Self-assemblies formed by four-arm star copolymers with amphiphilic diblock arms in aqueous solutions

The self-assembly of two star copolymers, each consisting of four diblock arms of either poly(?-caprolactone)-block-poly(ethylene oxide), PCL-PEO, or polylactide-block-poly(ethylene oxide), PLA-PEO, with PEO blocks in the centers of the stars, have been studied by a combination of light scattering, atomic force microscopy, fluorometry and ¹H NMR spectroscopy. Results of the study show that despite the very similar architecture of both star copolymers, the structures of their self-assembled nanoparticles differ. Unlike the (PLA-PEO)₄ star copolymer which forms core/shell flower-like micelles, the association of the (PCL-PEO)₄ copolymer leads to large micellar aggregates in which individual micelles are interconnected by shared unimers, having joint coronas formed by hydrophilic centers of the stars.     

Synthesis and aqueous solution characterization of amphiphilic diblock copolymers containing carbazole

A series of near-monodisperse diblock copolymers of 2-(N-carbazolyl)ethyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) of relatively low molecular weights (2600-24,000 g mol⁻¹) were synthesized by group transfer polymerization using tetrahydrofuran (THF) as a solvent. The molecular weight distributions and compositions of all the copolymers were obtained using gel permeation chromatography (GPC) in THF and proton nuclear magnetic resonance (¹H NMR) spectroscopy, respectively. Differential scanning calorimetry and thermal gravimetric analysis provided low glass transition temperatures (T_gs) of about 60 °C and decomposition temperatures between 320 and 450 °C for the copolymers, respectively. The three copolymers with the highest DMAEMA content were water-soluble below pH 7. Aqueous GPC at pH 3 showed that the water-soluble block copolymers formed micelles with apparent number average molecular weights above 100,000 g mol⁻¹.     

Novel amphiphilic diblock copolymers bearing acid-labile oxazolidine moieties: Synthesis, self-assembly and responsive behavior in aqueous solution

A novel oxazolidine based acid-labile monomer N-acryloyl-2,2-dimethyl-1,3-oxazolidine (ADMO) was synthesized and polymerized by reversible addition fragmentation chain transfer (RAFT) polymerization using poly(ethylene glycol) based chain transfer agent (PEG-CTA). The diblock copolymers PEG-b-PADMO were composed of hydrophilic PEG with fixed length and hydrophobic PADMO with different lengths, which formed core-shell micelles in water. Morphologies and sizes of micelles were obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS), which showed that the shapes of polymeric aggregates developed from small spherical micelles, worm-like micelles to larger size of vesicles, as the length of PADMO increased. The hydrolysis kinetics of the micelles was studied using ¹H NMR, DLS and release of loaded Nile Red dye, whose rate strongly depended on pH and micellar structure. It led to the disruption of polymeric micelles and concomitant release of the guest molecules, due to the transformation of hydrophobic PADMO into hydrophilic poly(2-hydroxyethyl acrylamide) (PHEAM).     

Synthesis and characterization of amphiphilic PMTFPS‐b‐PEO diblock copolymers

A series of new amphiphilic poly[methyl(3,3,3‐trifluoropropyl) siloxane]‐b‐poly(ethyleneoxide) (PMTFPS‐b‐PEO) diblock copolymers with different ratio of hydrophobic segment to hydrophilic segment were prepared by coupling reactions of end‐functional PMTFPS and PEO homopolymers. PMTFPS‐b‐PEO diblock copolymers synthesized were shown to be well defined and narrow molecular weight distributed by characterizations such as NMR, GPC, and FTIR. Additionally, the solution properties of these diblock copolymers were investigated using tensiometry and transmission electron microscopy. Interestingly, the critical micellization concentration increases with increasing length of hydrophobic chain. Transmission electron microscopy studies showed that PMTFPS‐b‐PEO diblock copolymers in water preferentially aggregated into vesicles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Multiple morphologies of self-assembled star aggregates of amphiphilic PEO-b-PNPMA diblock copolymers in solution, synthesis and micellization

