PEO Length Research Articles

Buffering Volume Change in Solid-State Battery Composite Cathodes with CO2-Derived Block Polycarbonate Ethers.

Polymers designed with a specific combination of electrochemical, mechanical, and chemical properties could help overcome challenges limiting practical all-solid-state batteries for high-performance next-generation energy storage devices. In composite cathodes, comprising active cathode material, inorganic solid electrolyte, and carbon, battery longevity is limited by active particle volume changes occurring on charge/discharge. To overcome this, impractical high pressures are applied to maintain interfacial contact. Herein, block polymers designed to address these issues combine ionic conductivity, electrochemical stability, and suitable elastomeric mechanical properties, including adhesion. The block polymers have “hard-soft-hard”, ABA, block structures, where the soft “B” block is poly(ethylene oxide) (PEO), known to promote ionic conductivity, and the hard “A” block is a CO2-derived polycarbonate, poly(4-vinyl cyclohexene oxide carbonate), which provides mechanical rigidity and enhances oxidative stability. ABA block polymers featuring controllable PEO and polycarbonate lengths are straightforwardly prepared using hydroxyl telechelic PEO as a macroinitiator for CO2/epoxide ring-opening copolymerization and a well-controlled Mg(II)Co(II) catalyst. The influence of block polymer composition upon electrochemical and mechanical properties is investigated, with phosphonic acid functionalities being installed in the polycarbonate domains for adhesive properties. Three lead polymer materials are identified; these materials show an ambient ionic conductivity of 10 –4 S cm–1, lithium-ion transport (tLi+ 0.3–0.62), oxidative stability (>4 V vs Li+/Li), and elastomeric or plastomer properties (G′ 0.1–67 MPa). The best block polymers are used in composite cathodes with LiNi0.8Mn0.1Co0.1O2 active material and Li6PS5Cl solid electrolyte–the resulting solid-state batteries demonstrate greater capacity retention than equivalent cells featuring no polymer or commercial polyelectrolytes.

Hierarchically Structured Conductive Polymer Binders with Silver Nanowires for High-Performance Silicon Anodes in Lithium-Ion Batteries.

Silicon (Si) anodes in lithium-ion batteries (LIBs) suffer from huge volume changes that lead to a rapid capacity decrease and short cycle life. A conductive binder can be a key factor to overcome this issue, maintaining continuous electron paths under pulverization of Si. Herein, composites of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly(vinyl alcohol) (PVA) are augmented with poly(ethylene glycol) (PEG) and poly(ethylene oxide) (PEO) as a binder for Si anodes, which forms hierarchical structures due to different chain lengths of PEG and PEO. The integration of PEG and PEO imparts higher electrical conductivity (∼40%) and stretchability (∼60%) through densely spread hydrogen bonding and cross-linking, compared to conductive polymer binders with PEO or PEG. Further, a silver nanowire (AgNW) network combined with the polymer binder supplies an effective three-dimensional (3D) electrical path, sufficient void space to buffer the volume changes, and highly adhesive interaction with the current collector. The fabricated Si anode demonstrates a higher specific capacity of 1066 mAh g-1 at 0.8 A g-1 after 100 cycles and improved rate capability.

PH- and thermo-responsive Pickering emulsion stabilized by silica nanoparticles and conventional nonionic copolymer surfactants

HypothesisPoly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) could be adsorbed on the silica surface via the hydrogen bonding between PEO and silanol (SiOH) groups. This interaction would be inhibited once SiOH is dissociated to SiO- at an increased pH value. Besides, the adsorption should be affected by temperature considering the nature of hydrogen bond. Hence, we speculate that silica nanoparticles modified in situ by adsorbed PEO-PPO-PEO possess a pH- and thermo-sensitive surface activity, making them a stimuli-responsive Pickering emulsifier. ExperimentsParaffin oil-in-water emulsions stabilized by silica nanoparticles and PEO-PPO-PEO were prepared. Stabilities, droplet morphologies and stimuli-responses were systematically studied using bottle test, optical microscopy and cryo-scanning electron microscopy (cryo-SEM). To clarify the emulsification mechanism, interfacial viscoelastic moduli and desorption energies were determined using the data obtained from drop shape analysis. FindingsSilica nanoparticles are hydrophobized and flocculated by adsorbed PEO-PPO-PEO at a relatively low pH and room temperature. Upon the pH or the temperature increased, particles regain their hydrophilicity and dispersity due to the desorption of surfactants. Emulsions stabilized by these surfactant-modified particles are pH- and thermo-responsive and can be repetitively switched between stabilization and destabilization. The switch temperature is controlled by the PEO length. The emulsification mechanism is verified in view of interfacial viscoelasticity and desorption energy. These findings demonstrate a novel and simple strategy of preparing pH- and thermo-responsive Pickering emulsions desirable to many industrial applications.

