湘大高分子专业英语Charpter 2-1.ppt

* Summary Many naturally occurring and some synthetic polymers are produced by condensation reactions which are described kinetically by the term step-reaction polymerization. Since a high fractional conversion (p) is required, only a relatively few useful linear polymers, such as polyesters and polyamides, may be synthesized by step reactions. Since the fractional conversions are very high, useful polymers may be produced by the stepwise condensation of a bifunctional acyl or sulfonyl chloride with a diamine or glycol. The rate constant k for these second- and third-order reactions is similar to corresponding reactions of monofunctional reactants and is essentially unchanged as the reactions proceed through dimers, tetramers, octamers, oligometers, and higher molecular weight polymers. This rate constant increases with temperature in accordance with the Arrhenius equation. The degree of polymerization DP of a reaction of bifunctional reactants may be calculated from the Carothers equation, DP = 1/(1- p). However, this value will be changed if cyclization occurs to form “wasted loops.” Since this is a step reaction, DP increases with time. High molecular weight linear polyesters may be produced by ester interchange or by interfacial condensation (Schotten-Baumann reaction). * 总结 许多天然存在的和一些合成聚合物是由这是由术语步反应聚合动力学描述的缩合反应制备。因为高的转换分数（P）是必需的，只有相对较少的有用的线性聚合物，如聚酯和聚酰胺，可以通过一步反应合成。 因为小数转换是非常高的，有用的聚合物可通过双官能的酰基或磺酰氯与二胺或二醇的逐步缩合来制备。的速率常数k为这些第二和第三阶的反应是类似的单官能反应物的相应的反应，基本上是不变的反应进行通过二聚体，四聚体，八聚体，oligometers，和较高分子量的聚合物。用这个温度的速率常数的增加按照Arrhenius方程。 （ - P 1）双官能团反应物的反应的聚合DP的程度可以从卡罗瑟斯方程，DP = 1 /计算。然而，如果发生环化，以形成该值将被改变“浪费环路。”由于这是一个两步反应，DP随时间增加。 高分子量的线型聚酯可以通过酯交换或通过界面缩聚（在Schotten-Baumann反应）来生产。 * Since the values of k at any temperature may be determined from the slope (2kA0) of the line when 1/(1 - p)2 is plotted against t, one may determine DPN at any time t from the expression. Returning again to consider the synthesis of polyesters, generally much longer reaction times are required to ef