Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.
DSC heating curve for the PEO‐b‐PCL block copolymer. 相似文献
pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and Rh of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔRh/Rh ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10?4 g · mL?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.
A novel approach to organic‐inorganic Janus‐like particles based on the alkalization process of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) micelles containing FeCl3 precursors in the P2VP cores in toluene is presented. It is found that by addition of a small amount of NaOH solution to a solution of the spherical PS‐b‐P2VP/FeCl3 micelles, organic‐inorganic Janus‐like particles with a produced α‐FeOOH domain on one side and PS‐b‐P2VP block copolymers on the other can be prepared. The Janus‐like nanoparticles obtained by this facile approach may have potential application in biomedical areas. 相似文献
In this work, the synthesis of 3‐methacryloxypropylheptaphenyl POSS, a new POSS macromer (denoted MA‐POSS) is reported. The POSS macromer is used to synthesize PEO‐b‐P(MA‐POSS)‐b‐PNIPAAm triblock copolymers via sequential atom transfer radical polymerization (ATRP). The organic‐inorganic, amphiphilic and thermoresponsive ABC triblock copolymers are characterized by means of nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) show that the hybrid ABC triblock copolymers are microphase‐separated in bulk. Cloud point measurements show that the effect of the hydrophiphilic block (i.e. PEO) on the LCSTs is more pronounced than the hydrophobic block (i.e. P(MA‐POSS)). Both transmission electron microscopy (TEM) and dynamic light scattering (DLS) show that all the triblock copolymers can be self‐organized into micellar aggregates in aqueous solutions. The sizes of the micellar aggregates can be modulated by changing the temperature. The temperature‐tunable self‐assembly behavior is interpreted using a combination of the highly hydrophobicity of P(MA‐POSS), the water‐solubility of PEO and the thermoresponsive property of PNIPAAm in the triblock copolymers. 相似文献
Amphiphilic poly(2‐alkyl‐2‐oxazoline) diblock copolymers of 2‐methyl‐2‐oxazoline (MOx) building the hydrophilic block and either 2‐nonyl‐2‐oxazoline (NOx) for the hydrophobic or 2‐(1H,1H′,2H,2H′‐perfluorohexyl)‐2‐oxazoline (FOx) for the fluorophilic block were synthesized by sequential living cationic polymerization. The polymer amphiphiles form core/shell micelles in aqueous solution as evidenced using small‐angle neutron scattering (SANS). Whereas the diblock copolymer micelles with a hydrophobic NOxn block are spherical, the micelles with the fluorophilic FOxn are slightly elongated, as observed by SANS and TEM. In water, the micelles with fluorophilic and lipophilic cores do not mix, but coexist.
The micellization on surfaces of two series of quasi‐diblock copoly(2‐oxazoline)s consisting of 2‐phenyl‐2‐oxazoline (PhOx) segments linked to either 2‐methyl‐2‐oxazoline (MeOx) or 2‐ethyl‐2‐oxazoline (EtOx) segments is investigated in detail. Those micelles are not pre‐existing in the initial ethanol solution but are formed during the spin‐coating process by the evaporation of the solvent inducing the precipitation of the less soluble PhOx segments. The morphology and size of the surface micelles vary according to the fraction of PhOx in the copolymers. Moreover, it is demonstrated that the chemical nature of the more soluble MeOx or EtOx segments also has an influence on the morphology of the resulting surface micelles.
Two different synthetic pathways give access to the amphiphilic block copolymer poly(ethylene oxide)‐block‐poly(tert‐butoxycarbonylaminomethylacrylate). In the first approach, two end‐functionalized segments are linked via click chemistry; and in the second approach, a poly(ethylene oxide) (PEO) based macroinitiator is chain extended via atom transfer radical polymerization (ATRP). In both cases the linking unit consists of an amide group, which is necessary to effectively deprotect the corresponding polymer precursor without cleavage of both segments. For this, amide‐containing ATRP initiators are employed and successful synthesis by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) analyses before comparing both pathways is demonstrated. After deprotection, a novel double hydrophilic block copolymer, poly(ethylene oxide)‐block‐poly(dehydroalanine), is obtained, which is investigated using SEC (aqueous and DMSO) and 1H‐NMR spectroscopy. Containing a potentially zwitterionic PDha segment and a high density of both amino and carboxylic groups, pH‐dependent aggregation of the block copolymer is expected and is studied using dynamic light scattering, revealing interesting solution properties. The corresponding polymers are applied in various areas including drug delivery systems or in biomineralization. 相似文献
We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr2(PPh3)2, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.
SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively. 相似文献
Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.
Copolymerization of carbon dioxide (CO2) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol?1) is synthesized via an alternating CO2/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.
Core–corona inversion of micelles of diblock copolymer poly(acrylic acid)‐block‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM), has been successfully realized by switching either pH or temperature. The strong interaction of doxorubicin with the PAA block and the pH‐sensitive drug release from the polymer make the system very useful as a controlled drug delivery system. The encapsulation of hydrophobic Nile Red molecules above the lower critical solution temperature of PNIPAM suggests that this polymer may be useful for removing hydrophobic pollutants.
Temperature‐ and pH‐sensitive diblock copolymers PAANa75‐b‐PNIPAMm are prepared by a combination of reverse and normal ATRP in aqueous solution at room temperature. The block copolymer is also stimuli‐sensitive with respect to salt in the aqueous solution, and forms spherical star‐like micelles with a PNIPAM core and an expanded PAANa shell for PAANa75‐b‐PNIPAM76 as well as spherical crew‐out micelles with a PNIPAM core for PAANa75‐b‐PNIPAM5110, as indicated by a fluorescence probe technique and TEM. A three‐stage model mechanism of phase transition driven by small molecule salt is proposed.
The reorganization kinetics of the “original” lamellar diblock copolymer poly(ε‐caprolactone)‐block‐poly(4‐vinylpyridine) crystals formed at 260 K is studied in the melting region from 270 K (10 K below the onset of the melting peak of original crystals) to 310 K (the melting peak temperature) on the time scale starting from 10?4 to 102 s by ultrafast differential scanning calorimetry. Different reorganization pathways are observed in this temperature range. Annealing at temperatures below 295 K leads to further stabilization of original crystals by secondary crystallization. At annealing temperatures higher than 295 K, crystals partially melt and the reorganization occurs via the melting–recrystallization. For even higher temperature, such as 310 K, the melting is completed within a few milliseconds and recrystallization starts from the nuclei formation. The sigmoidal recrystallization kinetics is analyzed by the Avrami equation. It is found that the copolymer experiences about one order of magnitude slower recrystallization rate and has higher melting peak temperatures of crystals formed after recrystallization than the homopolymer. The slower recrystallization kinetics in the copolymer is discussed from the viewpoint of the nanoscale spatial constraint and the intermediate state prior to the recrystallization.
In this study, we developed a novel blending strategy, namely, the gradual blending method, to tune the micellar structure. Different from the most commonly used premixing blending method, which different block copolymers are premixed in a common solvent before their individual self‐assembly, the gradual blending method involves gradually adding one type of block copolymer into the pre‐generated micellar solution formed from another type of block copolymer. Moreover, we obtained a novel mesh‐like vesicle from the self‐assembly of the mixtures of P4VP43‐b‐PS260‐b‐P4VP43 and P4VP43‐b‐PS366‐b‐P4VP43 in 1,4‐dioxane/water solution using the gradual blending method. 相似文献
This paper describes an unusual contrast inversion phenomenon in TEM imaging of PFS‐b‐PDMS block copolymer bulk samples. It is clearly observed especially in samples that show a lamellar morphology that the contrast inversion is accompanied by a contraction of the PDMS domains and an expansion of the Fe‐rich domains. The location of the iron‐ and silicon‐rich domains was monitored by EDX analysis. We infer that the contrast inversion was caused by electron beam radiation‐induced damage to, and possible cross‐linking of, PDMS chains. A simple way to selectively deposit metal on electron beam patterned polymer film was demonstrated.