Formation of genus vesicles in dilute aqueous solution by PtBAx‐b‐PS130‐b‐PEO90‐b‐PS130‐b‐PtBAx amphiphilic pentablock terpolymers

AbstractA series of linear symmetrical ABCBA pentablock terpolymers, poly(tert‐butyl acrylate)‐b‐polystyrene‐b‐poly(ethylene oxide)‐b‐polystyrene‐b‐poly(tert‐butyl acrylate) with constant lengths of PS and PEO blocks but different degree of polymerization x of PtBA block, namely PtBAx‐b‐PS130‐b‐PEO90‐b‐PS130‐b‐PtBAx (x = 40, 75, 100, 165, and 200), were found to form various vesicular nanostructures in dilute aqueous solution as observed by conventional transition electron microscopy (TEM), cryogenic transmission electron microscopy (cryo‐TEM) and scanning electron microscopy (SEM). Genus vesicles with nanometer sizes and various genus values (g), including individual spherical vesicles, tubular vesicles (g = 0), toroidal vesicles (g = 1) and the vesicles with even larger g values (g > 1) were observed, respectively. The g value of genus vesicles formed by PtBAx‐b‐PS130‐b‐PEO90‐b‐PS130‐b‐PtBAx pentablock terpolymers decreased with the increasing length of PtBA block. The formation mechanism of genus vesicles was preliminarily discussed by the combination of membrane bending energy, the area‐difference‐elasticity and the edge effect.

PEO-PPO Diblock Copolymers Protect Myoblasts from Hypo-Osmotic Stress In Vitro Dependent on Copolymer Size, Composition, and Architecture.

Poloxamer 188, a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), protects cellular membranes from various stresses. Though numerous block copolymer variants exist, evaluation of alternative architecture, composition, and size has been minimal. Herein, cultured murine myoblasts are exposed to the stresses of hypotonic shock and isotonic recovery, and membrane integrity was evaluated by quantifying release of lactate dehydrogenase. Comparative evaluation of a systematic set of PEO-PPO diblock and PEO-PPO-PEO triblock copolymers demonstrates that the diblock architecture can be protective in vitro. Short PPO blocks hinder protection with >9 PPO units needed for protection at 150 μM and >16 units needed at 14 μM. Addition of a tert-butyl end group enhances protection at reduced concentration. When the end group and PPO length are fixed, increasing the PEO length improves protection. This systematic evaluation establishes a new in vitro screening tool for evaluating membrane-sealing amphiphiles and provides mechanistic insight to guide future copolymer design for membrane stabilization in vivo.

Protein resistance efficacy of PEO-silane amphiphiles: Dependence on PEO-segment length and concentration