Novel amphiphilic block copolymers, poly(ethylene oxide)-b-poly(p-nitrophenyl methacrylate) (PEO-b-PNPMA) with controlled molecular weights and narrow molecular weight distribution were successively synthesized by ATRP of NPMA using PEO-Br as initiator. Self-assembling of the diblock copolymer PEO₁₁₃-b-PNPMA₂₈ in the different solvent mixtures yielded various morphologies of star micelle-like aggregates, such as spheres, vesicles, cauliflower-like aggregates and rod-like aggregates, which are determined by the nature of the common solvents and the selective solvents. Thus the critical selective solvent contents and the solvent contents in PNPMA-rich phase were measured, and they have the following order: ethanol > methanol > water, and THF > CH₃NO₂ > DMSO. The probable self-assembling mechanism is discussed. This method is convenient for preparation of multiple morphological star micelle-like aggregates in solution, especially from the amphiphilic block copolymers with relatively longer block shell.     

双亲性聚氨酯的制备和应用进展

综述了双亲性聚氨酯的结构分类,各种制备方法和亲疏水基团的引入方法,介绍了双亲性聚氨酯材料在弹性体、医用材料和表面活性剂等方面的应用。     

Synthesis and properties of amphiphilic star block copolymers with star macroinitiators based on a one‐pot approach

Previously, star polystyrenes (PSs) have been prepared by atom transfer radical polymerization (ATRP) of N‐[2‐(2‐bromoisobutyryloxy)ethyl]maleimide (BiBEMI) with a large excess of styrene (St) in one pot. But linear PSs were also present during the formation of the star polymers. In the work reported here, we found that control of the formation of star polymers using a one‐pot approach can be improved by using a two‐step process. The polymerization was conducted first at a low temperature to form multifunctional cores by copolymerization of BiBEMI and St. Second, on increasing the temperature, homopolymerization of St occurred to grow PS arms. Then a series of amphiphilic star polystyrene‐block‐poly(acrylic acid)s, (S₁₄A_x)₁₆, were prepared by ATRP of tert‐butyl acrylate with the star PSs as macroinitiators, followed by selective acidolysis of the poly(tert‐butyl acrylate) blocks. Their micellization was studied using dynamic light scattering, which suggested that (S₁₄A₁₁₂)₁₆ amphiphilic star block copolymers could form unimolecular micelles in a basic aqueous solution. Then pyrene molecules were encapsulated using the (S₁₄A₁₁₂)₁₆ amphiphilic star copolymers and the loading capacity was investigated with UV and fluorescence spectroscopy. © 2013 Society of Chemical Industry     

Synthesis and characterization of ZnO nanostructures templated using diblock copolymers

The development of self‐assembled ZnO nanoparticles within a diblock copolymer matrix using wet chemical processing specific to ZnO is reported. Diblock copolymers consisting of polynorbornene and poly(norbornene–dicarboxcylic acid) (NOR/NORCOOH) were synthesized with a block repeat unit ratio of 400 for the first block and 50 for the second block, to obtain spherical microphase separation. The block copolymer self‐assembly was used to template the growth of ZnO nanoparticles by introducing a ZnCl₂ precursor into the second polymer (NORCOOH) block at room temperature and processing the copolymer by wet chemical methods to substitute the chlorine atoms with oxygen. X‐ray photoemission spectroscopy (XPS) verified the conversion of ZnCl₂ to ZnO by monitoring the disappearance of the Cl 1s peak and the shift in the binding energy of the Zn 2p³ peak in the high‐resolution spectra. The substitution of Cl by O was found to be a highly preferential process, whereby only one approach using a weak base (NH₄OH) succeeded in effectively replacing Cl with O to result in spherical ZnO nanoparticles having a size ranging from 7 to 15 nm, as determined by transmission electron microscopy. The development of such block copolymer‐templated ZnO nanoparticles% is important in enabling the functionalization of large‐area nanodevice technologies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1058–1061, 2003     

Synthesis of amphiphilic triblock copolymers for the formation of magnesium fluoride (MgF2) nanoparticles

