Physical and chemical properties of polyacrylamide

Physical and chemical properties of polyacrylamide

Polyacrylamide is a water-soluble linear polymer formed by free radical initiated polymerization of acrylamide (AM) monomer. It has good flocculation properties and can reduce the frictional resistance between liquids. According to its ionic properties, it can be divided into four types: non-ionic, anionic, cationic, and amphoteric. Polyacrylamide (PAM) is insoluble in most organic solvents such as methanol, ethanol, acetone, ether, fatty hydrocarbons, and aromatic hydrocarbons, except for a few polar organic solvents such as acetic acid, acrylic acid, chloroacetic acid, ethylene glycol, glycerol, molten urea, and formamide. But these organic solvents have limited solubility and often require heating, otherwise they have little practical value. It can dissolve in water in any proportion, and the aqueous solution is a uniform and transparent liquid. The molecular weight has little effect on the solubility, but when the solution concentration is higher than 10%, the polymer with high molecular weight can show a gel like structure due to intermolecular hydrogen atom bonding. High molecular weight solutions are pseudoplastic fluids.

At appropriate low concentrations, polyacrylamide solution can be regarded as a network structure, with mechanical entanglement and hydrogen bonding between chains forming network nodes; When the concentration is high, the PAM solution is gel like because the solution contains many chain link contacts. PAM aqueous solution has good compatibility with many organic compounds that are miscible with water, and has good compatibility with electrolytes. It is insensitive to substances such as ammonium chloride, calcium sulfate, copper sulfate, potassium hydroxide, sodium carbonate, sodium borate, sodium nitrate, sodium phosphate, sodium sulfate, zinc chloride, boric acid, and phosphoric acid.

Polyacrylamide is a white powder or small granular material with a density of 1.302g/cm3 (23 ℃), a glass transition temperature of 153 ℃, and a softening temperature of 210 ℃. It generally contains a small amount of water when dried, and quickly absorbs water from the environment when dried. The homopolymer separated by freeze-drying is a white, soft, non crystalline solid, but when precipitated and dried from the solution, it becomes a glass like partially transparent solid. Fully dried polyacrylamide PAM is a brittle white solid. Commercial polyacrylamide is usually dried under moderate conditions with a water content of 5% to 15%. Polymer films prepared by casting on glass plates are transparent, hard, and fragile solids.

Heating to 210 ℃ under hypoxic conditions leads to weight loss due to dehydration; When heated to 210~300 ℃, the amide group decomposes to produce ammonia and water; When the temperature rises to 500 ℃, black flakes with only 40% of the original weight are formed.