Critical behavior and interfacial tension of mixtures of propylene glycol and ethylene glycol oligomers

This investigation presents an analysis of the critical behavior of mixtures of oligomers of propylene glycol, PG₁₇, and ethylene glycol, EG_n, withn=3, 4, 5, 6.4, 8.7, 12.1 and 22.1. The critical coordinates, _c andT _c were determined from the phase diagrams. The critical compositions compare very well with the Huggins-Flory predictions. The interaction parameter _n is around one for EG₃, EG₄ and EG₅ and it increases up to two for the higher oligomers. The break in the interaction parameter also corresponds to a minimum in the critical temperature. The phase diagrams and the interfacial tension were used to get the critical exponents and , respectively. The data were analysed with two approaches. First, from the temperature dependence of the length of the tie-lines and of the interfacial tension up to the upper critical solution temperature, UCST. Second, with the data at 30°C using the critical temperature of the systems as the variable. The first method led to =0.39±0.05 in good agreement with the result of the second method, =0.37±0.04. The exponents for the interfacial tension, , determined with the first method for PG₁₇ with EG_6.4, EG_8.7 and EG_12.1 are =1.66±0.11, 1.46±0.25 and 1.73±0.18, respectively. The second method led to =1.17±0.14. The critical exponents are compared to mean field and ising-3D predictions.     

Investigation of the thermal properties of glycidyl methacrylate–ethylene glycol dimethacrylate copolymeric microspheres modified by Diels–Alder reaction

Journal of Thermal Analysis and Calorimetry - The study describes the thermal properties of functional microspheres composed of glycidyl methacrylate (GMA) and crosslinking agent ethylene glycol...     

Hydrogen network fluctuations of associating liquids: dielectric relaxation of ethylene glycol oligomers and their mixtures with water

Complex dielectric spectra of ethylene glycol and of various derivatives as well as of mixtures of water with an ethylene glycol oligomer and with a poly(ethylene glycol) dimethyl ether oligomer have been measured. The spectra can be well represented by a Cole-Cole [Cole and Cole, J. Chem. Phys. 9, 341 (1941)] spectral function. The extrapolated low frequency (static) permittivity of this function has been evaluated to yield the effective dipole orientation correlation factor of the liquids. The relaxation time of the ethylene glycols displays a characteristic dependence upon the ratio of concentrations of hydrogen bond donating and accepting groups, indicating two opposing effects. With increasing availability of hydrogen bonding sites effects of association and also of dynamical destabilization increase. Both effects exist also in the mixture of water with the oligomers. They are discussed in terms of a wait-and-switch model of dipole reorientation in associating liquids. Another feature in the dependence of the dielectric relaxation time of poly(ethylene glycol)/water mixtures upon mixture composition has been tentatively assigned to precritical demixing behavior of the binary liquids in some temperature range.     

Rheological properties and phase behavior of a hydroxypropyl cellulose-poly(ethylene glycol) system

The relaxation and phase behavior of solutions of hydroxypropyl cellulose in poly(ethylene glycols) of various molecular masses has been studied by dynamic mechanical analysis. The dynamic mechanical data are compared with the results of microinterferometry and polarization-microscopy measurements. The combination of optical and mechanical characteristics makes it possible to construct generalized phase- relaxation diagrams for the binary systems under study. Solutions based on lowmolecular-mass poly(ethylene glycol) are characterized by LC equilibrium. With an increase in the molecular mass of poly(ethylene glycol) in a certain temperature-concentration region, amorphous phase separation takes place and the phase diagram is the superposition of LC and amorphous equilibria. The relaxation properties of the systems are sensitive to the phase state and its transformation.     

Synthesis of polyvinyltrimethylsilane-graft-poly(ethylene glycol) copolymers and properties of gas-separating membranes formed on their basis

A method is developed for the synthesis of the graft copolymer polyvinyltrimethylsilane-graft-poly(ethylene glycol) via the interaction of a brominated polymer with the methyl ether of a low-molecular-mass poly(ethylene glycol). Graft copolymer samples containing up to 79 wt % poly(ethylene glycol) are synthesized through this method. The properties of the graft copolymers and blends formed on their basis with a specially synthesized low-molecular-mass PEG derivative with a terminal trimethylsilyl group are investigated. Physical blends are prepared in order to increase the content of ethylene oxide groups while the film-forming properties of the composite materials are preserved. As shown by structural studies, the graft copolymers are amorphous single-phase systems, while the related blends are two-phase disperse systems, in which one phase is enriched in polytrimethylvinylsilane and the other is enriched in PEG. Studies of the gas-transport behavior of the samples reveal that the introduction of PEG, in contrast to the nonselective initial polymer, results in the formation of PVTMS-based materials that are selective for CO₂ in mixtures with H₂.     

Probing the association behavior of poly(ethylene glycol)-based amphiphilic comb-like polymer in NaCl solution

The effect of salt on the associative behavior of intramolecular aggregates obtained from poly(ethylene glycol)-based amphiphilic comb-like polymers in aqueous medium at pH 6.2 has been investigated by surface tension, fluorescence probe, dynamic light-scattering, and viscometry techniques. Results reveal that the addition of salt screens the electrostatic repulsion between the charges along the polymer backbone in the aggregates and consequently (1) reduces the surface activity at the air/water interface, (2) leads to the contraction of the polymer backbone, and (3) reduces the hydrodynamic sizes of the aggregates. In contrast, the hydrophobicity of the aggregates remains unperturbed.     

