Change of the thermal behavior of 55Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> ⋅ 45B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass at annealing close to the vitrification temperature

The characteristic properties of relaxation processes for 55Bi₂O₃ ? 45B₂O₃ glass were described. The pattern of changes of the vitrification temperature (T _g ) is found to be quasi-periodic; the value of the endothermic effect near T _g (ΔC’ _p ) and the difference between the softening point and the vitrification temperature (T _m –T _g ) were determined. The temperature-time parameters of the transition from quasi-periodic to the continuous change of the properties were determined and an explanation of such behavior of the system was offered.     

Local Symmetry of Cu2+ Ions in Sodium Silicate Glasses from Data of EPR Spectroscopy

Sodium silicate glasses with a constant ratio of oxide concentrations (mol %) SiO₂/Na₂O = 2.4 and with copper ions introduced in the form of CuO (from 1 to 10 mol %) are studied by the EPR method. The shape and width of the EPR line of copper ions are analyzed, and the spin-Hamiltonian parameters g _||, g , A _||, and A are determined by simulating the EPR spectrum and comparing the simulated and experimental spectra. The EPR spectrum of copper ions (1 mol %) is characterized by the parameters g _|| = 2.35, g = 2.065, A _|| = 135 × 10^–4 cm^–1, A = 7 × 10^–4 cm^–1, and H = 25 G. An analysis of this spectrum shows that the nearest environment of the Cu²⁺ ion has the shape of an elongated octahedron. The EPR spectrum of the sodium silicate glass containing 10 mol % Cu is a superposition of the spectrum of an octahedral complex (g _|| = 2.35, g = 2.075, A _|| = 135 × 10^–4 cm^–1, H = 40 G) and the spectrum of a cluster (g _|| = 2.35, g = 2.15, A _|| = 135 × 10^–4 cm^–1, H = 50 G).     

Thermodynamics of sorption in and free volume of poly(5,6-bis(trimethylsilyl)norbornene)

Thermodynamics of sorption of n-alkanes C₄-C₁₁ in poly(5,6-bis(trimethylsilyl)norbornene) was studied using the Inverse Gas Chromatography (IGC). Temperature dependences of the specific retention volume V_g and solubility coefficient S of various alkanes were obtained in the range 60-140 °C. For solubility coefficients, the following equation holds: where T_c is the critical temperature of solutes, T is the experimental temperature and S is expressed in cm³(STP)/cm³ atm. The partial molar enthalpies ΔH_m and entropies ΔS_m of mixing of different n-alkanes in this glassy polymer vary in much wider range than in rubbers and display positive correlations: for more exothermic mixing process the larger negative ΔS_m values are observed. It was shown that the ΔH_m in poly(5,6-bis(trimethylsilyl)norbornene) pass through a minimum, when the size of solutes increases. The coordinates of ΔH_m at minimum versus solute size provide an estimate of the size of free volume elements in this polymer. This conclusion was supported by variation of permeability in different glassy polymers studied using IGC and by the results of other methods for probing free volume in glassy polymers.     

New segment in new theory of polymer

Melting temperature (T_m) can be divided in two steps of (T_m–T_g) and T_g in the glass transition temperature. There are respective segments in both steps. The difference of elongation, which causes a separation between two arrays in segment, is of two kinds: mechanical and thermal. T_g is given as disappearance of the segment, which would not be so if the kind of elongation were the same. A prefix of micro at Brown on T_g is meaningless, because the segment can be explained from a different point view the phenomena shown as a sign of melting at T_g. T_g between polymer and components of C? C bond in repeat unit is given as T_g = Σ[1/n(1%)/a_i] = Σ[(1/n)T_gi], where α is the linear coefficient of thermal expansion, n is the total number of components, T_gi, α_i is the value of component i. A magnitude of elongation of component C_i is given as α_i with the result, which the side chains have functioned like a weighting function. Strength of linear polymer is connected with the total number of segments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Vinylidene fluoride copolymers with fluoroolefins

Summary Copolymers of vinylidene fluoride (VDF) with fluoroolefins of the series CF₂CFX (X = F, Cl, Br, CF₃ and C₅F₁₁) have been synthesized in the 0–16 mole % CF₂CFX range. Results of physico-chemical characterisation by means of DSC techniques (T_g, T_M, H_f) and X-ray diffraction are examined and related to the nature of the substituent of the fluoroolefin. The T_g/T_M ratio varies from 0.5 for the VDF homopolymer to higher values at increased CF₂CFX content, although to a different extent for the various series of copolymers. The results show that the Beaman-Boyer empirical rule (T_g/T_M=2/3), developed for homopolymers, also applies to some copolymeric systems.     

