pH responsiveness of dendrimer-like poly(ethylene oxide)s

Poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA), two polymers known to form pH-sensitive aggregates through noncovalent interactions, were assembled in purposely designed architecture -a dendrimer-like PEO scaffold carrying short inner PAA chains-to produce unimolecular systems that exhibit pH responsiveness. Because of the particular placement of the PAA chains within the dendrimer-like structure, intermolecular complexation between acrylic acid (AA) and ethylene oxide (EO) units-and thus macroscopic aggregation or even mesoscopic micellization-could be avoided in favor of the sole intramolecular complexation. The sensitivity of such interactions to pH was exploited to generate dendrimer-like PEOs that reversibly shrink and expand with the pH. Such PAA-carrying dendrimer-like PEOs were synthesized in two main steps. First, a fifth-generation dendrimer-like PEO was obtained by combining anionic ring-opening polymerization (AROP) of ethylene oxide from a tris-hydroxylated core and selective branching reactions of PEO chain ends. To this end, an AB(2)C-type branching agent was designed: the latter includes a chloromethyl (A) group for its covalent attachment to the arm ends, two geminal hydroxyls (B(2)) protected in the form of a ketal ring for the growth of subsequent PEO generations by AROP, and a vinylic (C) double bonds for further functionalization of the interior of dendrimer-like PEOs. Reiteration of AROP and derivatization of PEO branches allowed us to prepare a dendrimer-like PEO of fourth generation with a total molar mass of 52,000 g x mol(-1), containing 24 external hydroxyl functions and 21 inner vinylic groups in the interior. A fifth generation of PEO chains was generated from this parent dendrimer-like PEO of fourth generation using a "conventional" AB(2)-type branching agent, and 48 PEO branches could be grown by AROP. The 48 outer hydroxy-end groups of the fifth-generation dendrimer-like PEO obtained were subsequently quantitatively converted into inert benzylic groups using benzyl bromide. The 21 internal vinylic groups carried by the PEO scaffold were then chemically modified in a two-step sequence into bromoester groups. The latter which are atom transfer radical polymerization (ATRP) initiating sites thus served to grow poly(tert-butylacrylate) chains. After a final step of hydrolysis of the tert-butyl ester groups, double, hydrophilic, dendrimer-like PEOs comprising 21 internal junction-attached poly(acrylic acid) (PAA) blocks could be obtained. Dynamic light scattering was used to determine the size of these dendrimer-like species in water and to investigate their response to pH variation: in particular, how the pH-sensitive complexation of EO and AA units affects their overall behavior.     

Toward an easy access to dendrimer-like poly(ethylene oxide)s

Dendrimer-like poly(ethylene oxide)s (PEOs) were synthesized by an iterative divergent approach combining anionic polymerization of ethylene oxide from multi-hydroxylated precursors and branching reactions of PEO chain ends. Partial deprotonation of the hydroxyls (< 30%) and use of dimethyl sulfoxide as solvent proved crucial for a "controlled/living" polymerization of ethylene oxide at room temperature. These sequences of reactions allowed us to prepare a dendrimer-like PEO up to the eighth generation with a molar mass of 900 000 g mol(-1) and 384 external hydroxyl functions. All samples from generation 1 to 8 were characterized by 1H NMR spectroscopy, light scattering, and viscometry. The evolution of the intrinsic viscosity versus the generation number of these dendrimer-like PEO is similar to that of regular dendrimers.     

Dendritic Carrier Based on PEG: Design and Degradation of Acid‐sensitive Dendrimer‐like Poly(ethylene oxide)s

Degradable dendrimer‐like PEOs were designed using an original ABC‐type branching agent featuring a cleavable ketal group, following an iterative divergent approach based on the anionic ring opening polymerization (AROP) of ethylene oxide and arborization of PEO chain ends. A seventh generation dendrimer‐like PEO carrying 192 peripheral hydroxyls and exhibiting a molar mass of 446 kg · mol⁻¹ was obtained in this way. The chemical degradation of these dendritic scaffolds was next successfully accomplished under acidic conditions, forming linear PEO chains of low molar mass (≈2 kg · mol⁻¹), as monitored by ¹H NMR, SEC, and MALDI‐TOF mass spectrometry as well as by AFM.

