shells is presented. Using these dendritic core-shell architectures as nanocarriers, the encapsulation and transport of polar dyes of different sizes is studied. The results show that the acid-labile nanocarriers exhibit much higher transport capacities for dyes than unfunctionalized hyperbranched PEI. The cleavage of imine bonds and controlled release of the polar dyes revealed that weak acidic condition (pH approximately 5.0) could cleave the imine bonds linker and release the dyes up to five times faster than neutral conditions (pH = 7.4).

Hydroformylation with Dendritic‐Polymer‐Stabilized Rhodium Colloids as Catalyst Precursors

AbstractHydroformylation of 1‐hexene with rhodium colloids stabilized by poly(ethylene imine) amides with a hyperbranched polyamine core and a lipophilic periphery is reported. The catalyst selectivity for aldehydes increases with increasing temperature or pressure. The ratio of linear to branched aldehydes decreases with increasing temperature. At 80 °C and 90 atm, 1‐hexene is converted completely with 96% selectivity for aldehydes, with a ratio of linear/branched aldehydes of 58:42. Turnover numbers up to 3 × 104 (calculated with respect to the entire amount of Rh present) were observed. The results indicate that the catalyst precursor colloids serve as a reservoir for the formation of soluble Rh(I) complexes as the active species.magnified image

A New Synthetic Method for the Preparation of Star‐Shaped Polyisobutylene with Hyperbranched Polystyrene Core

AbstractFriedel–Crafts self‐grafting of polystyrene (PSt) under quasiliving carbocationic polymerization was utilized to develop a new rapid one‐pot method for the preparation of star‐shaped polyisobutylene (PIB). First, the polymerization of isobutylene led to PIB with predetermined molecular weight ($\overline M _{\rm n}$ = 2 000) and narrow molecular weight distribution ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.03). Then addition of relatively small amount of styrene after isobutylene consumption yielded PIB‐PSt diblocks. Multiple alkylation of the resulting PSt segments by the polystyryl cations led to hyperbranched PSt cores coupling PIB chains to form a star polymer in short reaction time (within an hour) compared to reported methods. The formation of star polymers by this self‐grafting mechanism was proved by gel permeation chromatography equipped with online viscosimeter and 1H NMR spectroscopy.magnified image

Dye-Encapsulation Selectivity of Amphiphilic Dendritic Boxes

Amphiphilic hyperbranched polyamidoamine (PAMAM) and poly(sulfone-amine) (HPSA) were prepared and their dye-encapsulation properties were investigated. Both of them can carry water-soluble dyes from aqueous solution into chloroform. The selectivity of host to guests and the influence of interaction between different dyes on loading capacity were also investigated by performing comparable experiments. Encapsulation capacities are considered to have relationship with the water-solubility of the hyperbranched polymer core, the polarity difference between the hydrophilic core and the hydrophobic shell, the molecular structure of dyes, and the interactions between dyes.

Amphiphilic Multi‐Arm Star‐Block Copolymers for Encapsulation of Fragrance Molecules

AbstractNovel amphiphilic multi‐arm star‐block copolymers with a hyperbranched core, a hydrophobic inner shell, and a hydrophilic outer shell have been prepared from a commercial hyperbranched polyester macroinitiator by ring‐opening polymerization of ε‐caprolactone, followed by atom transfer radical polymerization of tert‐butyl acrylate (tBuA). Hydrolysis of the tert‐butyl groups was then used to convert the poly(tBuA) blocks to poly(acrylic acid), resulting in stable amphiphilic core‐shell structures with significantly higher degrees of functionality than reported so far in the literature. A strong correlation between the maximum concentration of selected hydrophobic guest molecules and the concentration of amphiphilic star‐block copolymer in aqueous solution was observed by 1H NMR, demonstrating the capacity of these copolymers to encapsulate and disperse significant loadings (up to about 27 wt.‐%) of volatile hydrophobic molecules such as fragrances in water.magnified image

Cover Picture: Macromol. Chem. Phys. 2/2007

Cover: Schematic representation of an amphiphilic multi-arm star-block copolymer based on a hyperbranched polymer core. The copolymer was shown to be able to encapsulate and disperse significant loadings of volatile hydrophobic fragrances in aqueous media. Further details can be found in the Full Paper by C. Ternat, G. Kreutzer, C. J. G. Plummer, T. Q. Nguyen, A. Herrmann, L. Ouali, H. Sommer, W. Fieber, M. I. Velazco, H.-A. Klok, and J.-A. E. Månson* on page 131.