A series of amphiphilic poly(2‐hydroxyethyl methacrylate)‐b‐polydimethylsiloxane‐b‐poly(2‐hydroxyethyl methacrylate) (pHEMA‐b‐PDMS‐b‐pHEMA) (A‐B‐A) triblock copolymers were synthesized from three different carbinol‐terminated polydimethylsiloxanes with varying molecular weight. A carbinol‐terminated polydimethylsiloxane was modified with 2‐bromoisobutyryl bromide to obtain a macroinitiator. The block copolymers were characterized by NMR, GPC, and dynamic light scattering (DLS). Reverse micelles of a copolymer were formed in mixture of benzene/methanol solution which served as nanoreactors for the synthesis of magnesium fluoride (MgF₂) nanoparticles. The MgF₂ was prepared via chemical precipitation using magnesium chloride and potassium fluoride as reactants. The MgF₂‐triblock copolymer composites were synthesized as a function of MgF₂–weight ratio (0.5, 5, and 10 wt%) in copolymer. The MgF₂ colloids were dissolved in three organic solvents: methanol, isopropanol, and tetrahydrofuran. The polymer nanoparticles were characterized by DLS, transmission electron microscopy, thermogravimetric analysis, and X‐ray diffraction (XRD) analysis. The formation of MgF₂ crystals was observed by XRD. Particle size and particle size distribution showed significant changes in different solvents. The thermal stability of MgF₂ colloids increased as the amount of nanoparticle increased in polymeric matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adjustable temperature sensor with double thermoresponsiveness based on the aggregation property of binary diblock copolymers

This article presents a new and promising way to design a temperature sensor, which is based on the micellization or aggregation behavior of binary diblock copolymers of poly(ethylene glycol)‐b‐poly(N‐isopropylacrylamide) (PEG‐b‐PNIPAM) and poly(ethylene glycol)‐b‐poly(4‐vinylpyridine) (PEG‐b‐P(4‐VP)). The temperature sensor presents both a lower critical response temperature (LCRT) and an upper critical response temperature (UCRT), where the thermoreversible aggregating of PEG‐b‐P(4‐VP) and H₂SO₄ is used to control the LCRT, and the thermoreversible micellization of PEG‐b‐PNIPAM is used to control the UCRT. Furthermore, the LCRT can be altered by changing the H₂SO₄ concentration, and the UCRT can be adjusted by altering the PEG‐b‐PNIPAM concentration. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3144–3148, 2006     

Effect of hydrophilic chain length on the aqueous solution behavior of block amphiphilic copolymers PMMA‐b‐PDMAEMA

A series of amphiphilic block copolymers, polymethyl methacrylate (PMMA)‐b‐poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA), were synthesized by atom transfer radical polymerization (ATRP) method. Surface tension, dynamic light scattering (DLS), transmission electron microscope (TEM), and atomic force microscopy (AFM) studies were performed to investigate the aqueous micellar behavior of these block amphiphiles. At a fixed degree of polymerization (DP) of PMMA block (DP = 55), the PDMAEMA block length was found to have a significant influence on the critical micelle concentration (cmc) values and hydrodynamic size of aggregates. An increase in the DP of PDMAEMA from 11 to 337, resulted in a decrease in the cmc from 1.44 × 10^?5 to 5.81 × 10^?7 M (a factor of almost 24.8), and a decrease in the Z (2R_h) from 85.5 to 15.5 nm (pH = 4), respectively. TEM and AFM results indicated that by changing the soluble block lengths, spherical, short rod, crew‐cut, vesicles or large aggregates can be observed in the solution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Temperature and salt-induced micellization of some block copolymers in aqueous solution

Micellization of three commercial samples of ethylene oxide (EO)-propylene oxide (PO) (PEO-PPO-PEO) triblock copolymers (pluronics) P65 (EO₂₅PO₃₀EO₂₅, mw PPO=1750, %PEO=50), P85 (EO₂₅PO₄₀EO₂₅, mw PPO=2250, %PEO=50), and F88 (EO₁₀₂PO₄₀EO₁₀₂, mw PPO=2250, %PEO=80) in aqueous sodium chloride solution (0–3 M) was examined by cloud point, surface tension, dye spectral change, fluorescence, and viscosity measurements over a temperature range of 25–50°C. Salt-induced micellization and micelle growth were observed. The presence of sodium chloride enhanced hydrophobicity in the PPO moiety and reduced hydrophilicity of PEO moieties, favoring micellization at relatively lower concentrations than in water at ambient temperature. The effect of salt on micellization is similar to that of increasing temperature. The critical micelle concentrations (CMC) and critical micelle temperatures showed a marked decrease in the presence of added salt. CMC obtained by different methods were in good agreement.     

