Micelles with azobenzene at the coronas or the cores were prepared by the micellization of nonamphiphilic diblock copolymers through hydrogen bond cross-linking. We used 4-(phenylazophenoxymethyl)styrene (AS) as the azobenzene. A poly(vinylphenol)-block-poly(AS-co-styrene) diblock copolymer (PVPh-b-P(AS-co-St)) was prepared by combination of the nitroxide-mediated living radical polymerization and the hydrolysis. The copolymer contained ca. 1 mol% of the azobenzene units in the P(AS-co-St) blocks on the basis of 1H NMR analysis. The PVPh-b-P(AS-co-St) copolymer showed no micellization in 1,4-dioxane, the nonselective solvent. Dynamic light scattering demonstrated that the copolymer formed micelles in the presence of 1,4-butanediamine (BDA) in this solvent. 1H NMR analysis revealed that the azobenzene moieties were located at the coronas of the micelles, because the signals of the aromatic protons originating from the azobenzene had no changes in the shape and the intensity by the micellization. UV analysis supported the presence of the azobenzene at the micellar coronas. The size of the PVPh-b-P(AS-co-St) micelles was independent of the copolymer concentration. On the other hand, the aggregation number of the micelles was dependent not only on the copolymer concentration but also on the kind of the diamine. A poly(AS-co-vinylphenol)-block-polystyrene diblock copolymer (P(AS-co-VPh)-b-PSt) formed the micelles with the azobenzene at the cores of the micelles by BDA. UV analysis demonstrated that the azobenzene at the micellar cores still had the potential to function as photorefractive switching. 相似文献
Micelles with azo dye and UV absorbent at their cores or coronas were prepared from non-amphiphilic random diblock copolymers
by α,ω-diamine. Poly[4-(phenylazophenoxymethyl)styrene-ran-4-(2-hydroxybenzophenoxymethyl)styrene-ran-vinylphenol]-block-polystyrene (P(AS-r-HBS-r-VPh)-b-PSt) and poly(vinylphenol)-block-poly[4-(phenylazophenoxymethyl)styrene-ran-4-(2-hydroxybenzophenoxymethyl)styrene-ran-styrene] (PVPh-b-P(AS-r-HBS-r-St)) diblock copolymers were prepared by living radical polymerization mediated by 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl.
The former copolymer had a molecular weight of Mn[P(AS-r-HBS-r-VPh)-b-PSt] = 10,000-b-250,000 by 1H NMR and a molar ratio of AS:HBS:VPh = 0.01:0.01:0.98, while the latter had a molecular weight of Mn[PVPh-b-P(AS-r-HBS-r-St)] = 10,000-b-111,000 and a molar ratio of AS:HBS:St = 0.02:0.03:0.95. The copolymers showed no self-assembly in 1,4-dioxane because this
solvent was non-selective to the copolymers. Dynamic light scattering demonstrated that the copolymers formed micelles in
the solvent in the presence of α,ω-diamine. The hydrodynamic radii of the micelles slightly increased with the copolymer concentration
decrease, while the aggregation numbers were almost independent of the copolymer concentration. It was found that P(AS-r-HBS-r-VPh)-b-PSt formed smaller micelles with a lower aggregation number than PVPh-b-P(AS-r-HBS-r-St) because of the steric hindrance of the AS and HBS units present at the micellar coronas. 相似文献
A poly(vinylphenol)-block-polystyrene diblock copolymer (PVPh-b-PSt) forms micelles in the presence of 1,4-butanediamine (BDA) in 1,4-dioxane, a nonselective solvent. The micellization proceeds through the formation of hydrogen bond cross-linking between the PVPh blocks via BDA, and the dissociation and reconstruction of the micelles is reversibly controlled by temperature. We explored the thermodynamics and kinetics on the micellization of the nonamphiphilic PVPh-b-PSt copolymer by BDA. Light scattering studies demonstrated that an equilibrium existed between the micelles and the unimers. The equilibrium constants were determined for the dissociation and the reconstruction of the micelles on the basis of variation in the aggregation number of the micelles. The equilibrium constant of the dissociation showed a good agreement with the reciprocal of the equilibrium constant of the reconstruction. Based on the equilibrium constants, the standard Gibbs energy, enthalpy, and entropy of the dissociation and reconstruction were estimated. The standard enthalpy was Δ H° = 30–40 kJ mol−1 for the dissociation. The enthalpy of the reconstruction was obtained as a negative value, however, there was a negligible difference in the absolute values of Δ H° between the dissociation and the reconstruction. The rate constant of the micellization was ca. 102 times larger than the back reaction, and increased with a decrease in the temperature. 相似文献