     

Sequential functionalization of janus‐type dendrimer‐like poly(ethylene oxide)s with camptothecin and folic acid

Janus‐type dendrimer‐like poly(ethylene oxide)s (PEOs) of 1st, 2nd, and 3rd generation carrying terminal hydroxyl functions on one side and cleavable ketal groups on the other were used as substrates to conjugate folic acid as a folate receptor and camptothecin (CPT) as a therapeutic drug in a sequential fashion. The conjugation of both FA and CPT was accomplished by “click chemistry” based on the 1,3 dipolar cycloaddition coupling reaction. First, the hydroxyl functions present at one face of Janus‐type dendrimer‐like PEOs were transformed into alkyne groups through a simple Williamson‐type etherification reaction. Next, the ketals carried by the other face of the dendrimer‐like PEOs were hydrolyzed, yielding twice as many hydroxyls which were subsequently subjected to an esterification reaction using 2‐bromopropionic bromide. Before substituting azides for the bromide of 2‐bromopropionate esters just generated in the presence of NaN₃, an azido‐containing amidified FA derivative was reacted through click chemistry with alkyne functions introduced on the other face of the dendrimer‐like PEOs. A purposely designed alkyne‐functionalized biomolecule derived from CPT was conjugated to the azido functions carried by the dendritic PEOs by a second “click reaction.” In this case, twice as many CPT as FA moieties were finally conjugated to the two faces of the Janus‐type dendrimer‐like PEOs, the numbers of folate and CPT introduced being 2 and 4, 4 and 8, and 8 and 16 for samples of 1st, 2nd, and 3rd generation, respectively (route A). An alternate route for functionalizing the dendrimer‐like PEO of 1st generation consisted, first, in conjugating the azido‐containing CPT onto the alkyne groups present on one face of the dendritic PEO scaffold. The alkyne‐functionalized FA was further introduced by click chemistry after the bromides of 2‐bromopropionate esters were chemically transformed into azido groups. The corresponding prodrug thus contains 2 CPT and 4 FA external moieties (route B). Every reaction step product was thoroughly characterized by ¹H NMR spectroscopy. A preliminary investigation into the water solution properties of these functionalized dendritic PEOs is also presented. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

云母表面上低分子量聚氧乙烯熔体的“假不浸润”行为

在固体基底表面上,液体可以表现出不同的浸润性.若完全浸润,液体会铺展成膜;若部分浸润或不浸润,液体则会聚集成团.和上述经典的浸润行为不同,“假不浸润”(pseudo-dewetting)是一种比较特殊的现象,引起了人们的广泛关注.1955年Hare和Zisman[1]发现,将许多极性、两亲性和不稳定     

两亲嵌段树枝状分子Gx-PBE-b-Gx-PMPA(OH)x2的合成及多重氢键作用

合成了1~3代的嵌段树枝状分子聚苄醚-聚脂肪酯(Gx-PBE-b-Gx-PMPA, x=1,2,3)和两亲嵌段树枝状分子聚苄醚-周边含羟基的聚脂肪酯[Gx-PBE-b-Gx-PMPA(OH)x2, x=1,2,3]. PMPA(OH)x2-树枝片(Dendron)段周边的羟基数目分别是2, 4和8. 通过1H NMR, 13C NMR, FTIR和基质辅助激光解吸附电离飞行时间质谱(MALDI-TOF)(或场解析电离质谱)技术表征了Gx-PBE-b-Gx-PMPA和Gx-PBE-b-Gx-PMPA(OH)x2的结构. 同时, 采用变温FTIR光谱研究了在两亲嵌段树枝状分子中形成的氢键模式. 结果表明, 随着树枝片代数的增加, 两亲嵌段树枝状分子内趋向于形成作用较弱的分子内氢键, 说明形成3代两亲嵌段树枝状分子的三维结构削弱了羟基形成分子间氢键的能力.     

Self-assembling behavior of amphiphilic dendron coils in the bulk crystalline and liquid crystalline states

We prepared a series of amphiphilic dendron coils (1-3) containing aliphatic polyether dendrons with octadecyl peripheries and a poly(ethylene oxide) (PEO) coil (DP = 44). The molecular design in this study is focused on the variation of dendron generation (from first to third) with a fixed linear coil, upon which the thermal and self-assembling behavior of the dendron coils was investigated in the bulk. All the dendron coils exhibit two crystalline phases designated as k1 (both crystalline octadecyl chains and PEO) and k2 states (crystalline octadecyl chains and molten PEO). Crystallinities for both octadecyl peripheries and the PEO decrease as generation increases. In particular, the dendron coil (3) containing third generation shows a drastic reduction of the PEO crystallinity, which is attributed to the considerable chain folding and plasticization effects by the largest hydrophilic dendritic core segment. All the crystalline phases are bilayered lamellar morphologies. On going from k1 to k2, the periodic lamellar thickness decreases in the dendron coil (1) with first generation, but interestingly increases in 3. After melting of octadecyl peripheries, 1 shows no mesophase (i.e., liquid crystalline phase). Additionally, dendron coil 2 (3) displays a network cubic mesophase with Ia3d symmetry (micellar cubic with Pm3n) which is transformed into a lamellar (hexagonal columnar) mesophase upon heating. Remarkably, the temperature-dependent mesomorphic behavior in 2 and 3 is a completely reverse pattern in comparison with conventional linear-linear block copolymers. The unusual bulk morphological phenomena in the crystalline and liquid crystalline phases can be elucidated by the dendron coil architecture and the associated coil conformational energy.     

