Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

Influence of tacticity on Tβ, Tg,and TLL in poly(methyl methacrylate)s by the method of thermally stimulated current (TSC)

The thermally stimulated-current method (TSC) has been employed to determine the temperatures and intensities of T_β, T_g, and T > T_g for pure isotactic, pure syndiotactic, and five atactic specimens with syndiotactic triad content from 49.5 to 75%; T_g was found to increase linearly with syndiotactic triad content as T_g (°C) = 48.0 + 0.856 (% syn), with R² = 0.970 standard error 5.6°C; T_g for the syndiotactic specimen is 136.6°C measured, 133.6°C calculated. Several atactic specimens exhibit a second glass temperature 15 to 35 K above the regression line ascribed to some pure syndio content, and/or some isotactic–syndiotactic stereocomplexes. All specimens exhibited the liquid–liquid or T_LL transition (relaxation) which increases linearly with 100-% isotactic triad content. Isotactic PMMA shows a T′_LL relaxation 50 K above T_LL. The T_g and T_LL values obtained correlate extremely well with values from differential scanning calorimetry (DSC) determined in a separate study, as well as with most literature data. Intensities of T_g and T_LL by TSC are greatest for isotactic, next for syndiotactic, with a broad, low minimum for atactic materials. The intensity of a β relaxation increases slowly from isotactic to syndiotactic. The T_LL found by TSC compares well with literature values for isotactic PMMA obtained by several methods, and T_LL in the atactic region compares well with literature values for atactic material. The ratio T_LL/T_g ranges from 1.09 to 1.20 with no dependence on tacticity. T_g follows simple Arrhenius behavior with enthalpies of activation about one-half of the values normally calculated from dielectric and mechanical loss. The frequency dependences of T_LL and T′_LL follow a Vogel–WLF relationship with temperature. The origin of T_LL is discussed in terms of the Frenkel hypothesis of segment–segment interaction. Evidence for T_LL and T_LL from a variety of methods indicates that these two temperatures are not artifacts of the TSC method.     

Comments on a paper by Axelson and Mandelkern concerning 13C NMR spectra of polymers

It is shown that the ¹³C NMR spectral collapse temperatures T_c reported by Axelson and Mandelkern tend to give a constant ratio of T_c/T_g averaging 1.21 ± 0.05 and independent of T_g or of polymer structure. It is further shown that T_c is not a high-frequency value for T_g because this would require T_c/T_g to decline with increasing T_g. T_c/T_g agrees in numerical value with T_u/T_g, where T_ll is the liquid-liquid transition lying above T_g. Direct comparison of T_c and T_u for four polymers PIB, PnBA, atactic PP, and isotactic PMMA shows very close agreement. The various results suggest, but do not prove, that T_c from ¹³C NMR spectroscopy may be a new, direct measure for T_ll. A measured T_c of 233K for linear PE is compatible with a T_g near 195 K (233/195 = 1.19), whereas a T_g of 148 K gives the ratio 233/148 = 1.57, which is outside any value shown in tabulated form.     

The estimation of phase modifications in polymers by the method of “molecular probes” in gas chromatography—VI. The study of the transitions in poly(ethylene terephthalate)

Multiple transitions have been identified by inverse gas-chromatography for fractions of poly(ethylene terephthalate) with $\text{M}$_n between 1.47 and 2.69 × 10⁴. Depending on the thermal treatment, at least two liquid-liquid transitions T_ll⁽¹⁾ and T_ll⁽²⁾ have been observed in addition to T_g and T_m; this feature is generally considered as characteristic of semi-crystalline polymers. The similarity of the dependence of T_g and T_ll on the molecular weight of the polymer probes suggests a common molecular origin of these phenomena; the fact that T_ll >T_g indicates that the T_ll transitions involve longer chain segments. The melting temperature decreases with increasing molecular weight, suggesting again that the crystallinity and/or the size distribution will enlarge as the molecular weight of the polymer is made higher.     

