High PEO Content Research Articles

Carbon nanotube‐polybutadiene‐poly(ethylene oxide)‐based composite fibers: Role of cryogenic treatment on intrinsic properties

AbstractThe low‐temperature response and the notion of crystallization kinetics are critical for developing elastomeric composite fibers, thus the crystallization and mechanical properties are essential for the application of composites of polybutadiene at low temperatures. Despite the high amount of fiber joining and entanglement due to polymers' low glass transition, a defect‐free micro‐scale electrospun carbon nanotube (CNT)‐containing poly(ethylene oxide) (PEO) and polybutadiene (PBu) composite elastomeric fibers with uniform fiber diameter and distribution are successfully fabricated. Thermomechanical behavior analyzed via frequency‐dependent dynamic mechanical analysis under cryogenic conditions shows a remarkable increase in decomposition temperatures (Tend) and storage and loss modulus at cryogenic temperatures, particularly when small amounts of CNTs are present. Dynamic mechanical treatment from 120 K to elevated temperatures yields a pronounced logarithmic increase in Tend by an increase of PEO content (from BEC1 to BEC4) compared to the treatment from 300 K. Through X‐ray diffraction, large shifts toward larger 2θ and formation of new crystals are observed, particularly for the BEC4 sample with high PEO content. Nanoparticles after cryo‐treatment linked with crystallinity are registered by ultra‐high resolution scanning electron microscopy. Improving the thermal and mechanical properties is critical in developing high‐performance composite fibers for cryogenic engineering applications, especially for future research to facilitate them in aerospace and low‐temperature medical and surgical treatments.

3D-printed implantable devices with biodegradable rate-controlling membrane for sustained delivery of hydrophobic drugs

Implantable drug delivery systems offer an alternative for the treatments of long-term conditions (i.e. schizophrenia, HIV, or Parkinson’s disease among many others). The objective of the present work was to formulate implantable devices loaded with the model hydrophobic drug olanzapine (OLZ) using robocasting 3D-printing combined with a pre-formed rate controlling membrane. OLZ was selected as a model molecule due to its hydrophobic nature and because is a good example of a molecule used to treat a chronic condition schizophrenia. The resulting implants consisted of a poly(ethylene oxide) (PEO) implant coated with a poly(caprolactone) (PCL)-based membrane. The implants were loaded with 50 and 80% (w/w) of OLZ. They were prepared using an extrusion-based 3D-printer from aqueous pastes containing 36–38% (w/w) of water. The printing process was carried out at room temperature. The resulting implants were characterized by using infrared spectroscopy, scanning electron microscopy, thermal analysis, and X-ray diffraction. Crystals of OLZ were present in the implant after the printing process. In vitro release studies showed that implants containing 50% and 80% (w/w) of OLZ were capable of providing drug release for up to 190 days. On the other hand, implants containing 80% (w/w) of OLZ presented a slower release kinetics. After 190 days, total drug release was ca. 77% and ca. 64% for implants containing 50% and 80% (w/w) of OLZ, respectively. The higher PEO content within implants containing 50% (w/w) of OLZ allows a faster release as this polymer acts as a co-solvent of the drug.

Polyether Single and Double Crystalline Blends and the Effect of Lithium Salt on Their Crystallinity and Ionic Conductivity.

In this work, blends of Poly(ethylene oxide), PEO, and poly(1,6-hexanediol), PHD, were prepared in a wide composition range. They were examined by Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (PLOM) and Wide Angle X-ray Scattering (WAXS). Based on the results obtained, the blends were partially miscible in the melt and their crystallization was a function of miscibility and composition. Crystallization triggered phase separation. In blends with higher PEO contents both phases were able to crystallize due to the limited miscibility in this composition range. On the other hand, the blends with higher PHD contents display higher miscibility and therefore, only the PHD phase could crystallize in them. A nucleation effect of the PHD phase on the PEO phase was detected, probably caused by a transference of impurities mechanism. Since PEO is widely used as electrolyte in lithium batteries, the PEO/PHD blends were studied with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and the effect of Li-salt concentration was studied. We found that the lithium salt preferentially dissolves in the PEO phase without significantly affecting the PHD component. While the Li-salt reduced the spherulite growth rate of the PEO phase within the blends, the overall crystallization rate was enhanced because of the strong nucleating effect of the PHD component. The ionic conductivity was also determined for the blends with Li-salt. At high temperatures (>70 °C), the conductivity is in the order of ~10−3 S cm−1, and as the temperature decreases, the crystallization of PHD was detected. This improved the self-standing character of the blend films at high temperatures as compared to the one of neat PEO.