Designing macromolecules for therapeutic applications: polyester dendrimer-poly(ethylene oxide) "bow-tie" hybrids with tunable molecular weight and architecture

The design and preparation of new polyester dendrimer, poly(ethylene oxide) hybrid systems for drug delivery and related therapeutic applications, are described. These systems consist of two covalently attached polyester dendrons, where one dendron provides multiple functional handles for the attachment of therapeutically active moieties, while the other is used for attachment of solubilizing poly(ethylene oxide) chains. By varying the generation of the dendrons and the mass of the poly(ethylene oxide) chains, the molecular weight, architecture, and drug loading can be readily controlled. The "bow-tie" shaped dendritic scaffold was synthesized using both convergent and divergent methods, with orthogonal protecting groups on the periphery of the two dendrons. Poly(ethylene oxide) was then attached to the periphery of one dendron using an efficient coupling procedure. A small library of eight carriers with molecular weights ranging from about 20 kDa to 160 kDa were prepared and characterized by various techniques, confirming their well-defined structures.     

Preparation of comb‐like copolymers with amphiphilic poly(ethylene oxide)‐b‐polystyrene graft chains by combination of “graft from” and “graft onto” strategies

A novel method for preparation the comb‐like copolymers with amphihilic poly(ethylene oxide)‐block‐poly(styrene) (PEO‐b‐PS) graft chains by “graft from” and “graft onto” strategies were reported. The ring‐opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using α‐methoxyl‐ω‐hydroxyl‐poly(ethylene oxide) (mPEO) and diphenylmethyl potassium (DPMK) as coinitiation system, then the EEGE units on resulting linear copolymer mPEO‐b‐Poly(EO‐co‐EEGE) were hydrolyzed and the recovered hydroxyl groups were reacted with 2‐bromoisobutyryl bromide. The obtained macroinitiator mPEO‐b‐Poly(EO‐co‐BiBGE) can initiate the polymerization of styrene by ATRP via the “Graft from” strategy, and the comb‐like copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐PS] were obtained. Afterwards, the TEMPO‐PEO was prepared by ring‐opening polymerization (ROP) of EO initiated by 4‐hydroxyl‐2,2,6,6‐tetramethyl piperdinyl‐oxy (HTEMPO) and DPMK, and then coupled with mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐PS] by atom transfer nitroxide radical coupling reaction in the presence of cuprous bromide (CuBr)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) via “Graft onto” method. The comb‐like block copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐(PS‐b‐PEO)] were obtained with high efficiency (≥90%). The final product and intermediates were characterized in detail. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1930–1938, 2009     

Hydration of poly(ethylene oxide)s in aqueous solution as studied by dielectric relaxation measurements

The hydration state of poly(ethylene oxide)s (PEOs) in aqueous solutions was investigated using dielectric relaxation measurements at 25 degrees C over a frequency range up to 20 GHz, which is the relaxation frequency of water molecules in a bulk state. The dielectric relaxation spectra obtained indicated decomposition into two major and one minor relaxation modes with relaxation times of 8.3, 22, and 250 ps, respectively. The two major modes were attributed to rotational relaxation of water molecules belonging to the bulk state and water molecules hydrogen bonded to ethylene oxide (EO) monomer units. The number of hydration water molecules per EO unit depended on the molar mass of PEO (M) and reached a constant value of 3.7 at M > 1500, which agrees with the value obtained by other experiments.     

