Volume Fraction Of PEO Research Articles

Hydration of Spherical PEO-Grafted Gold Nanoparticles: Curvature and Grafting Density Effect

Nanoparticle modification by water-soluble polymers, such as poly(ethylene oxide) (PEO), relies on polymer hydration to ensure nanoparticle solubility, dispersion, and protection from undesirable interactions. The state of polymer hydration in grafted polymer layers is not easily assessible experimentally but can be ascertained from computer simulations. Using atomistic molecular dynamics simulations, we studied the equilibrium and dynamic properties of spherical PEO brushes grafted to gold nanoparticles of different radii (1, 2, and 3 nm). We obtained the volume fraction of PEO (Φ(r)) as a function of radial distance r (counted from micelle core center) which is found to follow the Daoud–Cotton model, Φ(r) ∼ r–4/3, except for low grafting density when PEO adsorption onto the gold surface is observed, in agreement with experimental observations. With an increase of grafting density σ (up to 4.17 nm–2), the PEO chains become more stretched and oriented along the radial direction leading to an increase of t...

Phase Behavior of Binary Polymer Blends Doped with Salt

We present cloud point measurements on low molecular weight binary polymer blends doped with salts that exhibit unusual phase behavior. These blends include poly(ethylene-alt-propylene)/poly(ethylene oxide) (PEP/PEO) doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI), NaTFSI, KTFSI, LiClO4, and sodium iodide NaI. The addition of salt dramatically decreases the miscibility of the binary blends and results in an asymmetric cloud point profile. The phase behavior is found to be governed by the concentration of the salt, the size of the anion, and the composition of the polymer mixture. The experimental results are compared with a recent theory, which predicts the effect of ions on the polymer phase diagram by taking into account both ion-induced cross-linking and self-energy effects. Furthermore, the coexistence curve of salt-doped PEP/PEO blends is determined quantitatively by 1H NMR spectroscopy when the volume fraction of PEO is maintained at 0.6. The coexistence curve does not coincide with the...

Asymmetric Polymersomes from an Oil-in-Oil Emulsion: A Computer Simulation Study.

Asymmetric vesicles are valuable for understanding and mimicking cell and practical biomedicine applications. Recently, a very straightforward methodology for fabricating asymmetric polymersome was developed by Lodge's group through the coassembly of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) block copolymers at the interface of a polystyrene/polybutadiene/chloroform (PS/PB/CHCl3) emulsion. However, the in-depth microscopic mechanism for the formation of asymmetric polymersomes remains unclear. To address this issue, in this article, the coassembly process for the formation of the asymmetric polymersomes in Asano's experimental system was systematically investigated by employing a dissipative particle dynamics (DPD) simulation. Our results definitely demonstrate the formation of the asymmetric polymersomes such as that in the experiments and that the bilayer formed through the folding and crossing of the PEO blocks. Besides, from the microscopic view, three stages can be discerned in the formation process: (1) the formation of micelles, (2) the micelle diffusion to the interface, and (3) the micelle rearrangement at the interface to form an asymmetric polymersome. Meanwhile, the incompatibility among PS, PB, and PEO is proven to be the main driving force for asymmetric polymersome formation. Moreover, the effects of the order of addition of copolymers and the volume fraction of PEO blocks on the structure of the asymmetric polymersomes are also investigated. We find that the formation process is affected severely by the order of addition, and adding PS-b-PEO first can make the asymmetric bilayer more perfect. Not only that, but perfect asymmetric polymersomes can be formed only when the volume fraction of PEO (fPEO) is greater than 0.55. We believe the present work can extend the knowledge of the self-assembly of asymmetric polymersomes, especially with respect to the self-assembly mechanism.

Effect of block copolymer morphology on crystallization and water transport

The effect of block copolymer morphology on polymer crystallization and water sorption was investigated using two amphiphilic block copolymers with minority hydrophilic phase. Such polymers have many potential membrane applications, including CO2 capture and water purification. A model block copolymer chemistry comprising polystyrene and poly(ethylene oxide) (PEO) is used in this work. Both block copolymers have strongly phase-separated order, one with lamellar morphology and another with cylindrical morphology. In addition to the block copolymer structure, the PEO phase is semicrystalline at room temperature. The block copolymer structure has dramatic consequences for the degree of PEO crystallinity even in the absence of water. Furthermore, the crystallinity is affected by water sorption. PEO melting and degree of crystallinity were determined as a function of water content. Water solubility was measured between 35 and 75 °C. Interestingly, water sorption properties are dictated almost exclusively by the amorphous PEO volume fraction, being low in the semicrystalline state (below 55 °C) and higher in the amorphous state (above 55 °C). At 55 °C, crystallite dissolution is observed with increasing water solubility. Water diffusion coefficient was also measured; it decreases monotonically with increasing water content. This concentration dependence of diffusion is explained by water clustering, which increases with increasing water content. In addition to block copolymer morphology playing a major role in PEO crystallinity, it has a significant effect on water diffusion in the amorphous polymers and is of practical importance as investigations at elevated temperature are not possible with homopolymer PEO.

