NIR light and enzyme dual stimuli‐responsive amphiphilic diblock copolymer assemblies

Using atom transfer radical polymerization (ATRP) and macromolecular azo coupling reaction, both o‐nitrobenzyl (ONB) group and azobenzene group were efficiently incorporated into the center of the amphiphilic diblock copolymer chain. The prepared diblock copolymer was well characterized by UV–vis, ¹H NMR, and GPC methods. Self‐assembly of the amphiphilic copolymer in selected solvents can result in uniform self‐assembly aggregates. In the presence of external stimuli [upconversion nanoparticles (UCNPs)/NIR light or enzyme], the amphiphilic diblock copolymer chain could be broken by the cleavage of ONB or azobenzene group, which would lead to the disruption of the self‐assembly aggregates. This photo‐ and enzyme‐triggered disruption process was proved by using transmission electron microscopy (TEM) and GPC method. Fluorescence emission spectra measurements indicated that the release of Nile red, a hydrophobic dye, encapsulated by the self‐assembly aggregates, could be successfully realized under the NIR light and enzyme stimuli. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2450–2457     

Mechanically driven reorganization of thermoresponsive diblock copolymer assemblies in water

Controlled formation of a variety of 3D structures was observed at high polymer weight fractions in water from a single diblock, consisting of poly(N-isopropylacrylamide), PNIPAM, and polystyrene, PSTY segments. The structures form through a mechanical process driven by swelling of hydrophilic polymer segments upon a change in temperature (see picture, SDS=sodium dodecylsulfate).     

Surfactant boundary lubricant film modified by an amphiphilic diblock copolymer

The effect of the uptake of a low-molecular-weight amphiphilic diblock copolymer on the morphology of didodecyldimethylammonium bromide (DDAB) adsorbed layers on mica, the interactions between two coated surfaces, and the frictional properties of the boundary film have been studied using an atomic force microscope and a dynamic surface forces apparatus nanotribometer. When DDAB-coated surfaces in aqueous solution were compressed, hemifusion or removal of the adsorbed surfactant bilayers could not be induced, and no frictional force could be measured between the surfaces, which display superior lateral cohesion and lubricant properties. Coadsorbing octadecyl end modified poly(ethylene oxide) chains at low density facilitates hemifusion, generating significant shear stress and leading to stick-slip instabilities. The mixed films regain their lateral cohesion at higher adsorbed copolymer densities, but an extra short-range attraction brings the adsorbed layers into adhesive contact without causing bilayer hemifusion. Here, noticeable frictional forces are also measured.     

Nickel dithiolene complexes encapsulated in biocompatible amphiphilic diblock copolymer nanoparticles

The goal of this study is to prepare novel hybrid nanoparticles, in the form of micellar nanoparticles in aqueous media, which will combine the properties of the amphiphilic diblock copolymers (such as PEO‐b‐PPhOx and PI‐b‐PEO) with the ones of the nickel 1,2‐dithiolene (1,2‐Ni DT) complexes. The structural and morphological analysis of these nanoparticles have revealed that they can be promising for photodynamic therapy and near‐infrared (NIR) optical imaging due to their size and absorption in NIR. The micellar nanoparticles have been studied not only in aqueous solutions but also under other physiological conditions, that is, PBS and PBS‐FBS buffer solutions. Their solutions are characterized by several methods, including UV–vis spectroscopy, light scattering, and FTIR. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2507–2513     

Crowding effect induced phase transition of amphiphilic diblock copolymer in solution

The crowding agent induced phase transition of amphiphilic block copolymers in solution was explicitly considered. The influence of the size and the volume fraction of the crowding agent on the phase separation of amphiphilic diblock copolymers is investigated by using self-consistent field theory (SCFT) method. The concentration of the disorder to order transition of the block copolymer decreases when the size of the crowding agent is larger than that of the solvent. The higher volume fraction of the crowding agent will induce the transition of the block copolymer from disorder to order state at a lower concentration. The relation between the size and the volume fraction of the crowding agent is elucidated. When the size of the crowding agent is larger, its volume fraction of the disorder to order transition of the block copolymer will be lower. The conformation of the crowding agent considered as a polymer chain is also studied and compared.     

