Controlling Internal Pore Sizes in Bicontinuous Polymeric Nanospheres

Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17?kDa and hydrophilic weight fractions of ?0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460?nm. Significantly, altering the block copolymer hydrophilic–hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19?nm

Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release

Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amounts of silica nanoparticles of approximately 18 nm diameter. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis. Encapsulation efficiencies can be calculated using disk centrifuge photosedimentometry, since the vesicle density increases at higher silica loadings while the mean vesicle diameter remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is observed at q ≈ 0.25 nm–1. A new two-population model provides satisfactory data fits to the SAXS patterns and allows the mean silica volume fraction within the vesicles to be determined. Finally, the thermoresponsive nature of the diblock copolymer vesicles enables thermally triggered release of the encapsulated silica nanoparticles simply by cooling to 0–10 °C, which induces a morphological transition. These silica-loaded vesicles constitute a useful model system for understanding the encapsulation of globular proteins, enzymes, or antibodies for potential biomedical applications. They may also serve as an active payload for self-healing hydrogels or repair of biological tissue. Finally, we also encapsulate a model globular protein, bovine serum albumin, and calculate its loading efficiency using fluorescence spectroscopy

Complementary light scattering and synchrotron small-angle X-ray scattering studies of the micelle-to-unimer transition of polysulfobetaines

YesAB and ABA di- and triblock copolymers where A is the hydrophilic poly(oligoethylene glycol methacrylate) (POEGMA) block and B is a thermo-responsive sulfobetaine block [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (PDMAPS) were synthesised by aqueous RAFT polymerisation with narrow dispersity (ĐM ≤ 1.22), as judged by aqueous SEC analysis. The di- and triblock copolymers self-assembled in salt-free water to form micelles with a PDMAPS core and the self-assembly of these polymers was explored by SLS and TEM analysis. The micelles were shown, by DLS analysis, to undergo a micelle-to-unimer transition at a critical temperature, which was dependent upon the length of the POEGMA block. Increasing the length of the third, POEGMA, block decreased the temperature at which the micelle-to-unimer transition occurred as a result of the increased hydrophilicity of the polymer. The dissociation of the micelles was further studied by SLS and synchrotron SAXS. SAXS analysis revealed that the micelle dissociation began at temperatures below that indicated by DLS analysis and that both micelles and unimers coexist. This highlights the importance of using multiple complementary techniques in the analysis of self-assembled structures. In addition the micelle-to-unimer morphology transition was employed to encapsulate and release a hydrophobic dye, Nile Red, as shown by fluorescence spectroscopy.Engineering and Physical Sciences Research Council (EPSRC), University of Warwic

Temperature-responsive polymer cubosomes from semi-crystalline amphiphilic block copolymers

Amphiphilic block copolymers self-assemble in water to form discrete aggregates of different morphologies so as to minimize the interaction of the hydrophobic moiety with the surrounding aqueous medium. The most commonly observed morphologies are spherical micelles, cylindrical micelles and vesicles; however, more complex morphologies such as disk-like micelles, toroids and internally-structured nanospheres are becoming more frequently observed and targeted in synthesis. The type of morphology formed is fundamentally dependent upon the block copolymer composition and structure, and so the synthesis of well-defined block copolymers is a necessity for the production of designer nanoparticles. To this end, controlledl"living" polymerization techniques are utilized to yield block copolymers with well-defined structure and functionality, and the synthesis of stimuli-responsive block copolymers allows for the formation of smart aggregates. This work presents the formation of nanospheres with complex internal structure from semi-crystalline amphiphilic block copolymers of poly( ethylene oxide) and poly( octadecyl methacrylate). The block copolymers were synthesized using atom transfer radical polymerization (ATRP) to enable control over the relative compositions and molecular weight. Aqueous dispersions of the block copolymers yielded complex polymer cubosomes: nanospheres with internal bicontinuous morphology. The internal structure was investigated and characterized using microscopy techniques and the. effects of block composition and preparation conditions on the morphology were investigated. The nanospheres exhibited temperature-responsive behaviour which stemmed from the hydrophobic PODMA block. The internal structure and thermal behaviour of these aggregates provide the possibility of their application as a temperature-controlled delivery system.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Octadecyl acrylate - Methyl methacrylate block and gradient copolymers from ATRP: Comb-like stabilizers for the preparation of micro- and nano-particles of poly(methyl methacrylate) and poly(acrylonitrile) by non-aqueous dispersion polymerization

