PEO Homopolymer Research Articles

Segmental Dynamics of Ethylene Oxide-Containing Polymers with Diverse Backbone Chemistries

The dielectric response of seven nonionic ethylene oxide-containing polymers are investigated. Four different backbone chemistries are considered, including polymethacrylate, polyester ether, polyphosphazene, and polysiloxane. The chemistry of the backbone and the linking chemistry to incorporate ether oxygen (EO) groups dramatically affect polymer segmental dynamics. The Tg of the inorganic backbone polymers is ∼15 °C lower than that of the PEO homopolymer. Polysiloxanes exhibit the lowest Tg of −86 °C when attached with pendent −(CH2–CH2–O)4–CH3 groups. The strength of the alpha relaxation is the same for the hydrocarbon backbone polymers (Δε = 10), whereas the dielectric constants of inorganic polymers with short pendent groups is lower (Δε = 3). The difference in relaxation strengths is due to restricted motion of ether oxygens close to the backbone. This effect diminishes as the relative backbone concentration is decreased by increasing the pendent EO length. As pendent EO chain length is increased, the segmental relaxation broadens due to ether oxygens experiencing different local environments.

Langmuir monolayers of non-ionic polymers: Equilibrium or metastability? Case study of PEO and its PPO–PEO diblock copolymers

Stability and reorganization in Langmuir films of PEO in PEO homopolymers and PPO–PEO block copolymers were investigated using film balance measurements. The apparent fractional losses of EO segments transferred into the subphase resulting from successive compression–expansion cycles have been estimated. The apparent loss is mainly Γmax, Mn and time-dependent. At surface concentrations Γ⩽0.32mg/m2, PEO films are in equilibrium. For 0.32⩽Γ⩽0.7mg/m2, the losses remain modest. Further compression leads to densification of the monolayer, requiring the interplay of thermodynamics and kinetic factors In the plateau regime, the loss is higher and constant for 1⩽Γmax⩽2mg/m2 upon maintaining the achieved surface area for 15min. Similar losses were obtained for PEO homopolymers of high Mn and PPO353–PEO2295. It suggests that the PEO remains anchored in a metastable state at the air–water interface at surface concentration well above the onset of the plateau. Additional losses are incurred for PEO homopolymers for monolayers kept compressed in the plateau for 2h. For the interpretation of these phenomena a combination of elements from self-consistent field theory and scaling is desirable with as a trend an increasing contribution of the latter with increasing surface concentration.

Self‐Organization of Poly(ethylene oxide) on the Surface of Aqueous Salt Solutions

It is demonstrated that stable Langmuir films of poly(ethylene oxide) (PEO) can be formed up to surface pressures of 30 mN m(-1) when potassium carbonate K2CO3 is added to the aqueous subphase. Generally, PEO homopolymer cannot stay on the water surface at a surface pressure ≥10 mN m(-1) due to its high water solubility. To prepare stable monolayer films, PEO can be modified with hydrophobic moieties. However, by exploiting the salting out effect by adding certain salts (K2CO3 or MgSO4) into the aqueous subphase, not only very stable films but also unusual self-organization can be achieved by the PEO homopolymer on the surface of the aqueous solution. Thus, a series of OH-terminated PEOs is found to form a stable monolayer at K2CO3 concentrations of 2 M and above in the aqueous subphase, and the stability of the film increases with an increase in K2CO3 concentration. Hysteresis experiments are also carried out. During the phase transition induced by progressive compression, self-organization into well-defined domains with sizes in the micrometer range are observed, and with further compression and holding of the film for 30 min and above the microdomains transform into a crystalline morphology as visualized by Brewster angle microscopy.

Thermoreversible partitioning of poly(ethylene oxide)s between water and a hydrophobic ionic liquid.

