英语翻译The term macromolecule,or polymer,is applied to substanc

英语翻译
The term macromolecule,or polymer,is applied to substances of high molecular weight that are composed of a large number (usually at least 100) of units of low molecular weight joined by covalent bonds.If the low molecular weight units making up the macromolecule are bonded end-to-end in a long chain and no covalent chemical bonds exist between the chains,the macromolecules are called linear polymers.Such polymers.Unless of extremely high molecular weight (1000000),can usually be dissolved and ,when heated,they soften or melt so that they can be extruded into fibers or molded into desired shapes.These polymers are said to be thermoplastic.On the other hand,if the polymer chains are linked together at numerous points,the polymer is one large three-dimensional molecule,infusible and insoluble.Such polymers are called cross-linked polymers,and the bonds connecting the chains are cross-links.Certain linear polymers,referred to as thermosetting,contain groups which ,when heated,react to give cross-linked polymers.
The process by which small molecules undergo multiple combination to form macromolecules is polymerization.Small molecules from which a macromolecule or polymer can be made are called monomers.Two types of polymerization are recognized :(1)condensation polymerization and (2)addition polymerization.A polymer-forming reaction involving elimination of a small molecule such as water or alcohol between monomer units is described as condensation polymerization.In addition polymerization,unsaturated or cyclic molecules add to each other without elimination of any portion of monomer molecule.The empirical formula of the polymer is then,of course,the same as that of the monomer.
Reactions capable of forming macromolecules by either addition or condensation polymerization must be functionally capable of proceeding indefinitely.Whenever two monomer molecules react,the product must contain a functional group capable of reacting with another molecule of monomer.In condensation polymerization,the monomer need have only one functional group -the presence of two or more functional groups usually leads to the production of cross-linked addition polymers.

所谓高分子或聚合物,是指由大量的轻量分子单位（通常最少有100）通过共价键连接一起组成高重量分子的物质.如果组成高分子的轻量分子单位是头尾连接成为一条长链,而链与链之间没有共价化学键,这种高分子被称作线性聚合物.除非属于特高的分子重量,这种聚合物通常可以被溶解,而当被加热时会变软或融化,因此可以挤压成纤维或模塑成需要的形状.这些聚合物叫做热塑性塑料.在另一方面,如果这些聚合物链条在多个点位连接在一起,这聚合物变成一个大型三维分子,不熔化也不溶解；这种聚合物称为交联聚合物,因为连接这些链条的键是交联的.一些被称为热硬化性的线性聚合物,其所含有的分子组当加热后,会反应生成交联聚合物.小分子经过多层次组合而形成高分子的过程叫做聚合反应.能够形成高分子或聚合物的小分子称为单体.公认的两种聚合反应是：（一）冷凝聚合反应及（二）加成聚合反应.单体分子之间涉及消除小分子如水或乙醇的聚合反应叫做冷凝聚合反应.在加成聚合反应中,非饱和或循环分子相互添加但不消除单体分子的任何部分.聚合物的实验公式当然是与单体相同的.
能以冷凝聚合或加成聚合生成高分子的反应,必须在机能上能够无限进行下去.每当两个单体分子产生反应,其产生物必须含有能与另外单体分子产生反应的功能组.在冷凝聚合反应中,单体仅需一个功能组,如果存在两个或以上,通常会导致交联加成聚合物的产生.