Synthesis of a thermoresponsive platinum nanocomposite using a three-layer onion-like polymer as template

Using a well-designed three-layer onion-like polymer as template, a one-pot procedure that led to stable, narrow-sized and thermoresponsive Pt nanocomposites is described. The polymer consists of an outer shell of thermoresponsive poly( N-isopropylacrylamide), an inner shell of crosslinked poly( N,N-dimethylaminoethyl acrylate) and a hyperbranched polyglycerol core. The core is physically trapped by the shell, with a few thiol groups located on the interface between the core and the shell. The polymer is used as a template for the synthesis of platinum nanoparticles, 1H NMR and TEM analyses suggest that the in-situ produced, narrow-sized Pt nanoparticle is loaded in the core part of the polymer so that the nanocomposite retains thermoresponsive activity.

Tuning the optical properties of hyperbranched polymers through the modification of the end groups

AbstractDye‐capped, hyperbranched, conjugated polymers were prepared by the modification of the peripheral bromo end groups of the hyperbranched polymer core with a palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction. The dye‐modified, hyperbranched polymers had high molecular weights and displayed good solubility in common organic solvents such as tetrahydrofuran, toluene, and chloroform. The structure of the dye‐modified, hyperbranched polymers was characterized by 1H and 13C NMR and elemental analysis. The thermal properties of five kinds of hyperbranched polymers were investigated with thermogravimetric analysis and differential scanning calorimetry. The optical properties of the dye‐capped, hyperbranched polymers were investigated with ultraviolet‐absorption and fluorescence spectroscopy. The hyperbranched structure could effectively reduce the aggregation of the peripheral dyes. The emission colors of the hyperbranched polymers could be easily tuned by end‐group modification. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 111–124, 2007

Synthesis of multi-arm star polystyrene with hyperbranched polyether core

Multi-arm star polystyrenes with hyperbranched poly(3-ethyl-3-oxetanemethanol) (PEOM, 3) core were synthesized by atom transfer radical polymerization (ATRP) method. The structures of polymers were confirmed by FT-IR and 1H NMR. GPC results showed that the resultant polymers had relatively low polydispersity indices (PD = 1.47–2.03). DSC analysis indicated that polystyrene star polymers had a glass transition temperature ( T g = 42.2–91.5 °C) that changed with the amount of the polystyrene in the polymers. In addition, the aggregation behavior of the multi-arm star polystyrenes in a selective solvent (THF/cyclohexane) was probed with polystyrene arms that encapsulated in the aggregates and PEOM cores hidden in the center of the micelles.

One‐pot synthesis of star‐shaped aliphatic polyesters with hyperbranched cores and their characterization with size exclusion chromatography

Star-shaped polymers, bearing a strictly defined number of linear arms, provide useful model structures for studies of branched macromolecular structures. In the dynamically growing area of biocompatible and biodegradable polymers, the synthesis and characterization of starshaped aliphatic polyesters are particularly advanced. Among others, some of our recent articles report the synthesis and characterization of 1-, 2-, 3-, 4-, 5-, 6-, 8, 13-, and 32-arm star-shaped poly(L-lactide)s by size exclusion chromatography (SEC), liquid chromatography under critical conditions (LC–CC), two-dimensional LC–CC/SEC, NMR, and fluorescence spectroscopy. The method perhaps most commonly used for starshaped polymer synthesis is based on the core-first approach, in which a multifunctional reagent (the core) plays the role of the (co)initiator and/or transfer agent. Another possibility in this area, originally developed by Rempp et al. for a styrene/divinylbenzene (DVB) system, was followed more recently by Lapienis and Penczek for an epoxide/diepoxide system. The principle of this approach is based on a two-step synthesis with the one-pot, arms-first coremethod. In the first step, a linear living polymer (the precursor) is prepared (e.g., polystyrene or polyepoxide). Then, in the second step, the resulting precursor initiates the polymerization of a tetrafunctional monomer (e.g., DVB or diepoxide), giving a highly branched macromolecular structure (the core). This communication reports the successful synthesis of highly branched, star-shaped aliphatic polyesters from various lactone and lactide/bislactone systems—e-caprolactone (CL)/5,50-bis(oxepan-2-one) (bis-CL), L,L-lactide (LA)/ bis-CL, CL/1,6-dioxaspiro[4,4]nonane-2,7-dione) (bis-BL), and LA/bis-BL—with aluminum isopropoxide [Al(OPr)3] as the initiator. Experimental evidence of the formation of starlike structures is provided by SEC and matrixassisted laser desorption/ionization time-of-flight (MALDITOF) analysis.

Macroscopic self-assembly of hyperbranched polyesters

We utilized melt polycondensation of 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) and 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP) to synthesize a hyperbranched polyester core and subsequent substitution by reaction of terminal hydroxyl with benzoyl chloride in DMF in the presence of TEA as the acceptors of HCl. It has been found that well-defined macroscopic structures can be formed via hydrogen bonding and π–π stacking interactions. Meanwhile, the molecular structures, the nature of the solvent, the molecular concentration, the volatilizing ratio of solvent, and self-assembly temperature also affected the self-assembly structures. The type of self-assembly method offers a synthetic route to well-defined one-dimensional organic macrostructures.