Glass transition temperatures of some linear polymers containing phenyl side groups

The glass transition temperatures of a number of poly(vinyl phenyl ketones), poly-(vinyl benzoates), and poly(phenyl acrylates) have been measured by a refractometric method. The effects exerted on T_g by the nature and position of the ring substituents and by the different groups binding the pendant phenyl rings to the polyvinyl chain are discussed. The importance of knowledge of the side-group motions in the glassy state for the interpretation of glass temperature data is emphasized.     

Lactone polymers. IV. Glass transition temperatures of monomeric lactones and their polymers

Glass transition temperatures were determined for a homologous series of unsubstituted lactone monomers varying in ring size from four to sixteen atoms. Examination of these transitions as a function of ring size shows a maximum in T_g for the seven-atom ε-caproalctone ring. This behavior is interpreted on the basis of a conformational change in lactones which occurs in rings containing seven to nine atoms. The T_g values of polylactones derived from these cyclic esters were determined and correlated with T_g values of the monomers. Except for the anomolous ε-caprolactone and the strained fourmembered lactone, an apparently constant difference between monomer and polymer T_g is observed. Treatment of the polylactones as methylene copolymers permits extrapolations of the T_g values to obtain that of polyethylene. Two values suggesting the γ and β transitions of polyethylene are obtained.     

Glass transition temperatures in binary polymer blends

Knowledge of the glass transition temperatures (T_gs) as function of composition reflects miscibility (or lack of it) and is decisive for virtually all properties of polymer‐based materials. In this article, we analyze single blend‐average and effective T_gs of miscible polymer blends in full concentration ranges. Shortcomings of the extant equations are discussed to support the need for an alternative. Focusing on the deviation from a linear relationship, defined as ΔT_g = T_g ? φ₁T_g,1 ? φ₂T_g,2 (where φ_i and T_g,i are, respectively, the weight fraction and the T_g of the i‐th component), a recently proposed equation for the blend T_g as a function of composition is tested extensively. This equation is simple; a quadratic polynomial centered around 2φ₁ ? 1 = 0 is defined to represent deviations from linearity, and up to three parameters are used. The number of parameters needed to describe the experimental data, along with their magnitude and sign, provide a measure of the system complexity. For most binary polymer systems tested, the results obtained with the new equation are better than those attained from existing T_g equations. The key parameter of the equation a₀ is related to parameters commonly used to represent intersegmental interactions and miscibility in binary polymer blends. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 80–95, 2008     

Prediction of glass transition temperatures of plasticized polymers

The classical free volume theory is modified semi-empirically to derive an expression useful for predicting the glass transition temperatures (T_g) for compatible polymer blends. This equation produces values of T_g in better agreement than those from the Kelley-Bueche equation with the dilatometric data for T_g of a number of plasticized polymers. The improvement is primarily attributed to the consideration of intermolecular interactions in the present investigation.     

Glass transition of polymers confined to nanoporous glasses

The glassy dynamics of poly(propylene glycol) (PPG) and poly(methyl phenyl siloxane) (PMPS) confined to nanoporous glasses (pore sizes 2.5–20 nm) investigated by dielectric spectroscopy, temperature modulated DSC and neutron scattering is compared. For both systems the relaxation rates estimated from dielectric spectroscopy and temperature modulated DSC agree quantitatively indicating that both experiments sense the glass transition.For PPG the glassy dynamics in nanopores is determined by a counterbalance of an adsorption and a confinement effect where the temperature dependence of the relaxation times obeys the Vogel/Fulcher/Tammann (VFT-) equation. The former effect results from an interaction of the confined macromolecules with the internal surfaces which in general slows down the molecular dynamics. A confinement effect leads to an acceleration of the segmental dynamics compared to the bulk state and points to an inherent length scale on which the glassy dynamics takes place. The step of the specific heat capacity c_p at the glass transition vanishes at a finite length scale of 1.8 nm. This result supports further the conception that a characteristic length scale is relevant for glassy dynamics.For PMPS down to a pore size of 7.5 nm the temperature dependence of the relaxation times follows the VFT-dependence and a confinement effect is observed like for PPG. At a pore size of 5 nm this changes to an Arrhenius-like behavior with a low activation energy. At the same pore size c_p vanishes for PMPS. This points to a dramatic change in the character of molecular motions responsible for glassy dynamics and supports further the relevance of a characteristic length scale on which it takes place.Quasielastic neutron scattering experiments on PMPS reveal that the microscopic dynamics characterized by the mean square displacement depends on confinement above the glass transition. The diffusive character of the relevant molecular motions seems to disappear at a length scale of about 1.6 nm.     