Calorimetric studies of PEO-b-PMMA and PEO-b-PiPMA diblock copolymers synthesized via atom transfer radical polymerization

Poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) and poly(ethylene oxide)-b-poly(isopropyl methacrylate) (PEO-b-PiPMA) diblock copolymers of different block ratios have been synthesized using atom transfer radical polymerization with functionalized PEO monomethylether as macroinitiator. The phase separation between the constituent blocks of the copolymers has been investigated by differential scanning calorimetry (DSC). In PEO-b-PMMA, the constituent blocks are completely miscible irrespective of their molar mass and block ratios. This behaviour remains the same for PEO-b-PiPMA with ≤15% PEO fraction; phase separation could only be observed for PEO-b-PiPMA with higher PEO content. These observations are supported by results of atomic force microscopy studies of films of two copolymers with comparable molecular weight and PEO fraction (≥24% PEO); a very well developed lamellar morphology was only observed for PEO-b-PiPMA, while the block domains were randomly dispersed in PEO-b-PMMA. Interestingly, the phase separation behaviour in PEO-b-PMMA with >30% PEO fraction has been found to be strongly dependent on its processing and thermal history. On the contrary, phase separation in PEO-b-PiPMA BCPs with ≥24% PEO fraction has not been affected by its processing or thermal history. Results indicate that the use of a block-selective solvent for the precipitation of the diblock copolymer promotes the formation of microphase separated structures even for copolymers with miscible blocks. The findings are relevant for ongoing attempts to utilize the microphase separation of such polymers to obtain well-defined nanoporous membranes and other materials.

PE-b-PEO block copolymer nanostructured thermosetting systems as template for TiO2 nanoparticles

Two different, molecular weight and blocks ratio, poly(ethylene-b-ethylene oxide) block copolymers (PE-b-PEO) were used as nanostructuration agent for epoxy based thermosets and as surfactant for sol-gel synthesized titanium dioxide (TiO2) nanoparticles. Obtained DSC results confirmed the miscibility of PEO block of PE-b-PEO block copolymer with epoxy monomer in PE-b-PEO/DGEBA unreactive mixtures and with DGEBA/MCDEA matrix in cured systems modified with PE-b-PEO block copolymer without or with TiO2 nanoparticles. The dilution effect caused by the addition of PE-b-PEO block copolymer on the epoxy/amine reaction mixture was verified.AFM phase images proved that nanostructured thermosetting systems can be reached in function of PE-b-PEO block copolymer content. Good dispersion and, in the case of the cured systems modified with higher molecular weight and higher PEO content PE-b-PEO block copolymer, selective localization of TiO2 nanoparticles can be achieved. The morphology of investigated thermosetting systems and the good dispersion of TiO2 nanoparticles depend on the PEO block content in PE-b-PEO block copolymer and its molecular weight.Transparent PE-b-PEO block copolymer nanostructured thermosetting systems with hydrophilic character and well dispersed or positioned TiO2 nanoparticles can be obtained.

