Polyacrylic acid (PAA) is a high molecular weight polymer whose structure is formed by connecting multiple acrylic monomers through polymerization reactions. Each monomer unit contains a carboxylic acid group, which enables PAA to form a polyelectrolyte in aqueous solution. The chemical structure of PAA endows it with multiple functions, including serving as a dispersant, thickener, flocculant, superabsorbent, and ion exchange resin.

The carboxyl groups of PAA can undergo ionization in aqueous solution, endowing the polymer with high negative charge density. This property makes PAA have good solubility and expansibility in water, forming viscous solution or hydrogel. The hydrogel form of PAA is widely used in sanitary products (such as diapers) because of its excellent water absorption and water retention.

In addition to its applications in water treatment and personal care products, PAA can also be used as a dispersing medium for abrasives in chemical mechanical polishing (CMP) processes in the electronics industry. In addition, the low toxicity of PAA makes it suitable as a food additive.

The synthesis of PAA is usually achieved through free radical polymerization, by polymerizing acrylic acid or its sodium salt. In industry, PAA products with different molecular weights and molecular weight distributions can be obtained by controlling the polymerization conditions. The molecular structure of PAA can adjust its hydrogel properties through covalent crosslinking, physical crosslinking or the formation of hydrogen bonds.

Derivatives of PAA, such as sodium polyacrylate, are used as thickeners, texture enhancers, film-forming agents, and emulsifying stabilizers in cosmetics and skin care products. The pH sensitivity of PAA makes it very useful in drug delivery systems, especially in tumor therapy, where the acidic environment of tumor cells can be utilized to achieve controlled drug release.

Structurally, the repeating units of PAA are homopolymers of acrylic acid with the molecular formula (C3H4O2) x, where x represents the number of repeating units. Because PAA contains a large number of carboxyl groups, which are sensitive to pH and ionic strength, the expansion rate of PAA hydrogel will be affected by solution pH and ionic strength. PAA hydrogels also have potential in biomedical applications due to their intelligent response characteristics.
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