Combination of an anionic terminator multifunctional initiator and divergent carbanionic polymerization: application to the synthesis of dendrimer-like polymers and of asymmetric and miktoarm stars

A new and versatile synthetic strategy that provides access to precisely defined and totally soluble multicarbanionic initiators has been implemented to obtain by divergent growth dendrimer-like samples of polystyrene (PS) (up to the seventh generation) or polybutadiene (PB) (up to the third generation) and also asymmetric and miktoarm stars. This strategy rests on lithium-halide exchange reactions to generate multicarbanionic species and on the design of an original reagent that can concomitantly react with living carbanionic chains/arms to deactivate them and produce multicarbanionic sites after exchange of its bromides against lithium. This reagent, 4,4'-dibromodiphenylethylene (1), functions as a TERminating agent and a Multifunctional INItiator (TERMINI), according to a concept first proposed by Percec in another context. Upon using this anionic TERMINI in living carbanionic polymerization and repeating the two steps of chain end derivatization by 1 and divergent arm growth from the multifunctional sites generated, perfectly defined dendrimer-like polystyrene and polybutadiene could be obtained up to the seventh generation for the former and up to the third generation for the latter. Each step, i.e., chain end modification and arm growth, was carefully monitored, and the dendrimer-like samples of PS and PB were all characterized by size exclusion chromatography equipped with a multiangle laser light scattering detector (SEC/LS) and high-temperature size exclusion chromatography equipped with a viscometric detector (HT-SEC). The viscosity behavior of these dendrimer-like polystyrenes--bell-shaped variation versus the number of generation--was found to be similar to that reported for regular dendrimers. This chemistry, namely this anionic TERMINI, was also exploited to derive three-arm asymmetric and miktoarm stars.     

Degradable poly(ethylene oxide) hydrogels formed by crosslinking with tert‐butylperoxybenzoate

Poly(ethylene oxide) (PEO, number‐average molecular weight: 2,000,000) was crosslinked by reaction with t‐butylperoxybenzoate in the melt. Upon swelling in water, the resulting hydrogels were acidic and suggested clear evidence of spontaneous hydrolysis that continued over periods of several weeks to give clear and low‐viscosity aqueous solutions of PEO oligomers. In contrast, in neutral media the gels did not show any signs of hydrolysis. As shown by UV, IR, and size exclusion chromatographic analysis, the PEO hydrolysis products consist of benzoic acid and hydroxyl‐ and carboxyl end‐functionalized low‐molecular‐weight PEOs. This is consistent with the acid‐catalyzed hydrolysis of acetal‐, orthoester‐, and similar end‐functionalized PEOs formed by radical coupling of various PEO radicals with benzoate, alkoxy, and other radicals. Titration of the hydrolysis mixtures indicated that the total molar amount of acid exceeds that of the maximum amount of benzoic acid produced during gel formation. However, the amount of benzoic acid equaled this maximum amount. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 520–527, 2003     

Globular Polymer Grafts Require a Critical Size for Efficient Molecular Sieving of Enzyme Substrates

A series of 2,2‐bis(hydroxymethyl)propionic acid dendrons of generation 2 through 8 having a strained cyclooctyne at the core and hydroxy groups at the periphery were prepared by a divergent method and used to functionalize azide‐decorated α‐chymotrypsin. The ability of the appended dendrons to selectively block enzyme activity (through a molecular sieving effect) was investigated using a small molecule substrate (benzoyl‐l ‐tyrosine p‐nitroanilide), as well as two proteins of different size (casein and bovine serum albumin). Additionally, the ability of dendrons to block complexation with a chymotrypsin antagonist, α‐antichymotrypsin, was investigated, and it was found that the dendron coating effectively prevented inhibition by this antagonist. We found that a critical generation is required to achieve efficient sieving with bis‐MPA dendrons, which illustrates the importance of macromolecular architecture and size in the shielding of proteins.     

Polymer Solvents For Electrochemical Reactions

Solubility of inorganic salts and potential window of poly(ethylene oxide) (PEO) were analyzed. Sufficient potential window (?1.6 to + 1.6 V vs Ag) was obtained for salt-containing PEOs when the ionic conductivity of the PEOs was higher than 3.0 × 10^?4 S/cm. PEO was then used as a polymer solvent for electrochemical redox reactions of heme proteins. Myoglobin was solubilized in salt-containing PEO oligomers only after PEO modification, and their reversible redox reactions were confirmed. The electrochemical reduction was slow because of the very low diffusion coefficient of the proteins in PEO oligomers. PEO-modi-fied myoglobin and hemoglobin showed reversible electron transfer reaction with ITO glass electrode at even 80 or 100°C in PEO oligomers.     

