Synthesis of PB−PEO and PI−PEO Block Copolymers with Alkyllithium Initiators and the Phosphazene Base <i>t</i>-BuP<sub>4</sub>

Förster, Stephan; Krämer, Eckart

doi:10.1021/ma981597u

Cited by 125 publications

(117 citation statements)

References 6 publications

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“…anionic polymerization, yielding a block copolymer with narrow polydispersity M w /M n = 1.02, where M w and M n are the weight-and numberaveraged molecular weights, respectively. The synthesis and characterization of PI-PEO is described in detail elsewhere (30). PEB 39 -PEO 102 (mean M w = 7,700 g·mol…”

Section: Methodsmentioning

confidence: 99%

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Trebbin¹,

Steinhauser

Perlich³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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164

147

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The flow orientation of anisotropic particles through narrow channels is of importance in many fields, ranging from the spinning and molding of fibers to the flow of cells and proteins through thin capillaries. It is commonly assumed that anisotropic particles align parallel to the flow direction. When flowing through narrowed channel sections, one expects the increased flow rate to improve the parallel alignment. Here, we show by microfocus synchrotron X-ray scattering and polarized optical microscopy that anisotropic colloidal particles align perpendicular to the flow direction after passing a narrow channel section. We find this to be a general behavior of anisotropic colloids, which is also observed for disk-like particles. This perpendicular particle alignment is stable, extending downstream throughout the remaining part of the channel. We show by microparticle image velocimetry that the particle reorientation in the expansion zone after a narrow channel section occurs in a region with considerable extensional flow. This extensional flow is promoted by shear thinning, a typical property of complex fluids. Our discovery has important consequences when considering the flow orientation of polymers, micelles, fibers, proteins, or cells through narrow channels, pipes, or capillary sections. An immediate consequence for the production of fibers is the necessity for realignment by extension in the flow direction. For fibrous proteins, reorientation and stable plug flow are likely mechanisms for protein coagulation.block copolymers | microfluidics | small-angle X-ray scattering T he flow orientation of anisotropic particles in narrow channels is relevant in many fields, ranging from the spinning and molding of fibers to the flow of cells or proteins through thin capillaries (1-4). It is commonly assumed that anisotropic particles align parallel to the flow direction (5). When flowing through thin channel sections, one expects the increased flow rate to improve the alignment. We investigated the alignment of anisotropic colloids (i.e., cylindrical micelles) flowing through thin sections of microchannels using synchrotron microfocus small-angle X-ray diffraction and polarized optical microscopy. Surprisingly, we find that anisotropic colloids orient perpendicular to the flow direction after passing through narrow channel sections. The perpendicular alignment is surprisingly stable, extending throughout the remaining part downstream of the channel. Ongoing experimental studies indicate that this observation holds for other anisotropic cylindrical or disk-like colloids as well. We show by microparticle image velocimetry and finite element fluid dynamics simulations that the perpendicular flow orientation is induced by perpendicular extensional flow in the expansion zone after the narrow section. Only close to the channel walls does shear flow dominate, leading to parallel flow orientation of anisotropic particles.In situ investigations of the flow orientation of colloids in solution under very well-defined flow conditi...

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Section: Methodsmentioning

confidence: 99%

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Trebbin¹,

Steinhauser

Perlich³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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164

147

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“…Polymer synthesis PB 33 -PEO 18 was synthesized using anionic polymerization 106 . Butadiene (Bd) and ethylene oxide (EO) monomers were purified and afterwards dried using liquid nitrogen and destilled over n-dibutylmagnesium (n-Bu 2 Mg) and nbutyl lithium (n-BuLi) to remove any traces of water.…”

Section: Methodsmentioning

confidence: 99%

“…Non-stabilized THF was used as eluent, and the system was calibrated with polystyrene standard samples having very narrow molar mass distributions. For EO polymerization, the remaining EO was added and 1-tert-Butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphor-anylidenamino]-2λ 5 ,4λ 5 -catenadi(phosphazene) (tBuP4) was injected afterwards in a molar n-BuLi:tBuP4 ratio of 1:1 to ensure exact stoichiometry 106 . The reaction was heated afterwards to 40 • C to start EO chain propagation.…”

Section: Methodsmentioning

confidence: 99%

Selecting analytical tools for characterization of polymersomes in aqueous solution

Habel

Ogbonna²,

Larsen

et al. 2015

RSC Adv.

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Selecting the appropriate analytical methods for characterizing the assembly and morphology of polymer-based vesicles, or polymersomes are required to reach their full potential in biotechnology. This work presents and compares 17 different techniques for their ability to adequately report size, lamellarity, elastic properties, bilayer surface charge, thickness and polarity of polybutadienepolyethylene oxide (PB-PEO) based polymersomes. The techniques used in this study are broadly divided into scattering techniques, visualization methods, physical and electromagnetical manipulation, sorting/purification, and simulation tools. Of the analytical methods tested, Cryo-TEM and AFM turned out to be advantageous for polymersomes with smaller diameter than 200 nm, whereas confocal microscopy is ideal for diameters > 400nm. Polymersomes in the intermediate diameter range can be characterized using FF-Cryo-SEM and NTA. SAXS provides reliable data on bilayer thickness and internal structure, Cryo-TEM on multilamellarity. Taken together, these tools are valuable for characterizing polymersomes per se but the comparative overview is also intended to serve as a starting point for selecting methods for characterizing polymersomes with encapsulated compounds or polymersomes with incorporated biomolecules (e.g. membrane proteins).

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“…Recently, giant bilayer vesicles with a typical size of 10 m made of a homogenous diblockcopolymer membrane, so-called polymersomes, could be obtained in aqueous solution [6]. In this Letter, we report on the remarkable property of polybutadiene (32)-b-polyethylenoxide (20) (PB-PEO) molecules [7] to self-assemble into giant vesicles with a wall formed either by a double bilayer, which is connected by a lattice of passages, or a tubular network with hexagonal symmetry. The passages form the dual lattice of the hexagonal tubular network.…”

mentioning

confidence: 93%

Giant Hexagonal Superstructures in Diblock-Copolymer Membranes

et al. 2002

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We have observed polymersomes of high genus with their vesicle wall organized on the micrometer scale either in a double bilayer connected by a lattice of passages or a tubular network with hexagonal symmetry. Experimentally found shape classes are identified within a theoretical phase diagram based on the bending energy of the polymer membrane. Pronounced morphological changes could be induced and controlled by temperature.

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Synthesis of PB−PEO and PI−PEO Block Copolymers with Alkyllithium Initiators and the Phosphazene Base t-BuP₄

Cited by 125 publications

References 6 publications

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Selecting analytical tools for characterization of polymersomes in aqueous solution

Giant Hexagonal Superstructures in Diblock-Copolymer Membranes

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Synthesis of PB−PEO and PI−PEO Block Copolymers with Alkyllithium Initiators and the Phosphazene Base t-BuP4

Cited by 125 publications

References 6 publications

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Anisotropic particles align perpendicular to the flow direction in narrow microchannels

Selecting analytical tools for characterization of polymersomes in aqueous solution

Giant Hexagonal Superstructures in Diblock-Copolymer Membranes

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Product

Resources

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Synthesis of PB−PEO and PI−PEO Block Copolymers with Alkyllithium Initiators and the Phosphazene Base t-BuP₄