Hierarchical Self-Assembled Photo-Responsive Tubisomes from a Cyclic Peptide-Bridged Amphiphilic Block Copolymer

Typically, the morphologies of the self-assembled nanostructures from block copolymers are limited to spherical micelles, wormlike micelles and vesicles. Now, a new generation of materials with unique shape and structures, cylindrical soft matter particles (tubisomes), are obtained from the hierarchical self-assembly of cyclic peptide-bridged amphiphilic diblock copolymers. The capacity of obtained photo-responsive tubisomes as potential drug carriers is evaluated. The supramolecular tubisomes pave an alternative way for fabricating polymeric tubular structures, and will expand the toolbox for the rational design of functional hierarchical nanostructures.     

Hierarchical Self‐Assembled Photo‐Responsive Tubisomes from a Cyclic Peptide‐Bridged Amphiphilic Block Copolymer

Typically, the morphologies of the self‐assembled nanostructures from block copolymers are limited to spherical micelles, wormlike micelles and vesicles. Now, a new generation of materials with unique shape and structures, cylindrical soft matter particles (tubisomes), are obtained from the hierarchical self‐assembly of cyclic peptide‐bridged amphiphilic diblock copolymers. The capacity of obtained photo‐responsive tubisomes as potential drug carriers is evaluated. The supramolecular tubisomes pave an alternative way for fabricating polymeric tubular structures, and will expand the toolbox for the rational design of functional hierarchical nanostructures.     

Influence of electric field on the phase transitions of the hexagonal cylinder phase of diblock copolymers.

We have used the cell dynamic simulations (CDS) method to study the evolution of asymmetric and symmetric diblock copolymers under electric fields. For symmetric diblock copolymers, long-range-ordered lamellar phases form readily under electric fields. For asymmetric diblock copolymers, sphere-to-cylinder phase transitions occur rapidly when strong electric fields are applied, but it takes longer for the system to form hexagonal cylinder structures. The results of these simulations suggest that the sphere phase is stable under weak electric fields, but a threshold electric intensity exists for the sphere-to-cylinder phase transition. In addition, we also studied the kinetic pathways of the transition of the lamellar phase to the hexagonal cylinder phase of the asymmetric diblock copolymers under electric fields. Hexagonal cylinder structures form when the lamellar phase is subjected to a sudden temperature jump. The scattering functions suggest that the hexagonal cylinder structures are very regular and possess very few flaws.     

Nanofabrication in Polymer Solutions

Nanostructured materials have drawn a great deal of attention in recent yearsbecause of their promising potentials in future applications.The fabrication of nano-materials has become a highly active research area involving scientists in many differentfields,e.g.,physics,chemistry,biology and materials science and engineering. Theinorganic synthesis including biomineralization by using intermolecular bonds to act in acooperative manner in order to construct organized supramolecular systems by s…     

Controlled stacking of charged block copolymer micelles

Using poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) triblock copolymers or a mixture of different molecular weight PAA-b-PS diblock copolymers, stacks of polymeric micellar assemblies, such as disks and Y-shaped cylinders, were formed through intermicellar interactions. Whereas micelles hierarchically stacked together, micellar interactions within the stack defined a uniform micelle geometry and size for up to micrometers in length. The kinetic pathway dependence and stability of the stacked assemblies were studied, and possible intermicellar interactions between micelles within the stacks are proposed.     