In contrast to modification with conventional PEO-silanes (i.e. no siloxane tether), silicones with dramatically enhanced protein resistance have been previously achieved via bulk-modification with poly(ethylene oxide) (PEO)-silane amphiphiles α-(EtO)3Si(CH2)2-oligodimethylsiloxane13-block-PEOn-OCH3 when n=8 and 16 but not when n=3. In this work, their efficacy was evaluated in terms of optimal PEO-segment length and minimum concentration required in silicone. For each PEO-silane amphiphile (n=3, 8, and 16), five concentrations (5, 10, 25, 50, and 100μmol per 1g silicone) were evaluated. Efficacy was quantified in terms of the modified silicones’ abilities to undergo rapid, water-driven surface restructuring to form hydrophilic surfaces as well as resistance to fibrinogen adsorption. Only n=8 and 16 were effective, with a lower minimum concentration in silicone required for n=8 (10μmol per 1g silicone) versus n=16 (25μmol per 1g silicone). Statement of SignificanceSilicone is commonly used for implantable medical devices, but its hydrophobic surface promotes protein adsorption which leads to thrombosis and infection. Typical methods to incorporate poly(ethylene oxide) (PEO) into silicones have not been effective due to the poor migration of PEO to the surface-biological interface. In this work, PEO-silane amphiphiles – comprised of a siloxane tether (m=13) and variable PEO segment lengths (n=3, 8, 16) – were blended into silicone to improve its protein resistance. The efficacy of the amphiphiles was determined to be dependent on PEO length. With the intermediate PEO length (n=8), water-driven surface restructuring and resulting protein resistance was achieved with a concentration of only 1.7wt%.

Dissipative Particle Dynamics Simulation on the Nanocomposite Delivery System of Quantum Dots and Poly(styrene-b-ethylene oxide) Copolymer

Dissipative particle dynamics (DPD) simulation was used to investigate the self-assembling dynamics process of poly(styrene-b-ethylene oxide) (PS-b-PEO) block copolymer and quantum dots (QDs) in an aqueous solution. The effects of molecular weight (MW) and segment construction of a PS–PEO block copolymer on the structure and size of the self-assembled micelles were discussed. The structural properties of micelles were characterized by a radial distribution function. The simulation results are qualitatively consistent with those of previous experiments and show that there are only small QD clusters. The hydrophobic PS chains form the micelle core, while the hydrophilic PEO chains form the shell. The size of the self-assembled PS–PEO/QDs micelle increases with the MW of PS-b-PEO block copolymer and the lengths of PEO and PS segments. The simulation results indicate that the assembling process includes four sequential transient stages: (1) the random distribution of all components in aqueous solution; (2) fo...

Enhancing the protein resistance of silicone via surface-restructuring PEO-silane amphiphiles with variable PEO length.

Silicones with superior protein resistance were produced by bulk-modification with poly(ethylene oxide) (PEO)-silane amphiphiles that demonstrated a higher capacity to restructure to the surface-water interface versus conventional non-amphiphilic PEO-silanes. The PEO-silane amphiphiles were prepared with a single siloxane tether length but variable PEO segment lengths: α-(EtO)3Si(CH2)2-oligodimethylsiloxane13-block-poly(ethylene oxide) n -OCH3 (n = 3, 8, and 16). Conventional PEO-silane analogues (n = 3, 8 and 16) as well as a siloxane tether-silane (i.e. no PEO segment) were prepared as controls. When surface-grafted onto silicon wafer, PEO-silane amphiphiles produced surfaces that were more hydrophobic and thus more adherent towards fibrinogen versus the corresponding PEO-silane. However, when blended into a silicone, PEO-silane amphiphiles exhibited rapid restructuring to the surface-water interface and excellent protein resistance whereas the PEO-silanes did not. Silicones modified with PEO-silane amphiphiles of PEO segment lengths n = 8 and 16 achieved the highest protein resistance.

Synthesis and properties of aromatic polyethers containing poly(ethylene oxide) side chains as polymer electrolytes for lithium ion batteries

Polymer electrolytes consisting of polar pyridine units in the backbone and poly(ethylene oxide) (PEO) side chains are designed for possible application in lithium ion batteries. In particular, aromatic polyethers bearing PEO side chains with varying length are synthesized either by copolymerization of the corresponding PEO based diols with different arylfluorides or by modification of dihydroxyl functionalized precursor polymers with poly(ethylene oxide) methyl ether tosylate. The formation of free standing films is dependent on the PEO content, polymers' composition as well as on the different monomers used. The mechanical properties study shows that the glass transition temperature can be controlled by varying the PEO content. Thermal stability is also influenced by the PEO length: the shorter the PEO side chain, the higher the stability. XRD analysis gives information about the desired amorphous character of these polymers, which is independent of the PEO content. Solid polymer electrolytes prepared by blending the PEO-based polymers with lithium salt and PEO 2000 (used as plasticizer) show ambient temperature conductivities in the range of 10−6 S/cm. To further improve conductivity doping of PEO-based polymers in liquid electrolyte (1 M LiPF6 in EC/DMC 1/1) in some cases results in high conductivities in the range of 10−3 S cm−1 at 80 °C.