Well‐defined amphiphilic PLA‐b‐PMPC diblock copolymers were synthesized. Bimimetic micelles were prepared and applied for release of anti‐cancer drugs (DOX). TEM and DLS analysis revealed a regular spherical shape with small diameter (less than 50 nm) of the micelle. The biocompatibility of PLA‐b‐PMPC micelles was studied, and it was found that the micelles possessed excellent cytocompatibility due to the zwitterionic phosphorylcholine group. DOX could be efficiently loaded into the micelles with a loading efficiency of 44–67%. The DOX‐loaded micelles showed lower cytotoxicity than free drugs and efficiently delivered and released the drug into cancer cells. With these properties, the PLA‐b‐PMPC polymer micelles are attractive as drug carriers for pharmaceutical application.
A novel dispersion polymerization of a diisocyanate and a diol for the preparation of spherical polyurethane particles is reported. An amphiphilic block copolymer, namely, poly(1,4‐isoprene)‐block‐poly(ethylene oxide) was used as a steric stabilizer. Monodisperse spherical particles were obtained in the size range from 0.2 to 2.0 μm. The polyurethane particle formation was dependent on the concentration of the steric stabilizer, the block segment molecular weight and the nature of dispersion medium. The polyurethane particles were stabilized by a mechanism involving physical adsorption of the steric stabilizer on the surface of the growing particle. 相似文献
Summary: RAFT polymerization was used to prepare PMMA‐b‐PNIPAM copolymers. Two different chain transfer agents, tBDB and MCPDB, were used to mediate the sequential polymerizations. Micellar solutions and gels were prepared from the resulting copolymers in aqueous solution. When heated above Tc of PNIPAM (about 31 °C), DLS revealed that PNIPAM coronas collapsed, resulting in aggregation of the original micelles. The micellar gels underwent syneresis above Tc as water was expelled from the ordered gel structure, the lattice periodicity of which was determined by SANS. A large decrease in lattice spacing was observed above Tc. The gel became more viscoelastic at high temperature, as revealed by shear rheometry which showed a large increase in G″.
Summary: Linear, three‐ and four‐armed block copolymers based on PEG and PSA were synthesized by melt polycondensation reactions. The CMC of the copolymer was measured using the dye solubilization method. The copolymers were found to self‐aggregate in water to form micelles above the CMC. The micellar solutions were prepared with different methods and investigated by DLS and AFM. The DLS method was used to measure the mean hydrodynamic diameters of the micelles. It was found that preparation method and condition of the micellar solution, as well as the structure and composition of the copolymer had effects on the hydrodynamic diameter of the copolymer micelles. AFM studies showed that the morphology of the micelle was spherical.
Synthesis of 3‐armed stars based on poly(ethylene glycol) and poly(sebacic anhydride). 相似文献
Summary: Bis(hydroxy)telechelic bisphenol A polycarbonate (PC) was prepared via melt polycondensation of bisphenol A (BPA) and diphenyl carbonate (DPC) using lanthanum(III ) acetylacetonate as a catalyst for transesterification. Subsequently, the polycarbonate was converted to a bifunctional macroinitiator for atom transfer radical polymerization (ATRP) with the reagent, α‐chlorophenylacetyl chloride. The macroinitiator was used for the polymerization of styrene (S) and methyl methacrylate (MMA) to give PS‐block‐PC‐block‐PS and PMMA‐block‐PC‐block‐PMMA triblock copolymers. These block copolymers were characterized by NMR and GPC. When styrene and methyl methacrylate were used in large excess, significant shifts toward high molecular weights were observed with quantitative consumption of the macroinitiator. Several ligands were studied in combination with CuCl as the ATRP catalyst. Kinetic studies reveal the controlled nature of the polymerization reaction for all the ligands used.
Formation of a bifunctional ATRP macroinitiator by esterification of bis(hydroxy)telechelic PC with α‐chlorophenylacetyl chloride. 相似文献
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