Morphology evolution in superheated crystal monolayer of low molecular weight poly(ethylene oxide) on mica surface

Using atomic force microscopy (AFM) coupled with a hot stage, we studied the morphological evolution of superheated poly(ethylene oxide) (PEO) crystal monolayer on the mica surface. The PEO possesses a number average molecular weight (M_n) of 4250 g/mol and a polydispersity of 1.03. The superheated monolayer was obtained when the entire periphery of a triply-folded chain crystal [IF(3)] was thickened to be a twice-folded chain crystal [IF(2)] ‘dam’. The IF(3) crystal was laterally confined by the IF(2) ‘dam’ and remained unchanged at its unconfined melting temperature (T_m). In superheated conditions, the interior IF(3) crystal unfolded, resulting in domains with a thickness in between the fold lengths of the IF(3) and the IF(2) crystals accompanied by hole formation. After its nucleation, the hole enlarged its area quickly and migrated long distances within the area bounded by the IF(2) crystal ‘dam’.     

Biodegradable multiblock PEO/PLA thermoplastic elastomers: molecular design and properties

Given the need for highly flexible biodegradable polymers, a series of poly(ethylene oxide)/poly(l-lactic acid) (PEO/PLA) (PELA) multiblock poly(ether-ester-urethane)s, were synthesized and characterized. The first step of the synthesis consisted of the ring-opening polymerization of l-lactide, initiated by the hydroxyl terminal groups of the PEO chain, followed by the chain extension of these PLA-PEO-PLA triblocks, using hexamethylene diisocyanate (HDI). The trimers comprised PEO segments in the 1000-10,000 molecular weight range, with the length of each PLA block covering the 200-10,000 interval. DSC and X-ray analyses revealed that, depending on their composition, amorphous matrices, monophasic crystalline materials and copolymers comprising two crystalline phases, were generated. The multiblock copolymers synthesized exhibited superior mechanical properties, with ultimate tensile strength values around 30 MPa, Young's moduli as low as 14 MPa and elongation at break values well above 1000%. Because of their phase segregated morphology, most of these multiblock copolymers displayed remarkable mechanical properties also when fully hydrated, with typical UTS values around 9 MPa.     

Effect of hard segment and concentration of NaClO4 on poly(ethylene oxide)–urethane/NaClO4 complex

Solid poly(ethylene oxide)–urethane electrolytes were prepared from blends of polyurethane and NaClO₄. The samples were characterized by FTIR, DSC, atomic force microscopy, and complex impedance analysis. The effect of the concentration of NaClO₄ on the poly(ethylene oxide)–urethane/NaClO₄ complex were studied. The results showed that the concentration of NaClO₄ had an important effect on the ion–polymer interaction, ion–ion interaction, glass‐transition temperature, morphologic structure, and ionic conductivity of the complex. We also prepared a model compound of hard segments and found that the conductivity of the complex decreased when the model compound was blended into the complex. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2502–2510, 2001     

The thermal degradation of PET and analogous polyesters measured by thermal analysis-Fourier transform infrared spectroscopy

The thermal degradation of two commercial poly(ethylene terephthalate) (PET) samples and two laboratory prepared polyesters, poly(ethylene isophthalate) and poly(diethylene glycol terephthalate), was studied using thermogravimetry and thermal analysis-Fourier transform infrared spectroscopy. The commercial PET samples were copolymerised with diethylene glycol and isophthalic acid groups in different proportions, and their thermal stabilities were found to differ. Through a study of the thermal degradation of poly(diethylene glycol terephthalate) and poly(ethylene isophthalate), it was found that diethylene glycol and isophthalate units promoted thermal degradation through increased chain flexibility and more favourable bond angles, respectively. The thermal degradation of all the polyesters tested lead to the formation of non-volatile residue. Infrared spectroscopic analysis indicated that the residue consisted almost exclusively of interconnected aromatic rings.     

