It has taken them a long time to overcome this image but nowadays the special properties of plastics are being appreciated which is establishing them as important materials in their own right. The ever increasing use of plastics in all kinds of applications means that it is essential for designers and engineers to become familiar with the range of plastics available and the types of performance characteristics to be expected so that they can be used to the best advantage.

二十世纪初，人们十分关注这些新合成材料。酚醛树脂（“电木粉”）于1905年问世，大约在第二次世界大战期间象尼龙、聚乙烯和丙烯酸类（“有机玻璃”）的材料相继出现。可惜塑料的许多早期应用带来的是廉价代用品的名声。这种印象花费了长久的时间才被消除，但如今，塑料的特性正在被人们认识到，而塑料也正在确立它们作为重要材料的地位。塑料在各种应用中的用途不断增加，这意味着对于设计师和工程师来说，通晓塑料应用的范围和预期的性能特征是十分必要的，以致能以最好的方式利用它们。

The words “polymers” and “plastics” are often taken as synonymous but in fact there is a distinction. The polymer is the pure material which results form the process of polymerisation and is usually taken as the family name for materials which have long chain-like molecules and this includes rubber. Pure polymers are seldom used on their own and it is when additives are present that the term plastic is applied. Polymers contain additives for a number of reasons. In some cases impurities are present as a result of the polymerisation additives such as stabilisers, lubricants, fillers, pigments, etc., are added to enhance the properties of the material.

单词“聚合物”和“塑料”通常被看作是同义的，但事实上是有区别的。聚合物是缘于聚合反应过程的纯物质，常常被看作具有长链分子材料的系列名称，这也包括橡胶。纯的聚合物很少独自使用，当存在添加剂时它适用于专有名词塑料。由许多原因聚合物含有添加剂。在某些情况下作为聚合反应的结果存在杂质，去除这些杂质以获得纯的聚合物可能是不经济的。在其它情况下，添加象稳定剂、润滑剂、填充剂、颜料等之类的添加剂，以增强材料的性能。

There are two important classes of plastics:

有两种重要类别的塑料：

(1) Thermoplastic materials. In a thermoplastic material the long chain-like molecules are held together by relatively weak Van der Waals forces.