Composition Dependence Of Tg Research Articles

The effect of benzenesulfonamide plasticizers on the glass transition temperature of an amorphous aliphatic polyamide

AbstractThe plasticizing effect of benzenesulfonamides (BSAs) on an amorphous aliphatic polyamide (AAPA) has been studied using dynamic mechanical analysis of copper‐supported spin‐coated mixtures. It follows that N‐(n‐butyl)BSA (BBSA), an amorphous liquid hydrogen bonding BSA, is fully miscible with AAPA because their mixtures are characterized by a single glass transition (Tg) throughout the compositional range. The Tg–composition dependence, however, is not linear because experimental results suggest a 20 K fall in Tg occurring around 0.65 BBSA units per amide unit, which coincides with the system shifting from a polymer‐like to a liquid‐like glass‐forming material. When considering a crystallizable hydrogen‐bonding plasticizer such as ethylBSA (EBSA), AAPA/EBSA mixtures become fully crystalline at a 1.3 EBSA unit per amide group. Nevertheless, melting point depression together with the single Tg observed throughout the compositional range on quenched (and therefore amorphous) samples confirms the miscibility of AAPA chains with the plasticizer. N,N‐DialkylBSAs, which lack the sulfonamide proton and therefore the possibility of hydrogen bonding with amide groups, quickly phase separate from AAPA, the glass transition of the latter staying mainly unaffected apart from a small (9 K) decrease at 10–15 mol% plasticizer.© 2001 Society of Chemical Industry

Characterization of miscible poly(ethylene oxide)/poly(phenyl methacrylate) system and the analysis of asymmetric Tg–composition dependence

Miscibility in the binary blend comprising of semicrystalline poly(ethylene oxide) (PEO) and fully amorphous poly(phenyl methacrylate) (PPhMA) was discovered for the first time. Differential scanning calorimetry, optical and scanning electron microscopy, and infrared spectroscopy were performed to characterize and demonstrate miscibility in the PEO/PPhMA system (in amorphous domains). The glass transition behavior suggests that the intermolecular interactions between the pairs are not particularly strong. The Fourier-transform infrared spectroscopy results also revealed a weak-to-moderate interaction via the phenyl ring might be likely. The overall behavior of the blend is a miscible system with weak non-specific interactions, and the apparent asymmetry in the T g–composition relationship has been analyzed with a detailed view of partially segregated PEO crystalline domains.

Miscibility of poly(1,4-cyclohexamethylene terephthalate) blends with polyarylate

The miscibility of poly(1,4-cyclohexamethylene terephthalate) (PCT) having an aliphatic cyclic segment blended with Polyarylate (PAR) was investigated by means of calorimetric measurements. It was found that all the PCT/PAR blends are miscible and show a single, composition-dependent glass transition temperature (Tg). The Tg composition dependence has been analyzed by using the Gordon–Taylor equation and the values of Tg obtained experimentally agree quite well with those calculated theoretically by using that equation. Also, the melting point depression phenomenon that occurred in miscible polymer pairs was observed up to 40 wt % PCT content. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1947–000, 2000

Kinematical studies of the glass transition in glassy Se80 − xTe20Sbx

The present paper reports kinematic studies of the glass transition in glassy Se80-xTe20Sbx alloys using the differential scanning calorimetric technique. The glass transition temperature (Tg) is found to increase monotonically with the heating rate. Tg also increases with the increase of Sb concentration in ternary Se80-xTe20Sbx system. From the heating rate dependence of glass transition temperature, the activation energy (Δ Et) for the relaxation time controlling the structural enthalpy, is calculated. The composition dependence of Tg and Δ Et is discussed in terms of the structure of the Se-Te-Sb glassy system.

Thermodynamic Study of the Glass Transition in Polyamine−Polyalcohol Mixtures: Entropy−Theoretical Interpretation of Anomalous Glass Transition Behavior

The glass transition temperatures of binary mixtures of polyamines and polyalcohols are investigated by differential scanning calorimetry (DSC). For all systems, the composition dependence of the glass transition temperature Tg shows clear maxima, in stark contrast to those of polyalcohol−polyalcohol mixtures reported previously. A thermodynamic analysis based on the entropy theory is carried out for (1,2-propanediamine)x(glycerol)1-x and (1,2-propanediamine)x(1,3-propanediol)1-x systems. The composition dependence of Tg predicted from the entropy theory of regular solutions (regular solution model, RSM) is not able to reproduce the anomalous behavior, and the excess configurational entropies ScE are negative and larger than 20 J K-1 mol-1 in absolute value at the minima. The origin of the large value of ScE is discussed with respect to the change of hydrogen bond network structure on mixing.