Influence of the PEO length in gas separation properties of segregating aromatic–aliphatic copoly(ether-imide)s

A complete series of aliphatic–aromatic copoly(ether-imide)s has been synthesized in this work. All these copoly(ether-imide)s had the same structure, BPDA–PEO–ODA, but different lengths of PEO in the final polymer. These copolymers have been thermally treated and characterized by several techniques. A direct relationship between the temperature of treatment, the improvement of phase segregation, and permeability has been demonstrated.The Maxwell model has been applied to predict permeability (for CO2, CH4 and N2) and it has been found that when the segregated PEO can be considered to be amorphous – it is at high temperatures when crystallinity disappears – the model fits reasonably well. This confirms that the aliphatic and aromatic portions of the copolymer behave approximately as a bi-phase of disperse domains within a continuous matrix.Results show that permeability is higher when the PEO chains are longer – when there is no crystallinity, or any kind of internal bonds, distorting the results – while selectivity does not depend on the PEO length in the copolymer. Remarkable are the results for the CO2/N2 gas pair, with selectivity-versus-permeability very near to the Robeson's upper bound at 30°C and even in closer proximity to the corresponding trade off line for higher permeation temperatures.

Structure and mechanical properties of waterborne polyurethane-based composites filled with self-assembled supramolecular nanoplatelets

New composites of waterborne polyurethane (WPU) as a matrix were prepared by incorporating rigid supramolecular nanoplatelets (SNs) as filler, which were self-assembled by the selective inclusion of β-cyclodextrin (β-CD) onto poly(propylene oxide) (PPO) segment in the poly(ethylene oxide)-block-PPO-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO). It is worth noting that, when the loading level of SN is lower than 3wt%, the SNs with moderate PEO length result in the simultaneous increase in strength, elongation and Young’s modulus in contrast with neat WPU. If there is no stretching free PEO chain, both strength and elongation decrease in spite of an increase in Young’s modulus. However, too long PEO chains result in the decrease of mechanical performances while the relatively higher loading-level of SNs also inhibits the enhancement of strength and elongation.

Solution behaviors and microstructures of PNIPAm-P123-PNIPAm pentablock terpolymers in dilute and concentrated aqueous solutions

The solution behaviors and microstructures of poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) pentablock terpolymers with various PNIPAm block lengths in dilute and concentrated aqueous solutions were investigated by micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and synchrotron small angle X-ray scattering (SAXS). Two lower critical solution temperatures (LCSTs) were observed for PNIPAmx-P123-PNIPAmx pentablock terpolymers in dilute solutions, which corresponded to LCSTs of PPO and PNIPAm blocks, respectively. The LCST of PPO block shifted from 24.4 °C to 29 °C when the length x of PNIPAm block increased from 10 to 97. The LCST of PNIPAm is around 34.5 °C-35.3 °C and less dependent on the block length x. The PNIPAmx-P123-PNIPAmx pentablock terpolymers formed "associate" structures and micelles with hydrophobic PNIPAm and PPO blocks as cores and soluble PEO blocks as coronas in dilute aqueous solutions at 20 °C and 40 °C, respectively, regardless of the relative lengths of PNIPAm, PPO and PEO blocks. The size of "associate" structures of PNIPAmx-P123-PNIPAmx pentablock terpolymers at 20 °C increased with increasing the length of PNIPAm block. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels formed in concentrated aqueous solutions (40 wt%) were strongly dependent on the environmental temperatures and relative lengths of PNIPAm, PPO and PEO blocks as revealed by SAXS. Increasing the length of PNIPAm block weakened the order structures of PNIPAmx-P123-PNIPAmx hydrogels. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels changed from mixed fcc and hex structures for PNIPAm10-P123-PNIPAm10 to isotropic structure for PNIPAm97-P123-PNIPAm97. Increasing temperature led to the transition from mixed hex and fcc structure to pure hex structure for PNIPAm10-P123-PNIPAm10 hydrogel at temperature above the LCSTs.

