Contribution of entanglements to the modulus of end-linked poly(ethylene oxide) networks

Poly(ethylene oxide) networks were made at 75 °C by end-linking of short linear chains with an excess of Tolonate HDT, a tri-functional aliphatic isocyanate. Molecular weights of poly(ethylene oxide)were 4000, 6000 and 12000. The observed elastic moduli were much higher than predicted from affine theory, indicating a large contribution from entanglements in contrast to the findings of previous studies. With increasing excess of cross-linker, the contribution from entanglements levels off at a value of approximately 5 MPa which is in good agreement with the rubber plateau modulus of pure poly(ethylene oxide).     

Model polyurethane networks prepared from poly(ethylene oxide) and poly(tetramethylene oxide)

Polyurethane elastomers of known degrees of cross-linking were prepared from hydroxylterminated poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) chains having numberaverage molecular weights in the range 880–6820 g mol^?1. The chains were end-linked into “model” trifunctional networks using a specially prepared aromatic triisocyanate. The networks thus obtained were studied with regard to their stress-strain isotherms in both the unswollen and swollen states, in elongation at 25°, and with regard to their equilibrium swelling in benzene at 57.9°. Values of the modulus in the limit at high deformation were in good agreement with corresponding results previously obtained on trifunctional networks of poly(dimethylsiloxane) (PDMS). Since PEO has a much higher value of the plateau modulus in the uncross-linked state, this agreement indicates that inter-chain entanglements do not contribute significantly to the equilibrium modulus of an elastomeric network. These values of the high deformation modulus are also in good agreement with recent molecular theories as applied to the non-affine deformation of a “phantom” network. The swelling equilibrium results were in very good agreement with the new theory of network swelling developed by Flory.     

Synthesis and characterization of semi- and full-interpenetrating polymer networks of poly(2,6-dimethyl-1,4-phenylene oxide) and polydimethylsiloxane

The synthesis and characterization of pseudo or semi- and full-interpenetrating polymer networks (IPNs) of poly(2,6-dimethyl-1,4-phenylene oxide) and polydimethylsiloxane were performed. We observed that in full IPNs, the elasticity of the IPN samples increased very drastically, as the composition of polydimethylsiloxane increased (i.e. 0–60%) while the tensile strength (TS) and the glass transition temperature (T_g) decreases. The pseudo IPNs appeared to consist of two phases while the full IPNs of lower siloxane content were miscible.     

Block copolymers of poly(m-phenylene isophthalamide) and poly(ethylene oxide) or polydimethylsiloxane: Synthesis and general characteristics

The syntheses of poly(m-phenylene isophthalamide-b-ethylene oxide) and poly(m-phenylene isophthalamide-b-dimethylsiloxane) are reported. The development of synthesis procedures for (AB)_n and predominantly triblock ABA and BAB sequences are discussed. Chemical compositions, dilute solution viscosities, and solubility behavior of these systems are also given some consideration. These considerations include the problems that arise in condensing block segments together when phase separation is occurring and developing control of the synthesis procedure to produce block systems of varying compositions.     

Morphology of single-chain single crystals of poly(ethylene oxide)

Single-chain particles of poly(ethylene oxide) (PEO) were prepared by spreading a 10^-4 wt.-% solution of PEO in benzene on a hot water surface. After isothermal crystallization at 317,2 ± 0,1 K for 10 h, regular-shaped single-chain crystals were observed. A variety of typical morphologies were also found, and some of them are discussed on the basis of the habit of PEO crystals and various twin modes.     

Poly(ethylene oxide)/poly(methyl methacrylate) (semi-)interpenetrating polymer networks: Synthesis and phase diagrams

Interpenetrating polymer networks (IPNs) of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) were prepared by simultaneous network formation. The PEO network was produced by acid-catlayzed self-condensation of α,ω-bis(triethoxysilane)-terminated PEO in the presence of small amounts of water. The PMMA network was formed by free radical polymerization of MAA in the presence of divinylbenzene as crosslinker. The reaction conditions were adjusted to obtain similar crosslinking kinetics for both reactions. An attempt was made to construct a phase diagram of the IPNs by measuring the composition of the IPNs at the moment of the appearance of the phase separation, as indicated by the onset of turbidity. This composition could be determined because the siloxane crosslinks of the PEO network could be hydrolyzed in aqueous NaOH with the formation of linear, soluble PEO chains. The phase diagram was compared with phase diagrams of blends of linear polymers and of semi-IPNs (crosslinked PMMA and linear PEO), obtained under similar conditions, i.e. polymerization of MMA in the presence of varying amounts of PEO. It was observed that the form of the phase diagrams of the linear polymers is similar to that of the IPNs, but is quite different from that of the semi-IPNs. Thus, homogeneous transparent materials containing up to 60% of PEO could be prepared in the blends and the IPNs, but in the semi-IPNs, phase separation occurred with PEO contents as low as 10%.     

