Non-surface activity and micellization of ionic amphiphilic diblock copolymers in water. Hydrophobic chain length dependence and salt effect on surface activity and the critical micelle concentration

We reported previously (Macromolecules 2003, 36, 5321; Langmuir, 2004, 20, 7412) that amphiphilic diblock copolymers having polyelectrolytes as a hydrophilic segment show almost no surface activity but form micelles in water. In this study, to further investigate this curious and novel phenomenon in surface and interface science, we synthesized another water-soluble ionic amphiphilic diblock copolymer poly(hydrogenated isoprene)-b-sodium poly(styrenesulfonate) PIp-h2-b-PSSNa by living anionic polymerization. Several diblock copolymers with different hydrophobic chain lengths were synthesized and the adsorption behavior at the air/water interface was investigated using surface tension measurement and X-ray reflectivity. A dye-solubilization experiment was carried out to detect the micelle formation. We found that the polymers used in this study also formed micelles above a certain polymer concentration (cmc) without adsorption at the air-water interface under a no-salt condition. Hence, we further confirmed that this phenomenon is universal for amphiphilic ionic block copolymer although it is hard to believe from current surface and interface science. For polymers with long hydrophobic chains (more than three times in length to hydrophilic chain), and at a high salt concentration, a slight adsorption of polymer was observed at the air-water interface. Long hydrophobic chain polymers showed behavior "normal" for low molecular weight ionic surfactants with increasing salt concentration. Hence, the origin of this curious phenomenon might be the macroionic nature of the hydrophilic part. Dynamic light scattering analysis revealed that the hydrodynamic radius of the block copolymer micelle was not largely affected by the addition of salt. The hydrophobic chain length-cmc relationship was found to be unusual; some kind of transition point was found. Furthermore, very interestingly, the cmc of the block copolymer did not decrease with the increase in salt concentration, which is in clear contrast to the fact that cmc of usual ionic small surfactants decreases with increasing salt concentration (Corrin-Harkins law). These behaviors are thought to be the special, but universal, characteristics of ionic amphiphilic diblock copolymers, and the key factor is thought to be a balance between the repulsive force from the water surface by the image charge effect and the hydrophobic adsorption.     

Association behavior of fluorine-containing and non-fluorine-containing methacrylate-based amphiphilic diblock copolymer in aqueous media

Fluorine-containing amphiphilic block copolymers, poly(sodium methacrylate)-block-poly(nonafluorohexyl methacrylate) (NaMAm-b-NFHMAn) (m:n = 61:12, 72:33, 64:57), and the corresponding non-fluorine-containing amphiphilic block copolymer, poly(sodium methacrylate)-block-poly(hexyl methacrylate) (NaMAm-b-HMAn) (m:n = 64:10, 69:37, 67:50), were synthesized. Both polyNaMA-b-polyNFHMA and polyNaMA-b-polyHMA formed micelles above critical micelle concentrations, (cmc's), around 3 x 10(-5) to 1 x 10(-4) mol/L, while neither polymer decreased surface tension of aqueous solutions. The size and shape of the micelles were examined by dynamic light scattering, small-angle neutron scattering, and small-angle X-ray scattering. PolyNaMA-b-polyHMA appeared to form only spherical micelles, while polyNaMA-b-polyNFHMA with a long NFHMA segment formed both spherical and rodlike micelles. The micelles of fluorine-containing block copolymers were obviously larger than those of non-fluorine-containing block copolymers with the same chain length and the same hydrophilic/hydrophobic chain ratio. The fluorine-containing block copolymer selectively solubilized fluorinated dye into the water phase when a mixture of decafluorobiphenyl and 2,6-dimethylnaphthalene was added to the micelle solution.     