Polystyrene-block-poly(ethylene oxide) Bottlebrush Block Copolymer Morphology Transitions: Influence of Side Chain Length and Volume Fraction

A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly(ethylene oxide) (PS-b-PEO) bottlebrush block copolymers (BBCP) upon varying PEO volume fraction (fPEO) from 22% to 81%. A series of PS-b-PEO BBCPs with different PEO side chain lengths were prepared using ring-opening metathesis polymerization (ROMP) of PEO–norbornene (PEO-NB) (Mn ∼ 0.75, 2.0, or 5.0 kg/mol) and PS–norbornene (PS-NB) (Mn ∼ 3.5 kg/mol) macromonomers (MM). A map of fPEO versus side chain asymmetry (Mn(PEO-NB)/Mn(PS-NB)) was constructed to describe the BBCP phase behavior. Symmetric and asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of fPEO from 28% to 72%. At high fPEO, crystallization of PEO was evident. Temperature-controlled SAXS and WAXS revealed the presence of high order reflections arising from phase segregation above the PEO melting point. A microphase transition temperature TMST was observed over a temperature range of 150–180...

Hierarchically Porous Polymer Monoliths by Combining Controlled Macro- and Microphase Separation.

The ability to tune polymer monolith porosity on multiple length scales is desirable for applications in liquid separations, catalysis, and bioengineering. To this end, we have developed a facile synthetic route to nanoporous polymer monoliths based on controlled polymerization of styrene and divinylbenzene from a poly(lactide) macro-chain transfer agent in the presence of nonreactive poly(ethylene oxide) (PEO). Simple variations in the volume fraction and/or molar mass of PEO lead to either polymerization-induced microphase separation or simultaneous macro- and microphase separation. These processes dictate the resultant morphology and allow for control of the macro- and microstructure of the monoliths. Subsequent selective etching produces monoliths with morphologies that can be tailored from mesoporous, with control over mesopore size, to hierarchically meso- and macroporous, with percolating macropores. This convenient synthetic route to porous polymer monoliths has the potential to be useful in applications where both rapid mass transport and a high surface area are required.

Interfacial tension-hindered phase transfer of polystyrene-b-poly(ethylene oxide) polymersomes from a hydrophobic ionic liquid to water.

We examine the phase transfer of polystyrene-b-poly(ethylene oxide) (PS-PEO) polymersomes from a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), into water. The dependence of the phase transfer on the molecular weight and PEO volume fraction (fPEO) of the PS-PEO polymersomes was systematically studied by varying the molecular weight of PS (10,000-27,000 g/mol) as well as by varying the volume fraction of PEO (fPEO) between 0.1 and 0.3. We demonstrate a general boundary for the phase transfer in terms of a reduced tethering density for PEO (σPEO), which is independent of the molecular weight of the hydrophobic PS. The reduced PEO tethering density was controlled by changing the polymersome size (i.e., increased polymersome sizes increase σPEO), confirming that it is the driving force in the transfer of PS-PEO polymersomes at room temperature. The phase transfer dependence on σPEO was also analyzed in terms of the free energy of polymersomes in the biphasic system. The quality of the aqueous phase, which affects the interfacial tension of the PS membrane, influenced the phase transfer. We systematically reduced the interfacial tension by adding a water-selective solvent, THF, which has a similar effect to increasing σPEO. The results indicate that the interfacial tension between the membrane and water plays an important role in the phase transfer with the corona and that the phase transfer can be controlled either by the dimensions of the polymersomes or by the suitability of the solvent for the membrane. The interfacial tension-hindered phase transfer of polymersomes in the biphasic water-[EMIM][TFSI] system will inform the design of temperature-sensitive and reversible nanoreactors and the separation of polydisperse particles according to size by tuning the quality of the solvent.