We describe a poly(ethylene oxide) (PEO) homopolymer "shuttle" between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). PEO homopolymers with varying molecular weight transferred reversibly and quantitatively between water at room temperature and [EMIM][TFSI] at an elevated temperature. The temperature of the transfer from water to [EMIM][TFSI] shows a linear dependence on PEO molecular weight and a dependence on polymer concentration consistent with expectation based on Flory-Huggins theory. These results are also consistent with the previously observed lower critical solution temperature (LCST) behavior of PEO in water. Dynamic light scattering study of the concentration and temperature dependence of the swelling degree of PEO corona of polybutadiene (PB)-PEO block copolymer micelles indicates that the solvent quality of [EMIM][TFSI] for PEO remains essentially the same as a good solvent over the temperature range of the PEO shuttle. Fundamental understanding of the PEO shuttle is of significance in development of systems for phase transfer of reagents and reaction products between ionic liquids and water.

Competitive Adsorption Between PEO-Containing Block Copolymers and Homopolymers at Silica

The ability to manipulate polymer adsorption is useful for applications involving colloidal stabilization, for example, paints, cosmetics, lubricants, and mineral and waste-water treatment. We have an ongoing interest on the use of organic molecules for modulating the aqueous solution and adsorption properties of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymers. In the present study, the influence of low molecular weight PEO homopolymer on the adsorption of a representative PEO–PPO–PEO block copolymer (Pluronic P105: EO37-PO56-EO37) at the surface of protonated silica nanoparticles dispersed in water is investigated. Pluronic P105 forms hydrophobic domains on the surface of protonated silica at a critical surface micelle concentration, csmc, of 0.02 wt% in the presence of 0.1 wt% silica nanoparticles in water, well below the cmc of Pluronic P105 in water (0.6 wt%). Dye solubilization experiments reveal an increase in the PEO–PPO–PEO block copolymer csmc with increasing amounts of added PEO homopolymer. The resulting critical displacer concentration for PEO homopolymer of molecular weights 200 and 600 Da was measured to be 0.1 wt% and 0.07 wt%, respectively, in the presence of 0.1 wt% silica nanoparticles. Capillary viscometry measurements indicate a decrease in the adsorbed layer thickness at the protonated silica surface with increasing PEO homopolymer concentration. The data presented herein are consistent with a physical model which considers “patches” of PEO–PPO–PEO block copolymer and PEO homopolymer adsorbed at the silica surface.

Coarse-Graining Poly(ethylene oxide)–Poly(propylene oxide)–Poly(ethylene oxide) (PEO–PPO–PEO) Block Copolymers Using the MARTINI Force Field

The MARTINI coarse-grain (CG) force field is extended for a class of triblock block copolymers known as Pluronics. Existing MARTINI bead types are used to model the non-bonded part of the potential while single chain properties for both homopolymers, poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), are used to develop the bonded interactions. The new set of force field parameters reproduces structural and dynamical properties of high molecular weight homo- and copolymers. The CG model is moderately transferable in solvents of different polarity and concentration; however, the PEO homopolymer model presents a reduced thermodynamic transferability especially in water probably due to the lack of hydrogen bonds with the solvent. Our simulations of a monolayer of Pluronic L44 show polymer-brush-like characteristics for the PEO segments which protrude into the aqueous phase. Other membrane properties not easily accessible using experimental techniques such as its membrane thickness are also calculated.

Effect of Poly(ethylene oxide) Homopolymer and Two Different Poly(ethylene oxide-b-poly(propylene oxide)-b-poly(ethylene oxide) Triblock Copolymers on Morphological, Optical, and Mechanical Properties of Nanostructured Unsaturated Polyester

Novel nanostructured unsaturated polyester resin-based thermosets, modified with poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and two poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) block copolymers (BCP), were developed and analyzed. The effects of molecular weights, blocks ratio, and curing temperatures on the final morphological, optical, and mechanical properties were reported. The block influence on the BCP miscibility was studied through uncured and cured mixtures of unsaturated polyester (UP) resins with PEO and PPO homopolymers having molecular weights similar to molecular weights of the blocks of BCP. The final morphology of the nanostructured thermosetting systems, containing BCP or homopolymers, was investigated, and multiple mechanisms of nanostructuration were listed and explained. By considering the miscibility of each block before and after curing, it was determined that the formation of the nanostructured matrices followed a self-assembly mechanism or a polymerization-induced phase separation mechanism. The miscibility between PEO or PPO blocks with one of two phases of UP matrix was highlighted due to its importance in the final thermoset properties. Relationships between the final morphology and thermoset optical and mechanical properties were examined. The mechanisms and physics behind the morphologies lead toward the design of highly transparent, nanostructured, and toughened thermosetting UP systems.