Y-shaped amphiphilic brushes with switchable micellar surface structures

We observed novel nanoscale surface structures of segregated pinned micelles and craterlike micelles formed by grafted Y-shaped molecules and their reversible reorganization in selective solvents. The Y-shaped molecules have two incompatible polymer chains (polystyrene and poly(tert-butyl acrylate)) attached to a functional stemlike segment capable of covalent grafting to a functionalized silicon surface. Postgrafting hydrolysis of poly(tert-butyl acrylate) arms imparts amphiphilicity to the brush. We demonstrated that spatial constraints induced by a chemical junction of two relatively short (6-10 nm) dissimilar arms in such Y-shaped molecules lead to the formation of segregated micellar surface nanostructures in the grafted layer. We proposed a model of these segregated pinned micelles and the corresponding reverse micelles (craterlike structures) featuring different segregation states of hydrophobic polystyrene and hydrophilic poly(acrylic acid) arms. The arms undergo conformational rearrangements in selective solvents in a controlled and reversible fashion. These nanoscale structural reorganizations define adaptive macroscopic wetting surface properties of the amphiphilic Y-shaped brushes. This surface structure and switchable behavior can be considered as a promising way toward the patterning of solid substrates with adaptive nanowells, which could be used for trapping of adsorbing nanoscale objects.     

Morphology Tailoring of Thin Film Block Copolymers on Patterned Substrates

It is well known that chemically patterned substrates can direct the assembly of adsorbed layers or thin films of block copolymers. For a cylinder‐forming diblock copolymer on periodically spot‐patterned substrates, the morphology of the block copolymer follows the pattern at the substrate; however, with different periodic spacing and spot size of the pattern, novel morphologies can be created. Specifically, we have demonstrated that new morphologies that are absent in the bulk system can be tailored by judiciously varying the mismatch between the width of the pattern and the periodic spacing of the bulk block copolymer, the top surface affinity, and spot size. New morphologies can thus be achieved, such as honeycomb and ring structures, which do not appear in the bulk system. These results demonstrate a promising strategy for fabrication of new nanostructures from chemically patterned substrates.     

Amphiphilic gradient copolymers of 2‐methyl‐ and 2‐phenyl‐2‐oxazoline: self‐organization in aqueous media and drug encapsulation

Gradient (or pseudo‐diblock) copolymers were synthesized from 2‐methyl‐2‐oxazoline and 2‐phenyl‐2‐oxazoline monomer mixtures via cationic polymerization. The self‐assembling properties of these biocompatible gradient copolymers in aqueous solutions were investigated, in an effort to use the produced nanostructures as nanocarriers for hydrophobic pharmaceutical molecules. Dynamic and static light scattering as well as AFM measurements showed that the copolymers assemble in different supramolecular nanostructures (spherical micelles, vesicles and aggregates) depending on copolymer composition. Fluorescence spectroscopy studies revealed a microenvironment of unusually high polarity inside the nanostructures. This observation is related partly to the gradient structure of the copolymers. The polymeric nanostructures were stable with time. Their structural properties in different aqueous media—PBS buffer, RPMI solution—simulating conditions used in pharmacological/medicinal studies, have been also investigated and a composition dependent behavior was observed. Finally, the hydrophobic drug indomethacin was successfully encapsulated within the gradient copolymer nanostructures and the properties of the mixed aggregates were studied in respect to the initial copolymer assemblies. The produced aggregates encapsulating indomethacin showed a significant increase of their mass and size compared to original purely polymeric ones. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of copolymer architecture on the micellization and gelation of aqueous solutions of copolymers of ethylene oxide and styrene oxide

The micellar properties and solubilization capacity of poorly water soluble drugs of several micellar and gel solutions of diblock and triblock copolymers of styrene oxide/ethylene oxide have been measured and compared with block copolymers of butylene oxide/ethylene oxide, showing that the solubilization capacity of the styrene oxide block is approximately four times that of a butylenes oxide block for dilute solutions. To continue establishing the correlation between micellar characteristics and solubilization capacity, we have found it interesting to compare the micellar and gelation properties of the diblock and triblock copolymers PSO10PEO135 and PEO69PSO8PEO69 (subindexes are the number-average block lengths), with different architecture but similar average block lengths. Surface tension measurements allowed the determination of the critical micelle concentrations at several temperatures and, so, to calculate standard enthalpies of micellization. Static and dynamic light scattering data permitted us to determine micellar parameters and to obtain qualitatively the extent of hydration of the copolymer micelle. A tube inversion method was used to define the mobile-immobile (soft-hard gel) phase boundary. To refine the phase diagram and observe the existence of additional phases, rheological measurements were done. The results are in good agreement with previous values published for PSOnPEOm and PEOmPSOnPEOm copolymers.     

