为了研究不同分子质量的聚丙烯酸（PAAH）在水溶液中的离解行为以及聚电解质（聚丙烯酸）与小分子弱电解质（丙烯酸（AAH）和醋酸（HAc））离解行为的差异。文中采用沉淀聚合法制备了聚合度在300~2 000范围内的聚丙烯酸，并使用pH计测量聚丙烯酸、丙烯酸和醋酸水溶液的pH值，以此来判定电解质在水溶液中的离解行为；然后从热力学角度和Flory-Huggins晶格模型推导出电解质在离解过程中的离解平衡方程。结果表明：聚丙烯酸在水溶液中的离解行为与聚合度基本无关。通过数学简化离解平衡方程得到传统平衡常数K_α 的计算公式，并赋予K_α 确切的物理意义：电解质水溶液在离解过程中离解水合效应相互作用能的相对强度参数。把数据代入离解平衡方程发现，聚电解质和小分子弱电解质均存在两种摩尔电离水合能ΔE，分别在低浓度区和高浓度区，这是丙烯酸、醋酸和聚丙烯酸在低浓度区都偏离了传统平衡常数K_α 理论线的原因。

In order to study the dissociation behavior of polyacrylic acid (PAAH) with different molecular weight in aqueous solution as well as the difference between the dissociation behavior of polyelectrolyte (polyacrylic acid) and small molecular weak electrolyte (acrylic acid (AAH) and acetic acid (HAc)), this paper prepared polyacrylic acid with polymerization degree in the range of 300~2 000 by precipitation polymerization method. The pH value of polyacrylic acid, acrylic acid and acetic acid aqueous solution was measured by pH meter to determine the dissociation behavior of electrolyte. Then from the thermodynamic point of view and Flory-Huggins lattice model, the paper derived the dissociation equilibrium equation of electrolyte in the dissociation process. The results show that the dissociation behavior of polyacrylic acid in aqueous solution is independent of the degree of polymerization. By simplifying the dissociation equilibrium equation, the calculation formula of the traditional equilibrium constant K_α was obtained and given its exact physical meaning: the relative strength parameter of the interaction energy of the dissociation hydration effect of electrolyte aqueous solution in the dissociation process. By substituting the data into the dissociation equilibrium equation, it is found that there are two kinds of molar ionization hydration energies ∆Es in polyelectrolyte and small molecule weak electrolyte, in the low concentration region and the high concentration region, respectively. This is the reason why acrylic acid, acetic acid and polyacrylic acid deviate from the traditional equilibrium constant K_α theoretical line in the low concentration region.