Investigation of the thermophysical properties of polymers by the temperature wave technique

The technique of temperature waves to measure the complex thermophysical characteristics of materials has been proposed. The relations for the moduli and arguments of these characteristics for the case of plane temperature waves have been calculated. The temperature dependences of the moduli and arguments of complex thermophysical characteristics of polyvinylacetate (PVAc) at different frequencies and also the temperature dependences of its vibrational and configurational heat capacities have been determined. It has been shown that the vibrational heat capacity of PVAc in the region of softening grows sharply and its configurational heat capacity goes through a peak. The segmental mobility has been found to affect the heat transfer in the polymer in an ambivalent way causing both a decrease and increase of thermal conductivity.

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Zusammenfassung Zur Bestimmung der komplexen thermophysischen Eigenschaften von Stoffen wurde eine Temperaturwellentechnik vorgeschlagen. Für den Fall zweidimensionaler Temperatur-wellen wurden die Verhältnisse von Moduli und Argumenten dieser Eigenschaften berechnet. Die Temperaturabhängigkeit von Moduli und Argumenten der komplexen thermophysischen Eigen-schaften von Polyvinylacetat (PVAc) bei verschiedenen Frequenzen und auch die Temperatur-abhängigkeit seiner Vibrations- und Konfigurations-Wärmekapazitäten wurden bestimmt. Es wurde gezeigt, daß die Vibrations-Wärmekapazität von PVAc im Erweichungsbereich scharf zunimmt und die Konfigurations-Wärmekapazität durch einen Peak geht. Man fand, daß die Segment-Mobilität den Wärmetransport im Polymer auf eine ambivalente Weise beeinflußt, in dem die Wärmeleit-fähigkeit entweder gesenkt oder angehoben wird.

     

家具白乳胶中苯系物含量测定

建立了气相色谱内标法测定家具白乳胶中苯系物含量的方法。样品中苯系物经甲醇提取、离心,上清液用60 m EN-20色谱柱分离,气相色谱检测,内标法定量。优化条件下苯系物回收率在96.84%~103.86%,相对标准偏差(RSD)为0.79%~2.28%,定量下限2.4~2.9 mg/L。方法操作简单,准确度和精密度较高,是一种检测白乳胶产品中苯系物含量的有效方法。     

Thermodynamics of Polyvinylacetate from 0 to 350 K

The temperature dependence of the heat capacity of vinyl acetate in the range 13 to 330 K and of polyvinylacetate between 4.9 and 330 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. Temperatures and enthalpies of physical transitions were measured. From the data obtained, the thermodynamic characteristics of melting of vinyl acetate and parameters of glass transition and glassy state of the monomer and polymer were calculated. The thermodynamic functions H^o(T)-H^o(0), S^o(T), G^o(T)-H^o(0) were estimated for both materials from 0 to 350 K. The results of calculation and the literature value of enthalpy of bulk polymerization of vinyl acetate at T=350 K were used for the estimation of the thermodynamic parameters of its polymerization process ΔH_pol ^o, ΔS_pol ^o, ΔG_pol ^oin the interval 0 to 350 K. A ceiling limiting temperature of polymerization T_ceil ^owas evaluated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enthalpies of solution of polyvinylacetate in chloroform,acetone, and methanol using titration calorimetry

Heats of mixing of the solvents chloroform, methanol, and acetone with their solutions in polyvinylacetate have been measured at 25°C using a titration calorimeter. Titration of pure solvent to solutions as well as titration of solutions to the pure solvent or to diluted solutions have been performed. The second method, called reverse titration, proved to be more sensitive than normal dilution titration at sufficiently low polymer concentration. Equations describing the relative sensitivity of both titration methods have been developed. The concentration range covered by the experiments is restricted to volume fractions of polyvinylacetate not higher than 0.1–0.15 due to the high viscosities of concentrated solutions. The interaction parameterX _H of the Flory-Huggins theory has been determined from the calorimetric data.X _H is positive for methanol solutions and negative for chloroform and acetone solutions reflecting endothermic and exothermic heat effects respectively.