Liquid-state transitions (T>T g) of poly(vinyl alcohol)

The two liquid state transitions,T _ll andT _ll, of non-crystalline, uncrosslinked poly(vinyl alcohol) were determined by differential scanning calorimetry.T _ll increased as the molecular weightM _n increased, whileT _ll remained almost constant. Crosslinking and crystallinity lead to disappearance of the transitionT _ll. The transitionT _ll was linked to mobility of whole chains, whereasT _ll was characteristic of segmental mobility.     

Tensile flow and stress–strain behavior over a wide temperature range for poly(butyl methacrylate) with a broad molecular weight distribution

The poly(butyl methacrylate) studied is a polymer with a normal molecular weight distribution and a relatively low molecular weight close to M_c, the critical molecular weight from the viscosity–molecular weight relation. The polymer was subjected to uniaxial extension and shear over a temperature range which included T_g. It was found that in the region of T_g an increase in applied stress is accompanied by a decrease both in the temperature shift factor a_T and in the activation energy for relaxation and rupture of polymer melts. Close attention is given to the long-term durability of the polymer. As is expected in the temperature range below T_g, its dependence on the stress is exponential, whereas at temperatures above T_g a power law fits the data. In the latter case a log-log plot of the long-term durability versus stress can be represented by two intersecting straight lines which can be replotted as a generalized straight line if the long-term durability values are normalized by the viscosity.     

Influence of monofunctional reactants on the physical properties of dimer acid‐based polyamides

Dimer acid‐based polyamides were synthesized by condensation polymerization in the absence and presence of monofunctional reactants. Acetic acid, oleic acid and propyl amine were used as monofunctional reactants. The influences of the equivalent percentage (E%) and type of monofunctional reactant on the physical properties of dimer acid‐based polyamides such as glass transition temperature (T_g), melting point (T_m), heat of fusion (ΔH), degree of polymerization (DP), number average molecular weight (M_n), and kinematic viscosity were investigated. The molecular weight and viscosity of dimer acid‐based polyamides decreased with the increase in equivalent percentage of monofunctional reactant. Differential scanning calorimetry (DSC) studies showed that acetic acid and propyl amine had higher effect on the thermal properties of polyamides than that of oleic acid. In the case of polyamides prepared in the presence of acetic acid, the values of T_g, T_m, and ΔH of the polyamides increased remarkably with the increase in acetic acid content. On the contrary, propyl amine had a decreasing effect on the values of T_g, T_m, and ΔH of the polyamides. Incorporation of oleic acid into the polymer structure had no significant effect on the values of T_g and T_m of the dimer acid‐based polyamides. Copyright © 2006 John Wiley & Sons, Ltd.     

Nature of the kinematic shear viscosity of water

Nature of the kinematic shear viscosity of water ν is discussed in the work. Dependences of ν on temperature t, reduced volume $ \tilde \upsilon Nature of the kinematic shear viscosity of water ν is discussed in the work. Dependences of ν on temperature t, reduced volume , and the average number of hydrogen bonds per one molecule n _H (t = T/T _c, =υ/υ_c, T _c and υ_c are critical values of temperature and reduced volume) are analyzed in detail on a liquid-vapor coexistence curve. It is shown that at T < T _H (T _H ≈ 310 K is the characteristic temperature of water) the formation of the kinematic shear viscosity is induced by activation. At T > T _H, the shear viscosity of water is the sum of two contributions. One of them is of the same nature as in simple liquids, and another is caused by effects of hydrogen bonds. The temperature dependence of ν in this temperature region has nothing in common with exponential formulas of activation theory. The explicit form of the functional dependence of the kinematic shear viscosity on t, , and n _H is found and substantiated. It is shown that the value and temperature dependence of n _H resulting in the experimental values of the kinematic shear viscosity of water agree well with the values corresponding to density and evaporation heat data. __________ Translated From Zhurnal Strukturnoi Khimii, Vol. 49, No. 6, pp. 1092–1100, November–December, 2008. Original Russian Text Copyright ? 2008 by N. P. Malomuzh and A. V. Oleinik     