Determination of the Fluctuation Free Volume Fraction for Glasses in the As–S(Se) Systems

The fraction f _g of fluctuation free volume frozen at the glass transition temperature is determined from the temperature dependence of the viscosity in terms of the Vogel–Fulcher–Tammann equation and the formula T _g = f _gln(1/f _g). The fluctuation free volume fractions obtained using these two procedures for glasses in the As–S(Se) systems are in quite reasonable agreement. It is demonstrated that the difference in the ratios between the fraction of fluctuation free volume and the lattice Grüneisen parameter for chalcogenide and oxygen-containing glasses is associated with the specific structure of the network of chalcogenide glasses. It is found that the dependence of the fluctuation free volume fraction on the mean coordination number Z _m, which characterizes the degree of connectivity of the network in noncrystalline materials, exhibits nonmonotonic behavior.     

Investigation of the fast relaxation in glass-forming selenium by low-frequency Raman spectroscopy

The low-frequency Raman spectra of liquid and vitreous selenium are investigated. It is demonstrated that the temperature dependence of the intensity of the fast relaxation at the glass transition temperature (T _g = 308 K) exhibits a specific feature. This feature manifests itself in a sharper increase in the intensity at temperatures T > T _g as compared to that observed at lower temperatures. The intensities of the fast relaxation at the critical temperature T _c are evaluated by the extrapolation of the linear dependence to the temperature range T > T _g in the framework of the mode-coupling theory. The new results obtained for selenium are compared with the available data for other glass-forming materials (boron oxide, toluene, arsenic sulfide). It is shown that, for all the glasses under investigation, the parameter describing the contribution of the fast relaxation to the Raman spectrum takes on the same value at the critical temperature T _c and is approximately equal to 0.3.     

Parameters of the Fluctuation Free Volume Theory for Glasses in the Ge-As-Se System

The fraction of fluctuation free volume (f _g = V _f/V) frozen at the glass transition temperature T _g is determined from the temperature dependence of the viscosity in the glass transition range in terms of the Vogel-Fulcher-Tammann equation and the formula _f T _g T _g = f _gln(1/f _g). The fluctuation free volume fractions f _g obtained according to these two procedures for glasses in the Ge-As-Se system are in quite reasonable agreement. The energies E _h of formation of fluctuation microvoids and their volumes V _h are calculated. It is demonstrated that the quantities f _g, E _h, and V _h and the ratio of the microhardness H to T _g depend substantially on the glass structure and can serve as characteristics of the rigidity of the glass networks. It is noted that the fluctuation free volume fraction f _g is a nonmonotonic function of the mean coordination number Z _m and that it exhibits a specific dependence on the lattice Grüneisen parameter . The Poisson ratios are estimated from the fluctuation free volume fraction f _g with the use of the relationship f _gln(1/f _g) = . It is shown that the Poisson ratios thus obtained are close to those calculated from the data on the transverse (V _s) and longitudinal (V _l) velocities of ultrasound.     