PBT-b-PEO-b-PBT triblock copolymers: Synthesis, characterization and double-crystalline properties

We demonstrated here a facile method to synthesize novel double crystalline poly(butylene terephthalate)-block-poly(ethylene oxide)-block-poly(butylene terephthalate) (PBT-b-PEO-b-PBT) triblock copolymers by solution ring-opening polymerization (ROP) of cyclic oligo(butylene terephthalate)s (COBTs) using poly(ethylene glycol) (PEG) as macroinitiator and titanium isopropyloxide as catalyst. The structure of copolymers was well characterized by 1H NMR and GPC. TGA results revealed that the decomposition temperature of PEO in triblock copolymers increased about 30 °C to the same as PBT copolymers, after being end-capped with PBT polymers. These triblock copolymers showed double crystalline properties from PBT and PEO blocks, observed from DSC and WAXD measurements. The melting and crystallization peak temperatures corresponding to PBT blocks increased with PBT content. The crystallization of PBT blocks showed the strong confinement effects on PEO blocks due to covalent linking of PBT blocks with PEO blocks, where the melting and crystallization temperatures and crystallinity corresponding to PEO blocks decreased significantly with increment of PBT content. The confinement effect was also observed by SAXS experiments, where the long distance order between lamella crystals decreases with increasing PBT length. For the triblock copolymer with highest PBT content (PBT54-b-PEO227-b-PBT54), this effect shows a 30 °C depression on PEO crystals' melting temperature and 77% on enthalpy, respectively, compared to corresponding PEO homopolymer. The crystal morphology was observed by POM, and amorphous-like spherulites were observed during PBT crystallization.

Interplay between Crystallization and Phase Separation in PS-b-PMMA/PEO Blends: The Effect of Confinement

Interplay between phase separation and crystallization under confinement for the blends of PEO homopolymers with different molecular weight and PS-b-PMMA block copolymer is studied. Phase structures of the blends are investigated by atomic force microscope (AFM) and theoretically simulated by the dissipative particle dynamics (DPD) method, and a phase diagram describing the phase structure is established. Low molecular weight PEO (PEO2) disperses uniformly in the PMMA block domain and causes a transition from cylinder phase to perforated lamellar phase, while high molecular weight PEO (PEO20) causes expansion of the cylinder domains and formation of disordered domains. Crystallization and melting behavior of the blends are detected by differential scanning calorimetry (DSC). The results show the liquid–liquid phase separation between PEO homopolymer and PMMA block under PS-b-PMMA microphase-separated structure is suppressed due to the hard confinement caused by glassy PS block. As a result, in the blends of PS-b-PMMA/PEO2, PEO2 is unable to crystallize, and in the blends of PS-b-PMMA/PEO20, PEO20 shows a more obvious melting point depression compared with the homopolymer blends of PMMA/PEO20.

Hexagonally Arranged Nanopore Film Fabricated via Selective Etching by 172-nm Vacuum Ultraviolet Light Irradiation

Highly ordered nanopore arrays were successfully fabricated using poly(ethylene oxide) (PEO) and polymethacrylate with azobenzene mesogen in side chains [PMA(Az)] block copolymer film based on irradiation of 172-nm vacuum ultraviolet (VUV) light. The block copolymer forms a highly ordered microphase-separated film with perpendicularly oriented PEO cylinders just by thermal annealing through a self-assembling process. We found that the etching rate of the PEO homopolymer was much higher than that of the PMA(Az) homopolymer at a chamber pressure of 102 Pa of atmosphere under VUV irradiation. The etching rate of the PEO component in the two systems of microphase separation and macrophase separation of the homopolymer blend crucially depended on the feature size of phase separation. In the PEO selective etching process of the block copolymer film, the water-contact angle of the film dramatically increased due to elimination of hydrophilic PEO. The resulting nanopore array film will be useful for low-density target materials.