Glass transition in ionic polymers: The acrylates

It is shown that the glass transition temperatures of the ionic acrylates are subject to the same correlation as found for the phosphates, silicates, and ionenes; the equation is T_g = 730 (q/a) ? 67, where q is the cation charge and a the separation between centers of charge for the cation and anion.     

Theoretical calculations of glass transition temperatures of plasticized polymers

Based on free volume, an equation has been derived enabling calculation of glass transition temperature (T_g) of plasticized polymers, knowing the plasticizer content, the thermal expansion coefficients and values of T_g of the polymer and plasticizer. Determined and calculated T_g are in satisfactory agreement up to the plasticizer concentration which dissolves the polymer.     

Glass transformation temperatures of polymers of olefin oxides and olefin sulfides

A number of polymers belonging to poly(olefin oxide) and poly(olefin sulfide) series have been prepared and their glass transformation temperatures determined by dilatometry and differential thermal analysis. In the poly(olefin oxide) series, the T_g remained practically unchanged as the length of the pendent alkyl group was increased from methyl to n-hexyl. However, a 20°C decrease in T_g was observed when the pendent group was changed from ethoxymethyl to n-hexoxymethyl. In the poly-(olefin sulfide) series, the T_g value decreased as the pendent alkyl group changes from methyl to ethyl. Replacement of ether oxygen in the polymer main chain by sulfide sulfur increased the T_g value. In some polymers, first-order transitions were observed, but their significance has not been assessed.     

Glass transition temperature versus conversion relationships for thermosetting polymers

Owing to enthalpy relaxation, values of the glass transition temperature (T_g) for partially reacted polymers may depend on the thermal history of samples and the heating rate used for measurements. Use of theoretical relations between T_g and the extent of reaction (x) of a thermoset must take this fact into account. The original DiBenedetto equation has been reevaluated as a convenient constitutive equation for expressing T_g versus x. An extension of Couchman's approach for the expression of the compositional variation of T_g enabled us to derive the same functionality as given by the DiBenedetto equation. Thus, the DiBenedetto equation may be regarded as based on entropic considerations applied to a model of the thermosetting polymer consisting of a random mixture of a fully reacted network with the initial monomers in an amount which depends on the particular conversion level. These two equations have been applied with success to different diepoxy-diamine copolymers.     

Glass transition in polymers monitored by synchronous scan spectra

The synchronous scan spectra (SSS) technique was successfully applied to monitor the macromolecular chain motions near the glass transition temperature in polystyrene (PS) and poly (vinyl methyl ether) (PVME) films on a copper substrate. In SSS of PS and PVME films, two peaks at 467 nm and 473 nm, which correlated to the light source spectrum of the spectrofluorimeter, were used to characterize the glass transition of polymers. By monitoring the intensity of peaks at 467 and 473 nm in the spectra, the intensity-temperature curves exhibited kinks near the glass transition. The kinks have also been shown in plots of I_R473/I_R467 vs. temperature, which implies the distinct fluctuation of SSS intensity distribution at the glass transition temperature of the polymer. As a spectroscopy measurement method with simplicity, rapidity and sensitivity, the SSS method was proved to be able to monitor the glass transition in polymers, which has been commonly measured by differential scanning calorimetry (DSC).     

Epoxy polymers: Glass transition/cure degree correlation

The correlation between the glass transition temperature,T _g , and the cure degree, , of epoxy polymers has been analysed on the basis of an extension of the Vogel-Tamman-Fulcher equation for the viscosity of polymers and glasses.A physical meaning has been given to the coefficients of the series expansion of the functionT _g=T _g ().This analysis allows one to verify that the experimental (T _g ,) data support the conclusion that, in the case of thermoset polymers, the ideal glass transition temperature,T _o, appearing in the VTF equation, is larger thanT _g .This conclusion may be supported by the thermodynamic interpretation ofT ₀ as the temperature at which the excess entropy of the systems tends to vanish: in the case of partially cured thermosets;T ₀ would represent the minimum temperature at which the system becomes able to enhance its cure degree.

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Zusammenfassung Die Korrelation zwischen der Glasumwandlungs-temperaturT _g und dem Aushärtungsgrad von Epoxidpolymeren wurde analysiert, und zwar basierend auf einer Erweiterung der Vogel-Tamman-Fulcher-Gleichung für die Viskosität von Polymeren und Gläsern. Den bei der Reihenentwicklung der FunktionT _g =T _g () auftretenden Koeffizienten wurde eine physikalische Bedeutung zugeschrieben. Diese Analyse ermöglicht nachzuweisen, daß die experimentellen Daten (T _g ), die Schlußfolgerung stützen, daß im Falle von hitzehärtbaren Polymeren die in der VTF-Gleichung auftretende sogenannte ideale GlasumwandlungstemperaturT ₀ höher alsT _g ist. Diese Konklusion wird auch durch die thermodynamische Interpretation vonT ₀ gestützt, nämlich als die Temperatur, bei der die Überschußentropie des Systems gegen Null geht: im Falle von teilweise ausgehärteten hitzehärtbaren Polymeren würdeT ₀ die minimale Temperatur darstellen, bei der eine Erhöhung des Aushärtungsgrades des Systems einsetzt.