Vitrification effect on the curing reaction of epoxy resin

Summary The curing reaction of diglycidyl ether of Bisphenol A(DGEBA) with triethylene tetramine(TETA) was studied by the differential scanning calorimetry(DSC). The reaction was affected as the vitrification occurred when the glass transition temperature(T_g) of the reaction mixture exceeded the curing temperature. In order to describe the curing reaction in the rubbery state as well as in the glassy state, the reaction kinetic equation containing the generalized WLF equation term was proposed and the parameters were determined from the DSC data.Nomenclature a_T time temperature shift factor, dimensionless - A_T temperature dependent frequency factor, /sec - A_Tg temperature dependent frequency factor at T_g, /sec - A_To temperature dependent frequency factor at T_g, /sec - A empirical parameter in temperature dependent frequency factor, dimensionless - B empirical parameter in temperature dependent frequency factor, K - C₁ empirical parameter in the generalized WLF equation, dimensionless - C₂ empirical parameter in the generalized WLF equation, K - D correction parameter in temperature dependent frequency factor, K - E activation energy, cal/mole - E_x/E_m ratio of lattice energies for crosslinked and uncrosslinked polymer, dimensionless - F_x/F_m ratio of segmental mobilities for crosslinked and uncrosslinked polymer, dimensionless - H_t cumulative heat generated up to time t, cal/g - H_RXN heat of reaction under complete conversion, cal/g - n reaction order, dimensionless - S _r scan rate of the DSC experiment, °C/sec - t time, second - T temperature, K - T_g glass transition temperature of the partially cured reaction mixture, K - T_go glass transition temperature of uncured reactant, 253 K - X conversion, dimensionless     

Preparation of poly(dinaphthyl alkylene ethers) by oxidative polyarylation and their crystallization behaviour

Di-1-naphthoxy alkanes are found to polycondense in a surprisingly clean oxidative polyarylation reaction, effected by iron(III) chloride in nitrobenzene solution at room temperature. By this reaction, polymers with the structure

in which m = 2–7 were prepared as high molecular weight, crystallizable, apparently linear thermoplastics. Glass transition temperatures, T_g, have been measured and show considerable variation with reduced solution viscosity and with previous thermal history; the polymer in which m = 4 has the highest melting point, 324°C. From the melt and from the amorphous state at room temperature, the rates of crystallization of the m-even polymers decrease with increasing m, but the m-odd polymers do not crystallize by thermal treatment. The m = 3 polymer crystallizes in contact with boiling xylene and the m = 5 polymer crystallizes from $\text{chloroform}\text{N-}\text{methyl}$ pyrollidone.     

Studies on the thermal properties of poly(phenylene sulfide amide)

Thermal properties of poly(phenylene sulfide amide) (PPSA) prepared using sodium sulfide, sulfur, and thiourea as sulfur sources which reacted with dichlorobenzamide (DCBA) and alkali in polar organic solvent at the atmospheric pressure, were studied. The glass transition temperature (T_g), melting point temperature (T_m), and melting enthalpy (ΔH_m) of the related polymers were obtained by use of differential scanning calorimetry analysis. The results are: T_g = 103.4–104.5°C, T_m = 291.5–304.7°C, and ΔH_m = 104.4–115.4 J/g. Thermal properties such as thermal decomposition temperature and decomposition kinetics were investigated by thermogravimetric analysis under nitrogen. The initial and maximum rate temperatures of degradation were found to be 401.5–411.7°C and 437–477°C, respectively. The parameters of thermal decomposition kinetics of PPSAs were worked out to be: activation energy of degradation was 135 to 148 kJ/mol and the 60-s half-life temperature was 360 to 371°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1227–1230, 1997     

Calorimetric study of block-copolymers of poly(n-butyl acrylate) and gradient poly(n-butyl acrylate-co-methyl methacrylate)

The nanophase separation in diblock and triblock copolymers consisting of immiscible poly(n-butyl acrylate) (block A) and gradient copolymers of methyl methacrylate (MMA) and n-butyl acrylate (nBA) (block M/A) were investigated by means of their heat capacity, C_p, as a function of the composition of the blocks M/A and temperature. In all copolymers studied, both blocks are represented by their C_p and glass transition temperature, T_g, as well as the broadening of the transition-temperature range. The low-temperature transition of the blocks A is always close to that of the pure poly(n-butyl acrylate) and is independent of the analyzed compositions of the block copolymer, but broadened asymmetrically relative to the homopolymer due to the small phase size. The higher transition is related to the glass transition of the copolymer block of composition M/A. Besides the asymmetric broadening of the transition due to the phase separation, it decreases in T_g and broadens, in addition, symmetrically with increasing acrylate content. The concentration gradient is not able to introduce a further phase separation with a third glass transition inside the M/A block.     