Surfactant-free synthesis of amphiphilic diblock copolymer nanoparticles via nitroxide-mediated emulsion polymerization

Amphiphilic hairy nanoparticles are prepared in a one step, batch, heterogeneous polymerization of styrene or n-butyl acrylate, using a water-soluble poly(sodium acrylate) alkoxyamine macroinitiator based on the SG1 nitroxide.     

Anomalous transition in aqueous solutions of a thermoresponsive amphiphilic diblock copolymer

The influence of shear flow on aggregation and disaggregation in aqueous solutions of the thermoresponsive methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (MPEG53-b-PNIPAAM113) copolymer that exhibits a lower critical solution temperature was investigated with the aid of turbidity, shear viscosity, and rheo small angle light scattering (rheo-SALS) methods. The turbidity results at quiescent conditions revealed a novel transition peak in the turbidity curve at intermediate temperatures, which reflects the delicate interplay between temperature-induced aggregation and shrinking of the species. A similar anomalous transition peak (located at the same temperature) was observed in the steady shear viscosity measurements at intermediate temperatures, and the amplitude of the peak was reduced with increasing shear rate as a consequence of breakup of interaggregate chains. At low temperatures (low sticking probability), enhanced shear rate generated interpolymer aggregates; whereas in the high-temperature domain (high sticking probability) association structures were broken up as the shear rate was increased. The rheo-SALS experiments disclosed growth of aggregates at low temperatures and destruction of association complexes at high temperatures. An increase of the cloud point temperature with rising shear rate is reported, which is interpreted as being a disruption of clusters under the influence of shear stresses.     

Synthesis and spectroscopy of CdS nanoparticles in amphiphilic diblock copolymer micelles

Amphiphilic diblock copolymers with the same hydrophilic but different hydrophobic blocks were used as stabilizing agents to prepare cadmium sulfide nanoparticles in aqueous solutions containing 5% of different nonaqueous solvents: methanol, THF, and acetone. Nearly spherical nanoparticles with a fair degree of monodispersity and quantum yields of 1.5%-2% were obtained. Optical absorption band edge of the CdS nanoparticles shows a >0.5 eV blueshift compared to that of bulk CdS, indicating a high degree of quantum confinement. The absorption spectra, while insensitive to the nature of the hydrophobic blocks, exhibited a clear dependence on the nature of the minor, nonaqueous solvents. The photoluminescence in all cases was broad and redshifted, indicating a predominance of surface trap-state emission. Time-resolved photoluminescence demonstrates that the trap states are populated within the first 500 fs, followed by decay with a broad range of time constants from 0.1 to >10 ns, low energy traps decaying at a slower rate than high-energy ones. Time-resolved photoluminescence anisotropy revealed that the nanoparticles experience a local microviscosity very similar to that of bulk water. The experimental observations suggest that nanoparticle formation takes place predominantly in the hydrophilic corona region of the micelles, around specific points with high local concentration of the Cd+2-coordinating basic amine groups of hydrophilic block and/or the minor, nonaqueous solvent component.     

Aqueous reversible addition‐fragmentation chain transfer dispersion polymerization of thermoresponsive diblock copolymer assemblies: Temperature directed morphology transformations

In this work, we demonstrate the formation of various 3D structures formed by a structural reorganization; a process not governed by self‐assembly. First, we packaged well‐defined diblocks, thermoresponsive poly(N‐isopropylacrylamide‐b‐styrene) or P(NIPAM‐b‐STY), into spherical particles made in situ using a reversible addition‐fragmentation chain transfer (RAFT) nanoreactor technique in water to obtain high polymer solids. The resultant spheres reorganized through a temperature stimulus to form equilibrium and kinetically trapped structures; we denote this process as temperature directed morphology transformation (TDMT). Cylinder and vesicle structures, other more unusual loop, buckled sphere and cauliflower (via ultrasound) structures were observed below the lower critical solution temperature (LCST) of PNIPAM. These structures were produced efficiently, rapidly, reproducibly at high polymer solids and can be stored for years in solution or be freeze‐dried and rehydrated without a change in structure, which becomes important in biological applications. We generated the first phase diagram for the TDMT changes of thermoresponsive diblock micelles in concentrated solutions (> 7% polymer solids) produced from narrow molecular weight diblock copolymers (PDI ～ 1.1). The sphere/cylinder and cylinder/vesicle transition in the phase diagram were surprisingly found to be predominantly dictated by the length of the hydrophilic block, poly(N‐isopropylacrylamide). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Multiple morphologies of amphiphilic diblock copolymer micelles in two and three dimensions

We show that in aqueous solution, diblock copolymers, where one block is hydrophobic and the other hydrophilic can undergo self-assembly in three dimensions in a manner similar to small molecule amphiphiles. In addition, two dimensional self-assembly has been studied at the air-water interface. We describe the various morphologies which have been observed in these systems and the parameters which we can use to tailor them.     