Morphology of ultrathin polymer films based on poly(ethylene oxide) blends

The structure of ultrathin (15–200 nm) films of two types prepared from polymer blends based on PEO (the crystallizable component), namely, PEO-poly(arylene sulfone oxide) (the amorphous component) and PEO-PB (the amorphous component), has been studied by atomic force microscopy. The content of PEO in both blends is 76 wt %. Ultrathin blend films have been applied on a Si substrate via substrate dipping into dilute solutions of polymer blends in chloroform at room temperature. The rate of the substrate lift has been varied from 0.1 to 1 mm/min. The amorphous-amorphous separation takes place during formation of ultrathin films of the above blends in the course of the substrate lift at the stage of gelation. The crystallization of PEO and dewetting in the resulting two-phase blend gels depend on the rate of the substrate lift and the rigidity of macromolecules of the amorphous component. Moreover, the predominant interaction of the substrate with one of the components plays a significant role in structure formation of ultrathin films of both polymer blends.     

Restricted self-diffusion in an aqueous solution of poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide) triblock copolymer

 The self-diffusion behavior of a triblock copolymer (PEO–b– PPO–b–PEO) in an aqueous solution of 20% (m/m) was investigated during a temperature-induced phase transition from liquid to gel state using pulsed field gradient NMR and static light scattering. The measured self-diffusivity shows a strong dependence on the observation time in the gel phase indicating the existence of diffusion barriers in the size range of about 0.6 μm. Additional static light-scattering measurements show a structure in the same size range of several hundred nanometers, which is far above molecular or micellar sizes and thus, has to be caused by larger clusters. The similarity in the space scales suggests that the restriction of molecular propagation is correlated with the grain boundaries between the domains of the poly-crystalline structure formed by the arranged micelles. Received: 28 October 1996 Accepted: 21 March 1997     

New neutral and ionic poly(ethylene oxide) networks by radical polymerization

New opportunities resulting from a turn to radical polymerization in the synthesis of poly(ethylene oxide) (PEO) networks are discussed and exemplified. Several series of such networks have been prepared by radical homo‐ and copolymerization in aqueous media of “macromonomers”, i.e. partly methacrylated poly(ethylene glycol) (PEG) of varied molecular weight (MW ≅ 2000‐12000) and functionality (f_n ≅ 1.25‐1.8). This family of gels as a whole has the volume swelling degree Q in the range of 10 to 200 ml/ml. The hydrogels are characterized by means of Q, elastic modulus, swelling pressure, and with the use of some probes. The swelling behaviour of neutral hydrogels of this kind is briefly resumed. The multifunctional junctions formed in the propagation reaction of methacrylate end groups determine their main peculiarity. Anomalous elastic behaviour of the swollen networks prepared at high concentration of polymer has been observed and attributed to the network chains stretching of the same nature as in polymer stars or brushes. The junctions' functionality (F ≈ 20‐300) is evaluated from these data as well as from MW of the soluble models of network junctions. The PEO networks with charged units in junctions have been obtained by copolymerization of macromonomers with some ionic (meth)acrylic monomers. These gels display all the polyelectrolyte features, e.g. enhanced Q values in water (up to 50‐70) and, contrary to neutral PEO gels, the strong dependence on salt content. However, the osmotic contribution of mobile ions into swelling is shown to be low due to localization of charges in the junctions. The hydrogels that combine PEO and polymethacrylic acid chains capable of interpolymer complexation have been prepared and studied. They show much higher swelling in pure water (Q up to 200), strong deswelling by NaCl, and very sharp drop in swelling (ca. two order in Q) at pH ≈ 4.5‐5.5 due to complexation.     

Crystallization kinetics of polymer brushes with poly(ethylene oxide) side chains

Isothermal crystallization rates of semicrystalline poly(methoxypoly(ethylene glycol) methacrylate) brushes on gold‐coated substrates were measured by polarized optical microscopy. Growth rates for crystal radii, which were essentially constant for each film, initially increased with film thickness and then leveled off for film thicknesses >300 nm. Avrami–Evans theory suggests that the spherulites exhibit one‐dimensional growth with heterogeneous nucleation. Compared with physisorbed analogs, polymer brushes crystallized slower due to the restriction of chain mobility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1955–1959, 2010     

The thermal analysis of polymer blends of poly(ethylene oxide)/poly(methyl methacrylate)

Thermal analysis of the PEO/PMMA system show for the blends with higher molecular weight PMMA two glass transition temperatures in the 75–80 w/w% PMMA range. Thermal treatment is accompanied by a shift of this composition range of two Tg to lower PMMA contents. On the other hand observed melting point depression in the 0–60 w/w% PMMA range indicate compatibility of the blend components. Small negative interaction parameters approaching zero with increasing PMMA content of the blend, support the possible incompatibility in the observed composition range of two Tg.