Poly(ethylene oxide) induced microstructure and hydrolytic degradation behavior changes of poly(butylene succinate)

Degradable polyesters exhibit wide application in many fields due to the fact that the waste of these polymers can be easily reclaimed, which greatly reduces the environmental risk. In this work, a small quantity of water-soluble poly(ethylene oxide) (PEO) was introduced into biodegradable poly(butylene succinate) (PBS). Crystallization behavior of the PBS matrix was comparatively investigated using polarized optical microscope (POM), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The results demonstrate that PEO affects the crystallization behavior of the PBS matrix, which is greatly dependent upon the PEO content. At relatively low PEO content, accelerated crystallization is achieved for the PBS matrix, while the role of PEO becomes inconspicuous at relatively high PEO content. The sample surface hydrophilicity was evaluated through contact angle measurement of distilled water. The results demonstrate that incorporating PEO into PBS greatly enhances the hydrophilicity of the sample surface. The hydrolytic degradation measurements were carried out under an alkaline condition. The results clearly show that the presence of PEO accelerates the hydrolytic degradation of the PBS matrix. Furthermore, the sample obeys the surface erosion mechanism. The mechanism for the largely enhanced hydrolytic degradation ability is then analyzed.

Crystallization kinetics and degradation of nanocomposites based on ternary blend of poly(L‐lactic acid), poly(methyl methacrylate), and poly(ethylene oxide) with two different organoclays

AbstractTernary polymer blends composed of poly(L‐lactic acid) (PLLA), poly(methyl methacrylate) (PMMA), and poly(ethylene oxide) (PEO) is used as matrix for nanocomposites with two clays: organically modified vermiculite (OVMT) and organically modified montmorillonite (Clo10A). The addition of PMMA in PLLA/PEO blend matrix reduces the chain mobility and retards the crystallization of PLLA/PEO. The retardation effect of PMMA on PLLA/PEO blend is less pronounced with higher PEO contents. The incorporation of OVMT and Clo10A is one common strategy to improve crystallization process as well as thermal and mechanical properties. The crystallization kinetics of polymer nanocomposites was found to be well described by the Mo method. The evolution of activation energy during nonisothermal course is analyzed using isoconversional method, and the trend of activation energy variation was found to be different for each of two organoclays. Thermal stability is improved by the incorporation of organoclays, where Clo10A induces better stability than that of OVMT. Enzymatic degradation tests showed that the nanocomposites with OVMT possessed higher stability on enzymatic attack and slower degradation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Induction and biological evaluations of self cross-linking chondroitin sulfate-poly(ethylene oxide) hydrogel

The biological properties of self cross-linked chondroitin sulfate (CS)-poly(ethylene oxide) (PEO) hydrogel including degradation, in vitro bone cell behaviors, and cellular compatibility were evaluated after the induction of its gel formation through use of different experimental conditions such as precursor composition, reaction temperatures, and precursor solution concentrations. The compositions of the CS-acrylate and PEO-thiol precursors had ratios of 25:75, 50:50, and 75:25. Hydrogel formations were induced with a mechanism of self cross-linking at the solution temperatures of 7, 23, 37, and 50 °C through use of different precursor solutions (2%, 3%, 5%, and 10%). Higher reaction temperatures and precursor concentrations induced quicker formation of the CS-PEO gel. While the 10% precursor solution became a hydrogel within 2 min at 50 °C, the 2% solution took approximately 462 min at 7 °C. While the CS-PEO gel with higher PEO content (25:75) swelled to 330%, the hydrogel with lower PEO content (75:25) swelled to 147% at 23 °C, indicating that higher PEO content induced higher gel swelling. The CS-PEO hydrogel (50:50) gradually degraded in vitro through addition of 0.5 unit of chondroitinase ABC every 2 days, which led to approximately 7% degradation over 24 days. A CCK-8 assay performed on the hydrogel surface showed initially higher cell adhesion on the higher concentration CS gel (75:25), even though the adhered cells seemed to detach from their surfaces over time. Live and dead assays demonstrated that both cells on the surface of and inside the hydrogel were viable for 7 days. The results of in vitro bromodeoxyuridine, 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide, and neutral red assays and evaluation of the gel covering on the cells cultured on the culture flask demonstrated excellent hydrogel cell compatibility (25:75, 50:50, and 75:25) compared to that of latex, the negative control. Open image in new window