Influence of substrate hydrophobicity on the adsorption of an amphiphilic diblock copolymer

The adsorption of poly(tert-butylmethacrylate)-block-poly(2-(dimethylamino-ethyl) methacrylate) (PtBUMA-b-PDMAEMA) was studied by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis performed on dried samples. The copolymer was dissolved in toluene at concentrations below (0.01 wt%) and above (0.05 and 1 wt%) the CMC; silicon (SiOH) and CH(3)-grafted silicon (SiCH(3)) were used as substrates. Whatever the concentration and the substrate, a layer of individual copolymer molecules, 1.5-3 nm thick, formed rapidly. The adsorbed amount was slightly higher and the resistance to AFM tip scraping was stronger on SiOH than on SiCH(3). This is attributed to hydrogen bonding between the PDMAEMA block and the OH groups of the silicon surface, leading to polarization of the adsorbed layer. Above the CMC, on SiOH, randomly scattered dot-like features (about 5 nm high) observed by AFM were attributed to individual micelles, which were not displaced by drying. On SiCH(3), the particles found on the top of the adsorbed layer were micelle aggregates, about 50 nm thick, the lateral size of which was strongly influenced by the rate of drying. This further difference between SiCH(3) and SiOH is tentatively attributed to the exposure of PDMAEMA by the adsorbed layer formed on SiCH(3), while only PtBUMA would be exposed by the layer adsorbed on SiOH. The red blood cell shape and the size of the micelles observed in single layers indicate that the PtBUMA corona was not made compact as a result of drying.     

嵌段共聚物核交联胶束的制备与载药性能研究

在DMAP的催化和DIPC的作用下,丙烯酸的双键被引入聚乙二醇-聚己内酯嵌段共聚物的疏水链段上,制备胶束过程中使用过硫酸铵催化位于胶束内核部分的双键交联,得到的核交联胶束。在包载甲氨喋呤释放过程中,核交联胶束的累积释放率明显比非核交联胶束的小,具有良好的缓释效果。     

Local mobility and structure of cationic amphiphilic diblock copolymer micelles in aqueous solutions

The local mobility and organization of micelles formed by the cationic diblock copolymer PS-poly(N-ethyl-4-vinylpyridinium bromide) in dilute aqueous solutions is studied by spin-probe ESR spectroscopy. Micelles composed of a hydrophobic PS core and a lyophilizing polyelectrolyte corona are prepared by two methods: dialysis from a nonselective solvent and direct dispersion of the diblock copolymer in water under long-term heating. Velocity-sedimentation studies and static and dynamic light-scattering measurements show that the micelles obtained by dialysis have smaller mean hydrodynamic sizes and weight-average molecular masses and are less polydisperse than micelles prepared by direct dispersion. The ESR spectra of spin probes localized in micelles of both types are found to be identical. This finding suggests that their local structure is independent of the dispersion procedure and molecular-mass characteristics. Probes are localized in the outer layer of the PS core near the core/shell boundary, and their local mobility is a factor of ∼2 higher than the local mobility of probes in the phase of the solid PS. It is inferred that the structure of the outer layer of the PS core in micelles is looser than the structure of PS in the solid phase. The localization sites of spin probes are partially penetrated by water.     

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.     

Order-order and order-disorder transitions in thin films of an amphiphilic liquid crystalline diblock copolymer

