Polymer Dissolution

玻璃态聚合物的溶解可以被认为是以第二类迁移为特征的溶剂渗透和由聚合物解缠控制的聚合物溶解的组合。在本工作中，建立了溶剂渗透的反常输运模型，并与聚合物溶解的解缠模型相耦合。溶剂渗透受聚合物的松弛或变形控制，扩散Deborah数是一个主要的模型参数。在解缠模型中，聚合物分子的溶解要求溶剂浓度大于临界凝胶浓度，并允许聚合物分子在一定时间内完成从凝胶态到液态的扩散运动的解缠。假设这一时间等于声誉时间，这是分子量、溶剂浓度和链刚性的函数。引入解缠钟的概念，作为控制溶解的物质时间钟。新模型可以解释许多实验观察，如溶剂类型和聚合物对溶解速度和凝胶层厚度的影响。对聚苯乙烯和聚甲基丙烯酸甲酯在不同溶剂中的表征良好的样品进行了干涉测量和临界角照明显微镜的实验研究。用椭偏仪测量了溶剂浓度分布和溶出速率。用脉冲梯度自旋回波核磁共振波谱测量了聚合物所需的自扩散系数。此外，还用聚丙烯酸和聚乙烯醇在水中进行了实验研究，考察了离子条件对溶出度的影响。

Dissolution of glassy polymers can be considered as a combination of solvent penetration featuring Case II transport and polymer dissolution controlled by polymer disentanglement. In the present work, an anomalous transport model is developed for solvent penetration and is coupled with a disentanglement model for polymer dissolution. Solvent penetration is controlled by the relaxation or deformation of polymer and the diffusional Deborah number is shown to be a major model parameter. In the disentanglement model, dissolution of polymer molecules requires that solvent concentration be greater than a critical gel concentration and that a polymer molecule be allowed a certain time to complete the disentanglement of diffusion movement from the gel state to liquid state. This time is assumed to be equivalent to the reputation time, which is a function of molecular weight, solvent concentration and chain rigidity. A concept of disentanglement clock is introduced as the material time clock controlling the dissolution. The new model may explain many experimental observations, such as effects of type of solvent and polymer on dissolution rate and the thickness of the gel layer. Experimental studies are performed with well- characterized samples of polystyrene and poly(methyl methacrylate) in various solvents using interferometry and critical angle illumination microscopy. The solvent concentration profiles and dissolution rates are measured using ellipsometry. The necessary self-diffusion coefficient of the polymer is measured by pulsed gradient spin echo NMR spectroscopy. In addition, experimental studies are performed using poly(acrylic acid) and poly(vinyl alcohol) in water to study the influence of ionic conditions on dissolution.