It is a linear polymer made from the polymerization of monomer Polyacrylamide. Because the monomer acrylamide contains bifunctional groups (double bond and amide group), it has the properties of amide and unsaturated olefin. PAM is divided into two kinds of dry powder and colloid. Dry powder is white or gray powder. The colloid is light yellow. It must be dissolved before it can be used. Therefore, PAM with good solubility must be prepared. The PAM structure can be divided into anionic, cationic, zwitterionic and nonionic. The solid content of the powder is greater than 92%, the relative molecular mass is (500 ~ 800) x104, and the solid content of the colloid is (8 +0.2)%.
The appearance of PAM is a hard glass-like solid (d2341. 032). Because the PAM chains are associated through -CONH, the separation between the chains is difficult. Therefore, the glass transition temperature of PAM is higher, generally greater than 200°C.
PAM is soluble in water at 50 to 60°C with a degree of hydrolysis of 5% to 35%. It is also soluble in organic solvents such as acetic acid, propionic acid, chloroacetic acid, ethylene glycol, glycerin, and amines. Because the monomer acrylamide undergoes chain transfer during polymerization to produce branched chains, the PAM polymer chain structure contains a cross-linked structure mainly composed of branched chains and imine bridges. Moderate cross-linking is relatively high in molecular weight and easy to dissolve, while more cross-linking, the product is insoluble. If the association of molecular chains is weakened, the glass transition temperature of PAM decreases and it is easier to dissolve. The addition of low molecular amide compounds (such as urea) can weaken the PAM interchain association, thereby improving the solubility of PAM. In addition, urea also has the effects of inhibiting product crosslinking and improving the relative molecular mass of PAM. At present, the preparation of high molecular weight PAM is the goal pursued, but the relative points
The larger the sub-mass, the more branches, so it increases the difficulty of PAM dissolution.
The dissolution of PAM can be carried out under moderate hydrolysis. The greater the degree of hydrolysis, the easier it is to dissolve. PAM is easily decomposed at greater than 200°C. Under 210°C anaerobic conditions, the dehydration of the amide group in PAM is converted to cyanogen
Base; PAM carbonized into black powder at 500°C. The amide group in the PAM molecule has high activity, including various properties such as thickening, flocculation and drag reduction. PAM itself is non-toxic, but because acrylamide remains in the PAM molecule, and acrylamide is toxic, the remaining amount of acrylamide in PAM is generally 1%. Used in water purification, sucrose juice clarification and other food and paper in contact with food, and the residual amount of acrylamide in PAM should be less than 0.05%. Polyacrylamide has a large number of pendant amide groups on its main chain. The chemical activity of the amide group is great, and it can react with various compounds to produce many derivatives of polyacrylamide. The amide group is also unique in that it can form strong hydrogen bonds with a variety of compounds that can form hydrogen bonds.
Most industrially produced polyacrylamide products contain different amounts of carboxyl groups and are anionic polymers. Acrylamide can be copolymerized with monomers with anionic groups or cationic groups to obtain anionic polyacrylamide or cationic polyacrylamide. In industry, polyacrylamide is reacted with formaldehyde and dimethylamine to synthesize cationic polyacrylamide via Mannich reaction. The industrial production of polyacrylamide has a polymerization degree of 20,000~30,000; the average relative molecular mass is (10~2000) x104 or so. According to the relative molecular mass range and whether it has ionic groups and ionic group content, polyacrylamide is divided into different brands in industry: nonionic polyacrylamide, anionic polyacrylamide and cationic polyacrylamide.
Polyacrylamide is sold mainly in two forms, one is powder and the other is colloid. The colloid is not easy to transport and inconvenient to use. Therefore, powdered polyacrylamide is welcomed by users. Recently, there has been a polymer dispersion called polyacrylamide latex, which has the property of being easily soluble in water, and therefore attracts people's attention. The size of relative molecular mass is one of the main performance indicators that distinguish polyacrylamide. Polyacrylamide with high molecular weight is mainly used as flocculant, polyacrylamide with medium molecular weight is mainly used as dry strength agent for paper, and low molecular weight The amount of polyacrylamide is used as a dispersant.
Polyacrylamide was first produced by Moureu using acryloyl chloride and ammonia at a low temperature in 1893, and was only industrialized in 1955. The first widely used is the uranium mining industry. Polyacrylamide is used to remove tiny impurities from the uranium salt aqueous solution. Now, polyacrylamide has been widely used in papermaking, mineral processing, tertiary oil extraction, sewage and drinking water treatment, building materials industry, food processing and other industries abroad.
In the 1960s, my country began to produce polyacrylamide, mainly used for the purification and electrolysis of salt water. The production scale at that time was small. Due to the rapid development of my country's petroleum industry in recent years, the application fields of polyacrylamide in petroleum exploitation and drilling have become more and more extensive. Its output has increased substantially and it is sold in two forms, colloid and powder. At the same time, hydrolyzed polyacrylamide, methylene polyacrylamide, sulfonated polyacrylamide and copolymers of acrylamide and some other monomers were also developed. These products have been widely used in industrial sectors such as oil extraction, water treatment, sugar refining, coal washing, mineral processing, and paper making, and have all received good results. With the continuous expansion of its application range, new products and new grades of polyacrylamide are also emerging, and it is expected that the production and application of polyacrylamide will get greater development.
Physical properties of acrylamide
Acrylamide is a water-soluble monomer, it is an important functional monomer, together with its derivatives such as methacrylamide, N-alkyl substituted acrylamide, hydroxymethylated acrylamide. Sulfomethylated acrylamide Amide, aminomethylated acrylamide, sulfomethylpropylated acrylamide, aminomethylpropyl acrylamide, N, N'-methylenebisacrylamide, etc. Their homopolymers and copolymers (including graft copolymers) are widely used for modification in production, improving efficiency, recycling materials, water treatment, minerals
Flotation, oil drilling and mining, etc.
Acrylamide is a colorless and odorless crystalline solid, highly toxic. The melting point is 84 ~ 86°C; the boiling points are 879°C (0.26kPa), 125°C (3.33kPa) and 103°C (0.67kPa); the relative density is d4201.122 (20/4°C); the refractive index is 1.460 (Calculated).
Polyacrylamide compounds can be dissolved in water as well as in many organic solvents. The dissolution of acrylamide in water and some organic solvents is shown in the table.
Dissolution of acrylamide in water and some organic solvents
|Solubility (30°C, g/100mL)||44.5||110||74||30||12.5||4.0||0.28||0.03||204|
Acrylamide is mainly soluble in water, ethanol, acetone, ether and trichloroethane, and slightly soluble in toluene and b
stable at room temperature, but it suddenly polymerizes when it is melted. Adding hydroquinone, tert-butylcatechol, phenyl-2-cyanamide or other antioxidants to the water solution can stabilize it. The main physical properties are shown in Table 2-2. Acrylamide has good thermal stability. In dark conditions
It will not produce polymer or only a small amount of polymer when heated at 80C for 24h, and it will gradually polymerize when heated above the melting point.
Table: Physical Properties of Acrylamide
|Characteristics (20°C)||Powder crystal|
|Melting point (°C)||84.5|
|Buddha Point (°C)||87°C2mmHg (Sublimation) (0.267kPa)|
|Solubility in water (20°C)||141gAAM/100gH2O|
|Solvent (50% aqueous solution)||Methanol, benzene + methanol|
|Vapor pressure (84. 5°C)||1. 6mmHg (crystal) (0.21kPa)|
|Density (20°C) (50% aqueous solution)||1042kg/m3|
|Viscosity (20°C), cP (50% aqueous solution)|
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