Structures of PEP–PEO Block Copolymer Micelles: Effects of Changing Solvent and PEO Length and Comparison to a Thermodynamic Model

Structures of poly(ethylene propylene)–poly(ethylene oxide) (PEP–PEO) block copolymer micelles were determined from small-angle X-ray scattering and static light scattering and compared to predictions from a thermodynamic model. Both the corona block length and the solvent water–ethanol ratio were changed, leading to a thorough test of this model. With increasing ethanol fraction, the PEP core–solvent interfacial tension decreases, and the solvent quality for PEO changes. The weight-average block masses were 5.0 kDa for PEP and 2.8–49 kDa for PEO. For the lowest PEO molar mass and samples in pure water (except for the highest PEO molar mass), the micelles were cylindrical; for other conditions they were spherical. The structural parameters can be reasonably well described by the thermodynamic model by Zhulina et al. [Macromolecules2005, 38 (12), 5330–5351]; however, they have a stronger dependence on solvent composition and PEO molar mass than predicted.

Abstract B115: Pharmacokinetics and biodistribution analysis using near-infrared emissive polymersomes.

Abstract Introduction: Near-infrared (NIR) emissive polymersomes are bi-layered vesicles that contain membrane-incorporated multi-porphyrin fluorophores for in vivo imaging. The high emission dipole strength NIR fluorescence of these particles allows for deeper tissue imaging relative to conventional fluorophores, creating a noninvasive technique for analysis of biodistribution and pharmacokinetics (PK) of nano-scale systems - a significant improvement over current methodology. Due to controllable membrane properties, both hydrophilic and hydrophobic compounds can be incorporated into polymersomes, offering application in tumor imaging and drug delivery. Methods: Poly(ethylene oxide)-block-polycaprolactone (PEO-b-PCL) copolymers were used to form polymersomes through thin film hydration followed by sonication, freeze/thaw cycles, and membrane extrusion. An ethyne-bridged zinc porphyrin trimer (ex = 772; em = 806nm) was incorporated into these films prior to hydration. High MW PEO(2kDa)-b-PCL(14.6kDa) and low MW PEO(1kDa)-b-PCL(4kDa) formed vesicles of 250nm and 200nm diameters, respectively. Results: Epithelial, endothelial, and liver cells were treated with PEO-b-PCL polymersomes to study the effects on proliferation and viability. These vesicles were found to be non-toxic to all three cell types. In vivo studies were carried out on balb/c mice by i.v. injection of NIR emissive polymersomes. A LI-COR Pearl® Impulse was used for real-time imaging during and after treatment, demonstrating that polymersomes could be successfully imaged deep within the mouse, due to minimal NIR scattering and absorbance and strong emission of the multi-porphyrin within the polymersome membrane. Upon injection of the polymersomes, fluorescence was detected immediately within the vasculature of the mice. Over time, fluorescence localized within the spleen and liver, as expected due to the mononuclear phagocytic system. Ex vivo biodistribution results confirmed these in vivo imaging data, with all other organs having at least an order of magnitude lower intensity. Fluorescence intensities in the spleen, liver, and femoral artery were quantified for at least 50 time points over 6 or 24 hours. Mathematical modeling was used to evaluate the intensity changes in these tissues and to estimate circulation half-lives from the change in fluorescence of the femoral artery. PK analysis of PEO(2k)-b-PCL(14.6k) 250nm polymersomes unexpectedly demonstrated circulation half-lives varying from 0.5–10 hours, perhaps due to particle aggregation. PEO(1k)-b-PCL(4k) 200nm polymersomes, on the other hand, provided consistent, yet much lower than anticipated, half-lives of 0.25 hours. This short circulation time may be due to the smaller PEO length, reducing the “stealth” characteristic of the particles. Conclusions: NIR-emissive polymersomes were found to be non-toxic to various cell lines, and were successfully used to analyze vesicle biodistribution and PK in real-time in vivo. It is expected that once a tumor model is added, the polymersomes will accumulate within the tumor perivascular space due to the EPR effect. In addition to NIR imaging agents, both water soluble and insoluble compounds can be incorporated into these structures, thus providing a nano-scale technology for tumor imaging and drug delivery. This work was supported by NIH training grant 5T32GM008555-18. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B115.