Synthesis and Assembly of Butyl Rubber–Poly(ethylene oxide) Graft Copolymers: From Surface Patterning to Resistance to Protein Adsorption

The patterning of copolymers on surfaces is of interest both for a fundamental understanding of polymer assembly processes and for applications ranging from microelectronics to biomaterials. Graft copolymers can provide new opportunities to control polymer composition and architecture, thus opening possibilities for new assembly processes and patterns. In this work, the reaction of a butyl rubber derivative functionalized with activated carbonates along the polymer backbone was reacted with amine terminated poly(ethylene oxide) (PEO–NH2) to provide butyl rubber–PEO graft copolymers. The high efficiency of this reaction allowed for control of the PEO content by the number of equivalents of PEO–NH2 used and its molecular weight, providing a small library of graft copolymers. This approach also provided butyl rubber–PEO graft copolymers with unprecedentedly high PEO content. Thin films of the polymers, prepared by spin-casting were studied by a number of techniques including atomic force microscopy, polarize...

Welding Kinetics in a Miscible Blend of High-Tg and Low-Tg Polymers

A model system consisting of poly(tetramethyl bisphenol A polycarbonate) (TMPC) and poly(ethylene oxide) (PEO) was used to study the adhesion between miscible blends of polymers with very different glass transition temperatures. Contact mechanics experiments were performed where identical miscible blend layers were held into contact and separated at elevated temperatures. These results were correlated with measurements of PEO diffusion using dynamic secondary ion mass spectrometry. For low PEO concentrations in the blend, adhesion was obtained above a critical temperature that was consistent with the Fox equation, but substantial adhesion was not obtained at any temperature for blends with higher PEO contents. The results indicate that adhesion requires sufficient mobility of the high-Tg TMPC component and can be enhanced by small additions of PEO. Larger additions of the highly mobile PEO lubricate the interface, eliminating the enhancement in adhesion that would otherwise result from diffusion of the hi...

Electrospinning of Sodium Alginate‐Pectin Ultrafine Fibers

In this study, we investigated the electrospinning process of sodium alginate-pectin fibers intended to be used as a carrier for stabilizing folic acid. Fiber-forming solutions containing 0.01% (w/w) folic acid were prepared by blending low- or medium-viscosity sodium alginate with pectin in a 70 : 30 ratio to form LSAP and MSAP solutions, respectively. Similar to other polysaccharide polymers reported previously, these solutions could not be electrospun. However, the incorporation of poly(ethylene oxide) (PEO) effectively enabled the electrospinning process. Electrospun fibers of different morphologies, ranging from fiber to fiber-bead, were obtained, depending on the blend ratio, concentration, and viscosity of the polymer-PEO solution used. Fibers electrospun from 3% MSAP/PEO (80%/20% w/w) had the smallest diameter (about 40 nm), whereas fibers containing higher PEO contents were larger in diameter. Bead-free fibers were formed when 4% LSAP/PEO (50/50) and 5% LSAP/PEO (80/20 to 50/50) were electrospun. The electrical conductivity and surface tension lowering effects of PEO on the polymer solution were likely the contributing factors for the observed electrospinning behaviors. By adjusting the formulation of the polymer solution, fibers of various morphologies may be obtained to suit different end-use applications. A study is currently ongoing to investigate the effectiveness of these fibers for stabilizing folic acid.

Fluorenyl cardo copolyimides containing poly(ethylene oxide) segments: Synthesis, characterization, and evaluation of properties

AbstractA set of new block copolyimides containing fluorenyl cardo moieties (FR) in the polyimide blocks and poly(ethylene oxide) (PEO) sequences has been prepared using the two‐step method of polyimide synthesis. The combination of both moieties led to novel copolyimides with good solubility in a variety of solvents, which could easily be processed into films. Copolyimides with PEO content from 30 to 56 wt % were amorphous, showed good mechanical properties, and absorbed less water than other PEO‐containing polyimides previously reported. Copolyimides with higher PEO content (60 and 65%) showed crystallinity and yielded soft films. All of the copolymers showed two glass transition temperatures, the first one around −25 °C attributed to the PEO segments, and the second one at much higher temperature, which corresponded to the polyimide domains. The thermal degradation occurred in two steps, the first one being associated with the degradation of the PEO segments and the second one with the generalized aromatic polyimide decomposition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8170–8178, 2008

