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1.
Novel thermo‐responsive poly(N‐isopropylacrylamide)‐block‐poly(l ‐lactide)‐block‐poly(N‐isopropylacylamide) (PNIPAAm‐b‐PLLA‐b‐PNIPAAm) triblock copolymers were successfully prepared by atom transfer radical polymerization of NIPAAm with Br‐PLLA‐Br macroinitiator, using a CuCl/tris(2‐dimethylaminoethyl) amine (Me6TREN) complex as catalyst at 25 °C in a N,N‐dimethylformamide/water mixture. The molecular weight of the copolymers ranges from 18,000 to 38,000 g mol?1, and the dispersity from 1.10 to 1.28. Micelles are formed by self‐assembly of copolymers in aqueous medium at room temperature, as evidenced by 1H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The critical micelle concentration determined by fluorescence spectroscopy ranges from 0.0077 to 0.016 mg mL?1. 1H NMR analysis in selective solvents confirmed the core‐shell structure of micelles. The copolymers exhibit a lower critical solution temperature (LCST) between 32.1 and 32.8 °C. The micelles are spherical in shape with a mean diameter between 31.4 and 83.3 nm, as determined by TEM and DLS. When the temperature is raised above the LCST, micelle size increases at high copolymer concentrations due to aggregation. In contrast, at low copolymer concentrations, decrease of micelle size is observed due to collapse of PNIPAAm chains. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3274–3283  相似文献   

2.
Amphiphilic biodegradable block copolymers [poly(sebacic anhydride)–poly(ethylene glycol)–poly(sebacic anhydride)] were synthesized by the melt polycondensation of poly(ethylene glycol) and sebacic anhydride prepolymers. The chemical structure, crystalline nature, and phase behavior of the resulting copolymers were characterized with 1H NMR, Fourier transform infrared, gel permeation chromatography, and differential scanning calorimetry. Microphase separation of the copolymers occurred, and the crystallinity of the poly(sebacic anhydride) (PSA) blocks diminished when the sebacic anhydride unit content in the copolymer was only 21.6%. 1H NMR spectra carried out in CDCl3 and D2O were used to demonstrate the existence of hydrophobic PSA domains as the core of the micelle. In aqueous media, the copolymers formed micelles after precipitation from water‐miscible solvents. The effects on the micelle sizes due to the micelle preparation conditions, such as the organic phase, dropping rate of the polymer organic solution into the aqueous phase, and copolymer concentrations in the organic phase, were studied. There was an increase in the micelle size as the molecular weight of the PSA block was increased. The diameters of the copolymer micelles were also found to increase as the concentration of the copolymer dissolved in the organic phase was increased, and the dependence of the micelle diameters on the concentration of the copolymer varied with the copolymer composition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1271–1278, 2006  相似文献   

3.
This article describes the syntheses and solution behavior of model amphiphilic dendritic–linear diblock copolymers that self‐assemble in aqueous solutions into micelles with thermoresponsive shells. The investigated materials are constructed of poly(benzyl ether) monodendrons of the second generation ([G‐2]) or third generation ([G‐3]) and linear poly(N‐isopropylacrylamide) (PNIPAM). [G‐2]‐PNIPAM and [G‐3]‐PNIPAM dendritic–linear diblock copolymers have been prepared by reversible addition–fragmentation transfer (RAFT) polymerizations of N‐isopropylacrylamide with a [G‐2]‐ or [G‐3]‐based RAFT agent, respectively. The critical micelle concentration (cmc) of [G‐3]‐PNIPAM220, determined by surface tensiometry, is 6.3 × 10?6 g/mL, whereas [G‐2]‐PNIPAM235 has a cmc of 1.0 × 10?5 g/mL. Transmission electron microscopy results indicate the presence of spherical micelles in aqueous solutions. The thermoresponsive conformational changes of PNIPAM chains located at the shell of the dendritic–linear diblock copolymer micelles have been thoroughly investigated with a combination of dynamic and static laser light scattering and excimer fluorescence. The thermoresponsive collapse of the PNIPAM shell is a two‐stage process; the first one occurs gradually in the temperature range of 20–29 °C, which is much lower than the lower critical solution temperature of linear PNIPAM homopolymer, followed by the second process, in which the main collapse of PNIPAM chains takes place in the narrow temperature range of 29–31 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1357–1371, 2006  相似文献   