Aggregation behaviour of well defined amphiphilic diblock copolymers with poly(N-isopropylacrylamide) and hydrophobic blocks

Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.     

Effect of temperature and pH values on aggregation behavior of polymeric surfactants in aqueous solution

A novel kind of polymeric surfactant based on carboxymethyl cellulose and poly(ethylene oxide) dodecyl ether acrylate (CMC‐AR₁₂EO₉) was synthesized through ultrasonic irradiation. Aggregation behavior in aqueous solution at different temperatures and pH values was investigated by dynamic laser scattering and fluorescence probe. The results show that, with the increase of temperature, polymeric surfactants are favorable to form multimolecular micelles with narrower polydispersity of size distribution. At a higher temperature, the multimolecular micelles tend to aggregate bigger sized particles that are unstable and would be disaggregated at higher shear rate. At the elevated pH values, the size of micelles reduces drastically because of strong damage of alkali to aggregates, whereas nonpolar and insoluble domains formed by the hydrophobic blocks of polymeric surfactants are insensitive to pH changes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 945–949, 2005     

Crosslinkable micelles from diblock amphiphilic copolymers based on vinylbenzyl thymine and vinylbenzyl triethylammonium chloride

Polymeric micelles (PMs) composed of self‐assembled amphiphilic block copolymers were synthesized from vinylbenzyl thymine (VBT) and vinylbenzyl triethylammonium chloride (VBA) exhibiting improved physical stability. Three diblock copolymers of different chemical compositions and similar molecular weights (polydispersities below 1.5) were obtained via nitroxide mediated radical polymerization. Critical micelle concentration (CMC) was determined by dye micellization method, the shift of the absorption peak of the anionic (EY) due to the interactions with non‐assembled chains and auto‐assembled copolymers was followed. Polymeric systems exhibited good stability revealing that a higher proportion of cationic monomers in the diblock reduce the CMC. Furthermore, after the core of PMs was photocrosslinked by UV irradiation, the CMC decreases notably. Kinetic release studies using EY dye as probe demonstrated that both, higher VBA ratios in the polymer and higher UV‐irradiation, slow down the dye release. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41947.     

pH- and temperature-responsive amphiphilic diblock copolymers of 4-vinylpyridine and oligoethyleneglycol methacrylate synthesized by RAFT polymerization

Diblock copolymers of 4-vinylpyridine (4VP) and oligoethyleneglycol methyl ether methacrylate (OEGMA) were synthesized for the first time using RAFT polymerization technique as potential drug delivery systems. Effects of the number of ethylene glycol units in OEGMA, chain length of hydrophobic P4VP block, pH, concentration and temperature on the solution behavior of the copolymers were investigated comprehensively. Copolymer chains formed micelles at pH values higher than 5 whereas unimeric polymers were observed to exist below pH 5, owing to the repulsion between positively charged P4VP blocks. The size of the micelles was dependent on the relative length of blocks, P4VP and POEGMA. Thermo-responsive properties of copolymers were investigated depending on the pH and length of P4VP block. The increase in the length of P4VP block decreased the LCST substantially at pH 7. At pH 3, LCST of copolymers shifted to higher temperatures due to the increased interaction of copolymers with water through positively charged P4VP block.     

