Dissociation Behavior of Polyacrylic Acid in Aqueous Solution

doi:10.12141/j.issn.1000-565X.220385

Abstract

Abstract:

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.

Key words: polyelectrolytes, thermodynamics, dissociation equilibrium equation, ionization equilibrium constant, Flory-Huggins lattice model

CLC Number:

O654.16

LI Wenbo, DU Xiaoxiao. Dissociation Behavior of Polyacrylic Acid in Aqueous Solution[J]. Journal of South China University of Technology(Natural Science Edition), 2023, 51(3): 83-90.

Figures/Tables 7

Table 1

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Table 2

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样品编号	单体体积分数/%	反应温度/℃	引发剂质量分数/%	聚合度
PAAH1	16.67	60	0.75	2 040
PAAH2	14.29	65	1.00	1 700
PAAH3	11.76	65	2.00	1 260
PAAH4	11.76	75	2.50	750
PAAH5	9.09	80	3.00	580
PAAH6	6.25	85	4.00	340

样品编号	高浓度区		低浓度区
样品编号	ΔE/（J·mol^-1）	R²	ΔE/（J·mol^-1）	R²
PAAH1	30 771	0.999 6	45 295	0.999 4
PAAH2	30 566	0.999 5	44 942	0.999 5
PAAH3	30 925	0.999 6	45 269	0.999 6
PAAH4	30 798	0.999 6	45 086	0.999 6
PAAH5	31 273	0.999 7	45 289	0.999 5
PAAH6	32 321	0.999 9	45 230	0.999 6
AAH	31 625	0.999 9	44 076	0.998 8

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