Enormously Wide Range Cylinder Phase of Liquid Crystalline PEO-b-PMA(Az) Block Copolymer

A series of amphiphilic liquid crystalline diblock copolymers, PEOm-b-PMA(Az)n, consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(methacrylate) moieties with side chains containing liquid crystalline (LC) azobenzene moieties, produced highly ordered microphase-separated films with PEO cylinders aligned perpendicular to the smectic LC layer of azobenzene in the PMA(Az) matrix. In this paper, morphological phase diagrams of PEOm-b-PMA(Az)n diblock copolymers above and below the isotropic transition temperature of LC azobenzene (Tiso) are presented. The diagrams are based on small-angle X-ray scattering (SAXS) measurements of approximately 70 kinds of polymers with varying degrees of polymerization in each block. An asymmetric phase diagram described against the volume fraction of PEO (fPEO) was obtained at temperatures above and below Tiso. The lamellar phase appears in the fPEO window 0.52 ≤ fPEO ≤ 0.78 above and below Tiso. Besides, the wide window, 0.087 ≤ fPEO < 0.52, allows the PEO cylinder phase to form below Tiso. In particular, the PEO sphere phase, observed above Tiso, was completely eliminated through an order–order transition (OOT) to the PEO cylinder phase in the window 0.087 ≤ fPEO ≤ 0.23. Such a large expansion in the PEO-cylinder-phase window could be attributed to the main chain of LC PMA(Az) being shorter than that of the flexible PEO chain, and LC azobenzene forming a smectic layer in the microphase separated system.

Phase behavior of LiClO4-doped poly(ε-caprolactone)-b-poly(ethylene oxide) hybrids in the presence of competitive interactions

The phase behavior of a series of LiClO4-doped poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) was studied as a function of PEO volume fraction (fPEO), doping ratio (r) and temperature (T). It is found that the morphology of the hybrids changes from disordered structure (DIS) to hexagonally packed cylindrical (HEX) structure and then to lamellar (LAM) structure as the volume fraction of the PEO/salt phase (fPEO/salt) increases at fPEO/salt < 0.5. Order–order transitions are observed upon heating some hybrids. An approximate phase diagram of the PCL-b-PEO/LiClO4 hybrids with fPEO/salt < 0.5 was constructed in terms of fPEO/salt and the segregation strength (χeffN). As compared with the phase diagram of the weakly segregated diblock copolymers, the phase diagram of the hybrids has two features: the boundaries of the LAM and HEX structures shifts to lower fPEO/salt and body-centered cubic spherical (BCC) structure is not observed for the samples studied. This can be attributed to the weaker ability of the salt inducing microphase separation at low fPEO and the conformational change of the PEO block induced by the salt. Some unexpected phase behaviors were observed for the hybrids with fPEO/salt > 0.5, including the hexagonally perforated layers (HPL) to LAM transition upon heating the same hybrid and HEX to gyroid (GYR) transition with the increase of doping ratio at the same temperature. These unexpected phase behaviors are qualitatively interpreted based on the competitive association of the PCL block with Li+ ions at elevated temperatures and higher doping ratios, which leads to re-distribution of the Li+ ions in different phases and the inconsistency between the calculated fPEO/salt and the real volume fraction of the PEO/salt phase.

Study on the compatibility and crystalline morphology of NBR/PEO binary blends

Compatibility property, as well as crystalline morphology, of NBR/PEO blends has been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM) thoroughly. There is no apparent shift of nitrile or ether groups in the FTIR spectra of NBR/PEO blends. Based on the calculations from glass transition temperature, the maximum volume fraction of PEO dissolved in NBR phase is about 6.41 % in blend with 5 wt% PEO content (PEO-5), indicating a weak intermolecular interaction in the NBR/PEO blends. From the characteristic absorption bands in the FTIR spectra, XRD and POM graphs, the crystallinity ratio of NBR/PEO blends decreases as the NBR content increases, which is further proved by DSC measurement that the crystallinity ratio and crystal melting temperature of pure PEO are 82.6 %, 69.9 °C, and that of PEO-5 are 16.9 %, 59.5 °C. This illuminates that the weak intermolecular interaction will affect the crystallinity ratio and crystal melting temperature of the NBR/PEO blends.