Temperature responsive bio-compatible polymers based on poly(ethylene oxide) and poly(2-oxazoline)s

This review covers the LCST behavior of two important polymer classes in aqueous solution, namely poly(2-oxazoline)s and systems whose thermo-responsiveness is based on their structural similarity to poly(ethylene oxide) (PEO). In order to elucidate the progress that has been made in the design of new thermo-responsive copolymers, experimental data that were obtained by different research groups are compared in detail. Copolymerization with hydrophilic or hydrophobic comonomers represents a suitable method to tune the coil to globule transition temperature of several homopolymers, and incorporation of other monomers provided further interesting features, such as pH responsiveness or sensing properties. In addition, living and controlled polymerization techniques enabled access to defined end groups and more advanced polymer architectures, such as graft copolymers or double responsive block copolymers. The effect of such structural variations on the temperature responsive behavior of the (co)polymers is discussed in detail.     

Nanostructures from photo-cross-linked amphiphilic poly(ethylene oxide)-b-alkyl diblock copolymers

Poly(ethylene oxide) monomethylether was functionalized by alkyl chains of various lengths (l=10-19 methylene groups) bearing a polymerizable methacrylate moiety. Each synthesis step on the polymer gives quantitative functionalization rates. The self-assembly of the amphiphilic polymers in water was studied by light scattering for various end-groups. Sterical and polar effects were shown to influence the micellization step. The cores of the micelles formed by PEO-C_l-methacrylate were irreversibly cross-linked by UV irradiation. Star polymers that are stable under dilution in good solvent are obtained after 1-min irradiation. The hydrodynamic radius and the molar mass of the nanoparticles depend on the amount of photoinitiator introduced in the cores.     

Polyimides with main-chain ethylene oxide units: synthesis and properties

This paper describes the synthesis of a new series of well-defined bis(ether anhydride)s based on ethylene oxide sequences of known length (up to six ethylene oxide units) with phthalic acid anhydride end-caps, and extends the synthesis of bisphenoxyamines based on ethylene oxide sequences to six ethylene oxide units. The dianhydrides and diamines were used in combination to synthesize a series of segmented polyimides of well-defined structures having defined sequences of from zero up to six ethylene oxide units separated by N-phenylphthalimide units. The polymers are characterized in terms of solubility, thermal stability, thermal transition behaviour, including crystal melting behaviour; glass-transition temperatures vary systematically with structure and composition. One polymer exhibits liquid crystallinity. The water absorption characteristics of the polymers, which vary from a hydrophobic aromatic polyimide to polymers containing up to 52.7 wt% ethylene oxide, were determined. The crystal melting behaviour is discussed in conjunction with data from other segmented polyimides containing similar structural units.     

Surface modification of kaolin. 2. Enhanced steric stabilisation of polymer-modified kaolin

The polymer-modified surface of kaolin was studied to determine the effect of changing the molecular weight of the polymer chain grafted on the surface. The particle was modified by attaching poly(ethylene oxide) to the surface using a urethane linkage. Upper critical flocculation temperature and contact angle measurements were conducted to quantify the changes in surface characteristics and stability in an aqueous dispersion. The effect of pH on stability and grafted density of polymer chains showed the mechanism of stabilisation to be that of enhanced steric stabilisation. The kaolin particle was also modified with the more hydrophobic poly(propylene oxide). The behaviour was characterised as for poly(ethylene oxide) and interesting differences in extent and mechanism for stabilisation were observed.     

The influence of competitive interactions on multiple eutectic phase behavior in poly(ethylene oxide) molecular complexes