4.
We developed a simple route to prepare stabilized micelles and nanovesicles in aqueous solutions. A hydrophobic poly(succinimide) (PSI) was conjugated with the hydrophilic poly(ethylene glycol) (PEG) as a new type of cross‐linkable unit. Spherical aggregates were formed when dissolving the amphiphilic PEG682b‐PSI130 copolymer in aqueous solutions directly, and polymer nanovesicles were prepared by a precipitation‐dialysis method using PEG455b‐PSI130 copolymer. Bifunctional primary amine was added to the micelle or nanovesicle solutions to prepare cross‐linked structures via aminolysis reaction of the succinimide units. The degree of cross‐linking was controlled by adjusting the molar ratio of the cross‐linker to the succinimide units. Increasing the degree of cross‐linking leads to the compaction of the micelle core thus reduced diameter. The cross‐linked polymer micelles or nanovesicles maintained their morphology in extremely diluted solutions because of their structural stability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010  相似文献   

5.
AB block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(amino acid) with a carboxyl group at the end of PEG were synthesized with α‐carboxylic sodium‐ω‐amino‐PEG as a macroinitiator for the ring‐opening polymerization of N‐carboxy anhydride. Characterizations by 1H NMR, IR, and gel permeation chromatography were carried out to confirm that the diblock copolymers were formed. In aqueous media this copolymer formed self‐associated polymer micelles that have a carboxyl group on the surface. The carboxyl groups located at the outer shell of the polymeric micelle were expected to combine with ligands to target specific cell populations. The diameter of the polymer micelles was in the range of 30–80 nm. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3527–3536, 2004  相似文献   

6.
A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M w/M n = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and zeta potential. The pK a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed owing to the ionization of the PAA blocks.  相似文献   

7.
Interactions between poly(N-substituted acrylamide)s and surfactants, such as sodium dodecyl sulfate (SDoS) and sodium decyl sulfate (SDeS), in aqueous solutions were investigated using a solvatochromic probe. The polymers used were poly(N,N-dimethylacrylamide) (PDMA), poly(N-isopropylacrylamide) (PIPA), poly(N-acryloylpyrrolidine) (PAPR), and poly(vinylpyrrolidone) (PVPy) for comparison. They were labeled with pyridinium dicyanomethylide chromophore as a solvatochromic probe, and the changes in the microenvironment polarity of the polymer upon association with surfactant micelles were investigated by monitoring the λmax in the absorption spectra of the probe molecule. It was found that the Gibbs free energy of micelle stabilization by polymer complexation for SDoS is 7.6, 4.1, and 2.2 kJ mol−1, and for SDeS 5.1, 2.9, and 0.8 kJ mol−1 with PIPA, PAPR, and PDMA, respectively. These results indicate that the complexation between polymer and surfactant is influenced not only by the alkyl-chain length of the surfactant, but also by the polymer side groups.  相似文献   

8.
Amphiphilic triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) (PMMA-b-PEO-b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with 1H and 13C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant Kv for pyrene in the micelle and in aqueous solution was about 105. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius Rh,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.  相似文献   

9.
Hydrophobically modified polyacrylamide (PAAm) was prepared by grafting PAAm with block copolymer of poly(ethylene oxide) and poly(propylene oxide), PEO‐PPO‐PEO, by melt method in the presence of benzoyl peroxide as initiator. The chemical structure of the graft copolymer was determined by FTIR and 1HNMR analyses. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (Γmax), the area per molecule at interface (Amin), and the effectiveness of surface tension reduction (ΠCMC) were determined at different temperatures from the adsorption isotherms of the prepared surfactants. The prepared surfactant was tested as emulsifier for water with xylene, cyclohexane, or petroleum crude oil synthetic emulsions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