Microstructure and rheological properties of polybutadienes

The viscosities, rubbery deformations, densities, and their dependence on temperature have been measured for several series of polybutadienes with molecular weights ranging from 5,000 to 400,000 and differing in proportions of cis and trans structures (cis content from 40 to 95%). On the basis of the viscosity measurements the critical molecular weight M_c has been determined, corresponding to a sharp change in the nature of the viscosity versus molecular weight dependence. Rubbery deformations are displayed pronouncedly in specimens with M > M_c and are closely related to the appearance of non-Newtonian flow. The value of M_c depends on the relative content of cis and trans forms. When M > M_c, the initial viscosity is a parameter sensitive to the microstructure of polybutadienes, so that with at a single molecular weight, depending on the ratio of cis and trans units, the viscosity may vary over a more than tenfold range. The glass transition temperature and activation energy of viscous flow rise regularly with increasing trans content in the polymer chain, these parameters becoming independent of the molecular weight for specimens with M > M_c within a series of polybutadienes of equal microtacticity. Thermomechanical investigations of polybutadienes also made it possible to define more accurately the boundaries of the crystallization region and the dependence of the melting point on the microtacticity. The results obtained are discussed on the basis of modern ideas of polymer structure.     

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     

The effects of monophenol chain terminators on the structure–property relationships of controlled epoxy networks

Five families of new controlled epoxy thermosets (CENs) using three monophenol chain terminators were prepared to study systematic changes in the structure and amount of the monophenol and the initial molecular weight between crosslinks (M_c,i) on the properties of epoxy thermosets. Glass transition temperature (T_g) decreases with monophenol mole fraction (χ) in proportion to both the concentration and flexibility of the chain terminator. Distinct serial relations for T_g depression were observed for the three M_c,i families. Dynamic mechanical analysis (DMA) shows significant perturbations of the relaxation behavior with added terminator as evidenced by decrease in peak tan δ and in post T_g damping. The rubbery coefficients of thermal expansion (CTE) increases with monophenol concentration only at χ > 0.05 and shows distinct curvature versus temperature, but is largely invariant with monophenol flexibility. The thermal stability of terminated CENs decreases only slightly with χ and little difference was found with monophenol structure. Most surprisingly, fracture toughness decreases markedly and discontinuously with χ depending on M_c,i. The values of the critical monophenol concentration at which fracture toughness markedly decreases (χ_c) are inversely proportional to M_c,i but are independent of monophenol flexibility. No correlation of χ_c with any of the calculated network structure parameters was apparent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1632–1640, 2008     

Viscosity of poly(vinyl acetate) and its concentrated solutions

Data on the viscosity of poly(vinyl acetate) (PVOAc) and its concentrated solutions in diethyl phthalate (DEP) and cetyl alcohol (CeOH) are examined over the molecular weight range 8 × 10³ < M < 1.3 × 10⁶, the range 0.15 < φ < 1.0 of the volume fraction φ of polymer, the temperature range 308 to 430°K for PVOAc and its solutions in DEP, and at 396°K in CeOH. The latter is the θ temperature for dilute solutions of PVOAc in CeOH. The data are analyzed with the relation η = KX_c(αφM/M_c)^a exp[1/β(T – T₀)], where a is 1 or 3.4 for αφM less than or greater than a constant M_c, respectively, and X_C, is a constant. The expansion factor α_φ of the chain dimension is found to be essentially unity for φ > ca. 0.25, increasing with decreasing φ for smaller φ. Both β and T₀ depend on φ, and T₀ also depends on M at low M.     