The effect of network architecture on the thermal and mechanical behavior of epoxy resins

The effects of crosslink functionality (f_c), molecular weight between crosslinks (M_c), and chain stiffness display on the thermal and mechanical behavior of epoxy networks are determined. Both f_c and M_c are controlled by blending different functionality amines with a difunctional epoxy resin. Chain stiffness is controlled by changing the chemical structure of the various amines. In agreement with rubber elasticity theory, the rubbery moduli are dependent on f_c and M_c, but independent of chain stiffness. The glassy moduli and secondary relaxations of these networks are relatively independent of f_c, M_c, and chain stiffness. However, the glass transition temperatures (T_g) of these networks are dependent on all three structural variables. This trend is consistent with free volume theory and entropic theories of T_g. f_c, M_c, and chain stiffness control the yield strength of these networks in a manner similar to that of T_g and is the result that both properties involve flow or relaxation processes. Fracture toughness, as measured by the critical stress intensity factor (K_Ic), revealed that f_c and M_c are both critical parameters. The fracture behavior is the result of the fracture toughness being controlled by the ability of the network to yield in front of the crack tip. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1371–1382, 1998     

Preparation and characterization of hydrogels based on acryloyl end-capped four-arm star-shaped poly(ethylene glycol)-branched-oligo(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) via Michael-type addition reaction

An acryloyl end-capped four-arm star-shaped poly(ethylene glycol)-branched-oligo(l-lactide) (4A-PEG-PLA) macromer was firstly prepared. A novel kind of hydrogels was synthesized via the Michael-type addition reaction between (2S,3S)-1,4-bis-sulfanylbutane-2,3-diol (dithiothreitol) and this macromer. Gelation time was determined visually as the time when the precursor solution did not flow on inverting the vials. Hydrogel structure was characterized by FTIR analysis, swelling and degradation tests. It was found that colorless and transparent hydrogels were quickly generated in situ. The gelation time, swelling and degradation behaviors of this kind of hydrogels could be adjusted by changing the concentration of the macromer solution in PBS buffer (pH 7.4). This novel hydrogel is expected to be used as a biomedical material.     

Alteration of the selectivity of hybridization of immobilized oligonucleotide probes by co-immobilization with charged oligomers of ethylene glycol

A significant challenge exists in the creation of an environment for immobilized probe oligonucleotides that offer good structural regularity and reproducibility, where nearest neighbour interactions provide for control of selectivity, yet where the degree of hybridization does not alter nearest neighbour interactions. This new work explores whether a “matrix isolation” method will produce the desired environment for the probe molecules. The DNA oligonucleotide probes are polyelectrolytes with charged backbones and significant flexibility. It is possible to isolate the probe molecules by surrounding each, on average, with a sheath of immobilized oligomer that is not based on complementary nucleic acid, yet that is a polyelectrolyte in order to control the surface density and charge within the mixed film. Preliminary work investigates a mixture of dT₂₀ as the probe oligonucleotide, and a 20-mer oligomer primarily containing ethylene glycol phosphate, as a matrix isolation material in a 1:20 mole ratio, respectively. Melt temperature (T_m) measurements indicate that the thermodynamic stability of the probe molecules can be adjusted using the oligomer matrix to achieve lower T_m values by up to 5 °C, with full retention of selectivity for discrimination of single base pair mismatches even under conditions where the probes at a surface are saturated with complementary target.     

Influence of poly (ethylene glycol) on the thermal, mechanical, morphological, physical-chemical and biodegradation properties of poly (3-hydroxybutyrate)

Blends of poly (3-hydroxybutyrate) (PHB) with poly (ethylene glycol) (PEG), (PHB/PEG), in different proportions of 100/0, 98/2, 95/5, 90/10, 80/20 and 60/40 wt%, respectively, were investigated for their thermal properties (using differential scanning calorimetry and thermogravimetric analysis), tensile properties, water vapor transmission rate, enzymatic biodegradation (using light microscopy) and mass retention. The addition of plasticizer did not alter the thermal stability of the blends, although an increase in the PEG content reduced the tensile strength and increased the elongation at break of pure PHB.     

Copolymerization of styrene with N-vinylformamide and ethylene glycol dimethacrylate and characteristics of the formed particles

Emulsion and emulsifier-free emulsion polymerization of styrene, N-vinylformamide, and ethylene glycol dimethacrylate are investigated with the goal to form positively charged monodisperse submicron crosslinked particles. The effects of the monomer ratio, the type and concentration of the buffer salt, and the emulsifier concentration on the monomer conversion and on the shapes, size distributions, and surface characteristics of the formed particles are studied. It is shown that, in the surface layers, amino groups prevail over carboxylic groups. The total surface concentration of acidic and basic groups increases with the degree of crosslinking of particles and as a result of their subsequent surface hydrolysis.     