Interaction of Urea with Pluronic Block Copolymers by 1H NMR Spectroscopy

Solution 1H NMR techniques were used to characterize the interaction of urea with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. The urea was established to interact selectively with the PEO blocks of the block copolymer, and the interaction sites were found not to change with increasing temperature. Such interactions influence the self-assembly properties of the block copolymer in solution by increasing the hydration of the block copolymers and stabilizing the gauche conformation of the PPO chain. Therefore, urea increases the critical micellization temperature (CMT) values of PEO-PPO-PEO copolymers, and the effect of urea on the CMT is more pronounced for copolymers with higher PEO contents and lower for those with increased contents of PPO segments.

Synthesis and Interfacial Behavior of Amphiphilic Hyperbranched Polymers: Poly(ethylene oxide)−Polystyrene Hyperbranches

We report the synthesis of novel hyperbranched amphiphilic poly(ethylene oxide)−polystyrene (PEO−PS)n copolymers obtained by controlled radical polymerizations: nitroxide mediated polymerization (NMP) and reversible addition−fragmentation chain transfer (RAFT). The macroinimers used to synthesize copolymers have the general structure AB*, where A stands for PEO with a terminal double bond and B* stands for a PS block with a terminal initiating group (TEMPO or RAFT CTA). Bulk NMP yielded copolymers with higher molecular weight and higher polydispersity. RAFT polymerization in solution gave hyperbranched copolymers with higher molecular weight but lower polydispersity. Langmuir monolayers displayed reversible amphiphilic behavior at the air−water interface. The random, mixed character of short hydrophilic and hydrophobic fragments results in peculiar surface behavior: unlike regular linear and star block copolymers, the amphiphilic hyperbranched macromolecules with higher PEO content are spread at the air...

Formation of Mesoglobular Phase of PNIPAM-g-PEO Copolymer with a High PEO Content in Dilute Solutions

Free radical copolymerization of N-isopropylacrylamide (NIPAM) and poly(ethylene oxide) (PEO) macromonomer (Mw = 5000) end-capped with methacrylate in water at 45 °C, higher than PNIPAM's lower critical solution temperature (∼32 °C), resulted in (PNIPAM-g-PEO) copolymer with 48 wt % of PEO. As expected, the grafting of PEO on the PNIPAM chain backbone was heterogeneous because PEO is hydrophilic and stayed on the periphery of the PNIPAM segments collapsed at the reaction temperature. The copolymer is soluble in water at lower temperatures. When the solution temperature is raised to ∼34 °C, a limited number of the copolymer chains can collapse and associate to form stable narrowly distributed mesoglobules with a collapsed PNIPAM core and a swollen PEO shell, different from either individual single-chain globules or macroscopic precipitation. The formation of such mesoglobules was studied by a combination of static and dynamic laser light scattering. We found that the mesoglobular formation has two transition stages, occurring at ∼34 and ∼47 °C. The transition at ∼34 °C is related to the contraction of the PNIPAM segment between two grafted PEO chains. The high-temperature transition is attributed to the stretch and collapse of the grafted PEO chains on the periphery. The fast heating generally resulted in smaller mesoglobules, which is due to a competition between intrachain contraction and interchain association as well as the viscoelastic effect.