Analysis of the melt viscosity and glass transition of polystyrene

The melt viscosity, the glass transition, and the effect of pressure on these are analyzed for polystyrene on the basis of the Tammann-Hesse viscosity equation: log η = log A + B/(T ? T₀). Evidence that the glass transition is an isoviscosity state (log η_g ? 13) for lower molecular weight fractions (M < M_c) is reviewed. For a polystyrene fraction of intermediate molecular weight (M ? 19,000; t_g = 89°C.), it is shown that B is independent of the p–v–T state of the polymer liquid and that dT₀/dP = dT_g/dP. This is consistent with the postulate that B is determined by the internal barriers to rotation in the isolated polymer chain. Relationships are derived for flow “activation energies” at constant pressure and at constant volume, and for the “activation volume.” Values for polystyrene along the zero-pressure isobar and along the constant viscosity, glasstransition line are reported. For the latter, ΔV_g* is constant and corresponds to about 10 styrene units. The “free volume” viscosity equation: log η = log A + b/2.3?, is reexamined. For polystyrene and polyisobutylene, ?_g/b = 0.03, but ?_g and b themselves differ appreciably in these polymers. The parameter b is the product of an equilibrium term Δα and the kinetic term B, and none of these is a “universal” constant for different polymers. The physical significance of the free volume parameter ?, particularly with regard to the “excess” liquid volume, remains undefined. Two new relationships for dT_g/dP, one an exact derivation and the other an empirical correlation, are presented.     

Comments on “some evidence against the existence of the liquid-liquid transition. IV. The temperature dependence of shear viscosity”

A formal definition of T_LL as a function of M?ⁿ for polystyrene was prepared with literature T_LL values from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and zero-shear melt viscosity η₀. Data from six authors using anionically prepared PS and blends thereof were involved. The resultant linear least-squares regression line, T_LL(°C) = 148.5 ? 11.487 × 10⁴M? [standard error in T_LL (calculated) 4.056 K, correlation coefficient R² = 0.9534] is considered valid from M?_n = 2000 to the entanglement molecular weight M_c = 35,000. The “best” T_LL values reported by Orbon and Plazek from double Arrhenius plots are well below this line for M?_v = 47,000, 16,400, 3400, and above it for M?_v = 1100. These best T_LL values are artifacts arising from no or insufficient data points above or below T_LL and/or too many data points near T_g. The associated high enthalpies of activation which they report confirm this diagnosis. The fact that these artificial T_LL values tend to disappear when checked by the three-parameter Vogel equation, logη = logA + B exp[(T ? T_∞)^?1], has no relevance to the controversy concerning the existence and meaning of T_LL. The claim by Orbon and Plazek that T_LL values obtained by TBA, DSC, and melt viscosity are all artifacts of the individual methods by which they were obtained is inconsistent with the excellent master plot which they generate. Alternative plotting devices which reveal T_LL > T_g from η₀ vs. T^?1 data, as developed by van Krevelen and Hoftyzer and by Utracki and Simha (not previously considered by either party), are reviewed. A statistical examination of the nature of the Vogel–Fulcher–Tammann–Hesse equation, based on synthetic data, is presented. Evidence for T_LL in atactic polypropylene is offered based on published data by Plazek and Plazek. T_LL is considered to possess both relaxational and quasiequilibrium attributes, just as T_g does.     

Kinetic Studies of Bulk Ge22Se78−xBix (x=0, 4 and 8) Semiconducting Glasses

Results of phase transformations, enthalpy released and specific heat of Ge₂₂Se_78–xBi_x(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T _g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T _g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T _g, at a heating rate of 5 K min^–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol^–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T _c–T _g and the enthalpy released during the crystallization process. Below T _g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Identification of relaxation processes in pure polyethylene oxide (PEO) films by the dielectric permittivity and electric modulus formalisms