Synthesis and characterization of side chain polymer with helical PLLA segments containing mesogenic end group

Series of mesogenic biphenol derivatives HO6OPPOn (n = 4,6,8) were prepared by asymmetric reaction and purified. Then HOLAxO6OPPOn were prepared with controlled molecular weights by adjusting the feed ratios of HO6OPPOn, SnOct₂ catalyst and LLA by Ring-Opening Polymerization. P-AOLAxO6OPPOn materials were obtained in high yields by the free radical polymerization of polymerizable macromonomers of AOLAxO6OPPOn synthesized by esterization of HOLAxO6OPPOn with acrylic acid in the presence of DCC/DMAP. Their molecular weights were characterized by ¹H NMR and GPC. Differential Scanning Calorimeter method and Polarized Optical Microscopy method were used to study their thermal behaviors. Both AOLAxO6OPPOn and P-AOLAxO6OPPOn materials are found to form LCs with increased T_g, T_m and T_i with longer O-LLA segment length. Polymerization of AOLAxO6OPPOn also resulted in the increase of T_g, T_m and T_i. X-ray diffraction measurements revealed the presence of smectic phase in these materials. The O-LLA segments are in helical structure from CD spectra and this makes the resulting polymer materials good candidate of optical materials for huge optical rotation power.     

A Study of Sodium–Copper and Sodium–Nickel Polyphosphate Glasses by Differential Scanning Calorimetry1

Sodium polyphosphate and sodium–copper and sodium–nickel copolyphosphate glasses (with the ratio Na : M = 9 : 1 and 8 : 2, where M is Cu or Ni) are studied. The glass transition (T _g) and melting (T _m) temperatures are determined by differential scanning calorimetry (DSC). It is revealed that the T _gand T _mtemperatures depend on the molecular weight M _t(determined from terminal groups) of polymeric glasses, the Na : M ratio, and the glass synthesis conditions. The activation energies are calculated, and the thermodynamic parameters H, S, and C _pare measured.     

Thermal cross-link behavior of an amorphous poly (para-arylene sulfide sulfone amide)

Cross-link behavior of an amorphous poly (para-arylene sulfide sulfone amide) synthesized via low temperature solution polycondensation was observed for the first time, when the polymer was subject to a series of thermal curing at 260 °C in air condition. The formation of cross-link network was demonstrated by the DSC and TGA results that T_g of the polymer enhanced from 259.17 °C to 268.89 °C, and the 1% weight loss temperature increased remarkably from 243.75 °C to 345.87 °C. EPR analysis further suggested that two kinds of free radicals, CO and C, induced by thermal curing were responsible for this cross-link behavior. According to FT-IR spectrum, the origin of these free radicals was confirmed as amide CO group in the polymer backbone. The cross-linking type was attributed to conventional radical cross-link reaction and the cross-link mechanism was discussed in detail subsequently.     

Structure and properties of shape-memory polyurethane block copolymers

Segmented polyurethanes containing soft segments with lower molecular weight exhibit shape-memorizing properties. Structure and properties of shape-memorizing polyurethanes (S-PUs) were studied. S-PUs are characterized by a rather high glass transition temperature: T_g of S-PUs is usually in the range of 10–50°C. A Pplot of 1/T_m against–In X_A is approximately linear, indicating that the hard segments are randomly distributed along the molecular chain. S-PUs with a hard segment of 67–80 mole % form negative spheruiites; they give a faint scattering maximum in a small-angle X-ray diffraction pattern. On the other hand, S-PUs with a hard segment of 50 mole % form fine birefringent elements, giving diffuse scattering in its SAXD pattern. A cyclic test of an S-PUs above T_g indicates that the residual strain increases and the recovery strain decreases with increasing cycle and maximum strain. It has been suggested by dynamic mechanical investigation that the shape-memorizing property of the S-PUs may be ascribed to the molecular motion of the amorphous soft segments. © 1996 John Wiley & Sons, Inc.     