Binary mixtures of poly(ethylene oxide) and resorcinol exhibit two eutectic phase transitions at 40 and 80 °C, which are separated by a single-phase stoichiometric complex at ≈33 mol% resorcinol. These eutectic temperatures increase slightly at higher molecular weights of poly(ethylene oxide). The eutectics and the molecular complex are absent in ternary mixtures with either 25 or 40 wt% poly(2-vinylpyridine) because both polymers contain electron-pair donors which participate in hydrogen bonding interactions with the hydroxyl groups of the small-molecule aromatic. In contrast, 25 wt% polystyrene does not disrupt the bi-eutectic phase behavior of poly(ethylene oxide) and resorcinol because polystyrene is inert in these ternary mixtures. The lightest lanthanides with the largest ionic radii in the first-row of the f-block, like LaCl₃(H₂O)₆ and CeCl₃(H₂O)_x, are more effective than neodymium, terbium and ytterbium trichloride hexahydrates from the viewpoint of (i) competing with resorcinol, (ii) interacting with poly(ethylene oxide), (iii) eliminating eutectic melting, and (iv) disrupting the 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol. High-resolution ¹³C solid state NMR spectroscopy identifies resorcinol in several different molecular environments. Multiple resonances are observed for chemically equivalent, but morphologically and crystallographically inequivalent, ¹³C sites in the solid state. The isotropic chemical shift of the phenolic ¹³C site in this small-molecule aromatic is very sensitive to the strength of intermolecular interactions in various phases. For example, self-association of resorcinol in pure crystalline phase γ yields a phenolic carbon chemical shift at 155 ppm. The formation of a 2:1 stoichiometric complex between poly(ethylene oxide) and resorcinol in co-crystallized phase β is identified by a phenolic carbon chemical shift at 158 ppm. When resorcinol and poly(2-vinylpyridine) interact in a homogeneous amorphous phase, the phenolic carbon resonance appears at a chemical shift of 160 ppm. A resorcinol-rich disordered crystalline phase in ternary mixtures with poly(ethylene oxide) and poly(2-vinylpyridine) yields a phenolic carbon resonance at 159 ppm. Temperature-composition projections of the binary and ternary phase diagrams, constructed via differential scanning calorimetry, allow one to interpret ¹³C NMR spectra of these strongly interacting blends and complexes in the solid state.     

Synthesis and characterization of amphiphilic graft copolymer poly(ethylene oxide)-graft-poly(methyl acrylate)

A novel well-defined amphiphilic graft copolymer of poly(ethylene oxide) as main chain and poly(methyl acrylate) as graft chains is successfully prepared by combination of anionic copolymerization with atom transfer radical polymerization (ATRP). The glycidol is protected by ethyl vinyl ether first, then obtained 2,3-epoxypropyl-1-ethoxyethyl ether (EPEE) is copolymerized with EO by initiation of mixture of diphenylmethyl potassium and triethylene glycol to give the well-defined poly(EO-co-EPEE), the latter is deprotected in the acidic conditions, then the recovered copolymer [(poly(EO-co-Gly)] with multi-pending hydroxyls is esterified with 2-bromoisobutyryl bromide to produce the ATRP macroinitiator with multi-pending activated bromides [poly(EO-co-Gly)_(ATRP)] to initiate the polymerization of methyl acrylate (MA). The object products and intermediates are characterized by NMR, MALDI-TOF-MS, FT-IR, and SEC in detail. In solution polymerization, the molecular weight distribution of the graft copolymers is rather narrow (M_w/M_n < 1.2), and the linear dependence of Ln [M₀]/[M] on time demonstrates that the MA polymerization is well controlled.     

Poly(ethylene oxide)/polybutadiene based IPNs synthesis and characterization

Interpenetrating polymer networks (IPNs) were prepared from hydroxytelechelic polybutadiene (HTPB) and poly(ethylene oxide) (PEO) via an in situ process. The PEO network was obtained by free radical copolymerization of poly(ethylene glycol) methacrylate and dimethacrylate. Addition reactions between HTPB and a pluri-isocyanate cross-linker (Desmodur^® N3300) led to the HTPB network. Polymerization kinetics were followed by Fourier transform spectroscopy in the near and middle infrared. Mechanical properties and the IPN morphology were investigated by dynamic mechanical analysis and transmission electron microscopy. The relation between the formation rates of the two networks and the IPN final morphology is discussed.     