Non-surface activity and micellization behavior of cationic amphiphilic block copolymer synthesized by reversible addition-fragmentation chain transfer process

Cationic amphiphilic diblock copolymers of poly(n-butylacrylate)-b-poly(3-(methacryloylamino)propyl)trimethylammonium chloride) (PBA-b-PMAPTAC) with various hydrophobic and hydrophilic chain lengths were synthesized by a reversible addition-fragmentation chain transfer (RAFT) process. Their molecular characteristics such as surface activity/nonactivity were investigated by surface tension measurements and foam formation observation. Their micelle formation behavior and micelle structure were investigated by fluorescence probe technique, static and dynamic light scattering (SLS and DLS), etc., as a function of hydrophilic and hydrophobic chain lengths. The block copolymers were found to be non-surface active because the surface tension of the aqueous solutions did not change with increasing polymer concentration. Critical micelle concentration (cmc) of the polymers could be determined by fluorescence and SLS measurements, which means that these polymers form micelles in bulk solution, although they were non-surface active. Above the cmc, the large blue shift of the emission maximum of N-phenyl-1-naphthylamine (NPN) probe and the low micropolarity value of the pyrene probe in polymer solution indicate the core of the micelle is nonpolar in nature. Also, the high value of the relative intensity of the NPN probe and the fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene (DPH) probe indicated that the core of the micelle is highly viscous in nature. DLS was used to measure the average hydrodynamic radii and size distribution of the copolymer micelles. The copolymer with the longest PBA block had the poorest water solubility and consequently formed micelles with larger size while having a lower cmc. The "non-surface activity" was confirmed for cationic amphiphilic diblock copolymers in addition to anionic ones studied previously, indicating the universality of non-surface activity nature.     

Sphere-to-rod transition of non-surface-active amphiphilic diblock copolymer micelles: a small-angle neutron scattering study

Micellization behavior of amphiphilic diblock copolymers with strong acid groups, poly(hydrogenated isoprene)-block-poly(styrenesulfonate), was investigated by small-angle neutron scattering (SANS). We have reported previously (Kaewsaiha, P.; Matsumoto, K.; Matsuoka, H. Langmuir 2005, 21, 9938) that this strongly ionic amphiphilic diblock copolymer shows almost no surface activity but forms micelles in water. In this study, the size, shape, and internal structures of the micelles formed by these unique copolymers in aqueous solution were duly investigated. The SANS data were well described by the theoretical form factor of a core-shell model and the Pedersen core-corona model. The micellar shape strongly depends on the hydrophobic chain length of the block copolymer. The polymer with the shortest hydrophobic chain was suggested to form spherical micelles, whereas the scattering curves of the longer hydrophobic chain polymers showed a q-1 dependence, reflecting the formation of rodlike micelles. Furthermore, the addition of salt at high concentration also induced the sphere-to-rod transition in micellar shape as a result of the shielding effect of electrostatic repulsion. The corona thickness was almost constant up to the critical salt concentration (around 0.2 M) and then decreased with further increases in salt concentration, which is in qualitatively agreement with existing theories. The spherical/rodlike micelle ratio was also constant up to the critical salt concentration and then decreased. The micelle size and shape of this unique polymer could be described by the common concept of the packing parameter, but the anomalously stable nature of the micelle (up to 1 M NaCl) is a special characteristic.     

New amphiphilic diblock copolymers: surfactant properties and solubilization in their micelles

