Polymer Dissolution

玻璃状聚合物的溶解可以被认为是溶剂渗透和聚合物解缠控制的聚合物溶解的结合。在本工作中，建立了溶剂渗透的异常输运模型，并与聚合物溶解的解纠缠模型相结合。溶剂渗透受聚合物的松弛或变形控制，扩散底波拉数是模型的主要参数。在解缠模型中，聚合物分子的溶解需要溶剂浓度大于临界凝胶浓度，并且需要让聚合物分子在一定时间内完成从凝胶态到液态扩散运动的解缠。这个时间假定等于信誉时间，信誉时间是分子量、溶剂浓度和链刚性的函数。引入了解纠缠时钟的概念，作为控制溶解的物质时间时钟。新模型可以解释许多实验观察，如溶剂和聚合物的类型对溶解速率和凝胶层厚度的影响。实验研究进行了良好的表征样品的聚苯乙烯和聚（甲基丙烯酸甲酯）在各种溶剂使用干涉测量和临界角照明显微镜。用椭偏法测定了溶剂的浓度分布和溶解速率。采用脉冲梯度自旋回波核磁共振波谱法测定了聚合物所需的自扩散系数。此外，还利用聚丙烯酸和聚乙烯醇在水中进行了实验研究，研究了离子条件对溶解的影响。

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.