Polyacrylamide

Just a reminder, what are the latest studies?

　　Polyacryamide (abbreviated as PAM) refers to linear polymers obtained either as homopolymers of acrylamide or through copolymerization with other monomers. It has good thermal stability. Due to the presence of polar groups—amide groups—in its structural units, hydrogen bonds can easily form, endowing it with good water solubility and high chemical reactivity; it can thus be modified to produce various derivatives with branched or network structures through grafting and cross-linking. As a result, polyacrylamide, with its range of derivatives and various valuable properties, holds great significance in water treatment; it is the most widely used coagulant for water treatment among organic polymers. 　　Research and production of polyacrylamide in our country began in the 1960s. The manufacturing process primarily relies on the traditional aqueous polymerization method: a 8–10% AM aqueous solution is polymerized directly under the action of an initiator. For the dry powder, a 20–30% AM aqueous solution is used for medium-concentration polymerization. After polymerization, the resulting colloid is processed through granulation, kneading, drying, and crushing to produce polyacrylamide. This process is relatively safe, simple, and cost-effective. Reverse emulsion polymerization – The AM aqueous solution is decomposed into monomers in the oil phase with the help of surfactants, thereby forming an emulsion system. Emulsion polymerization takes place under the action of an initiator, resulting in the formation of stable, high-molecular-weight, instantly soluble polyacrylamide latex products. After dehydration through azeotropic distillation, polyacrylamide in powder form is obtained. This process is suitable for producing polyacrylamide latex or dry powder products with high molecular weights and a narrow molecular weight distribution. There is also the inverse suspension polymerization method – a polymerization reaction in which the AM aqueous solution is suspended as small droplets in an organic solution, resulting in polyacrylamide beads with high molecular weight and rapid solubility. Radiation-initiated method – The amide monomer is directly polymerized under ultraviolet or R-ray irradiation to yield a solid product. This method is simple in process but requires significant investment, and the resulting products have a wide molecular weight distribution. Most applications of polyacrylamide require some kind of ionic functionality. The properties of ions can alter the solubility, viscosity, and properties of the polyacrylamide solution. The production of product derivatives is achieved through copolymerization or via subsequent reactions of polyacrylamide.

It is generally used as a flocculant in water treatment, right?

Anti-dispersants that can be used in building materials for underwater concrete

Polyacrylamide, abbreviated as PAM, is a water-soluble linear polymer synthesized through the polymerization of the monomer acrylamide. The monomer acrylamide has highly reactive chemical properties; a series of chemical reactions can occur at its double bond and amide group. By using different processes to introduce various functional groups, products with different molecular weights and charges can be obtained. The average molecular weight of PAM ranges from several thousand to over several million; it possesses multiple functional groups along its chain structure, can be largely ionized in water, and belongs to the category of polymeric electrolytes. Based on the properties of their dissociable groups, they are classified into anionic types (such as --COOH, --SO3H, --OSO3H, etc.), cationic types (such as --NH3OH, --NH2OH, -CONH3OH), and non-ionic types. The product appears as a white powder; it is soluble in water and practically insoluble in benzene, ether, esters, propylene glycol, and other common organic solvents. Its aqueous solution is a nearly transparent viscous liquid. It is not considered a hazardous substance, being non-toxic and non-corrosive. The solid form of PAM is hygroscopic, with this hygroscopicity increasing as the ionic strength rises. PAM has good thermal stability ； It maintains good stability at 100°C, but decomposes easily at temperatures above 150°C to produce nitrogen, undergoing imination between molecules and becoming insoluble in water; its density is 1.302 g/mL at 23°C. The glass transition temperature is 153°C, and PAM exhibits non-Newtonian flow behavior under stress. 　　Usage properties 　　1) Flocculation: PAM enables suspended particles to be flocculated through electro-neutralization and bridging adsorption. 　　2) Adhesiveness: It can exert an adhesive effect through mechanical, physical, and chemical means. 　　3) Resistance reduction: PAM can effectively reduce the frictional resistance of fluids; adding a small amount of PAM to water can reduce this resistance by 50–80%. 　　4) Thixotropy: PAM exhibits thixotropic properties under both neutral and acidic conditions; it tends to hydrolyze when the pH is above 10. When it has a semi-reticular structure, thickening will be more pronounced. 　　Brief introduction to the working principle of PAM 　　1) Principle of flocculation: When PAM is used for flocculation, it is related to the surface properties of the substances to be flocculated, particularly their zeta potential, viscosity, turbidity, and the pH value of the suspension. The zeta potential on the particle surface is what prevents aggregation; by adding PAM with an opposite surface charge, this zeta potential can be reduced rapidly, thereby facilitating aggregation. 　　2) Adsorption bridging: PAM molecular chains are anchored to the surfaces of different particles, and polymer bridges are formed between these particles, causing the particles to aggregate and settle. 　　3) Surface adsorption: Various adsorptions of particles onto the polar groups on PAM molecules. 　　4) Reinforcing effect: The PAM molecular chains bind the dispersed phase together through various mechanical, physical, and chemical mechanisms, forming a network that serves to reinforce the structure.

How is it synthesized specifically? Who knows the synthesis process? Please share! Thank you!