Several series of amphiphilic diblock copolymers are investigated as macrosurfactants in comparison to reference low-molar-mass and polymeric surfactants. The various copolymers share poly(butyl acrylate) as a common hydrophobic block but are distinguished by six different hydrophilic blocks (one anionic, one cationic, and four nonionic hydrophilic blocks) with various compositions. Dynamic light scattering experiments indicate the presence of micelles over the whole concentration range from 10(-4) to 10 g x L(-1). Accordingly, the critical micellization concentrations are very low. Still, the surface tension of aqueous solutions of block copolymers decreases slowly but continuously with increasing concentration, without exhibiting a plateau. The longer the hydrophobic block, the shorter the hydrophilic block, and the less hydrophilic the monomer of the hydrophilic block is, the lower the surface tension is. However, the effects are small, and the copolymers reduce the surface tension much less than standard low-molar-mass surfactants. Also, the copolymers foam much less and even act as anti-foaming agents in classical foaming systems composed of standard surfactants. The copolymers stabilize O/W emulsions made of methyl palmitate as equally well as standard surfactants but are less efficient for O/W emulsions made of tributyrine. However, the copolymer micelles exhibit a high solubilization power for hydrophobic dyes, probably at their core-corona interface, in dependence on the initial geometry of the micelles and the composition of the block copolymers. Whereas micelles of copolymers with strongly hydrophilic blocks are stable upon solubilization, solubilization-induced micellar growth is observed for copolymers with moderately hydrophilic blocks.     

Surface activity of new invertible amphiphilic polyesters based on poly(ethylene glycol) and aliphatic dicarboxylic acids

The surface active properties of aqueous solutions of invertible amphiphilic alternated polyesters differing by hydrophilic-lipophilic balance (HLB) and molecular weight have been determined over the wide concentration range. The polyesters are based on poly(ethylene glycol) (PEG) of two molecular weights and aliphatic dicarboxylic acids (decanedioic and dodecanedioic). The surface activity of the polyesters and their ability to form micellar assemblies (which was recently shown for organic solvents) has been confirmed in water. The central role of the balance of hydrophilic to hydrophobic groups ratio in the formation of polymeric arrangements having hydrophobic pockets and external hydrophilic shell has been shown. The effect of molecular weight has been found considerable as well. Two changes in slope have been observed for the more hydrophobic polyesters in the surface tension vs log concentration curve. The change at low concentration is believed to originate from the formation of polyester assemblies with a hydrophobic interior and hydrophilic exterior due to the interaction of hydrophobic fragments and macromolecular flexibility. The higher concentration region exhibits behavior consistent with a cmc, which was confirmed by additional dye solubilization experiments. Molecular structure of the polyester micelles is determined by the solubilization of a solvatochromic dye. The experiment confirmed that micellization of polyesters is accompanied by the association of more hydrophobic (aliphatic) constituents forming the micelle interior. The hydrophilic fragments (ethylene oxide groups) are involved in the formation of micelle exterior.     

Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has been confirmed by surface tension measurements, whereas the influence of the surfactant on the copolymer self-assembling has been studied by measurement of the 1H NMR self-diffusion coefficients and by small-angle neutron scattering. As a rule, the surfactant decreases the heterogeneity of the micellar structures formed by the copolymer in water. Moreover, increasing the content of SDS results in the increasingly more important extension of the poly(ethylene oxide) (PEO) corona chains and the copolymer micelle deaggregation. The stability of the micelles against SDS increases with the length of the hydrophobic block. Preliminary two-dimensional NMR measurements with nuclear Overhauser enhancement have confirmed the spatial vicinity between SDS and the constitutive blocks of the copolymer.     

Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.     

pH-responsive non-surface-active/surface-active transition of weakly ionic amphiphilic diblock copolymers

The weakly ionic amphiphilic diblock copolymer polystyrene-b-poly(acrylic acid) was synthesized by nitroxy radical-mediated living radical polymerization with precise control of block length, block ratio, and polydispersity. Systematical surface tension experiments and foam formation observations revealed that this polymer was non-surface active under neutral and alkaline (pH 10) conditions, while it was surface active under an acidic condition (pH 3). This result supports our proposed origin of non-surface activity; the image charge repulsion at the air/water interface is essential in addition to very stable micelle formation in the bulk solution. At a higher pH (pH 12), the polymer showed slight surface activity since the added NaOH played a role as an added salt. The critical micelle concentration (cmc) was estimated by static light scattering. Cmc increased with increasing added salt (NaCl) concentration as was observed for other strongly ionic non-surface-active polymers. Hence, this trend is characteristic for non-surface-active polymers. The pH dependence of cmc was minimum at pH 8–10. Since the acrylic acid block is fully ionized under this condition, the strong image charge repulsion at this condition accelerated micelle formation at a low polymer concentration, which consequently decreased cmc. Micelles in bulk solution were confirmed by dynamic light scattering, and the salt concentration and pH dependencies of the hydrodynamic radius of the micelles were also estimated. The pH-responsive non-surface-active/surface-active transition observed in this study strongly supports the fact that the image charge repulsion is an essential factor for non-surface activity in addition to stable micelle formation in solution.     