Self-assembly of block copolymer micelles in an ionic liquid

Four amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) diblock copolymers were shown to aggregate strongly and form micelles in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]). The universal micellar structures (spherical micelle, wormlike micelle, and bilayered vesicle) were all accessed by varying the length of the corona block while holding the core block constant. The nanostructures of the PB-PEO micelles formed in an ionic liquid were directly visualized by cryogenic transmission electron microscopy (cryo-TEM). Detailed micelle structural information was extracted from both cryo-TEM and dynamic light scattering measurements, with excellent agreement between the two techniques. Compared to aqueous solutions of the same copolymers, [BMIM][PF(6)] solutions exhibit some distinct features, such as temperature-independent micellar morphologies between 25 and 100 degrees C. As in aqueous solutions, significant nonergodicity effects were also observed. This work demonstrates the flexibility of amphiphilic block copolymers for controlling nanostructure in an ionic liquid, with potential applications in many arenas.     

pH/enzyme/light triple-responsive vesicles from lysine-based amphiphilic diblock copolymers

We report the synthesis of pH- and enzyme-responsive amphiphilic diblock copolymers through reversible addition-fragmentation chain transfer polymerization of a lysine-derived methacrylate monomer comprising p-nitrobenzyl carbamate (pNBC) functionality using a poly(ethylene glycol)-modified macro-chain transfer agent. Depending on the hydrophobic block length, the diblock copolymers self-assemble to form spherical micelles, wormlike micelles, and bilayered vesicles in the aqueous solution. The responsive behaviors of the polymeric vesicles to pH, enzyme, and light are investigated in detail. As the pH lowers to pH 5.0, the polymeric vesicles undergo a morphological transition from vesicles to spherical micelles. In the presence of nitroreductase and a cofactor NADH, the decomposition of pNBC releases the ε-NH₂ of the lysine moiety and hence induces the generation of the vesicles with crosslinked membranes at pH 7.4. Moreover, owing to the degradation of pNBC moiety under UV irradiation, the polymeric vesicles also demonstrate a photo-responsive feature. As the irradiation time prolongs, it is observed a light-triggered morphological transition from vesicles to wormlike micelles with network-like structures.     

Nonlithographic micro- and nanopatterning of TiO2 using polymer stamped molecular templates

The polymer-on-polymer stamping technique was used to template patterned TiO2 onto polymer thin films. Polystyrene-b-polyvinyl pyridine diblock copolymer (PS-b-PVP) was stamped on a layer-by-layer assembled thin film of poly(allylamine hydrochloride) and poly(acrylic acid). After rinsing the surface with a good solvent for the block copolymer, an adsorbed PS-b-PVP monolayer remained on the polyelectrolyte film, resulting in a pattern of alternating hydrophobic and carboxylic acid containing hydrophilic regions. The surface was used as a template for the selective deposition of TiO2 on the multilayer surface, using an acid-catalyzed hydrolysis of(NH4)2TiF6. Using this novel approach, we have successfully demonstrated the patterning of TiO2 film on a polyelectrolyte multilayer. Finally, nanoscale features consisting of 200 nm lines alternating with a 350 nm period was accomplished. This paper represents the first such attempt to create an all-polymer nonlithographic template for the directed deposition of TiO2 or related metal oxides; this technique, which utilizes the versatile polyelectrolyte multilayer process, enables the construction of complex polymer-inorganic microstructures suitable for electrooptical and photonic applications.     

Polyethylene diblock copolymers: Direct synthesis and morphological analysis

Polystyrene and polybutadiene were block copolymerized with high density polyethylene using a transformation reaction from an anionic to a Ziegler-Natta type polymerization. Various reaction parameters were investigated and optimized. Efficiencies of conversion of the anionic block to diblock were as high as 33% (100% normalized) consistent with the known 3/1 Li-R/Ti relationship in the active catalyst species. The activity of the polymeric Li-R/Ti catalyst with regards to ethylene polymerization was as high as 40 000 grams of polymer/mole Ti. Characterization of the resultant polymers is consistent with diblock copolymer structures but transmission electron microscopy shows distinct differences between the morphological behavior of these materials and the now well established morphological behavior of amorphous-amorphous diblock copolymers. These differences are readily explained by consideration of the interactions between the competing thermodynamic processes of microphase separation and crystallization.     