Oxidation-induced micellization was attained for a diblock copolymer containing 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO). Poly(4-vinylbenzyloxy-TEMPO)-block-polystyrene (PVTEMPO-b-PSt) showed no self-assembly in carbon tetrachloride, a nonselective solvent. Dynamic light scattering demonstrated that the copolymer self-assembled into micelles of 49.5-nm hydrodynamic diameter when chlorine gas was added to the copolymer solution. The UV and electron spin resonance (ESR) analyses verified that as TEMPO was oxidized into the one-electron oxidant, that is, oxoaminium chloride (OAC) by the chlorine, the nonamphiphilic block copolymer became amphiphilic in nature, and thus, the polymers underwent micellization. An investigation of the relation between the micellization and the oxidation degree of the TEMPO into the OAC revealed that the micellization was induced by only 16% of the OAC. It was confirmed that the POAC-b-PSt micelles were spherical in shape by transmission electron microscopy observation. The micelles served as a two-electron oxidizing agent for benzyl alcohol to quantitatively give benzaldehyde. The micellar structure was maintained after the oxidation of benzyl alcohol without any dissociation into unimers because the OAC was converted into an insoluble hydroxylamine–hydrochloride salt. On the other hand, the micelles reacted with N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPD) to produce Wurster’s blue chloride by a one-electron transfer from TMPD to the OAC, converting themselves into PVTEMPO-b-PSt unimers. 相似文献
In this study,the maleic anhydride(MAH)and styrene(St)dual monomers grafted polypropylene(PP)and poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS),i.e.PP-g-(MAH-co-St)and SEBS-g-(MAH-co-St)are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS(70/10/10/10)model quaternary blends.Both PS and SEBS are encapsulated by the hard shell of PP-g-(MAH-co-St)in the dispersed domains(about 2μm)of the PA6/PS/PP-g-(MAH-co-St)/SEBS(70/10/10/10)quaternary blend.In contrast,inside the dispersed domains(about 1μm)of the PA6/PS/PP/SEBS-g-(MAH-co-St)(70/10/10/10)quaternary blend,the soft SEBS-g-(MAH-co-St)encapsulates both the hard PS and PP phases and separates them.With increasing the content of the compatibilizers equally,the morphology of the PA6/PS/(PP+PP-g-(MAH-co-St))/(SEBS+SEBS-g-(MAH-co-St))(70/10/10/10)quaternary blends evolves from the soft(SEBS+SEBS-g-(MAH-co-St))encapsulating PS and partially encapsulating PP(about 1μm),then to PS exclusively encapsulated by the soft SEBS-g-(MAH-co-St)and then separated by PP-g-(MAH-co-St)inside the smaller domains(about 0.6μm).This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers.The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain,which results in the further improved mechanical properties.Compared to the uncompatibilized blend,the blend with both 10 wt%PP-g-(MAH-co-St)and 10 wt%SEBS-g-(MAH-co-St)has the best mechanical properties with the stress at break,strain at break and impact failure energy improved significantly by 97%,71%and 261%,respectively.There is a strong correlation between the structure and property in the blends. 相似文献
Light scattering and transmission electron microscope (TEM) measurements were preformed for micelles of a nonamphiphilic poly(vinylphenol)-block-polystyrene diblock copolymer (PVPh-b-PSt) to determine the shape of the micelles. The micelles were prepared by the self-assembly of the copolymer in 1,4-dioxane,
a nonselective solvent, in the presence of 1,4-butanediamine. The logarithm of the normalized time correlation function of
the scattered field, lnG1(τ), linearly decayed versus the delay time, τ. The diffusion coefficient measured in the range of the scattering angles from 30° to 150° was almost independent of the