Preparation and solution behavior of a thermoresponsive diblock copolymer of poly(ethyl glycidyl ether) and poly(ethylene oxide)

A thermoresponsive diblock copolymer, poly(ethyl glycidyl ether)-block-poly(ethylene oxide) (PEGE-b-PEO), is synthesized by successive anionic ring-opening polymerization of ethyl glycidyl ether and ethylene oxide using 2-phenoxyethanol as a starting material, and its solution behavior is elucidated in water. In a dilute 1 wt % solution, the temperature-dependent alteration in the polymer hydrodynamic radius (RH) is measured in the temperature range between 5 and 45 degrees C by pulse-gradient spin-echo NMR and dynamic light scattering. The RH value increased with temperature in two steps, where the first step at 15 degrees C corresponds to the core-shell micelle formation and the second step at 40 degrees C corresponds to the aggregation of the core-shell micelles. The formation of the core-shell micelles is supported by the solubilization of a dye (1,6-diphenyl-1,3,5-hexatriene) in the hydrophobic core, which is recognized for a copolymer solution in the temperature range between 20 and 40 degrees C. In this temperature range, the core-shell micelles and the unimers coexist and the fraction of the former gradually increases with increasing temperature, suggesting equilibrium between the micelles and the unimers. In the concentrated regime (40 wt % solution), the solution forms a gel and the small-angle X-ray scattering measurements reveal the successive formation of hexagonal and lamellar liquid crystal phases with increasing temperature.     

Cylindrical micelles from the aqueous self-assembly of an amphiphilic poly(ethylene oxide)-b-poly(ferrocenylsilane) (PEO-b-PFS) block copolymer with a metallo-supramolecular linker at the block junction

A supramolecular AB diblock copolymer has been prepared by the sequential self-assembly of terpyridine end-functionalized polymer blocks by using Ru(III)/Ru(II) chemistry. By this synthetic strategy a hydrophobic poly(ferrocenylsilane) (PFS) was attached to a hydrophilic poly(ethylene oxide) (PEO) block to give an amphiphilic metallo-supramolecular diblock copolymer (PEO/PFS block ratio 6:1). This compound was used to form micelles in water that were characterized by a combination of dynamic and static light scattering, transmission electron microscopy, and atomic force microscopy. These complementary techniques showed that the copolymers investigated form rod-like micelles in water; the micelles have a constant diameter but are rather polydisperse in length, and light scattering measurements indicate that they are flexible. Crystallization of the PFS in these micelles was observed by differential scanning calorimetry, and is thought to be the key behind the formation of rod-like structures. The cylindrical micelles can be cleaved into smaller rods whenever the temperature of the solution is increased or they are exposed to ultrasound.     

Silica nanoparticles at interfaces modulated by amphiphilic polymer and surfactant

The interfacial behavior of silica nanoparticles in the presence of an amphiphilic polymer poly( N-isopropylacrylamide) (PNIPAM) and an anionic surfactant sodium dodecyl sulfate (SDS) is studied using neutron reflectivity. While the nanoparticles do not show any attraction to hydrophilic and hydrophobic surfaces in pure water, presence of the amphiphilic polymer induces significant adsorption of the nanoparticles at the hydrophobic surface. This interfacial behavior is activated due to interaction of the nanoparticles with PNIPAM, the amphiphilic nature of which leads to strong adsorption at a hydrophobic surface but only weak interaction with a hydrophilic surface. The presence of SDS competes with nanoparticle-PNIPAM interaction and in turn modulates the interfacial properties of the nanoparticles. These adsorption results are discussed in relation to nanoparticle organization templated by dewetting of charged polymer solutions on a solid substrate. Our previous studies showed that nanoparticle assembly can be induced to form complex morphologies produced by dewetting of the polymer solutions, such as a polygonal network and long-chain structures. This approach, however, works on a hydrophilic substrate but not on a hydrophobic substrate. These observations can be explained in part by particle-substrate interactions revealed in the present study.     