Highly Symmetric Patchy Multicompartment Nanoparticles from the Self-Assembly of ABC Linear Terpolymers in C-Selective Solvents

Multicompartment micelles, especially those with highly symmetric surfaces such as patchy-like, patchy, and Janus micelles, have tremendous potential as building blocks of hierarchical multifunctional nanomaterials. One of the most versatile and powerful methods to obtain patchy multicompartment micelles is by the solution-state self-assembly of linear triblock copolymers. In this article, we applied the simulated annealing method to study the self-assembly of ABC linear terpolymers in C-selective solvents. Simulations predict a variety of patchy and patchy-like multicompartment micelles with high symmetry and also yield a detailed phase diagram to reveal how to control the patchy multicompartment micelle morphologies precisely. The phase diagram demonstrates that the internal segregated micellar structure depends on the ratio between the volume fractions of the two solvophobic blocks and their incompatibility, whereas the overall micellar shape depends on the copolymer concentration. The relationship between the interfacial energy, stretching energy of chains and the micellar morphology, micellar morphological transition are elucidated by computing the average contact number among the species, the mean square end-to-end distances of the whole terpolymers, the AB blocks in the terpolymers, the AB diblock copolymers, and angle distribution of terpolymers. The anchoring effect of the solvophilic C block on micellar structures is also examined by comparing the morphologies formed from ABC terpolymers and AB diblock copolymers.     

Formation of vesicles in block copolymer-fluorinated surfactant complexes

Spherical micellar aggregates have been obtained in chloroform by mixing poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers with perfluorinated surfactants (FS) bearing a carboxylic acid head. These micellar aggregates are resulting from the self-assembly of the insoluble P4VP/fluorinated complexes into a core surrounded by the soluble PS coronal chains. Their characteristic features have been studied as a function of various parameters including the composition of the PS-b-P4VP copolymer, the tail length of the fluorinated surfactant, the 4VP/FS molar ratio, the number of carboxylic acid group (1 or 2) on the surfactant, the presence of the PS block and of the fluorine atoms on the surfactant. Dilution of these initial micellar aggregates triggers a morphological reorganization resulting in the formation of more stable vesicles. The extent of this morphological transition is related to the solubility of the P4VP/fluorinated complexes during the dilution process. This transition is complete for short P4VP/FS complexes, incomplete for long P4VP/FS complexes, and not observed whenever an alpha,omega-difunctional FS is used in P4VP/FS complexes, leading to a cross-linked core. Finally, the spheres-to-vesicles transition has been advantageously used in order to encapsulate molecules, as demonstrated by confocal fluorescence microscopy.     

Effect of diblock copolymers on dynamic mechanical properties of polyethylene/polystyrene blends

A systematic investigation of the dynamic mechanical properties of high-density polyethylene (HDPE)/high-impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible blend.     

Self-assembled architectures from biohybrid triblock copolymers

The synthesis and self-assembly behavior of biohybrid ABC triblock copolymers consisting of a synthetic diblock, polystyrene-b-polyethylene glycol (PSm-b-PEG113), where m is varied, and a hemeprotein, myoglobin (Mb) or horse radish peroxidase (HRP), is described. The synthetic diblock copolymer is first functionalized with the heme cofactor and subsequently reconstituted with the apoprotein or the apoenzyme to yield the protein-containing ABC triblock copolymer. The obtained amphiphilic block copolymers self-assemble in aqueous solution into a large variety of aggregate structures. Depending on the protein and the polystyrene block length, micellar rods, vesicles, toroids, figure eight structures, octopus structures, and spheres with a lamellar surface are formed.     