square of the magnitude of the scattering vector. The linear decay of lnG1(τ) vs τ and the angular-independence of the diffusion coefficient suggested that the monodisperse spherical micelles were formed
by the micellization. The TEM observations confirmed the formation of uniform spheres. 相似文献
Well-defined polystyrene-block-poly(styrene-co-acrylonitrile) PS-block-P(S-co-AN) and poly(styrene-co-acrylonitrile-co-5-vinyltetrazole) PS-block-P(S-co-AN-co-5VT) block copolymers with various content of acrylonitrile units in the statistical block were synthesized by nitroxide mediated radical polymerization (NMRP) and post-functionalized using efficient “click” chemistry process. In the second step, acrylonitrile units were successfully modified using 1,3-dipolar cycloaddition (“click” chemistry) type polymer analogue reaction. The original pristine diblock copolymers can be molecularly dissolved in THF and dioxane while the “tetrazolated” versions aggregate to clusters as determined by dynamic light scattering (DLS). Small-angle X-ray scattering (SAXS) and Transmission Electron Microscopy (TEM) revealed ordered lamellar morphology with interlamellar spacing d = 60 nm increasing to d = 80 nm for “tetrazolated” diblock copolymers. The morphological features of diblock copolymer thin layers observed by Atomic Force Microscopy (AFM) depend on the tunable content of both acrylonitrile and 5-vinyltetrazole units and on the quality (polarity) of the solvents used. 相似文献
The micelle formation of poly[(4-pyridinemethoxymethyl)styrene]-block-polystyrene (PPySt-b-PSt) was studied in the nonselective solvent using perfluoroalkyl carboxylic acids. PPySt-b-PSt showed no self-assembly into micelles in THF, because this solvent was nonselective for the copolymer. Dynamic light scattering demonstrated that the diblock copolymer formed the micelles in the solvent in the presence of perfluoroalkyl carboxylic acids in which the number of carbons in the perfluoroalkyl chains was over eight. 1H NMR revealed that the micellization proceeded through the salt formation of the pyridinium perfluoroalkyl carboxylate and through the aggregation of the perfluoroalkyl chains in the counter anions. The hydrodynamic radius and the aggregation number of the micelles increased with an increase in the length of the perfluoroalkyl chain. The copolymer needed less carboxylic acid with longer perfluoroalkyl chain to form the micelles. The copolymer produced the micelles with lower aggregation number and higher critical micelle concentration at higher temperature, although the micellar size was almost independent of the temperature. The micelles were unstable with respect to the variation in the temperature, and were dissociated into the unimers with the increase in the temperature. The micelles, however, were reconstructed by decreasing the temperature. This dissociation–reconstruction of the micelles was controlled reversibly not only by the temperature but also by the concentration of the perfluoroalkyl carboxylic acid. An increase in the acid concentration suppressed the dissociation into the unimers, while promoting the reconstruction of the micelles. 相似文献
Novel wormlike nanostructures were self‐assembled in bulk films of a well defined diblock copolymer with azobenzene moieties, which was prepared by atom transfer radical polymerization (ATRP). For comparison, a homopolymer with almost the same repeat units of azobenzene as those in the copolymer was also prepared. They both had well defined structures and exhibited a smectic liquid crystalline phase. Upon annealing the copolymer films, poly(methyl methacrylate) formed a matrix with excellent optical properties, and the azobenzene segment in the minority phase self‐assembled into a wormlike mesogenic domain in the bulk films. Such block copolymer films exhibited stability and transparency by eliminating the scattering of visible light, indicating their potential application as photoresponsive functional materials. Although wormlike morphologies have been obtained in micelles from block copolymer solutions, to the best of our knowledge, such wormlike nanostructures have never been explored in bulk films.