Experimental measurement of coil-rod-coil block copolymer tracer diffusion through entangled coil homopolymers.

The diffusion of coil-rod-coil triblock copolymers in entangled coil homopolymers is experimentally measured and demonstrated to be significantly slower than rod or coil homopolymers of the same molecular weight. A model coil-rod-coil triblock was prepared by expressing rodlike alanine-rich α-helical polypeptides in E. coli and conjugating coillike poly(ethylene oxide) (PEO) to both ends to form coil-rod-coil triblock copolymers. Tracer diffusion through entangled PEO homopolymer melts was measured using forced Rayleigh scattering at various rod lengths, coil molecular weights, and coil homopolymer concentrations. For rod lengths, L, that are close to the entanglementh length, a, the ratio between triblock diffusivity and coil homopolymer diffusivity decreases monotonically and is only a function of L/a, in quantitative agreement with previous simulation results. For large rod lengths, diffusion follows an arm retraction scaling, which is also consistent with previous theoretical predictions. These experimental results support the key predictions of theory and simulation, suggesting that the mismatch in curvature between rod and coil entanglement tubes leads to the observed diffusional slowing.

Adsorption of Pluronic block copolymers on silica nanoparticles

Polymers on the surface of nanoparticles are of great scientific and technological importance since they dictate many important properties and functions of dispersed systems. We investigate here the organization of a representative poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer on silica nanoparticles dispersed in water. Pluronic P105 (EO36PO56EO36) adsorbs on protonated silica and starts forming hydrophobic domains above a certain bulk polymer concentration, called critical surface micelle concentration (csmc), which is lower than the critical micelle concentration (cmc) of Pluronic P105 in plain water. The csmc decreases with increasing particle concentration and decreasing particle size. Below its csmc, the PEO–PPO–PEO block copolymer adsorption on protonated silica nanoparticles is similar to the adsorption of PEO homopolymers. Above the csmc, the block copolymers form micelle-like aggregates on protonated silica nanoparticles, as suggested by the adsorbed layer thickness, adsorbed polymer amount, and presence of hydrophobic domains.

Fusion of poly(vinyl acetate-b-vinyl alcohol) spherical micelles in water induced by poly(ethylene oxide)

Rapid and reversible morphology changes in aqueous dispersions of amphiphilic block copolymers are important for the development of complex fluids with switchable bulk properties. In this communication, we report the unusual ability of poly(ethylene oxide) to induce the fusion of spherical poly(vinyl acetate-b-vinyl alcohol) (PVAc-b-PVA) amphiphilic block copolymer micelles in water. While PVAc-b-PVA block copolymer micelles (diameters ∼22–25 nm) undergo depletion–flocculation upon addition of large amounts of 11 kg mol−1 PEO homopolymer (30.7 wt% in H2O), addition of relatively small amounts of PEO (3.1 wt% in the final dispersion) triggers their fusion into worm-like micelles. Diluting the worm-like micelle dispersions with pure water induces their reversion to spherical micelles. We suggest two tentative mechanisms for this morphology change induced by PEO homopolymer addition.