The ac‐impedance of bulk‐like films of pure polyethylene oxide (PEO) polymer was measured as a function of frequency f in the range 0.1 to 10⁷ Hz at various constant temperatures T (155 − 330 K ). The as‐measured data were analyzed by electric permittivity and modulus formalisms to unveil which dielectric and conductive relaxation processes were responsible for their relaxation behavior below/above glass transition temperature T_g of pure PEO polymer. At T > T_g , none of the α ‐, β ‐, or γ ‐relaxations could be inferred for studied pure PEO films from frequency variation of measured imaginary part ε′′(f, T) of complex dielectric permittivity , as low‐frequency losses masked real dielectric contribution to the measured ε′′(f, T) at low frequencies and high temperatures. However, at T < T_g , a broad, relaxation process has been observed in the high‐frequency part of their isothermal ε′′(f, T) − f spectra, which can be related to the β ‐ or γ ‐dielectric relaxation process. Nonlinear regressions of the measured ε′′(f, T) − f data for T < T_g yielded moral fits to a simple addition of a Havriliak‐Negami function, and a Bergman‐loss Kohlrausch‐Williams‐Watts‐type function, with the relaxation time τ_max(T) obtained from Havriliak‐Negami‐fitting parameters, was found to follow a thermally activated Arrhenius‐like relaxation behavior. Conversely, representation of the imaginary part M′′(f, T > T_g) − f spectra of complex electric modulus was found to depict 2 overlapped relaxation processes, which were detached well by a nonlinear regression of a simple superposition of 2 different M′′(f)  expressions having the form of the universal Bergman loss function, where it was found that the relaxation time is also thermally activated.     

Glass‐transition temperature: Conversion relationship in the polycyclotrimerization of 4,4′‐thiodiphenylcyanate

Polycyclotrimerization of 4,4′‐thiodiphenylcyanate was adopted as a model system for general thermosetting polymers for studying the relationship between the glass‐transition temperature (T_g) and conversion (α) during network formation. Existing expressions for T_g‐α relationship were used and compared. The experimental T_g‐α data were well fitted to several one‐parameter equations although the physical significance of parametric values thus obtained could not be unambiguously identified. Among the two‐parameter models, both the Hale–Macosko–Bair equation and the so‐called “original” DiBenedetto equation were well fitted by experimental data (when the mean‐field crosslink density was used), yielding parametric values consistent with the original designated physical meanings within the corresponding theoretical frames. Relationships between the parameters in different theories were also discussed. Incidentally, a discontinuity of ΔC_pT_g at the gel point was observed (i.e., ΔC_pT_g is of different values in the pregel and postgel regimes, respectively). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 726–738, 2000     

Synthesis of Diblock Copolymers With Cellulose Derivatives. 2. Characterization and Thermal Properties of Cellulose Triacetate-Block-Oligoamide-15

Well-defined A-block-B type cellulose derivatives consisting of cellulose triacetate (CTA) and oligoamide-15 were synthesized. Chemical structures of the diblock copolymers were characterized by MALDI-TOF MS, ¹H-NMR, and GPC. Influence of length of CTA and oligoamide-15 segments on their thermal properties was investigated by means of differential scanning calorimetry (DSC). All diblock copolymers displayed T _g, T _c, and T _m transition temperatures. Their T _g and T _m values increased with the increase of molecular weight of CTA segment. The crystallinity of diblock copolymers increased after isothermal crystallization at 200 °C. Its X-ray analysis revealed that the diblock copolymer had CTA II crystal structure. Thermal analysis supported microphase separation between CTA and oligoamide-15 segments at room temperature, because T _g and T _m values of polyamide-15 are −7 °C and 170–180 °C, respectively.     

Influence of MgO (CaO) on the structure of silicate-phosphate glasses

Thermal and structural properties of model silicate-phosphate glasses containing the different amounts of the glass network modifiers, i.e. Mg²⁺ and Ca²⁺ were studied. To explain the changes of the parameters characterizing the glass transition effect (T_g, Δc_p) and the crystallization process (T_c, ΔH) depending on the cations modifiers additions, analysis of the bonds and chemical interactions of atoms in the structure of glasses was used. ³¹P MAS-NMR spectra of SiO₂–P₂O₅–MgO(CaO)–K₂O glasses show that the phosphate complexes are mono- and diphosphate. It has been found that increasing amounts of Mg²⁺ or Ca²⁺ cations in the structure of glasses causes the reduction of the degree of polymerization of the phosphate framework (Q¹→Q⁰). The influence of increasing of modifiers in the structure of silicate- phosphate glasses on the number of non-bridging oxygens per SiO₄ tetrahedron and density of glasses was presented.