Control of the PEO Chain Conformation on Nanoparticles by Adsorption of PEO-block-Poly(l-lysine) Copolymers and Its Significance on Colloidal Stability and Protein Repellency

The physical adsorption of PEO(n)-b-PLL(m) copolymers onto silica nanoparticles and the related properties of poly(ethylene oxide) (PEO)-coated particles were studied as a function of the block copolymer composition. Copolymers adopt an anchor-buoy conformation at the particle surface owing to a preferential affinity of poly(L-lysine) (PLL) blocks with the silica surface over PEO blocks when a large excess of copolymer is used. The interdistance between PEO chains at particle surface is highly dependent on the size of PLL segments; a dense brush of PEO is obtained for short PLL blocks (DP = 10), whereas PEO chains adopt a so-called interacting "mushroom" conformation for large PLL blocks (DP = 270). The size of the PEO blocks does not really influence the copolymer surface density, but it has a strong effect on the PEO layer thickness as expected. Salt and protein stability studies led to similar conclusions about the effectiveness of a PEO layer with a dense brush conformation to prevent colloidal aggregation and protein adsorption. Besides, a minimal PEO length is required to get full stabilization properties; as a matter of fact, both PEO(45)-b-PLL(10) and PEO(113)-b-PLL(10) give rise to a PEO brush conformation but only the latter copolymer efficiently stabilizes the particles in the presence of salt or proteins.

Synthesis, characterization and application for lithium-ion rechargeable batteries of hollow silica nanospheres

Hollow silica nanospheres with uniform size of about 30 nm have been successfully synthesized using a template of ABC triblock copolymer micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS–PVP–PEO) with a core–shell–corona architecture. In this type of triblock copolymers, the PS block (core) works as a template of the void space of hollow silica, the PVP block (shell) acts as a reaction field for the sol–gel reaction of tetramethoxysilane (TMOS), and the PEO block (corona) stabilizes the polymer/silica composite particles. Use of polymers with different chain lengths of PS, PVP, and PEO led to hollow silica with tunable cavity size and wall thickness. The obtained hollow particles were thoroughly characterized by X-ray diffraction (XRD), thermal (TG/DTA) and nitrogen sorption analyses, infra-red (FT IR) and nuclear magnetic resonance (29Si MAS NMR) spectroscopies, and transmission electron microscopy (TEM). The efficiency of hollow silica nanospheres for lithium-ion rechargeable batteries is demonstrated for the first time. The hollow silica nanoparticles exhibited high cycle performance of up to 500 cycles in the lithium rechargeable batteries through the alloying/dealloying process. The tiny grain size of hollow nanospheres results in less volume expansion and/or contraction during charge/discharge cycles.

The Effect of PEO Length on the Self-Assembly of Poly(ethylene oxide)−Tetrapeptide Conjugates Prepared by “Click” Chemistry

Two series of poly(ethylene oxide)-tetrapeptide conjugates have been prepared using a "Click" reaction between an alkyne-modified tetra(phenylalanine) or tetra(valine) and various azide-terminated poly(ethylene oxide) (PEO) oligomers. Three different PEO precursors were used to prepare these conjugates, with number-average molecular weights of 350, 1200, and 1800 Da. Assembly of mPEO-F4-OEt and mPEO-V4-OEt conjugates was achieved by dialysis of a THF solution of the conjugate against water or by direct aqueous rehydration of a thin film. The PEO length has a profound effect on the outcome of the self-assembly, with the F4 conjugates giving rise to nanotubes, fibers, and wormlike micelles, respectively, as the length of the PEO block is increased. For the V4 series, the propensity to form beta-sheets dominates, and hence, the self-assembled structures are reminiscent of those formed by peptides alone, even at the longer PEO lengths. Thus, this systematic study demonstrates that the self-assembly of PEO-peptides depends on both the nature of the peptides and the relative PEO block length.