Stressing Lipid Membranes: Effects of Polymers on Membrane Structural Integrity

Cell membrane dysfunction due to loss of structure integrity is the pathology of tissue death in trauma, muscular dystrophies, reperfusion injuries and some common diseases. It is now established that certain poly(ethylene oxide) (PEO)-based biocompatible polymers, such as Poloxamer 188, Poloxamine 1107, and PEO homopolymers, are effective in sealing of injured cell membranes, and thus prevent acute necrosis. Despite the highly potential application of PEO-based polymers for these medical problems, the fundamental mechanism of how these polymers interact with cell membranes are still under debate. Here, the effects of these polymers on structural integrity of lipid vesicles were explored under osmotic and oxidative stress. Through fluorescence leakage assays, time-lapse fluorescence microscopy, dynamic light scattering and isothermal titration calorimetry, we identified that the surface-adsorbed hydrophilic polymers efficiently inhibits the loss of structural integrity of lipid vesicles under external stimuli, while the insertion of the hydrophobic polymers increases membrane permeability. To elucidate the mechanism by which hydrophilic polymers help restore membrane integrity while their hydrophobic counterparts disrupt it, 1H Overhauser Dynamic Nuclear Polarization (ODNP)-NMR spectroscopy, a newly developed NMR technique that is highly effective in differentiating weak surface adsorption versus translocation of polymers to membranes, was employed to detect polymer-lipid membrane interactions through the modulation of local hydration dynamics in lipid membranes. Our study shows that P188, the most hydrophilic poloxamer known as a membrane sealant, weakly adsorbs onto the membrane surface, yet effectively retards membrane hydration dynamics. Contrarily, P181, the most hydrophobic poloxamer known as a membrane permeabilizer, initially penetrates past lipid headgroups and enhances intrabilayer water diffusivity. Consequently, our results illustrate that the relative hydrophilic/hydrophobic ratio of the polymer dictates its functions.

Graft Polymerization of Anti-Fouling PEO Surfaces by Liquid-Free Initiated Chemical Vapor Deposition

Poly(ethylene oxide) (PEO), a biomedically important polymer, has been synthesized using a novel liquid-free initiated chemical vapor deposition (iCVD) via a ring-opening cationic polymerization mechanism. In addition, a grafting scheme was used to graft polymerize PEO onto amine-terminated surfaces. FTIR, NMR, and XPS showed a stoichiometric match to linear PEO homopolymer. In addition, XPS confirmed the graft polymerization of PEO to amine anchors on silicon with a high graft density. XPS and GPC were used to measure independently the grafted polymer molecular weight that also showed a narrow weight distribution. The grafted iCVD PEO surfaces were effective in minimizing nonspecific protein adsorption using a fluorescently labeled bovine serum albumin assay.

Characterization of Functional Poly(ethylene oxide)s and Their Corresponding Polystyrene Block Copolymers by Liquid Chromatography under Critical Conditions in Organic Solvents

Separation of functional poly(ethylene oxide) PEO and PEO block copolymers was investigated using liquid chromatography under critical conditions (LCCC) with a mixture of organic solvents as eluent. The optimum eluent is a mixture of 58.05% chloroform, 6.45% methanol, and 35.50% n-heptane (v/v/v) using a reverse phase (C8) column. Unlike what was expected, the elution mechanism is governed by the interaction of a polar end-group with the column. In these conditions, poly(ethylene oxide) (PEO) functionalized with either an acrylate or alkoxyamine moieties were separated. This allows us to investigate the efficiency of the synthesis of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) and polystyrene-b-poly(ethylene oxide) b-polystyrene (PS-b-PEO-b-PS) block copolymers prepared via the combination of 1,2 radical intermolecular addition followed by the nitroxide-mediated polymerization NMP of styrene. Amphiphilic diblock PEO-b-PS and triblock PS-b-PEO-b-PS copolymers were also separated from PEO homopolymers usi...

Characterization of Polystyrene‐block‐Polyethylene Oxide Diblock Copolymers and Blends of Homopolymers by Liquid Chromatography at Critical Conditions (LCCC)

AbstractIn the present study, diblock copolymers of PS‐b‐PEO synthesized by sequential living anionic polymerization as well as the blends of PS, PEO homopolymers will be investigated by using liquid chromatography at critical conditions. Critical conditions will be established for the PS block of the copolymer. At these conditions, the PS block is chromatographically invisible and does not contribute to retention so the block copolymer is separated according to the block length of the PEO block. At the critical conditions of PS, it is also possible to separate the PS homopolymer formed. The critical conditions will be established in such a way that the non‐critical PEO block elutes in size exclusion chromatography (SEC) mode.