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Zusammenfassung Die Thermoanalyse des Systemes PEO/PMMA ergab für Gemische mit PMMA höheren Molekülgewichtes zwei Glasumwandlungspunkte /Tg/ im Bereich 75–80 m/m% PMMA. Eine Wärmebehandlung ist vom Verschieben dieses Bereiches mit den zwei Tg in Richtung niedrigerem PMMA-Gehalt begleitet. Weiterhin zeigt die Schmelzpunktserniedrigung im Bereich 0–60 m/m% PMMA die Kompatibilität der Gemischkomponenten. Kleine negative, mit steigendem PMMA-Gehalt des Gemisches gegen Null haltende Wechselwirkungsparameter unterstreichen die Möglichkeit einer Inkompatibilität im beobachteten Bereich der zwei Tg.

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120–230°. 2 3590 . . . 150°, . .

     

Dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains

The mean-square dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains have been determined from dielectric constant measurements on dilute solutions of the polymers in benzene. The values obtained are in good agreement with those predccted using the rotational isomeric state models for these chains. In addition, the unperturbed dimensions of poly(hexamethylene oxide) have been calculated as a function of molecular weight, using the isomeric state theory.     

The structure of poly(ethylene oxide)8: NaBPh4 from a single crystal oligomer and polycrystalline polymer

We show that the structure of a polymer electrolyte may be solved by growing single crystals of an oligomeric (short chain) complex which provided an adequate starting model for refinement of the equivalent polymeric structure using powder diffraction: the efficacy of this method has been demonstrated by determining for the first time the structure of an 8 : 1 complex, poly(ethylene oxide)(8) : NaBPh(4).     

Effects of electrolytes on adsorbed polymer layers: poly(ethylene oxide)-silica system

The effects of various electrolytes on the adsorption of poly(ethylene oxide) onto silica have been studied. The salts were the chlorides of Na+, Mg2+, Ca2+, and La3+. The methods used were adsorption isotherms, found using a depletion method with phosphomolibdic acid, photon correlation spectroscopy, and solvent relaxation NMR. All the salts increased the particle-polymer affinity and adsorbed amount according to the adsorption isotherms, and a linear relationship was found between the initial slope of the isotherms and the ionic strength of the solution. Final adsorbed amounts were approximately 0.4-0.5 mg m(-2). The polymer layer thicknesses as found by PCS were of the same order as the radius of gyration of the polymer and increased with both the concentration and the valency of the salt due to increased adsorption. Solvent relaxation NMR showed that NaCl is too weak to have a noticeable effect on the polymer train layer, but the divalent salts clearly did increase both the strength of solvent binding close to the silica surface and the amount of PEO required to reach the maximum train density.     

Characterization and demulsification of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers

Four poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers with different molecular weights and PPO/PEO composition ratios were synthesized. The characterization of the PEO-PPO-PEO triblock copolymers was studied by surface tension measurement, UV-vis spectra, and surface pressure method. These results clearly showed that the CMC of PEO-PPO-PEO was not a certain value but a concentration range, in contrast to classical surfactant, and two breaks around CMC were reflected in both surface tension isotherm curves and UV-vis absorption spectra. The range of CMC became wider with increasing PPO/PEO composition ratio. Surface pressure Pi-A curves revealed that the amphiphilic triblock copolymer PEO-PPO-PEO molecule was flexible at the air/water interface. We found that the minimum area per molecule at the air/water interface increased with the proportion of PEO chains. The copolymers with the same mass fractions of PEO had similar slopes in the isotherm of the Pi-A curve. From the demulsification experiments a conclusion had been drawn that the dehydration speed increased with decreased content of PEO, but the final dehydration rate of four demulsifiers was approximate. We determined that the coalescence of water drops resulted in the breaking of crude oil emulsions from the micrograph.     

Synthesis and characterization of poly(ethylene oxide)/polylactide/poly(ethylene oxide) triblock copolymer

Poly(ethylene oxide/polylactide/poly(ethylene oxide) (PEO/PL/PEO) triblock copolymers, in which each block is connected by an ester bond, were synthesized by a coupling reaction between PL and PEO. Hydroxyl‐terminated PLs with various molecular weights were synthesized and used as hard segments. Hydroxyl‐terminated PEOs were converted to the corresponding acid halides via their acid group and used as a soft segment. Triblock copolymers were identified by Fourier transform infrared spectroscopy, ¹H NMR, and gel permeation chromatography. Differential scanning calorimetry (DSC) and X‐ray diffractometry of PEO/PL/PEO triblock copolymers suggested that PL and PEO blocks were phase‐separated and that the crystallization behavior of the PL block was markedly affected by the presence of the PEO block. PEO/PL/PEO triblock copolymers with PEO 0.75k had two exothermic peaks (by DSC), and both peaks were related to the crystallization of PL. According to thermogravimetric analysis, PEO/PL/PEO triblock copolymer showed a higher thermal stability than PL or PEO. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2545–2555, 2002     

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 K_n were analyzed by means of the nucleation and crystal growth theory. For uncured complexes, the surface free energy of folding, σ_e, increased with increasing novolac content, whereas for cured complexes, σ_e displayed a maximum with the variation of composition. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2726–2736, 1999