Synthesis, characterisation and in vitro anti-angiogenic potential of dendron VEGF blockers

To overcome the lack of in vivo stability of certain peptides used in cancer treatment and to increase their retention time in the extracellular matrix of the target tissue, the anti-angiogenic WHLPFKC sequence is synthesised at the uppermost branching generation of a poly(ε-lysine) dendron. The root of these dendrons is designed to interact preferentially with macromolecules of the extracellular matrix, whilst the uppermost branching generation of the dendron increased the exposed density of the bioactive peptide. Bioactivity testing of the blockers is performed on HUVECs. The results show that the dendron tethered with VEGF blockers was still able to inhibit proliferation and angiogenesis. Their relatively larger structure did not prevent the interaction with VEGF.     

On the transition between a heterogeneous and homogeneous corona in mixed polymeric micelles

Two-dimensional NMR and small-angle neutron scattering experiments were performed on comicelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO, and poly(acrylic acid)-block-poly(acryl amide), PAA-b-PAAm, in aqueous solutions to study whether a transition between a heterogeneous (Janus-type) and homogeneous corona can be observed upon a variation of parameters that are anticipated to affect the miscibility of the PEO and PAAm coronal blocks. Investigated were the effect of a salt-induced decrease in micellar aggregation number, P agg for 1相似文献   

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

The 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     

Hydroxyl-terminated dendritic oligomers from bile acids: synthesis and properties

[reaction: see text] The high reactivity of the chloroacetyl group has been exploited for the synthesis of bile acid based first and second generation dendrons with multiple hydroxyl groups. The synthesis involves only a few steps and avoids the use of protecting groups for the terminal hydroxyl groups. These dendritic structures with facially amphiphilic bile acid backbones on the periphery were able to solubilize cresol red, a hydrophilic dye, in a nonpolar solvent. HPLC analysis of the dendrons suggests that hydrophobicity increases with increase in oligomer size, but in each generation, the dendrons with a higher degree of branching are less hydrophobic.     

Preparation of the amphiphilic macro‐rings of poly(ethylene oxide) with multi‐polystyrene lateral chains and their extraction for dyes

A novel method for synthesis of amphiphilic macrocyclic graft copolymers with multi‐polystyrene lateral chains is suggested, by combination of anionic ring‐open polymerization (AROP) with atom transfer radical polymerization (ATRP). The anionic ring‐opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using triethylene glycol and diphenylmethylpotassium (DPMK) as coinitiators; the monomer reactivity ratio of them are r_1(EO) = 1.20 ± 0.01 and r_2(EEGE) = 0.76 ± 0.02 respectively. The obtained linear well‐defined α,ω‐dihydroxyl poly(ethylene oxide) with pendant protected hydroxylmethyls (l‐poly(EO‐co‐EEGE)) was cyclized by reaction with tosyl chloride (TsCl) in the presence of solid KOH. The crude cyclized product containing the extended linear chain polymer was hydrolyzed and then purified by treat with α‐CD. The pure cyclic copolymer with multipendant hydroxymethyls [c‐poly(EO‐co‐Gly)] was esterified by reaction with 2‐bromoisobutyryl bromide, and then used as macroinitiators to initiate polymerization of styrene (St), and a series of amphiphilic macrocyclic grafted copolymers composed of a hydrophilic PEO as ring and hydrophobic polystyrene as side chains (c‐PEO‐g‐PS) were obtained. The intermediates and final products were characterized by GPC, NMR and MALDI‐TOF in detail. The experimental results confirmed that c‐PEO‐g‐PS shows stronger conjugation ability with the dyes than the corresponding comb‐PEO‐g‐PS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5824–5837, 2007     

Synthesis,Characterization, and Thermogravimetric Studies of a Phosphorus-Containing Dendron Built from 1,5-Diaminonaphthalene at the Core

A facile divergent synthesis of a phosphorus-containing dendron containing 1,5-diaminonaphthalene is described. The phosphorus-containing dendron, functionalized with a 1,5-diaminonaphthalene unit at the core and phenolic OH groups grafted at the periphery, has been accomplished in a versatile, simple fashion, using Schiff's condensation and nucleophilic substitution reactions with POCl₃, 3-hydroxy-benzaldehyde, 4-hydroxy-benzaldehyde, and 3-amino-phenol iteratively. The structures of intermediate dendrons were characterized by infrared, NMR (¹H, ¹³C, and ³¹P), liquid chromatography–mass spectrometry, and C, H, N analysis. The structure of the final dendron (6) was confirmed by infrared, NMR (¹H, ¹³C, and ³¹P), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and C, H, N analysis. The thermal stability and degradation of the resulting final dendron was checked by thermal gravitometric analysis/differential thermal analysis.