Three random and three block copolymers of methyl methacrylate (MMA) and octadecyl acrylate (ODA) were synthesized by atom transfer radical polymerization. These copolymers were assessed for their application as stabilizers in the one-step non-aqueous dispersion (NAD) polymerization of MMA and of acrylonitrile (AN) in a non-polar solvent mixture of hexane and dodecane. In all cases stable spherical micro-particle colloidal dispersions were formed with particle diameters in the range of 62-2725 nm for PMMA. Uniform monodisperse PMMA particles with standard deviations in size distributions of less than 5% were obtained in two cases demonstrating the utility of ODA:MMA copolymers as replacement preformed stabilizers in the one-step synthesis of MMA micro-spheres. Overall the block copolymer PMMA(64)-block-PODA(36) gave greater control over size when varying the solvent: monomer ration than a related gradient PMMA-PODA copolymer. These copolymers were further used as stabilizers in the one-step NAD polymerization of MMA with ethylene glycol dimethacrylate (EGDMA) under similar conditions allowing for the preparation of monodisperse cross-linked PMMA particles with diameters ranging from 110 to 1700 nm. The general utility of the copolymers as stabilizers was demonstrated by the NAD polymerization of acrylonitrile (AN) in non-polar solvent mixture of hexane and dodecane giving 'crumpled' latex dispersions with particle diameters in the range 85-483 nm. (C) 2010 Elsevier Ltd. All rights reserved

Assessing internal structure of polymer assemblies from 2D to 3D CryoTEM: Bicontinuous micelles

The self-assembly behaviour of block copolymers in solution has been of significant interest over the past two decades for a number of applications — for example, as delivery vectors and micro-reactors. More recently, attention has turned to the formation of aggregates with complex internal structure, such as multi-compartment micelles and the so-called “Janus” particles (biphasic aggregates) for their promising application as vectors for the simultaneous inclusion of chemically-different encapsulates and their possible catalytic and templating properties. The challenge has been to observe these complex aggregates in such a way as to be able to characterise their internal morphology whilst preserving their intricate structure. To this end, cryogenic transmission electron microscopy (cryoTEM) has become a powerful and indeed a necessary tool for the elucidation and observation of self-assembled polymer systems. Through its use, a new class of complex micelles has been discovered: amphiphilic block copolymer nanospheres with internal bicontinuous structure. These structures have been observed from a variety of block copolymer amphiphiles, although rarely. Intriguingly, there is no seemingly obvious unifying blueprint for their formation. This review will present the importance of cryoTEM in the elucidation and characterisation of internally-structured polymeric aggregates in recent years and highlight its significance in the definition of bicontinuous dispersions

Self-Assembled Amphiphilic Block Copolymers

No abstract availabl

Temperature-Responsive Nanospheres with Bicontinuous Internal Structures from a Semicrystalline Amphiphilic Block Copolymer

Internally structured self-assembled nanospheres, cubosomes, are formed from a semicrystalline block copolymer, poly(ethylene oxide)-block-poly(octadecyl methacrylate) (PEO39-b-PODMA17), in aqueous dispersion. The PODMA block provides them with a temperature-responsive structure and morphology. Using cryo-electron tomography, we show that at room temperature these internally bicontinuous aggregates undergo an unprecedented order?disorder transition of the microphase-separated domains that is accompanied by a change in the overall aggregate morphology. This allows switching between spheres with ordered bicontinuous internal structures at temperatures below the transition temperature and more planar oblate spheroids with a disordered microphase-separated state above the transition temperature. The bicontinuous structures offer a number of possibilities for application as templates, e.g., for biomimetic mineralization or polymerization. Furthermore, the unique nature of the thermal transition observed for this system offers up considerable possibilities for their application as temperature-controlled release vessels