Self-assembled polypeptide-block-poly(vinylpyrrolidone) as prospective drug-delivery systems

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.     

Controlling the melting of kinetically frozen poly(butyl acrylate-b-acrylic acid) micelles via addition of surfactant

We have studied the melting of polymeric amphiphilic micelles induced by small-molecule surfactant and explained the results by experimental determination of the interfacial tension between the core of the micelles and the surfactant solutions. Poly(n-butyl acrylate-b-acrylic acid) (PBA-b-PAA) amphiphilic diblock copolymers form kinetically frozen micelles in aqueous solutions. Strong interactions with surfactants, either neutral or anionic [C12E6, C6E4, sodium dodecyl sulfate (SDS)], were revealed by critical micelle concentration (cmc) shifts in specific electrode and surface tension measurements. Since both polymer and surfactant are either neutral or bear negative charges, the attractive interactions are not due to electrostatic interactions. Light scattering, neutron scattering, and capillary electrophoresis experiments showed important structural changes in mixed PBA-b-PAA/surfactant systems. Kinetically frozen micelles of PBA-b-PAA, that are hardly perturbed by concentration, ionization, ionic strength, and temperature stresses, can be disintegrated by addition of small-molecule surfactants. The interfacial energy of the PBA in surfactant solutions was measured by drop shape analysis with h-PBA homopolymer drops immersed in small-molecule surfactant solutions. The PBA/water interfacial energy gammaPBA/H2O of 20 mN/m induces a high energy cost for the extraction of unimers from micelles so that PBA-b-PAA micelles are kinetically frozen. Small-molecule surfactants can reduce the interfacial energy gammaPBA/solution to 5 mN/m. This induces a shift of the micelle-unimer equilibrium toward unimers and leads, in some cases, to the apparent disintegration of PBA-b-PAA micelles. Before total disintegration, polymer/surfactant mixtures are dispersions of polydisperse mixed micelles. Based on core interfacial energy arguments, the disintegration of kinetically frozen polymeric micelles was interpreted by gradual fractionation of objects (polydisperse dispersion mechanism), whereas the disintegration of polymeric micelles in a thermodynamically stable state was interpreted by an exchange between a population of large polymer-rich micelles and a population of small surfactant-rich micelles (bidisperse dispersion mechanism). Finally, in our system and other systems from the literature, interfacial energy arguments could explain why the disintegration of polymer micelles is either partial or total as a function of the surfactant type and concentration and the hydrophobic block molar mass of the polymer.     

无规共聚物自组装球形胶束表面亲水性的耗散粒子动力学模拟

建立了含不同亲疏水粒子比的双亲性无规共聚物粗粒化模型. 采用耗散粒子动力学方法模拟了两亲性无规共聚物选择性溶剂自组装球形胶束表面的亲水性能. 模拟结果表明, 无规共聚物在选择性溶剂中自组装得到实心球形胶束, 球形胶束表面的亲水性与聚合物链亲水粒子含量、溶剂的选择性有关. 随着聚合物链所含亲水粒子增加, 球形胶束表面的亲水性增强. 球形胶束表面的亲水性随着疏水粒子与溶剂粒子间的排斥参数增大而增强, 模拟结果与实验结论一致. 该模拟方法给出的胶束微结构信息可以为双亲无规共聚物分子设计及自组装双亲胶束制备提供一定的理论指导.     

