POTENTIOMETRIC TITRATIONS OF POLYMETHACRYLIC ACID
POTENTIOMETRIC TITRATIONS OF POLYMETHACRYLIC ACID
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DOI：
10.1002/pol.1947.120020409
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发表时间：
1947-01-01
影响因子：
3.4
通讯作者：
SPITNIK, P
中科院分区：
文献类型：
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作者：
KATCHALSKY, A;SPITNIK, P
对不同浓度、不同相对分子质量的聚甲基丙烯酸在中性盐存在下以及在二氧六环-水混合物中进行了电位滴定。结果表明，溶液的pH值满足关系：pH=pK-nlog[(1-α)/α])。如果引入合适的活度因子，pK和n与相对分子质量和浓度无关。该方程既适用于自由酸溶液，也适用于酸混合物。聚乙酸烯丙酯-马来酸类型的共聚物表现出更复杂的曲线。这条曲线属于“二次曲线”类型。它的每一个分支都很好地符合方程式(2)。对该公式进行了分析，认为它是麦克斯韦-帕金顿统计因子作用的结果，也是随机扭结分子伸展时伴随的熵减小的结果。这种拉伸是由电离羧基之间的排斥力引起的。给出了各电离度在任何pH下的分布曲线。活性校正意味着一个或两个羧基大小的小单位。在盐溶液中的行为不仅取决于活度修正，而且还取决于盐析因子。这一因素在多价盐中很高。用活度因子随介电常数的变化可以较好地解释二氧六环-水混合体系的滴定曲线。
Potentiometric titrations of polymethacrylic acid were performed at different concentrations, different molecular weights, and in the presence of neutral salts, as well as in dioxane‐water mixtures. It was shown that the pH of the solutions fulfills the relation, pH = pK — n log [(1 — α)/α]. pK and n are independent of the molecular weight and concentration if a suitable activity factor is introduced. The equation is applicable to free acid solutions as well as acid mixtures. Copolymers of the type, polyallyl acetate‐maleic acid, show a more complicated curve. The curve is of the “polydibasic” type. Each branch of it fits equation (2) well. The formula is analyzed and is proposed to be the result of the action of the Maxwell‐Partington statistical factor, as well as of the decrease in entropy accompanying the stretch of the randomly kinked molecule. This stretch is caused by the repulsive forces between the ionized carboxyl groups. The distribution curves of the various degrees of ionization present, for any pH, are given. The activity correction implies small units of the size of one or two carboxyl groups. The behavior in salt solutions is dependent not only on the activity correction, but also on the salting‐out factor. This factor is high in polyvalent salts. The titration curves in dioxane‐water mixtures are satisfactorily accounted for by the change in the activity factor with the dielectric constant.