高分子专业英语课文翻译(3)

for example, sodium chloride and add it slowly to s fixed quantity of water. The salt, which represents a low molecular weight compound, dissolves in water up to s point (called saturation point) but, thereafter, any further quantity added does not go into solution but settles at the bottom and just remains there as solid. The viscosity of the saturated salt solution is not very much different from that of water. But if we take a polymer instead, say, polyvinyl alcohol, and add it to a fixed quantity of water, the polymer does not go into solution immediately. The globules of polyvinyl alcohol first absorb water, swell and get distorted in shape and after a long time go into solution. Also, we can add a very large quantity of the polymer to the same quantity of water without the saturation point ever being reached. As more and more quantity of polymer is added to water, the time taken for the dissolution of the polymer obviously increases and the mix ultimately assumes a soft, dough-like consistency. Another peculiarity is that, in water, polyvinyl alcohol never retains its original powdery nature as the excess sodium chloride does in a saturated salt solution. In conclusion, we can say that (1) the long time taken by polyvinyl alcohol for dissolution, (2) the absence of a saturation point, and (3) the increase in the viscosity are all characteristics of a typical polymer being dissolved in a solvent and these characteristics are attributed mainly to the large molecular size of the polymer. The behavior of a low molecular weight compound and that of a polymer on dissolution are illustrated in Fig.1.2.

发现另一种不同的聚合物行为和低分子量化合物行为是关于溶解过程。例如，让我们

研究一下，将氯化钠慢慢地添加到固定量的水中。盐，代表一种低分子量化合物，在水中达到点（叫饱和点）溶解，但，此后，进一步添加盐不进入溶液中却沉到底部而保持原有的固体状态。饱和盐溶液的粘度与水的粘度不是十分不同，但是，如果我们用聚合物替代，譬如说，将聚乙烯醇添加到固定量的水中，聚合物不是马上进入到溶液中。聚乙烯醇颗粒首先吸水溶胀，发生形变，经过很长的时间以后进入到溶液中。同样地，我们可以将大量的聚合物加入到同样量的水中，不存在饱和点。将越来越多的聚合物加入水中，认为聚合物溶解的时间明显地增加，最终呈现柔软像面团一样粘稠的混合物。另一个特点是，在水中聚乙烯醇不会像过量的氯化钠在饱和盐溶液中那样能保持其初始的粉末状态。总之，我们可以讲（1）聚乙烯醇的溶解需要很长时间，（2）不存在饱和点，（3）粘度的增加是典