10.
Poly(ethylene glycol) (PEG) is often used to biocompatibilize surfaces of implantable biomedical devices. Here, block copolymers consisting of PEG and l ‐cysteine‐containing poly(amino acid)s (PAA's) were synthesized as polymeric multianchor systems for the covalent attachment to gold surfaces or surfaces decorated with gold nanoparticles. Amino‐terminated PEG was used as macroinitiator in the ring‐opening polymerization, (ROP), of respective amino acid N‐carboxyanhydrides (NCA's) of l ‐cysteine (l ‐Cys), l ‐glutamate (l ‐Glu), and l ‐lysine (l ‐Lys). The resulting block copolymers formed either diblock copolymers, PEG‐b‐p(l ‐Gluxcol ‐Cysy) or triblock copolymers, PEG‐b‐p(l ‐Glu)xb‐p(l ‐Cys)y. The monomer feed ratio matches the actual copolymer composition, which, together with high yields and a low polydispersity, indicates that the NCA ROP follows a living mechanism. The l ‐Cys repeat units act as anchors to the gold surface or the gold nanoparticles and the l ‐Glu repeat units act as spacers for the reactive l ‐Cys units. Surface analysis by atomic force microscopy revealed that all block copolymers formed homogenous and pin‐hole free surface coatings and the phase separation of mutually immiscible PEG and PAA blocks was observed. A different concept for the biocompatibilization of surfaces was followed when thiol‐terminated p(l ‐Lys) homopolymer was first grafted to the surface and then covalently decorated with HOOC‐CH2‐PEG‐b‐p(Bz‐l ‐Glu) polymeric micelles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 248–257  相似文献   

11.
The mononuclear Au(III)-complex ([Au(C18H18N2O4)Cl]) and hydrogensquarate ([C22H21N2O8]) of dipeptide phenylalanyltyrosine (H–Phe–Tyr–OH) have been synthezised, characterized spectroscopically and structurally by means of solid-state linear-polarized IR-spectroscopy, 1H- and 13C-NMR, ESI-MS, HPLC-MS–MS, FAB-MS, TGS and DSC methods. The structure of the Au(III)-complex has been predicted theoretically by DFT calculations. The dipeptide coordinated in a tridentate manner via –NH2, –COO and N-groups. One Cl ion is attached to the metal centre as a terminal ligand, yielding a planar AuN2OCl chromophor. The hydrogensquarate consists in positive charged dipeptide moiety and negative one hydrogensquarate (HSq) anion stabilizing by strong intermolecular hydrogen bonds.  相似文献   

12.
Stable and aggregation‐free “gold nanoparticle–polymeric micelle” conjugates were prepared using a new and simple protocol enabled by the hydrogen bonding between surface‐capping ligands and polymeric micelles. Individual gold nanoparticles were initially capped using a phosphatidylthio–ethanol lipid and further conjugated with a star poly(styrene‐block‐glutamic acid) copolymer micelle using a one‐pot preparation method. The morphology and stability of these gold–polymer conjugates were characterized using transmission electron microscopy (TEM) and UV–vis spectroscopy. The self‐assembly of this class of polymer‐b‐polypeptide in aqueous an medium to form spherical micelles and further their intermicelle reorganization to form necklace‐like chains was also investigated. TEM and laser light scattering techniques were employed to study the morphology and size of these micelles. Polymeric micelles were formed with diameters in the range of 65–75 nm, and supermicellular patterns were observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3570–3579, 2007  相似文献   

13.
Mixed micelles of polystyrene‐b‐poly(N‐isopropylacrylamide) (PS‐b‐PNIPAM) and two polystyrene‐b‐poly(ethylene oxide) diblock copolymers (PS‐b‐PEO) with different chain lengths of polystyrene in aqueous solution were prepared by adding the tetrahydrofuran solutions dropwise into an excess of water. The formation and stabilization of the resultant mixed micelles were characterized by using a combination of static and dynamic light scattering. Increasing the initial concentration of PS‐b‐PEO in THF led to a decrease in the size and the weight average molar mass (〈Mw〉) of the mixed micelles when the initial concentration of PS‐b‐ PNIPAM was kept as 1 × 10?3 g/mL. The PS‐b‐PEO with shorter PS block has a more pronounced effect on the change of the size and 〈Mw〉 than that with longer PS block. The number of PS‐b‐PNIPAM in each mixed micelle decreased with the addition of PS‐b‐PEO. The average hydrodynamic radius 〈Rh〉 and average radius of gyration 〈Rg〉 of pure PS‐b‐PNIPAM and mixed micelles gradually decreased with the increase in the temperature. Both the pure micelles and mixed micelles were stable in the temperature range of 18 °C–39 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1168–1174, 2010  相似文献   