Rigid interpenetrating polymer network foams prepared from a rosin-based polyurethane and an epoxy resin

A series of rigid interpenetrating polymer network (IPN) foams, based on a rosin-based polyurethane and an epoxy resin, were prepared by a simultaneous polymerization technique. The changes in the chemical structure, dynamic mechanical properties, and morphology of the rigid IPN foams were investigated by Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical thermal analysis, and scanning electron microscopy. The FTIR analysis showed clearly that the cure rate of the rosin-based rigid polyurethane foam and the epoxy resin were different and, as a result, these two networks formed sequentially in the final rigid IPN foams. All of the rigid IPN foams exhibited a single, broad glass transition that shifted to lower temperature as the epoxy resin content increased. The experimental composition dependence of Tg's of the rigid IPN foams showed slight positive deviation from the Fox equation for homogeneous polymer systems. No phase separation was observed from the scanning electron microscopy investigation. It could be concluded that these two component networks were compatible in the final rigid IPN foams. This compatibility could be attributed to a graft structure in the polyurethane and the epoxy resin networks arising from the reaction of the hydroxyl groups of the epoxy resin with the isocyanate groups of MDI, and from the reaction of the hydroxyl groups of the polyols with the epoxide groups of the epoxy resin, as suggested by FTIR analysis. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 271–281, 1998

Study of free volume in high-vinyl polybutadiene/cis-polyisoprene blends using positron annihilation spectroscopy

High-Vinyl Polybutadiene (HVBD)/cis-Polyisoprene (CPI) blends were characterized by Differential Scanning Calorimetry (DSC) and Positron Annihilation Lifetime Spectroscopy (PALS). A single DSC glass transition temperature Tg is ob- served, whose composition dependence strongly deviates from additivity, and shows an apparent cusp when the weight fraction of HVBD E 0.75. The free-volume hole size, Vh, and the scaled fractional free volume, hps/C,A I3Vh were determined by PALS from the orthopositronium (o-Ps) intensities, I3, and lifetimes, t3, over a temperature range encompassing Tg and the temperature at which ''positronium bubble'' formation occurs. In the glass, Vh and hps/C are smaller for CPI than for HVBD, but the thermal expansion coefficient for hole volume, af, is larger in the melt for CPI than for HVBD; thus, an iso-hole volume temperature occurs in these blends at Tiso E0 347C. Above and below Tiso, Vh and hps/C each show a negative departure from additivity. A quantitative interpretation of the cusp in the composition dependence of Tg can be obtained, via a modified analysis of Kovacs, using free-volume quantities from PALS, with the ratio of scaling constants CCPI/CHVBD as an adjustable parameter. At high temperatures, the positron bubble size is smaller in CPI than in HVBD. This agrees with the observation that the thermal expansivity of hole volume, and, hence the internal pressure are larger in the equilibrium melt of CPI. The effect of e / -irradiation on the o-Ps intensity was investigated. I3 decreases more rapidly in the melt as T r Tg, and then more slowly in the glass, suggesting that the effect is due to trapping of radical or ionic species which

Precipitation of bcc nanocrystals in bulk Mg–Cu–Y amorphous alloys

Coexistent amorphous and nanoscale bcc-Mg7Li3 phases were found in slowly quenched alloys of the Mg65–xLixCu25Y10 system containing 3 to 15 at. % Li. The crystallization behavior of these alloys has been studied. The grain size of the nanocrystalline bcc phase which is formed ranges from 2 to 20 nm. The volume fraction of nanocrystalline phases as well as the grain size of the nanocrystals increase as the Li composition increases. Transmission electron microscopy studies suggest that the alloy exhibits phase separation in the undercooled liquid state and that the nucleation and growth of the bcc-nanocrystals is related to the phase separation. Some characteristic thermal properties of the glassy phase are presented, and the composition dependence of Tg and Tx is discussed. It is concluded that the addition of a small amount of Li is essential for the production of a bcc nanocrystalline phase in the Mg–Li–Cu–Y system.

Thermal study of glass transitions in binary systems of simple hydrocarbons

Glass transition phenomena of four binary systems composed of simple hydrocarbons were studied by means of the differential thermal analysis (DTA). For all the systems, a definite glass transition was observed and a monotonous relation between the glass transition temperature (Tg) and composition (x) was obtained. The composition dependence ofTg was analyzed in terms of the entropy theory based on the regular solution model. The theoretical prediction could not reproduce our results other than (1-butene)x(1-pentene)1−x system. This disagreement is considered to be due to deviations of the present systems from the regular solution, and the accompanying excess configurational entropy ScE was estimated as a function of composition. Extraordinarily large values of ScE? were obtained for (propene)x(propane)1−x and (propene)inx(1-pentene)1−x systems.

Approach to the composition dependence of the glass transition temperature of compatible polymer blends, 2 The effect of local chain orientation

AbstractIn a previous publication a new concept has been presented for the composition dependence of the glass transition in compatible polymer blends. The concept starts with the idea that besides conformational energy barriers, contacts due to interaction are responsible for both conformation and “free” volume distribution. In accordance with the Flory‐Huggins lattice theory, the contact probability has been related to the volume fraction of the components, corrected for the different volume expansion coefficients. The concept accounts for both chainspecific and interaction‐specific contributions. It is concluded that local chain orientation due to the increased hetero‐contact interaction may explain the observed molecular weight influences on the composition dependence of Tg of polymer blends. Using experimental data for poly(vinyl methyl ether)‐polystyrene (PVME‐PS) blends it is shown that this local chain orientation due to hetero‐interaction is extremely strong in blends of the low molecular weight PS with high MW PVME. Thus, apparently, the stiffer component is dominating the Tg behaviour of compatible polymer blends.