Multi-morphological biodegradable PLGE nanoparticles and their drug release behavior

A series of amphiphilic tri-block copolymers based on poly(lactide- co-glycolide)- b-poly(ethylene oxide)- b-poly(lactide- co-glycolide) (PLGE) with various segment ratios of PEO/PLGA and segment lengths of PEO were synthesized. Multi-morphological biodegradable nanoparticles – PLGE-NPs were fabricated by an improved emulsion/solvent evaporation technique in the absence of surfactant. By adjusting segment ratio of PLGA/PEO (w/w) and molecular weight of PEO, various morphological and nanoscale sized spheres, elliptic spheres, short rods and threads could be formed. The auto-assembling mechanism of the PLGE-NPs and influencing effectors of composition of the PLGE on morphology of the PLGE-NPs were discussed. The PLGE-NPs were biodegradable, and the factors that affected the degradation rate of the PLGE-NPs were also discussed. By using the amphiphilic PLGE polymer, the biodegradable nanoscale immunosuppressive agent – multi-morphological Cyclosporine (CsA)-loaded PLGE-NPs was fabricated. CsA release behavior of the CsA-loaded PLGE-NPs in vitro was determined, and the effect factors on CsA release behavior of the CsA-loaded PLGE-NPs were discussed.

Structure and Mechanical Properties of an O70 (Fddd) Network-Forming Pentablock Terpolymer

Symmetric poly(ethylene oxide-b-styrene-b-isoprene-b-styrene-b-ethylene oxide) (OSISO) pentablock terpolymers with narrow molecular weight distributions in all blocks were synthesized by anionic polymerization. These OSISO pentablock terpolymers have a common poly(styrene-b-isoprene-b-styrene) (SIS) core containing equal volume fractions of polyisoprene and polystyrene but having different lengths of terminal poly(ethylene oxide) (PEO) chains. Small-angle X-ray scattering, transmission electron microscopy, dynamic mechanical spectroscopy, and differential scanning calorimetry were used to identify two-domain lamellae, O70 (the orthorhombic Fddd network), and three-domain lamellae (LAM3) in the OSISO materials; these morphologies were previously identified in poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock terpolymers with comparable compositions. Mechanical tensile testing was employed to probe the consequences of adding different lengths of semicrystalline PEO to the ends of intrinsically tough ...

Lyotropic Phase Behavior of Poly(ethylene oxide)−Poly(butadiene) Diblock Copolymers: Evolution of the Random Network Morphology

The phase behavior of poly(ethylene oxide)−poly(butadiene) (PEO-PB) diblock copolymers mixed with water was studied using small-angle X-ray scattering (SAXS), cryogenic scanning electron microscopy (cryo-SEM), cryogenic transmission electron microscopy (cryo-TEM), and dynamic mechanical spectroscopy. Two sets of diblocks were synthesized by adding different lengths of PEO to hydroxy terminated PB with degrees of polymerization NPB = 46 and 170. Two-component mixtures were investigated as a function of block composition and copolymer molecular weight, between 1 and 100 wt % polymer content. Melt phase behavior is consistent with established theory and known experimental behavior for diblock copolymers. Various lyotropic liquid crystalline structures, notably lamellae (L), hexagonally packed cylinders (H), and spheres (S) arranged on cubic (body-centered cubic, face-centered cubic) lattices, were documented as a function of water content. At the higher molecular weights (NPB = 170), a random network phase (N) was identified over a sizable portion of the phase portrait, located between hexagonally ordered cylinders and ordered lamellae. This new structure, along with branching of cylindrical micelles in the dilute limit, bear a striking similarity to experimentally observed and theoretically predicted phase behavior in certain ternary water/oil/surfactant systems. These findings demonstrate that block copolymer surfactants are characterized by at least four structural building blocks—spheres, cylinders, bilayers, and branched cylinders—above a threshold molecular weight.