Micellization phenomena of biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and poly(ethylene oxide)

This paper reports the studies on micelle formation of new biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer with various PHB and PEO block lengths in aqueous solution. Transmission electron microscopy showed that the micelles took an approximately spherical shape with the surrounding diffuse outer shell formed by hydrophilic PEO blocks. The size distribution of the micelles formed by one triblock copolymer was demonstrated by dynamic light scattering technique. The critical micellization phenomena of the copolymers were extensively studied using the pyrene fluorescence dye absorption technique, and the (0,0) band changes of pyrene excitation spectra were used as a probe for the studies. For the copolymers studied in this report, the critical micelle concentrations ranged from 1.3 x 10(-5) to 1.1 x 10(-3) g/mL. For the same PEO block length of 5000, the critical micelle concentrations decreased with an increase in PHB block length, and the change was more significant in the short PHB range. It was found that the micelle formation of the biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and PEO was relatively temperature-insensitive, which is quite different from their counterparts consisting of poly(alpha-hydroxyalkanoic acid) and PEO.     

Dissipative particle dynamics simulations of toroidal structure formations of amphiphilic triblock copolymers

In this paper, the dynamic assembly of toroidal micelle structures of amphiphilic triblock copolymers in dilute solution has been investigated using dissipative particle dynamics simulations. The amphiphilic molecule is represented by a coarse-grained model, which contains hydrophilic and hydrophobic particles. Some microstructures of complex morphology having toroidal micelles have been observed in the simulations; the toroidal micelle formation is in accordance with the theoretical prediction of the toroidal structure in cylindrical micelle suspensions by Pochan et al. (Science 2004, 306, 94). These findings are very interesting, and these complex morphologies enrich our knowledge of the potential products obtained from the self-assembly of block copolymers.     

Di(n-butyl) itaconate end-functionalized polymers: Synthesis by group transfer polymerization and solution characterization

In this study we present our efforts to homo- and co-polymerize, using group transfer polymerization (GTP), a dialkyl diester of itaconic acid, a naturally-derived unsaturated dicarboxylic acid. The monomer employed, di(n-butyl) itaconate (DBI), did not seem to polymerize by GTP to high conversion, but it displayed the remarkable ability to contribute to the polymer 1–2 units, suggesting that it would make a good end-functionalizing reagent for GTP. This was demonstrated by preparing by GTP hydrophilic homopolymers, and in situ adding to them DBI which is hydrophobic. The thus-obtained amphiphilic end-functionalized copolymers formed in water small micelles, whose aggregation numbers and radii of gyration were characterized using small-angle neutron scattering.     

Controlled Synthesis of PCL/PVP Copolymer by RAFT Method and Its Hydrophilic Block-Dependent Micellar Behaviors

A range of poly(ε-caprolactone)/poly(N-vinyl-2-pyrrolidone) amphiphilic block copolymers with well-de ned hydrophilic chain length were synthesized by the living/controlled reversible addition fragmentation chain transfer polymerization method. The composition and struc-ture of the targeted resultants were characterized with ¹H NMR, ¹³C NMR, FT-IR spec-troscopy and gel permeation chromatography. The various block copolymers were success-fully employed to fabricate the spherical micelle with core-shell morphological structure. The poly(N-vinyl-2-pyrrolidone) block-dependent characteristics of the copolymeric micelles were investigated by uorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The solubilization of the hydrophobic ibuprofen as a model drug in the micelle solution was also explored. It was found that the drug loading contents are related to the micellar morphology structure determined by hydrophilic chain length in the copolymer.     

聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质的研究

采用核磁共振 (NMR)、动态激光光散射 (DLS)、透射电子显微镜 (TEM )等方法研究了规整性聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质 ,研究表明两亲接枝共聚物在选择性溶剂中可形成球状胶束 ,溶液的浓度、温度和聚合物结构等因素影响其胶束的大小、形态