ChemInform Abstract: STRUCTURAL STUDY OF GERMANATE GLASSES IRRADIATED WITH Γ‐RAYS AND THERMAL NEUTRONS

AbstractZur Untersuchung der Strukturveränderungen infolge 60Co‐γ‐ und Neutronen‐Bestrahlung werden Gläser der Zusammensetzung xK2O·(100‐x)GeO2·2 SnO2 119Sn‐Mößbauer‐spektroskopisch untersucht.

Structural Study of Germanate Glasses Irradiated with γ-Rays and Thermal Neutrons

Abstract 119Sn Mössbauer study of 60Co-γ ray and thermal neutron irradiated potassium germanate glasses containing a small amount of SnO2 has been performed to investigate the structural change of the glasses. The γ- and the thermal neutron-irradiation results in a disappearance of the distinct composition dependence of the Mössbauer parameters (quadrupole splitting and linewidth) observed before the irradiation. DTA measurement of the irradiated glasses also reveals drastic decreases in glass transition temperature (Tg) amounting to 20–120 °C and a simultaneous disappearance of the distinct composition dependence of Tg observed before the irradiation. This suggests a disruption of the chemical bond between germanium and oxygen atoms constituting GeO6 units. On the other hand, Mössbauer measurement at lower temperatures reveals that a parameter of intermolecular force constant (θ2M) obtained from the temperature dependence of the absorption area undergoes little change by the irradiations. This suggests that the irradiations bring about little changes in the ionic bond and the interatomic distance between tin and oxygen atoms, and that the irradiated germanate glasses can still be regarded as polymers from the lattice vibrational point of view.

The influence of thermal properties on the glass transition temperature in styrene/divinylbenzene network–diluent systems

AbstractThe depression of glass transition temperature in polystyrene and styrene/divinylbenzene networks, by the addition of ethylbenzene, ethyl acetate, and m‐diethylbenzene, respectively, has been investigated by differential scanning calorimetry. The predictive quality of the Couchman–Karasz treatment for the composition dependence of Tg in compatible systems was found to provide excellent agreement with experimental results for the depression of Tg by ethylbenzene, provided certain modifications were made. Qualitatively, the theory predicts that for a given diluent, the depression of Tg is particularly sensitive to the incremental change in heat capacity of the pure polymer or network. The behavior of ethylbenzene provided good quantitative agreement with the theory, provided that the incremental change in heat capacity of the diluent at its Tg was approximated by ΔCp = constant/T and that the incremental change in heat capacity of the network at Tg represents only those units capable of thermal activation. The anomalous behavior observed on plasticization by ethyl acetate and m‐diethylbenzene could in part be explained by a reduction in solvent quality or syneresis of diluent in the highly crosslinked samples.

Conformational effects on the composition dependence of Tg in binary copolymers

An equation is proposed for the glass transition temperature ( T g ) of binary copolymers, using the criterion that ΔF = 0. The equation is used in an investigation of the composition dependence of T g for rotational isomeric state models of S/MMA, VDC/MA, ET/EA and E/P copolymers, and of a-PP. A comparison is made of calculated and experimental T g values, the coincidence of which supports the conclusion that the composition dependence of T g for these copolymers and for a-PP may be governed by the first and second order interaction energies about a skeletal bond of an isolated chain molecule.

Glass-Forming Composition Regions and Glass Transition Temperatures for Aqueous Electrolyte Solutions

As a first stage in a study of the low-temperature-region behavior of aqueous solutions, the composition regions of a large number of binary salt-water systems in which macroscopic samples can be obtained in the vitreous state have been determined. The glass transition temperatures Tg within these regions have also been measured. Correlations of the magnitude of Tg at a given composition with the formal charge on the cation (for salts with a common anion) and with the viscosity “B” coefficient of the anion (for salts with a common cation) are presented. In addition, an important correlation is found with the basicity of the anion which is interpreted in terms of the bonding of anions to the protons of the water molecules in the cationic hydration sheath. Thermodynamic relations for the composition dependence of Tg are presented. From the breaks in the otherwise monotonic composition dependence of Tg in the chloride systems, the existence of low temperature liquid–liquid immiscibility regions is proposed and is utilized in discussion of “total” hydration numbers. The Tg for pure water, obtained by extrapolation of the data, is found to be in agreement with the value obtained for vapor-deposited vitreous ice but to be incompatible with the value predicted from thermodynamic data; an interpretation in terms of different short-range order possibilities for water molecules is offered.