14.
Poly(β-benzyl-l-aspartate)-block-poly(vinylpyrrolidone) diblock copolymers (PAsp(OBzl)-b-PVP) having both hydrophobic and hydrophilic segments of various lengths were synthesized by a combination of ATRP and ROP. These amphiphilic diblock copolymers formed polymeric micelles consisting of a hydrophobic PAsp(OBzl) core and a hydrophilic PVP shell in aqueous solution. The block copolymer was characterized using 1H NMR and gel permeation chromatography (GPC) analysis. Due to its core–shell structure, this block polymer forms unimolecular micelles in aqueous solutions. The micelle properties of PAsp(OBzl)-b-PVP diblock copolymer were extensively studied by dynamic light scattering (DLS), fluorescence spectroscopy, and transmission electron microscopy (TEM). PAsp(OBzl)-b-PVP copolymers displayed the lowest CMC and demonstrated little cytotoxicity when exposed to SW-1990 pancreatic cancer cells. In order to assess its application in biomedical area, the anti-inflammation drug prednisone acetate was loaded as the model drug in the polymeric nanoparticles. In vitro release behavior of prednisone acetate was investigated, which showed a dramatic responsive fast/slow switching behavior according to the pH-responsive structural changes of a micelle core structure. All of theses features are quite feasible for utilizing it as a novel intelligent drug-delivery system.  相似文献   

15.
Gaussia luciferase assay was used to measure the anti‐hepatitis C (anti‐HCV) potency of tributyltin(IV)[3‐(3′,5′‐dimethylphenylamido)propanoate] in infected Huh 7.5 cells (human hepatocellular cell). Interaction of the organotin(IV) complex with cetyl N,N,N‐trimethylammonium bromide (CTAB) micelles was studied using UV–visible and steady‐state florescence spectroscopy. The anti‐HCV study showed a log IC50 value of 0.96 nm for the complex. The complex–CTAB interaction parameter showed that partition of the complex from bulk water to the CTAB micelle was a spontaneous process, and the red shift in visible spectra of the complex confirmed its increased solubility into micelles. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
Micelle structure in aqueous colloids in the isotropic liquid phase (L1) of a nonionic amphipile (n-dodecyl octa(oxyethylene glycol) monoether (C12E8) has been investigated as a function of concentration and temperature using light scattering (LS), viscometry, NMR, and small-angle X-ray scattering (SAXS).The spherical micelles, having a radius of 28–31 Å, remain in a wide concentration range from very dilute to ca. 42 wt %. The micelle size increases sligthly with increasing temperature in the range of 25–60 °C. In the concentrated colloids, the spherical micelles are likely to be arranged in a certain ordered structure. Even at such a high concentration as 30 wt %, the isotropic colloid shows Newtonian flow. This suggests that interaction between micelles in the ordered structure is very weak and the structure is very fragile. Moreover, coexistence of the isotropic phase and the ordered structure in L1 phase is discussed.  相似文献   

17.
A number of mononuclear manganese(II) and manganese(III) complexes have been synthesized from tridentate N2O aminophenol ligands (HL1–HL5) formed by reduction of corresponding Schiff bases with NaBH4. Three types of tridentate N2O aminophenols have been prepared by reducing with NaBH4which are (a) Schiff bases obtained by bromo salicylaldehyde reaction with N,N-dimethyl/N,N-diethyl ethylene diamine (HL1, HL2), (b) Schiff bases obtained by condensing salicylaldehyde/bromo salicylaldehyde and picolyl amine (HL3, HL4), (c) pyridine-2-aldehyde and 2-aminophenol (HL5). All the manganese complexes have been prepared by direct addition of manganese perchlorate to the corresponding ligands and were characterized by the combination of i.r., u.v.–vis spectroscopy, magnetic moments and electrochemical studies. The u.v.–vis spectra of all of the manganese(III) complexes show two weak d–d transitions in the 630–520 nm region, which support a distorted octahedral geometry. The electron transfer properties of all of the manganese(III) complexes (1–4 and 6) exhibit mostly similar characteristics consisting two redox couples corresponding to the MnIII → MnII reductions and MnIII → MnIV oxidations. The electronic effect on the potential has also been studied by changing different substituents in the ligands. In all cases, an electron-donating group stabilizes the higher oxidation state and electron withdrawing group prefers the lower oxidation state. The cyclic voltammogram of [MnII(L5)2] shows an irreversible oxidation MnII → MnIII at −0.88 V, followed by another quasi-reversible oxidation MnIII → MnIV at +0.48 V. The manganese(III) complex (3) [Mn(L3)2]ClO4has been characterized by X-ray crystallography.  相似文献   

