Bercea Maria, Wolf Bernhard A
Institut für Physikalische Chemie der Johannes Gutenberg-Universität Mainz, Welder-Weg 13, D-55099 Mainz, Germany.
J Chem Phys. 2006 May 7;124(17):174902. doi: 10.1063/1.2193153.
Vapor pressures (headspace sampling in combination with gas chromatography) and glass transition temperatures [differential scanning calorimetry (DSC)] have been measured for solutions of polystyrene (PS) in either toluene (TL) (10-70 degrees C) or cyclohexane (CH) (32-60 degrees C) from moderately concentrated solutions up to the pure polymer. As long as the mixtures are liquid, the vapor pressure of TL (good solvent) is considerably lower than that of CH (theta solvent) under other identical conditions. These differences vanish upon the vitrification of the solutions. For TL the isothermal liquid-solid transition induced by an increase of polymer concentration takes place within a finite composition interval at constant vapor pressure; with CH this phenomenon is either absent or too insignificant to be detected. For PS solutions in TL the DSC traces look as usual, whereas these curves may become bimodal for solutions in CH. The implications of the vitrification of the polymer solutions for the determination of Flory-Huggins interaction parameters from vapor pressure data are discussed. A comparison of the results for TL/PS with recently published data on the same system demonstrates that the experimental method employed for the determination of vapor pressures plays an important role at high polymer concentrations and low temperatures.
已测定了聚苯乙烯（PS）在甲苯（TL）（10 - 70℃）或环己烷（CH）（32 - 60℃）中的溶液从适度浓溶液到纯聚合物的蒸气压（顶空进样结合气相色谱法）和玻璃化转变温度[差示扫描量热法（DSC）]。在其他相同条件下，只要混合物为液态，TL（良溶剂）的蒸气压就显著低于CH（θ溶剂）的蒸气压。这些差异在溶液玻璃化时消失。对于TL，在恒定蒸气压下，聚合物浓度增加引起的等温液 - 固转变在有限的组成区间内发生；对于CH，这种现象要么不存在，要么不显著以至于无法检测到。对于PS在TL中的溶液，DSC曲线看起来正常，而对于PS在CH中的溶液，这些曲线可能会变成双峰。讨论了聚合物溶液玻璃化对从蒸气压数据测定弗洛里 - 哈金斯相互作用参数的影响。将TL/PS体系的结果与最近发表的关于同一体系的数据进行比较表明，用于测定蒸气压的实验方法在高聚合物浓度和低温下起着重要作用。