A novel thermo-responsive diblock copolymer of poly(N-vinyl-2-pyrrolidinone)-block-poly(N-isopropylacrylamide) (PNVP-b-PNIPAM) was synthesized. FT-IR, 1H-NMR and SEC results confirmed the successful synthesis of PNVP-b-PNIPAM diblock copolymer via anionic polymerization. The polymeric micelles formed from PNVP-b-PNIPAM copolymer in aqueous solution were developed and characterized as a potential thermo-responsive and biocompatible drug delivery system. Micellization of the diblock copolymer in aqueous solution was characterized by dynamic laser scattering (DLS), turbidity measurement, tension measurement and transmission electron microscopy (TEM). The thermo-responsive polymeric micelles with the size ranges of 200 to 260 nm and thickness of 30 nm are localized, selected and targeted for drug release, having a great potential in response to external-stimulus such as temperatures from 35 to 39°C. The critical micellization concentration (cmc) of PNVP-b-PNIPAM in aqueous solution is 0.0026 wt% determined by turbidity measurement. The size of micelles determined by DLS increased from 163 to 329 nm with increasing concentration of PNVP-b-PNIPAM from 0.25 to 0.5 wt% in aqueous solution at 40°C, which is determined by DLS. 相似文献
We report novel micellar carriers, comprising pendant cinnamyl moieties in the core-forming block, designed to increase the solubilization of caffeic acid phenethyl ester (CAPE) in aqueous media. Amphiphilic poly(ethylene oxide)-block-poly(α-cinnamyl-ε-caprolactone-co-ε-caprolactone) (PEO-b-P(CyCL-co-CL) diblock copolymers were synthesized by ring-opening copolymerization of α-propargyl-ε-caprolactone and ε-caprolactone from a monofunctional PEO macroinitiator and subsequent attachment of cinnamyl groups via click reaction. In addition, a linear PEO-b-PCL diblock copolymer was synthesized and used in this study for comparison. Next, nanosized micelles from PEO-b-P(CyCL-co-CL) and PEO-b-PCL were formed via the solvent evaporation method and then loaded with CAPE. Dynamic and electrophoretic light scattering, and transmission electron microscopy were used to characterize both blank and loaded carriers. The potential of the micelles comprising pendant cinnamyl group to solubilize CAPE in water was evaluated in a comparative fashion to that of nonmodified PEO-b-PCL diblock copolymer. 相似文献
A series of novel pH‐ and temperature‐responsive diblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly[(L ‐glutamic acid)‐co‐(γ‐benzyl L ‐glutamate)] [P(GA‐co‐BLG)] were prepared. The influence of hydrophobic benzyl groups on the phase transition of the copolymers was studied for the first time. With increasing BLG content in P(GA‐co‐BLG) block, the thermal phase transition of the diblock copolymer became sharper at a designated pH and the critical curve of phase diagram of the diblock copolymer shifted to a higher pH region. Notably, when the BLG content in P(GA‐co‐BLG) block was more than 30 mol.‐%, the diblock copolymer responded sharply to a narrow pH change in the region of pH 7.4–5.5.
Blocks copolymers styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and styrene-b-(ethylene-co-propylene) (SEP, SEPSEP), with different styrene content and number of blocks in the chain, were functionalized with glycidyl methacrylate (GMA) by melt radical grafting. The influence of monomer concentration, radical initiator and copolymer structure on the grafting degree was examined. The grafted copolymers were characterised by DSC and capillary rheometry. Blends of PET with functionalized SEBS and SEPSEP showed a marked improvement of phase morphology and elongation at break when compared to blends with unfunctionalized copolymers. 相似文献
This is the first light scattering study demonstrating that the size of micelles, the aggregation number, and the mobility of the core blocks of the micelles could be controlled by the length of the cross-linker in the micellar cores. The core cross-linked micelles were prepared using a poly[(4-pyridinemethoxy-methyl)styrene]-block-polystyrene (PPySt-b-PSt) diblock copolymer and perfluoroalkyl dicarboxylic acid. The PPySt-b-PSt copolymer formed the micelles in THF, a nonselective solvent, in the presence of the perfluoroalkyl dicarboxylic acid. The light scattering studies demonstrated that the micellar size and aggregation number were dependent on the chain length of the perfluoroalkyl dicarboxylic acid. Perfluoroazelaic acid produced micelles with a larger hydrodynamic radius and higher aggregation number than tetrafluorosuccinic acid. The micellization proceeded through the formation of the pyridinium carboxylate and the cross-linkage between the PPySt blocks via the dicarboxylic acid. The core cross-linked micelles were thermally stable and maintained its structure with changes in the temperature. A 1H NMR analysis revealed that the micelles prepared by perfluoroazelaic acid had more mobility of the core blocks than those by tetrafluorosuccinic acid. 相似文献
A novel amphiphilic diblock copolymer composed of a hydrophilic poly(ethylene oxide) block and a hydrophobic block copolymerized by azobenzene‐containing methacrylate and N‐isopropylacrylamide was synthesized using ATRP. The polymer micelles showed dual responsiveness to heat and light. The size of the micelles was dependent on temperature and the encapsulated substance in the hydrophobic cores was released during heating and cooling processes. The hydrophobicity of the micellar cores appeared as a reversible change in response to light with neither disruption of the micelles nor leakage of the encapsulated substance while H‐aggregation of the azobenzene moieties was detected.