Star‐shaped amphiphilic block polyurethane with pentaerythritol core for a hydrophobic drug delivery carrier

To obtain polyurethane micelles with excellent stability as a drug delivery carrier, star‐shaped amphiphilic block polyurethane (SAPU) was successfully synthesized by the ‘arm‐first’ method, using methoxypoly(ethylene glycol) and poly(ε‐caprolactone) diol as soft segments, hexamethylene diisocyanate as hard segments and pentaerythritol as the core. The structure of the SAPU was characterized by Fourier transform infrared spectroscopy, ¹H NMR spectroscopy and gel permeation chromatography. The micellization behaviour and micelle properties of SAPU were measured by the pyrene fluorescence probe technique, ¹H NMR, SEM and dynamic light scattering. The results indicated that SAPU could self‐assemble to form nanomicelles in aqueous solution and that the micelles showed excellent stability upon dilution and storage. Indometacin as a model drug could be incorporated into SAPU micelles and be released sustainedly. Meanwhile, the hydrophilic segment content and the molecular weight of SAPU had effects on the micelle properties. In addition, SAPU exhibited good cytocompatibility estimated by methylthiazole‐tetrazolium assay. © 2016 Society of Chemical Industry     

Preparation and morphology of amphiphilic polystyrene–poly (2‐vinylpyridine) heteroarm star copolymers prepared by ATRP

BACKGROUND: The self‐assembly of amphiphilic copolymers has been demonstrated to be a powerful route towards supramolecular objects with novel architectures, functions and physical properties. In this study, the synthesis and morphology of amphiphilic linear polystyrene (PS)‐block‐poly(2‐vinylpyridine) (P2VP) and heteroarm star PS‐star‐P2VP copolymers are studied. The dispersion of silver nanoparticles with the prepared PS‐block‐P2VP and PS‐star‐P2VP copolymers is also discussed. RESULTS: Amphiphilic copolymers with different P2VP chain lengths were successfully synthesized using atom transfer radical polymerization (ATRP). The copolymers prepared had low polydispersity indices. Various aggregate morphologies, including spheres, vesicles, rods, large compound micelles, two‐dimensional ring‐like and three‐dimensional hollow structures, were formed by varying the hydrophilic coil length and the selective solvent content. Silver nanoparticles showed good dispersion behavior in both types of copolymers. CONCLUSION: Based on this study, it will be possible to prepare metal/copolymer nanocomposites by direct mixing. Further, the PS‐block‐P2VP and PS‐star‐P2VP copolymers prepared can be used in the preparation of nanoporous films as templates and nanoparticles as nanoreactors. They can also be applied in terms of oil recovery, paints and cosmetics formulations, as well as in pharmaceutical and medical applications as rheological agents. Copyright © 2008 Society of Chemical Industry     

Synthesis and self-association in aqueous media of poly(ethylene oxide)/poly(ethyl glycidyl carbamate) amphiphilic block copolymers

New temperature sensitive AB, ABA, and BAB amphiphilic block copolymers consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(ethyl glycidyl carbamate) blocks were synthesized by anionic polymerization followed by chemical modification reactions. The self-association of the block copolymers in aqueous media was studied by UV-vis spectroscopy and dynamic and static light scattering. The obtained block copolymers spontaneously form micelles in aqueous media. The critical micellization concentration varied from 0.5 to 4 g/L depending on the copolymer architecture and composition. The influence of the temperature upon the self-association of the block copolymers was investigated. The increase of temperature did not affect the value of the critical micellization concentration, but led to the formation of better defined micelles with narrow size distribution.     

Small-angle light scattering studies of macrophase separation in segmented polyurethane block copolymers

Quantitative small-angle light scattering (SALS) analysis is carried out on two similar segmented polyurethane block copolymers. The polyurethane prepared from toluene diisocyanate, is optically transparent, while a polyurethane prepared using the same soft segment, but with 4-4′ diphenyl methane diisocyanate, scatters light appreciably. SALS investigation of the latter sample shows clearly that the scattering arises from the presence of long-range density fluctuations. Analysis of the density fluctuations is accomplished with the Debye-Bueche theory for random two-phase systems, incorporating a correction for the effects of multiple scattering. Application of this procedure leads to a correlation length of 4200 nm; corresponding well with the structure observed in optical photo-micrographs. The occurrence of phase separation during polymerization is discussed as a possible origin for the observed macrophase structure.