Relation of the number of cross-links and mechanical properties of multi-walled carbon nanotube films formed by a dehydration condensation reaction

Multi-walled carbon nanotube (MWCNT) films were prepared by employing a condensation reaction utilizing 1,3-dicyclohexylcarbodiimide (DCC) to cross-link each MWCNT with carboxylic acid and hydroxyl groups. Morphological changes in the resultant MWCNT films were monitored using scanning electron microscopy and showed that the MWCNTs were randomly intertwined in the films. The prepared MWCNT films were 17 mm in diameter and 20 microm in thickness, and the apparent density was 0.59 g/cm(3). Fourier transform-infrared spectroscopy confirmed that each MWCNT modified with carboxylic acid and hydroxyl groups was cross-linked through the ester bond. It was found that the ratio of the number of ester cross-links and carbon atoms of the nanotubes per unit apparent volume (cm(3)) of condensed-MWCNT films was 5.27 x 10(-3) using thermogravimetric analysis (TGA). The tensile strength and Vickers hardness of condensed-MWCNT films achieved an average of 15 and 9.2 MPa, respectively, and were greater than those of free-standing MWCNT films without ester bond.     

Quantum chemical study on the thermal Diels-Alder reaction of cyclohexadiene and methyl crotonate

AM1 molecular orbital method using the unrestricted Hartree-Fock(UHF) calculations has been applied to investigate the thermal reaction of cyclohexadiene and methyl crotonate. The calculated results indicate that the thermal Diels-Alder reaction proceeds to product through the concerted path and two radical pathways.     

Molecular adsorption and the chemistry of plasma-deposited thin organic films: Deposition of oligomers of ethylene glycol

Weakly ionized, radio-frequency, glow-discharge plasmas formed from methyl ether or the vapors of a series of dimethyl oligo(ethylene glycol) precursors (general formula: H-(CH₂OCH₂)_n-H;n=1 to 4) were used to deposit organic thin films on polytetrafluoroethylene. X-ray photoelecton spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) of the thin films were used to infer the importance of adsorption of molecular species from the plasma onto the surface of the growing, organic film during deposition. Films were prepared by plasma deposition of each precursor at similar deposition conditions (i.e., equal plasma power (W), precursor flow rate (F), and deposition duration), and at conditions such that the specific energy (energy/mass) of the discharge (assumed to be constrained byW/FM, whereM=molecular weight of the precursor) was constant. At constantW/FM conditions, two levels of plasma power (and, hence, twoFM levels) and three substrate temperatures were examined. By controlling the energy of the discharge (W/FM) and the substrate temperature, these experiments enabled the study of effects of the size and the vapor pressure of the precursor on the film chemistry. The atomic % of oxygen in the film surface, estimated by XPS, and the intensity of theC-O peak in the XPS C_ls spectra of the films, were used as indicators of the degree of incorporation of precursor moieties into the plasma-deposited films. Analysis of films by SIMS suggested that these two measures obtained from XPS were good indicators of the degree of retention in the deposited films of functional groups from the precursors. The XPS and SIMS data suggest that adsorption of intact precursor molecules or fragments of precursor molecules during deposition can have a significant effect on film chemistry. Plasma deposition of low vapor pressure precursors provides a convenient way of producing thin films with predictable chemistry and a high level of retention of functional groups from the precursor.     

Relation between the network structure and dynamic mechanical properties of a typical amine-cured epoxy polymer

The dynamic mechanical properties of a series of epoxy polymers of known network structure have been investigated. It was shown that the distance between crosslinks could be predicted from either the shift in the glass transition temperature T_g or by use of the dynamic modulus above T_g. The front factor in the equation of state for rubber elasticity was near unity for stoichiometric equivalence of epoxy and amine and increased slowly with excess of either component.     

Effect of thermal cycling and open-hole size on mechanical properties of polymer matrix composites

This paper investigates the effects of thermal cycling on mechanical degradation of polymer matrix composites (PMCs). Un-notched and open-hole specimens are tested using developed thermal cycling apparatus and tensile test machine. In addition, the hole-size effect of open-hole tension glass/epoxy composite laminates is investigated. The tensile strength, mass loss and surface degradation of the specimens were obtained during 250 cycles. Experimental results showed that the holes diameter is the main parameter to control the thermal cycling effects on open hole structure. Also, it is found that laminates with smaller holes have higher tensile strength variation than those with larger holes. The results showed that increment of the hole diameter and number of cycles decreases the tensile strength.     

环十二碳酮与苯基乙二醇反应产物的分离及确定

环十二碳酮(1)与苯基乙二醇(2)在对甲苯磺酸催化下的反应粗产物具有浓郁的花香,最初我们以为这种香气来源于缩酮2-苯基-1,4-二氧杂螺[4,11]十六烷(3):但该反应粗产物经反复重结晶后得到的无色晶体却没有香气、经红外、~1H核磁等谱图及碳氢分析鉴定该无色晶体确是缩酮3.既然缩酮3没有气味,则反应粗产物的香气必然来自反应中的副产物。薄层色谱分析表明,该反应中副产物较多。我们猜测,副反应可能主要来自2。