Thin Films of Poly(isoprene-b-ethylene Oxide) Diblock Copolymers on Mica: An Atomic Force Microscopy Study

The structural behavior of three amphiphilic semicrystalline poly(isoprene-b-ethylene oxide) block copolymers (PI-b-PEO) with different PEO volume fraction (f(PEO) = 0.32, 0.49, and 0.66), spin-coated on freshly cleaved mica surfaces from aqueous solutions, was investigated by atomic force microscopy. We focus on the dependence of the resulting thin film nanostructures on the molecular characteristics (f(PEO) and molecular weight) and the adsorbed amount. The nanostructures obtained immediately after spin-coating were robust and remained unchanged after annealing and/or aging. The PEO affinity for the highly hydrophilic mica and the tendency of the hydrophobic and low surface energy PI to dewet and be at the free interface caused the soft PI-b-PEO micelles to collapse leading to the formation of 2D dendritic networks over mica. We show that, for all three polymers, the dendritic monolayer thickness can be predicted by a model consisting of a PEO crystallized layer (directly on top of mica) of the same thickness in all cases and a PI brush layer on top. In thicker areas, polymer material self-assembled into conelike multilamellar bilayers on top of the monolayer and oriented parallel to the substrate for both symmetric and asymmetric diblock copolymers with the lowest f(PEO). We compare the lateral morphology of the films and discuss the thickness heterogeneity, which results from the coupling and competition of crystallization kinetics, phase separation, and wetting/dewetting phenomena highlighting the role of the two blocks to inhibit or enhance certain morphologies. We show that the deviation of the f(PEO) = 0.32 thin film from its bulk phase structure (cylinders in hexagonal lattice) continues for several lamellar bilayers away from the substrate. For the asymmetric PI-b-PEO polymer with the higher PEO volume fraction (f(PEO) = 0.66) and higher APT, laterally extensive stacks of flat-on lamellar crystallites formed on the surface demonstrating the crucial role of the PEO crystallization.

Liquid crystalline and ion-conducting properties of mesogenic dendron–coil-dendron copolymers: characterization of LC phases using normalized conductivity

We synthesized three dendron–coil-dendron block copolymers consisting of ionophilic poly(ethylene oxide) (PEO) coils and mesogenic dendrons with four octadecyl peripheries via stepwise click reactions. The obtained polymers were doped with lithium triflate, whose concentration per ethylene oxide unit was 0.05. As characterized by optical polarized microscopy (POM) and X-ray scattering techniques, polymer 1 with the shortest PEO coil (Mn = 2000 g mol−1) did not show the liquid crystalline (LC) phase, while its ionic sample (1-Li+) exhibited a hexagonal columnar LC phase. On the other hand, 2 and 3 (with PEOs of Mn = 4000 and 8000 g mol−1, respectively) displayed identical LC morphologies to 2-Li+ and 3-Li+, respectively, although the phase transition temperatures increased upon salt doping. For 2 and 2-Li+, gyroid and lamellar LC phases were observed with increasing temperature, while 3 and 3-Li+ showed only a lamellar LC phase. The observed ion-transporting behavior was strongly dependent upon the connectivity of ion-conducting domain structures. The investigation of the morphology–conductivity correlation using a normalized conductivity (σ* = σ/f, where σ and f are the original conductivity and the PEO volume fraction) indicated that the 3-D gyroid LC phase showed the highest value, while the lowest conductivity was found in the 1-D columnar structure at identical temperatures. Additionally, the gyroid to lamellar phase transition temperature of 2-Li+ could be determined by the σ*, which was consistent with the X-ray data. Consequently, the results can be explained by the fact that the ionic pathway becomes complicated when going from higher to lower dimensional structures in polygrain samples.

Ionic Conductivities of Block Copolymer Electrolytes with Various Conducting Pathways: Sample Preparation and Processing Considerations

We explored the relationship between ionic conductivities and morphology in a lithium perchlorate-doped poly(styrene-b-ethylene oxide) (PS–PEO) system using ac impedance spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy. To aid in morphological analysis, a flow alignment technique was used to orient nanoscale domains in order to facilitate characterization of nanostructures such as hexagonally perforated lamellae (HPL), hexagonally packed cylinders (HEX), and lamellae (LAM). Over the PEO volume fraction (fPEO) from 0.70 to 0.75, the neat PS–PEO exhibits a morphological transition from HPL to HEX, while the salt-doped PS–PEO shows morphological transitions from LAM to HPL to HEX. Additionally, experiments on hot-pressed specimens show that 3-D conducting pathways (HPL and HEX) exhibit much higher normalized conductivities than the corresponding 2-D conducting pathway (LAM) even after accounting for nonrandom domain orientations and slight PEO molecular weight changes across samples. Our results further suggest that using block copolymer electrolytes with 3-D conducting pathways can prevent a decrease in through-plane conductivities caused by the partial nanostructure alignment during sample preparation.