18.
Poly(vinyl alcohol-b-styrene) (poly(VA-b-St)) diblock copolymers with different syndiotacticity of poly(vinyl alcohol) (PVA) block were synthesized via consecutive telomerization, atom transfer radical polymerization, and saponification. These amphiphilic block copolymeric micelles were prepared by dialysis against water. Dynamic light scattering and transmission electron micrograph measurements confirmed the formation of a micelles, and the size of a micelle was less than 100 nm and increased with the molecular weight of polystyrene (PS) block. From the fluorescence emission spectrum measurements using pyrene as a fluorescence probe, the copolymers formed micelles with critical micelle concentration (CMC) in the range of 0.125–4.47 mg/l. The CMC values increase with decrease of the molecular weight of the PS block and increase of the syndiotacticity of PVA block. Kinetic stability study of micelles showed increased stability for block copolymers containing PVA block with higher syndiotacticity.  相似文献   

19.
The multi‐thermo‐responsive block copolymer of poly[2‐(2‐methoxyethoxy)ethyl methacrylate]‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PMEO2MA‐b‐PVEA) displaying phase transition at both the lower critical solution temperature (LCST) and the upper critical solution temperature (UCST) in the alcohol/water mixture is synthesized by reversible addition‐fragmentation chain transfer polymerization. The poly[2‐(2‐methoxyethoxy)ethyl methacrylate] (PMEO2MA) block exhibits the UCST phase transition in alcohol and the LCST phase transition in water, while the poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] (PVEA) block shows the UCST phase transition in isopropanol and the LCST phase transition in the alcohol/water mixture. Both the polymer molecular weight and the co‐solvent/nonsolvent exert great influence on the LCST or UCST of the block copolymer. By adjusting the solvent character including the water content and the temperature, the block copolymer undergoes multiphase transition at LCST or UCST, and various block copolymer morphologies including inverted micelles, core‐corona micelles, and corona‐collapsed micelles are prepared. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4399–4412  相似文献   

20.
Two new phenol based macroacyclic Schiff base ligands, 2,6-bis({N-[2-(phenylselenato)ethyl]}benzimidoyl)-4-methylphenol (bpebmpH, 1) and 2,6-bis({N-[3-(phenylselenato)propyl]}benzimidoyl)-4-methylphenol (bppbmpH, 2) of the Se2N2O type have been prepared by the condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate (for specific reactions) phenylselenato(alkyl)amine. These ligands with Cu(II) acetate monohydrate in a 2:1 molar ratio in methanol form complexes of the composition [(C6H2(O)(CH3){(C6H5)CN(CH2)nSe(C6H5)}{(C6H5)CO}2Cu] (3 (n = 2), 4 (n = 3)) with the loss of phenylselenato(alkyl)amine and acetic acid. In both these complexes, one arm of the ligand molecule undergoes hydrolysis, and links with Cu(II) in a bidentate (NO) fashion, as confirmed by single crystal X-ray crystallography of complex 3. The selenium atoms do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN2O2 core. The average Cu–N and Cu–O distances are, respectively, 1.973(3) and 1.898(2) Å. The N–Cu–N and O–Cu–O angles are, respectively, 167.4(11)° and 164.5(12)°. The compounds 1–4 have been characterized by elemental analysis, conductivity measurements, mass spectrometry, IR, electronic, 1H and 77Se{1H} NMR spectroscopy and cyclic voltammetry. The interaction of complex 3 with calf thymus DNA has been investigated by a spectrophotometric method and cyclic voltammetry.  相似文献   

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