Synthesis and characterization of alternating poly(amide urethane)s from ε-caprolactone, diamines and diphenyl carbonate

The synthesis of alternating poly(amide urethane)s 5a-d was performed in three steps using ε-caprolactone, diamines, and diphenyl carbonate as starting materials. The microstructure and nature of the end groups of the poly(amide urethane)s were determined by means of ¹H NMR spectroscopy, which reveals an alternating sequence of amide and urethane linkages in a linear chain with hydroxy and phenyl urethane end groups. The molecular weight and polydispersity of the polymers obtained (, ) were determined by means of gel permeation chromatography. The thermal properties determined by means of DSC show that the poly(amide urethane)s 5a-d are semicrystalline materials having one or two endothermic transitions similar to the poly(amide urethane)s 10a-d prepared from ε-caprolactam, amino alcohols, and diphenyl carbonate. Thermogravimetric analysis of poly(amide urethane)s 5a-b shows a single step decomposition, while poly(amide urethane)s 10a-c decompose in two steps indicating that different degradation mechanisms are operating.     

Block copolymers comprising poly(ethylene oxide) and poly(hydroxyethyl methacrylate) blocks: synthesis and characterization

Monofunctional poly(ethylene oxide) macroinitiators with a molecular weight of 2000, 5000, 10?000, 20?000 and bifunctional poly(ethylene oxide) macroinitiators with a molecular weight of 20?000 were used for the atom transfer radical polymerisation (ATRP) of hydroxyethyl methacrylate (HEMA) in ethylene glycol as a solvent. The polymerisation proceeds in a controlled way up to high conversions. The molecular weight of the obtained copolymers increases linearly with conversion. A high rate of polymerisation was observed for the ATRP of HEMA. The effect of the poly(ethylene oxide) moiety on the course of the reaction is limited to solvating effects. The surface analysis of poly(ethylene oxide)/poly(hydroxyethyl methacrylate) block copolymers by means of atomic force microscopy in tapping mode using phase imaging shows phase separated domains with characteristic features related to the volume fraction of the respective blocks.     

Miscibility of C60-end-capped poly(ethylene oxide) with poly(vinyl chloride)

The miscibility of blends of single [60]fullerene (C₆₀)-end-capped poly(ethylene oxide) (FPEO) or double C₆₀-end-capped poly(ethylene oxide) (FPEOF) with poly(vinyl chloride) (PVC) has been studied. Similar to poly(ethylene oxide) (PEO), both FPEO and FPEOF are also miscible with PVC over the entire composition range. X-ray photoelectron spectroscopy showed the development of a new low-binding-energy Cl2p doublet and a new high-binding-energy O1s peak in FPEO/PVC blends. The results show that the miscibility between FPEO and PVC arises from hydrogen bonding interaction between the α-hydrogen of PVC and the ether oxygen of FPEO. From the melting point depression of PEO, FPEO or FPEOF in the blends, the Flory-Huggins interaction parameters were found to be −0.169, −0.142, −0.093 for PVC/PEO, PVC/FPEO and PVC/FPEOF, respectively, demonstrating that all the three blend systems are miscible in the melt. However, the incorporation of C₆₀ slightly impairs the interaction between PEO and PVC.     

Time-resolved conformational analysis of poly(ethylene oxide) during the hydrogelling process

We investigated a drastic conformation change in a poly(ethylene oxide) (PEO) chain during the hydrogelation process using infrared (IR) spectroscopy and quantum chemical calculations (QCCs). Time-resolved in situ IR spectra of the hydrogelling process of a semi-crystalline PEO solid were measured using a flow-through cell. It was found from the time-resolved IR study that gauche conformations around the C-C bonds in the crystalline phase PEO chain maintain their conformations even after hydrogelation, while at least half of the trans conformations around the C-O bonds change into gauche conformations upon hydrogelling. With regard to the phenomena of these conformation changes after contacting water, the destruction and hydrogelation of the crystalline phase around the C-C bonds of the hydrophobic moiety occur prior to changes around the C-O bonds of the hydrophilic moiety. In addition, our QCC confirmed that the stable hydration structure of bridging water, wherein the two hydroxyl groups in a water molecule donate hydrogen bonds to every other ether oxygen atoms in the PEO chain.     