Super‐toughness in compatibilized poly(butylene terephthalate)/poly(ethylene‐octene) copolymer blends

AbstractPoly(butylene terephthalate) (PBT)/poly(ethylene‐octene) (PEO) blends containing 1.0 wt% epoxy and from 0 to 30 wt% PEO were obtained by extrusion and injection molding. The blends were composed of two pure amorphous phases. The observed torque increases showed that epoxy reacted with PBT, leading to a fine and homogeneous morphology up to 15 wt% PEO content, which appeared larger and more heterogeneous at higher PEO contents. Toughness values fifteen‐fold those of pure PBT were obtained with only 13 wt% PEO. The tensile properties, including ductility, decreased with increasing PEO content, indicating that the adhesion level necessary for high ductility is higher than that necessary for super‐toughness. The inter‐particle distance (τ) was the main parameter that controlled toughness. The comparison of the results of this work with those of the same PBT/PEO blends with two different compatibilizers provides additional strong evidence of the adhesion at the interphase as the main parameter that controls the critical τ in these modified thermoplastic/rubber blends.

Design of segmented poly(ether ester) materials and structures for the tissue engineering of bone

In this study, PEOT/PBT segmented copolymers of different compositions have been evaluated as possible scaffold materials for the tissue engineering of bone. By changing the composition of PEOT/PBT copolymers, very different mechanical and swelling behaviors are observed. Tensile strengths vary from 8 to 23 MPa and elongations at break from 500 to 1300%. Water-uptake ranges from 4 up to as high as 210%. The in vitro degradation of PEOT/PBT copolymers occurs both by hydrolysis and oxidation. In both cases degradation is more rapid for copolymers with high PEO content. PEOT/PBT scaffolds with varying porosities and pore sizes have been prepared by molding and freeze-drying techniques in combination with particulate-leaching. The most hydrophilic PEOT/PBT copolymers did not sustain goat bone marrow cell adhesion and growth. However, surface modification by gas plasma treatment showed a very much improved polymer–cell interaction for all PEOT/PBT copolymer compositions. Their mechanical properties, degradability and ability to sustain bone marrow cell growth make PEOT/PBT copolymers excellent materials for bone tissue engineering.

Miscibility, crystallinity and morphological behavior of binary blends of poly(ethylene oxide) and poly(methyl vinyl ether–maleic acid)

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(methyl vinyl ether– co–maleic acid) (PMVE–MAc). Single T g was observed for all blends, indicating miscibility. The dependence of T g on the weight per cent of PEO presents a negative deviation from linearity at high PEO content, associated to a greater blend free volume, mobility and flexibility than in pure PEO. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites as the PMVE–MAc is added is observed. FTIR provided evidence of specific interaction between the polymers.

Crystallization kinetics of crosslinkable polymer complexes of novolac resin and poly(ethylene oxide)

Results of a study on the isothermal crystallization and thermal behavior of both uncured and hexamine-cured novolac/poly(ethylene oxide) (PEO) complexes are reported. The crystallization behavior of PEO in complexes is strongly influenced by factors such as composition, crystallization temperature, complexation, and crosslinking. The time dependence of the relative degree of crystallinity at high conversion deviated from the Avrami equation. The cured complexes exhibited an obvious two-stage crystallization (primary crystallization and crystal perfection), and this was more evident at higher crystallization temperature and high PEO-content. The addition of a noncrystallizable component into PEO caused a depression of both the overall crystallization rate and the melting temperature. In general, complexation and curing resulted in an increase in the overall crystallization rate. Complexation and curing are beneficial to the nucleation of PEO. Additionally, curing led to changes of the nucleation mechanism. Experimental data on the overall kinetic rate constant Kn were analyzed by means of the nucleation and crystal growth theory. For uncured complexes, the surface free energy of folding, σe, increased with increasing novolac content, whereas for cured complexes, σe displayed a maximum with the variation of composition. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2726–2736, 1999

Phase behavior of poly(ethylene oxide) and sulfonated polystyrene blends with and without solvent

The phase behavior of poly (ethylene oxide) (PEO) and poly(styrene-co-sodium sulfonated styrene) (SPS) blends has been examined as a function of copolymer composition. The mixtures show complex coacervation in dilute benzene/methanol (9/1, v/v) solution. The presence of intermolecular interactions between PEO and SPS in solution is verified by viscometry. Interaction between PEO and SPS in the solid state was supported by small-angle x-ray scattering; however, binary blends containing low PEO content show high miscibility, whereas the blends with high PEO content show phase separation.