Simultaneous Conduction of Electronic Charge and Lithium Ions in Block Copolymers

The main objective of this work is to study charge transport in mixtures of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) block copolymers and lithium bis(trifluoromethanesulfonyl) imide salt (LiTFSI). The P3HT-rich microphase conducts electronic charge, while the PEO-rich microphase conducts ionic charge. The nearly symmetric P3HT-PEO copolymer used in this study self-assembles into a lamellar phase. In contrast, the morphologies of asymmetric copolymers with P3HT as the major component are dominated by nanofibrils. A combination of ac and dc impedance measurements was used to determine the electronic and ionic conductivities of our samples. The ionic conductivities of P3HT-PEO/LiTFSI mixtures are lower than those of mixtures of PEO homopolymer and LiTFSI, in agreement with published data obtained from other block copolymer/salt mixtures. In contrast, the electronic conductivities of the asymmetric P3HT-PEO copolymers are significantly higher than those of the P3HT homopolymer. This is unexpected because of the presence of the nonelectronically conducting PEO microphase. This implies that the intrinsic electronic conductivity of the P3HT microphase in P3HT-PEO copolymers is significantly higher than that of P3HT homopolymers.

Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2‐vinyl pyridine)‐b‐(ethylene oxide) block copolymer

AbstractThe crystallization behavior of two molecular weight poly(ethylene oxide)s (PEO) and their blends with the block copolymer poly(2‐vinyl pyridine)‐b‐poly(ethylene oxide) (P2VP‐b‐PEO) was investigated by polarized optical microscopy, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy (AFM). A sharp decreasing of the spherulite growth rate was observed with the increasing of the copolymer content in the blend. The addition of P2VP‐b‐PEO to PEO increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP‐b‐PEO. Glass transition temperatures, Tg, for PEO/P2VP‐b‐PEO blends were intermediate between those of the pure components and the value increased as the content of PEO homopolymer decreased in the blend. AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO. Lamellar crystal morphology with sheaf‐like lamellar arrangement was observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation was observed for 50 and 20 wt% blends. The isothermal crystallization kinetics of PEO was progressively retarded as the copolymer content in the blend increased, since the copolymer hinders the molecular mobility in the miscible amorphous phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Viscoelastic Properties, Ionic Conductivity, and Materials Design Considerations for Poly(styrene-b-ethylene oxide-b-styrene)-Based Ion Gel Electrolytes

The viscoelastic properties and ionic conductivity of ion gels based on the self-assembly of a poly(styrene-b-ethylene oxide-b-styrene) (SOS) triblock copolymer (Mn,S = 3 kDa, Mn,O = 35 kDa) in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMI][TFSA]) were investigated over the composition range of 10–50 wt % SOS and the temperature range of 25–160 °C. The poly(styrene) (PS) end-blocks associate into micelles, whereas the poly(ethylene oxide) (PEO) midblocks are well-solvated by this ionic liquid. The ion gel with 10 wt % SOS melts at 54 °C, with the longest relaxation time exhibiting a similar temperature dependence to that of the viscosity of bulk PS. However, the actual values of the gel relaxation time are more than 4 orders of magnitude larger than the relaxation time of bulk PS. This is attributed to the thermodynamic penalty of pulling PS end-blocks through the PEO/[EMI][TFSA] matrix. Ion gels with 20–50 wt % SOS do not melt and show two plateaus in the storage modulus over the temperature and frequency ranges measured. The one at higher frequencies is that of an entangled network of PEO strands with PS cross-links; the modulus displays a quadratic dependence on polymer weight fraction and agrees with the prediction of linear viscoelastic theory assuming half of the PEO chains are elastically effective. The frequency that separates the two plateaus, ωc, reflects the time scale of PS end-block pull-out. The other plateau at lower frequencies is that of a congested micelle solution with PS cores and PEO coronas, which has a power law dependence on domain spacing similar to diblock melts. The ionic conductivity of the ion gels is compared to PEO homopolymer solutions at similar polymer concentrations; the conductivity is reduced by a factor of 2.1 or less, decreases with increasing PS volume fraction, and follows predictions based on a simple obstruction model. Our collective results allow the formulation of basic design considerations for optimizing the mechanical properties, thermal stability, and ionic conductivity of these gels.