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T _g () - - . qT _g =T _g (). T _g , T ₀, -- , T _g . T ₀, , . ,T ₀ , .

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Work supported by the Progetto Finalizzato Chimica Fine e Secondaria of the Italian C.N.R., grant No. 84.01304.95     

Glass transition temperatures of copolymers of ethyl acrylate and vinylidene chloride

Glass transition temperatures of poly(ethyl acrylate-vinylidene chloride) and reactivity ratios for the copolymerization of the parent monomers are reported. All the copolymers have glass transition temperatures higher than those of polyethylacrylate or polyvinylidene chloride: the copolymer containing equal molar quantities of each monomer has the highest. The data are accounted for in terms of the fractions of AA. AB and BB diads contained in the copolymers.     

Glass transition temperatures of butyl acrylate–methyl methacrylate copolymers

The glass transition temperatures T_g of butyl acrylate–methyl methacrylate copolymers obtained by free radical polymerization in 3 and 5 mol/L benzene solution have been measured using differential scanning calorimetry (DSC) and the values have been correlated using Johnston's equation with inter‐intramolecular copolymer structure. From the data calculated with copolymer prepared at low conversion, the variation of glass transition temperature with copolymer conversion has been theoretically predicted. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2512–2520, 1999     

Glass transition temperatures of polymer materials,measured by thermomechanical analysis

The linear expansions of two materials have been measured, a double-base propellant and a carboxyl-terminated polybutadiene. The glass transition temperature,T _g and expansion coefficients below and aboveT _g have been calculated. The influence of the heating and cooling rates and sample thickness has been investigated. The results show that the value ofT _g is dependent on the rates of heating and cooling but not on the sample thickness. Extrapolating to zero rate gives the sameT _g for both heating and cooling. The expansion coefficients are not influenced by the rates of heating and cooling or by the sample thickness.

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Zusammenfassung Die lineare Ausdehnung wurde an zwei Stoffen, einem doppelbasischen Triebstoff und einem Polybutadien mit Carboxyl-Endung gemessen. Die Glas-Übergangs-temperaturT _g und die Ausdehnungskoeffizienten unterhalb und oberhalb vonT _g wurden berechnet. Der Einfluss der Aufheiz- und Abkülhgeschwindigkeiten und die Stärke der Probe wurden geprüft. Die Ergebnisse zeigen, daß der Wert vonT _g der von Aufheiz- und Abkühlgeschwindigkeit, nicht aber von der Probenstärke abhängt. Die Extrapolierung auf die Geschwindigkeit 0 ergibt denselbenT _g -Wert bei Aufheizung und Kühlung. Die Ausdehnungskoeffizienten werden durch die Aufheiz- und Abkühlgeschwindigkeit oder durch die Probenstärke nicht beeinflusst.

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Résumé On a mesuré la dilatation linéaire de deux matériaux, un agent de propulsion à base double et un polybutadiène avec un carboxyle comme groupe terminal. On a calculé la températureT _g de la transition vitreuse ainsi que les coefficients de dilatation au-dessous et au-dessus deT _g . L'influence des vitesses de chauffage et de refroidissement ainsi que l'épaisseur de l'échantillon ont été étudiées. Les résultats montrent que la valeur deT _g dépend des vitesses de chauffage et de refroidissement, mais pas de l'épaisseur de l'échantillon. L'extrapolation à la vitesse zéro donne la même valeur de la températureT _g lors du chauffage et du refoidissement. Les coefficients de dilatation ne sont influencés ni par les vitesses de chauffage ou de refroidissement ni par l'épaisseur de l'échantillon.

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. T_{g g}. , . , _g , . _g , . , .

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This is the last paper belonging to the Fifth Scandinavian Symposium on Thermal Analysis.     

Pyrolysis gas chromatography of some fluorine-containing polymers

Pyrolysis gas chromatography of the polymers of 1,3,3,3-tetrafluoropropene, 3,3,4,4,5,5,5-heptafluoropentene-1 and of the copolymers of tetrafluoroethylene with the above and with 3,3,3-trifluoropropene and with isobutene in all instances gave only 3 to 19% of volatiles below C₁₆, distributed among many peaks. This and the absence of significant char indicate predominantly a random scission mechanism of decomposition.