Nanostructure Dependent Surface Energy of Silica Nanorod Arrays through Block Copolymer Templating Processes

ABSTRACTThe self-assembled block copolymer films with poly (ethylene oxide) (PEO) and hydrophobic polymetharylate (PMA) with azobenzene mesogen in the side chain, denoted as PEOm-b-PMA(Az)n, were used as the template to prepare hexagonally ordered silica nanorod arrays by immersing the template films in the silicate precursor containing tetraetoxysilane (TEOS). The diameter and the center-to-center distance of the SiO2 nanorod arrays were controlled by selecting the block copolymer with different PEO volume fraction. In addition, the contact angles of different kinds’ solvents for the SiO2 nanorod arrays were characterized. We further found, the diameter and the period distance of silica nanorods are very important factors for controlling the contact angle of different kind’s solvents on the surface of the SiO2 nanorod arrays.

Effect of Molecular Weight and Salt Concentration on Conductivity of Block Copolymer Electrolytes

The ionic conductivity, σ, of mixtures of nearly symmetric polystyrene-block-poly(ethylene oxide) copolymers and Li[N(SO2CF3)2] (LiTFSI) salt was measured as a function of molecular weight, salt concentration, and temperature. The molecular weight of the poly(ethylene oxide) block, MPEO, was varied from 7 to 98 kg/mol. The molar ratio of lithium to ethylene oxide, r, was varied from 0.02 to 0.10. In general, σ increases with increasing MPEO for all values of r. The data can be summarized by plots of normalized conductivity, σn, versus MPEO, where σn = σ/(fϕPEOσPEO), ϕPEO is the PEO volume fraction in the copolymer, σPEO is the conductivity of PEO homopolymer, and f is a morphology-dependent factor set equal to 2/3 for our lamellar samples. The temperature-dependent conductivity data at a given salt concentration collapse onto a single curve when plotted in this format. At r = 0.085, σn values reach a plateau in the vicinity of unity in the high MPEO limit. At other values of r, σn continues to increase wi...

Synthesis and Characterization of Coil−Rod−Coil Triblock Copolymers Comprising Fluorene-Based Mesogenic Monodisperse Conjugated Rod and Poly(ethylene oxide) Coil

A series of coil−rod−coil triblock copolymers (i.e., F3T8EO8, F3T8EO17, F3T8EO45, and F3T8EO125) with a mesogenic monodisperse conjugated oligomer comprising 3 fluorene, 8 thiophene, and 2 phenyl units as the rod and poly(ethylene oxide) (PEO) as the coil were synthesized. A reference compound, that is F3T8ME2, with the identical rod but without PEO was also prepared for comparison. The volume fraction of PEO (fPEO) was 0, 0.16, 0.28, 0.50, and 0.73 for F3T8ME2, F3T8EO8, F3T8EO17, F3T8EO45, and F3T8EO125, respectively. It was found that the introduction of PEO into the triblock copolymers encouraged the formation of H-type aggregation and fPEO-dependent highly ordered mesophases while fPEO < 0.73. For F3T8ME2, only nematic mesophase was observed. In contrast, F3T8EO8 and F3T8EO17, with fPEO of 0.16 and 0.28, respectively, are smectic A (SA) mesomorphism. For F3T8EO45 with fPEO of 0.50, several highly ordered phases, such as hexagonal columnar crystalline phase and rectangular columnar, smectic B (SB) and ...

Controlling the morphology of polybutadiene–poly(ethylene oxide) diblock copolymers in bulk and the orientation in thin films by attachment of alkyl side chains

A polybutadiene19-block-poly(ethylene oxide)94 (PB–PEO) has been modified by free-radical additions of 2-ethylhexanethiol, 1-decanethiol, and 1-dodecanethiol separately to the PB block. The block copolymers were characterized by DSC, SAXS, XRD and AFM measurements. Above the melting temperature of PEO, PB–PEO showed hexagonal morphology having PB cylinders in the PEO matrix. The addition of alkyl side chains decreased the volume fraction of PEO and the morphology changed to lamellar for ethylhexyl side chains and to reversed hexagonal morphology with PEO cylinders in the PB/alkyl chain matrix for decyl and dodecyl side chains. Below the melting temperature of PEO, all polymers showed lamellar morphology. In the case of dodecyl side chains, the lamellar morphology oriented perpendicular to the air/film interface and was stable against high temperature annealing.