Influences of poly(ether urethane) introduction on poly(ethylene oxide) based polymer electrolyte for solvent-free dye-sensitized solar cells

A poly(ether urethane) (PEUR)/poly(ethylene oxide) (PEO)/SiO₂ based nanocomposite polymer is prepared and employed in the construction of high efficiency all-solid-state dye-sensitized nanocrystalline solar cells. The introduction of low-molecular weight PEUR prepolymer into PEO electrolyte has greatly enhance the electrolyte performance by both improving the interfacial contact properties of electrode/electrolyte and decreasing the PEO crystallization, which were confirmed by XRD and SEM characteristics. The effects of polymer composition, nano SiO₂ content on the ionic conductivity and I₃⁻ ions diffusion of polymer-blend electrolyte are investigated. The optimized composition yields an energy conversion efficiency of 3.71% under irradiation by white light (100 mW cm⁻²).     

Dynamics of Poly(ethylene glycol)-Tethered, pH Responsive Networks

Smart biomaterials composed of pH responsive polymers, poly((meth)acrylic acid), were synthesized using a precipitation polymerization technique. The microparticles were grafted with poly(ethylene glycol) (PEG) chains that are capable of complexing with the hydroxyl groups of the polyacid and interpenetrating into the mucus gel layer upon entry into the small intestine. Upon introduction of an alkaline solution, these materials imbibe a significant amount of water and create a highly viscous suspension. These materials have the necessary physicochemical properties to serve as mucoadhesive controlled release drug carriers for the oral delivery of drugs.     

Apparent elongational viscosity of dilute polymer solutions

Apparent elongational viscosity studies were made on dilute solutions of high molecular weight polymers using a fiber spinning apparatus designed for low shear viscosity liquids with substantial elongational effects. The experimental method involved the flow of solutions of polyacrylamide and poly(ethylene oxide) from a tube into an evacuated vessel. Experimental results showed that the apparent elongational viscosity obtained from the jet shape increased linearly with the stretch rate.     

High molecular arborescent polyoxyethylene with hydroxyl containing shell

Arborescent polyoxyethylene of high molar mass (2×10⁵ g/mol) and narrow molar mass distribution was synthesized in a three-stage process. In the first stage a triblock copolymer of ethylene oxide (central block, DP ca. 90) and 2,3-epoxypropanol-1 (short flanking blocks, DP ca. 5) was synthesized. The potassium alcoholate derived from this copolymer was used to initiate the polymerization of ethylene oxide and the subsequent addition of protected glycidol (1-etoxyethyl glycidyl ether). After deprotection the short polyglycidol blocks were used as branching units for the next generation. Repeated step by step process leads to the ‘pom-pom like’ branched polyoxyethylene macromolecules enriched with the reactive hydroxyl groups in the outer shell. The branched structure of the obtained polymers was evidenced by the size exclusion chromatography and NMR spectroscopy.     

Properties of Poly(vinyl chloride)/poly(ethylene oxide)/polyaniline Conductive Films: The Effect of Poly(ethylene glycol) Diglycidyl Ether

The effect of polyaniline and poly(ethylene glycol) diglycidyl ether on tensile properties, morphology, thermal degradation, and electrical conductivity of poly(vinyl chloride)/poly(ethylene oxide)/polyaniline conductive films was studied. The poly(vinyl chloride)/poly(ethylene oxide)/polyaniline conductive films were prepared using a solution casting technique at room temperature until a homogeneous solution was produced. Poly(vinyl chloride)/poly(ethylene oxide)/polyaniline/poly(ethylene glycol) diglycidyl ether conductive films exhibit higher electrical properties, tensile strength, modulus of elasticity but lower final decomposition temperature than poly(vinyl chloride)/poly(ethylene oxide)/polyaniline conductive films. Scanning electron microscopy morphology showed that the polyaniline more widely dispersed in the poly(vinyl chloride)/poly(ethylene oxide) blends with the addition of poly(ethylene glycol) diglycidyl ether as surface modifier.