Characterization of mechanical properties of thermoplastic films by creep measurements

Plasticized poly(methyl methacrylate) and methyl methacrylate/acrylate copolymer films were examined by isothermal creep at low loads measured at several temperatures from ～T_g to T_g + 15°C. Viscosity calculated using η = σ/3\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} was plotted vs temperature giving precise values for T_g based on a viscosity criterion of η = 10¹³ poises. Creep fracture data at various temperatures below T_g were interpreted using the maximum apparent viscosity measured at the minima of strain rate vs strain curves. Plots of η_max VS stress at several temperatures gave values of ΔT_g/Δσ of ?1° to 2°C/10⁶ N/m² in agreement with treatment of ΔT_g/Δσ based on free volume. Fracture occurred at low elongations when η_max was ≥10¹³ poises, and at higher elongations when η_max was <10¹³ poises supporting the concept that fracture is related to the lowering of T_g under stress. Plots of log σ VS log ε_b (the elongation at fracture) had the same form as that for crosslinked elastomers above T_g reported by T. L. Smith. Plots of log \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}_b VS log ε_b also had the same form supporting proposals on the rate sensitivity of fracture.     

An essential work of fracture study of the toughness of thermoset polyester coatings

The fracture toughness of a range of thermoset polyester paints with different cross-link densities has been studied, using the essential work of fracture (EWF) method. The glass transition temperature, T_g, of each of the materials was measured using differential scanning calorimetry, and found to lie between 8 and 46 °C. EWF tests were performed on the paint films at a range of temperatures around the measured glass transition temperature of each material. The essential work of fracture, w_e, at T_g was found to decrease with increasing cross-link density from around 20 kJ/m² at a cross-link density of 0.4 × 10⁻³ mol/cm³ to around 5 kJ/m² for cross-link densities of approximately 1 × 10⁻³ mol/cm³ or higher. A maximum in the essential work of fracture was observed at around T_g when w_e was plotted versus temperature, which could be attributed to the effect of an α-relaxation at a molecular level. The polyesters were found to be visco-elastic, and the applicability of the EWF test to the study of these visco-elastic thermoset materials is discussed.     

Thermal properties and crystallization behaviors of polylactide/redwood flour or bamboo fiber composites

A series of polylactide/redwood flour (PLA/RWF) and polylactide/bamboo fiber (PLA/BF) composites were successfully prepared using a solution mixing procedure. Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (XRD) were employed to characterize these composites. Thermal properties and crystallization behaviors of PLA composites were determined by their respective techniques of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). With the increasing content of fibers, the glass transition temperature (T _g ), crystallization temperature (T _c ), and melting temperature (T _m ) of PLA/RWF composites decreased first and then increased, but T _g and T _m of PLA/BF composites increased first and decreased afterwards. It is suggested that fibers could improve the segmental mobility of PLA; meanwhile, the different morphologies, sizes, and densities of RWF and BF have different effects on thermal properties of composites. Under the increasing content of RWF, the crystallization rate of the composite increased first and decreased afterwards. When the content of RWF was 5%, the crystallization rate was at its maximum. It could be possible that the addition of fibers was able to nucleate PLA and increase the degree of crystallinity, but the excess content of fibers easily led to heterogeneous composites and subsequent poor crystallization behaviors. In a word, thermal properties and crystallization behaviors of PLA composites were regularly changing by increasing content of fibers.     

Synthesis and characterization of polyamide resins from soy-based dimer acids and different amides

A series of soy-based polyamides with different dimer acids and diamines were synthesized using a condensation polymerization technique. The molecular weight of polyamides prepared from 1,4-phenylenediamine increases greatly with a reaction temperature above 260°C. The physical properties of the polyamides, such as glass transition temperature (T_g), melting point (T_m), decomposition temperature (T_d), crystalline behavior, and mechanical strength strongly depend on their molecular weight and flexibility of diamines used. The aromatic-based polyamides have a higher T_g, T_m, T_d, and stronger mechanical strength than that of aliphatic-based polyamides. X-ray diffraction patterns of the samples indicate that all of the resins synthesized present a typical semicrystalline morphology. Polyamides made from hydrogenated dimer acid possess lower T_g and higher mechanical strength, compared with polyamides from unsaturated dimer acid with different dimer and trimer ratios. These results are analyzed and discussed in accordance with the influence of rigid aromatic segments and the microstructure of different dimer acids. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:305–314, 1998