Study of Spherulitic Structures by Analyzing the Spherulitic Growth Rate of the Other Component in Binary Crystalline Polymer Blends

The structures in spherulites of poly(butylene succinate) (PBSU) are discussed by analyzing the spherulitic growth rate of poly(ethylene oxide) (PEO) inside PBSU spherulites of PBSU/PEO blends, which are binary blends of crystalline polymers where PBSU spherulites fill the whole volume before PEO spherulites nucleate and grow inside PBSU spherulites. The results indicated that a PBSU spherulite contains wide amorphous regions and that PBSU crystals suppress the molecular mobility of PEO very little. It also implied that PEO crystallizes primarily in interfibrillar regions in PBSU spherulites. The same equation as that for crystalline/ amorphous blends was applicable to the dependence of the spherulitic growth rate of PEO, GPEO ,o n the crystallization temperature by using the same activation energy for molecular transport as in a melt. The variation of GPEO with the blend composition could be ascribed to the volume fraction of PEO in the amorphous region of PBSU spherulites.

Effect of lithium trifluoromethanesulfonate on the phase diagram of a liquid-crystalline amphiphilic diblock copolymer

Phase transitions and nanometre-scale ordered structures of a binary system of a liquid-crystalline amphiphilic diblock copolymer, poly(ethylene oxide)-b-poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate} [PEOm-b-PMA(Az)n, where m and n are the degrees of polymerization of the PEO and PMA(Az) domains, respectively], and lithium trifluoromethanesulfonate (LiCF3SO3) were investigated by differential scanning calorimetry and small-angle X-ray scattering (SAXS). PEO114-b-PMA(Az)51 formed a highly ordered hexagonally packed PEO cylinder structure in the temperature range below 393 K and transformed to a body-centred-cubic structure in the isotropic state above 393 K. The PEO114-b-PMA(Az)51/LiCF3SO3 systems with various LiCF3SO3 concentrations (molar ratio 0 < LiCF3SO3/EO = fLi < 1) formed the hexagonally packed cylinder structure at room temperature. From the effects of LiCF3SO3 concentration on the phase transitions, the size and the order of the hexagonally packed cylinder structure, it was found that PEO114-b-PMA(Az)51 and LiCF3SO3 formed a complex efficiently at a molar equivalent of three ethylene oxide repeating units per LiCF3SO3 unit. The ordering of the hexagonally packed cylinder structure decreased with increasing LiCF3SO3 concentration and the radius of the PEO cylinder evaluated by SAXS profile fitting increased from 2.7 to 8.3 nm. For the PEO114-b-PMA(Az)51/LiCF3SO3 system with fLi = 1, the hexagonally packed cylinder structure remained even in the isotropic state because the PEO volume fraction (ϕPEO) increased from ϕPEO = 0.06 (fLi = 0) to ϕPEO = 0.23 (fLi = 1) on the formation of the LiCF3SO3/PEO complex.

Synthesis and characterization of a vinyl‐terminated benzoxazine monomer and its blends with poly(ethylene oxide)

AbstractA vinyl‐terminated benzoxazine (VB‐a), which could be polymerized through ring‐opening polymerization, was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine. This VB‐a monomer was then subjected to blending with poly(ethylene oxide) (PEO), followed by thermal curing, to form poly(VB‐a)/PEO blends. The specific interactions, miscibility, morphology, and thermal properties of these blends were investigated with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Before curing, we found that PEO was miscible with VB‐a, as evidenced by the existence of a single composition‐dependent glass transition temperature (Tg) for each composition. The FTIR spectra revealed the presence of hydrogen‐bonding interactions between the hydroxyl groups of poly(VB‐a) and the ether groups of PEO. Indeed, the ring‐opening reaction and subsequent polymerization of the benzoxazine were facilitated significantly by the presence of PEO. After curing, DMA results indicated that the 50/50 poly(VB‐a)/PEO blend exhibited two values of Tg: one broad peak appeared in the lower temperature region, whereas the other (at ca. 327 °C, in the higher temperature region) was higher than that of pristine poly(VB‐a) (301 °C). The presence of two glass transitions in the blend suggested that this blend system was only partially miscible. Moreover, SEM micrographs indicated that the poly(VB‐a)/PEO blends were heterogeneous. The volume fraction of PEO in the blends had a strong effect on the morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 644–653, 2007