In this study, we quantitatively investigated the temperature-dependent phase transition behaviors of thin films of an interesting amphiphilic diblock copolymer, poly(ethylene oxide)-b-poly(11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate) (p(EO)-b-p(MAAZ)) and the resulting morphological structures by using synchrotron grazing incidence X-ray scattering (GIXS) and differential scanning calorimetry. The quantitative GIXS analysis showed that the diblock copolymer in the homogeneous, isotropic melt state undergoes phase-separation near 190 degrees C and then forms a body-centered cubic (BCC) structure of spherical p(EO) domains in the p(MAAZ) matrix, at which point the p(EO) domains and the p(MAAZ) matrix are both in amorphous, liquid states. The BCC structure of spherical p(EO) domains is converted to a hexagonal cylinder structure near 120 degrees C, which is induced by the transformation of the isotropic phase of the p(MAAZ) matrix to the smectic A phase, which is composed of a laterally ordered structure of p(MAAZ) blocks with fully extended side groups. The resulting hexagonal cylinder structure is very stable below 120 degrees C. This microscopic hexagonal cylinder structure is retained as the smectic A phase of the p(MAAZ) matrix undergoes further transitions to smectic C near 104 degrees C and to a smectic X phase near 76 degrees C, while the amorphous, liquid phase of the p(EO) cylinders undergoes crystallization near -15 degrees C. These complicated temperature-dependent disorder-order and order-order phase transitions in the films were found to take place reversibly during the heating run. A face-centered orthorhombic structure of p(EO) domains was also found during the heating run and is an intermediate structure in the hexagonal cylinder structure to BCC structure transformation. We use these structural analysis results to propose molecular structure models at various temperatures for thin films of the diblock polymer.     

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.     

Synthesis and chiral micellization behavior of optically active amphiphilic diblock copolymer bearing quinine pendants

A novel optically active amphiphilic diblock copolymer bearing quinine pendants poly(ethylene oxide)‐b‐poly(glycidyl triazolyl‐L ‐quinine) (MPEO‐b‐PGTQ) was synthesized by “click” reaction of alkyne‐modified diblock copolymer poly(ethylene oxide)‐b‐poly(glycidyl propargyl ether) (MPEO‐b‐PGPE) and 9‐N₃‐quinine. The structure and composition of copolymers were characterized by gel permeation chromatography, ¹H nuclear magnetic resonance spectroscopy (¹H NMR), elemental analysis and optical rotation measurements, which showed that the synthetic route could provide the copolymer with well‐defined composition and with similar optical activity compared to its parent quinine. The micellization behavior of this chiral copolymer was investigated in different solvent systems. The results from fluorescence spectroscopy, UV spectroscopy, dynamic light scattering, transmission electron microscopy, ¹H NMR and circular dichroism (CD) spectroscopy indicated that the MPEO‐b‐PGTQ could form regular chiral spherical micelles in H₂O and Tetrahydrofuran‐H₂O (10:90, V/V) systems, and the state of aggregated chiral micelles depended on the nature of the medium. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3640–3650, 2009     

Polymeric vesicles with a hydrophobic interior formed by a thiophene-based all-conjugated amphiphilic diblock copolymer

The diblock copolymer, BP26, assembled into polymeric vesicles with double layers that formed a hydrophobic crystalline interior and a hydrophilic amorphous exterior in methanol, a selective solvent for the PEGT block. The vesicles were demonstrated to encapsulate a hydrophobic guest polyfluorene (PF).     

Remarkably stable amphiphilic random copolymer assemblies: A structure–property relationship study

Synthesis of a library of amphiphilic random copolymers from a single reactive pre‐polymer and their self‐assembly is reported. Post‐polymerization modifications of the parent polymer containing pendant N‐hydroxy succinimide (NHS) ester groups with various oligooxyethylene (OE) amines produce amphiphilic random copolymers with same degree of polymerization and equal extent of randomness. ¹H‐NMR and FT‐IR data indicate quantitative substitution in all cases. The critical aggregation concentration (CAC) for all the polymers is estimated to be in the range of 10^?5 M. Stability of these nano‐aggregates is studied by photoluminescence using time dependent F—rster Resonance Energy Transfer (FRET) between co‐encapsulated lipophilic dyes namely DiO and DiI in the hydrophobic pocket of the aggregates. These studies suggest remarkably high stability for all systems. However those with shorter hydrophilic pendant chains are found to be even more robust. Morphology is examined by high resolution transmission electron microscopy (HRTEM) which reveals multi‐micellar clusters and vesicles for polymers containing short and longer OE segments, respectively. Encapsulation efficacy is tested with both hydrophobic and hydrophilic guest molecules. All of them can encapsulate hydrophobic guest pyrene while a hydrophilic dye Calcein can be sequestered only in vesicle forming polymers. Lower critical solution temperature (LCST) is exhibited by only one polymer that contains the shortest OE chains. All polymers exhibit excellent cell viability as determined by MTT assay. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4932–4943