含羧基聚合物的电导滴定

Studies on the Conductometric Titration of Polymer Containing Carboxyl Groups

用电导滴定法测定含羧基聚合物在甲醇溶液中的羧基含量时,若采用氢氧化纳水溶液为滴定剂,在滴定曲线上难以确定终点.为此,本文提出两种滴定体系:对具体样品选用适当量的混合溶含水剂;在聚酸溶液中加入中性盐(KCl),KCl 的当量浓度与被滴定物的羧基估计当量浓发相当.结合粘度滴定的结果,本文对电导滴定出现异常滴定曲线提出了初步解释.

In the methanol solution of polymeric acid,the content of carboxyl groups hasbeen analy zed by the conductometric titration.While the aqueous solution ofsodium hydroxide was used as the titrant,the titration curve appeared to be quitedifferent from that of simple weak acid(e.g.CH_3.COOH),so that the end pointcould not be ascertained.In orded to overcome this difficulty,we have found twodifferent systems:1)by adding suitable amount of water,2)by adding suitableamount of simple salt(KC1)to the nonaqueous polyacid solution.The end pointcan then be determined from the conductometric titration curve in both systemsvery easily and accurately.The KCl-system method appears to be simplier.ThePhenolphthalcin-indicator end points in both systems are consistent with that ofthe conductometric titration method,but the reproducibility of the latter isbetter.In comparison together with the result of the viscosity titration,an explanationof the anomaly of the conductometric titration curve with pure methanol as thesolvent has been given.