低摩尔质量组分对polymer熔体的增塑和反增塑作用
Plasticization and antiplasticization of polymer melts diluted by low molar mass species
摘要：
利用广义熵理论推导出被结构性分子添加剂稀释的聚合物熔体的玻璃形成分析，该理论涉及亚当-吉布斯模型和基于聚合物熔体晶格模型的构型熵直接计算的结合，其中包括单体结构效应。抗增塑伴随着相对于纯聚合物的玻璃混合物的“增韧”，并且发现当稀释剂是与聚合物基质具有强烈吸引力的相互作用的小物种时发生这种效果。增塑导致玻璃化转变温度T_g降低和脆性主体聚合物在玻璃态下的“软化”。与聚合物基质具有弱吸引力相互作用的小添加剂促进塑化。计算了全柔性短链低聚物稀释聚苯乙烯的T_g的变化，以及T_g下等温压缩系数的相对变化，以表征添加剂作为增塑剂或抗增塑剂的程度。该理论预测，降低的脆性可以伴随着分子添加剂对玻璃的增塑和反增塑。通过分析稀释剂的性质（内聚能、链长和刚度）对稀释聚合物熔体中玻璃形成的影响，合理地解释了这些分子添加剂对聚合物的玻璃化转变温度和脆性的普遍降低。在改变流体组成时引起的固定温度下的玻璃形成的描述直接暗示了作为聚合物浓度的函数的结构弛豫时间的Angell方程，并且计算出的“零迁移率浓度”与逆聚合指数N成线性比例。
英文摘要：
An analysis of glass formation for polymer melts that are diluted by structured molecular additives is derived by using the generalized entropy theory, which involves a combination of the Adam-Gibbs model and the direct computation of the configurational entropy based on a lattice model of polymer melts that includes monomer structural effects. Antiplasticization is accompanied by a "toughening" of the glass mixture relative to the pure polymer, and this effect is found to occur when the diluents are small species with strongly attractive interactions with the polymer matrix. Plasticization leads to a decreased glass transition temperature T_g and a "softening" of the fragile host polymer in the glass state. Plasticization is prompted by small additives with weakly attractive interactions with the polymer matrix. The shifts in T_g of polystyrene diluted by fully flexible short oligomers are evaluated from the computations, along with the relative changes in the isothermal compressibility at T_g to characterize the extent to which the additives act as antiplasticizers or plasticizers. The theory predicts that a decreased fragility can accompany both antiplasticization and plasticization of the glass by molecular additives. The general reduction in the T_g and fragility of polymers by these molecular additives is rationalized by analyzing the influence of the diluent's properties (cohesive energy, chain length, and stiffness) on glass formation in diluted polymer melts. The description of glass formation at fixed temperature that is induced upon change the fluid composition directly implies the Angell equation for the structural relaxation time as function of the polymer concentration, and the computed "zero mobility concentration" scales linearly with the inverse polymerization index N.
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