PDEGMA-b-PDIPAEMA copolymers via RAFT polymerization and their pH and thermoresponsive schizophrenic self-assembly in aqueous media

We report on a new doubly responsive polymeric system of amphiphilic diblock copolymers, namely poly(di-[ethylene glycol] methyl ether methacrylate)-b-poly(2-[diisopropylamino] ethyl methacrylate), PDEGMA-b-PDIPAEMA, obtained by the reversible addition-fragmentation chain transfer (RAFT) polymerization technique. Molecular characterization by size exclusion chromatography (SEC), nuclearmagnetic resonance (¹H-NMR) and infrared spectroscopy (FT-IR) confirms the successful synthesis of these novel block copolymers. The PDEGMA-b-PDIPAEMA block copolymers formed aggregates in aqueous media in response to solution pH and temperature changes, as evidenced by dynamic and static light scattering techniques, as well as fluorescence spectroscopy. Aggregates with PDEGMA core and PDIPAEMA corona domains are formed at elevated temperatures and low pH, whereas aggregates with PDIPAEMA cores and PDEGMA coronas are formed at neutral and high pH. Overall structural characteristics and solution behavior of the copolymers are affected by the copolymer composition. The obtained results provide valuable new information on the behavior and design guidelines for the construction of stimuli responsive, “schizophrenic” polymeric nanostructures with potential application in the biomedical field.     

Synthesis and characterization of well‐defined optically active methacrylic diblock copolymers

A new, simple, and cost‐effective approach toward the development of well‐defined optically active diblock copolymers based on methacrylate monomers is described for the first time. Starting from the low‐cost optically active (S)‐(?)‐2‐methyl‐1‐butanol, a new optically active methacrylic monomer, namely, (S)‐(+)‐2‐methyl‐1‐butyl methacrylate [(S)‐(+)‐MBuMA], was synthesized. Reversible addition fragmentation chain transfer polymerization was then used for preparing well‐defined poly[(S)‐(+)‐MBuMA] homopolymers and water‐soluble diblock copolymers based on [(S)‐(+)‐MBuMA] and the hydrophilic and ionizable monomer 2‐(dimethyl amino)ethyl methacrylate (DMAEMA). The respective homopolymers and diblock copolymers were characterized in terms of their molecular weights, polydispersity indices, and compositions by size exclusion chromatography and ¹H NMR spectroscopy. Polarimetry measurements were used to determine the specific optical rotations of these systems. The structural and compositional characteristics of micellar nanostructures possessing an optically active core generated by p((S)‐(+)‐MBuMA)‐b‐p(DMAEMA) chains characterized by predetermined molecular characteristics may be easily tuned to match biological constructs. Consequently, the aggregation behavior of the p[(S)‐(+)‐MBuMA]‐b‐p[DMAEMA] diblock copolymers was investigated in aqueous media by means of dynamic light scattering and atomic force microscopy, which revealed the formation of micelles in neutral and acidified aqueous solutions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Exploiting photoinduced reactions in polymer blends to create hierarchically ordered, defect-free materials

Computer simulations reveal how photoinduced chemical reactions can be exploited to create long-range order in binary and ternary polymeric materials. The process is initiated by shining a spatially uniform light over a photosensitive AB binary blend, which thereby undergoes both a reversible chemical reaction and phase separation. We then introduce a well-collimated, higher intensity light source. Rastering this secondary light over the sample locally increases the reaction rate and causes formation of defect-free, spatially periodic structures. These binary structures resemble either the lamellar or hexagonal phases of microphase-separated diblock copolymers. We measure the regularity of the ordered structures as a function of the relative reaction rates for different values of the rastering speed and determine the optimal conditions for creating defect-free structures in the binary systems. We then add a nonreactive homopolymer C, which is immiscible with both A and B. We show that this component migrates to regions that are illuminated by the secondary, higher intensity light, allowing us to effectively write a pattern of C onto the AB film. Rastering over the ternary blend with this collimated light now leads to hierarchically ordered patterns of A, B, and C. The findings point to a facile, nonintrusive process for manufacturing high quality polymeric devices in a low-cost, efficient manner.