Synthesis and Applications of Cationic Polyacrylamide · Previous Article: Classic Marketing Stories – The Smart Newspaper · Next Article: Phosphonate Polycarboxylates and Other Water Treatment Agents Abstract: Polyacrylamide (PAM) was modified into cationic polyacrylamide (CPAM) through a Mannich reaction, in which N-methylethanamine or diethanamine was used in place of the commonly used dimethylamine. When the molar ratio of diamine to formaldehyde is greater than 1.2:1, and by first adding the formaldehyde solution to the PAM solution and then adding the amine solution to the reaction mixture after the reaction is complete, CPAM with an amination degree of over 50% can be obtained after reacting at 40–50°C for 3–4 hours. Methods for reducing the viscosity of PAM solutions with a concentration of >1.0×10 CPAM were explored. Keywords: Mannich reaction ； Cationic flocculant ； degree of amination ； Polyacrylamide: The use of polyacrylamide (PAM) for treating wastewater dates back over 50 years. In recent years, as the sources of wastewater have become increasingly complex, making treatment more difficult, cationic polymers have received considerable attention ； This is because it can not only form adsorption bridges with various particles in wastewater, but also neutralize the negative charges on the surfaces of these particles, thereby destabilizing them and causing them to flocculate, which facilitates sedimentation and filtration for dehydration. The main methods for synthesizing cationic flocculants at present are copolymerization and modification. Due to the mutual repulsion between ion groups and the low ion activity, it is difficult to obtain products with high relative molecular mass and high degree of ionization using the copolymerization method ； The modification method can be applied to non-ionic chains with a relatively high molecular weight, thereby overcoming the shortcomings of the copolymerization method. Modifying PAM using the Mannich reaction is a good method for cationizing PAM, namely by first aminomethylating it and then reacting it with dimethyl sulfate or halomethanes to obtain quaternary ammonium salts of PAM. The author reacted low-alkyl amines with PAM and formaldehyde (FD) respectively to synthesize cationic polyacrylamide (CPAM), investigated the effect of reaction conditions on the degree of amination, and explored methods to reduce the viscosity of the product. l Experimental Section 1.1 Raw Materials and Instruments PAM, self-made, MW>1.0×10 ； FD, CP, Hubei University Chemical Plant ； Dimethylamine (DMA), CP, Shanghai Sains Reagents Co., Ltd ； Diethylamine (DEA), CP, Wuhan Jiangbei Chemical Reagents Factory ； N-Methylethanamine (MEA), CP, Xilong Chemical Factory ； Ethylenediamine (EDA), CP, Wuhan Jiangbei Chemical Reagents Factory ； N,N-Z. Methylmalondiamine (DMADA), N-methyldiazahexane (MDAH), CP, imported from Japan. NDJ-185 Digital Viscometer (30°C), Shanghai Tianping Instrument Factory ； HORIBA OCMA A300 oil content analyzer, Japan ； S-721 Spectrophotometer, Shanghai Lingguang Technology Co., Ltd. 1.2 Mannich reaction: 100 g of a solution with w(PAM) of 3–5 was added to a 250 mL three-necked flask. The temperature was increased and stirring was carried out evenly. An appropriate amount of FD and amine was added (in a two-step process: FD was added first; after about 1 hour of reaction, the amine was then added) ； The one-step method involves the sequential addition of FD and amine, reacting for a predetermined time before cooling and discharging the product. Its amination degree was determined by colloid titration [5]. 1.3 Detection of flocculation effect: Various products were prepared into solutions with a mass fraction of 1, added to colorimetric tubes containing oily wastewater, the tubes were sealed, and shaken up and down to ensure uniform mixing. They were then placed in a constant temperature water bath at 70°C, and the time at which floccules appeared as well as their appearance were observed and recorded. The oil content was measured using an oil meter, while the transmittance was determined using a spectrophotometer. 2 Results and Discussion 2.1 Effect of pH value on the reaction process Since cross-linking reactions occur easily under acidic conditions, while cross-linking is suppressed under alkaline conditions, the pH of the system was adjusted to 11–12 using the inert substance ethylene glycol. 2.2 Preliminary comparison of several amines A comparison was made of the amines used to modify PAM, such as DMA, DEA, MEA, EDA, DMADA, MDAH, etc. Among them, DMA is a commonly used amine that is inexpensive and readily available. However, considering that the length of the alkyl chain attached to the amine may increase the hydrophobicity of the PAM chains, thereby accelerating the flocculation process of the product, comparative experiments were conducted; the results are shown in Table 1. As can be seen from Table 2, DEA, MEA, DMADA, and DMA all exhibit good oil removal performance, whereas EDA has poor oil removal efficiency, likely due to its low amination rate. The following experiments use DMA, DEA, DMADA, and MEA respectively for in-depth study in order to identify the best product. 2.3 Effect of feeding sequence on degree of amination: There are two ways to feed FD and amine: in two steps or in one step. Different feeding methods have a certain impact on the degree of amination, as shown in Table 3. As can be seen from Table 3, the degree of amination for two additions is higher than that for one addition, because generally the reactant concentration is high at the beginning of the reaction, resulting in a fast reaction rate; as the reaction progresses, the reactant concentration decreases and the reaction rate slows down ； If added in batches, the fluctuations in the reactants in the raw material are reduced, and the degree of amination also increases. Adding them separately also prevents FD from reacting with the amine first, allowing FD to react more thoroughly with PAM. The order of addition has varying effects on different amines; the difference in degree of amination between the two DMA addition methods is relatively small, which is related both to the different structures of the amines and to their different heat of solubility in water. The purity of commercially available DEA and MEA is over 95%, and they generate a large amount of heat when added to the reaction system; this heat accelerates the reaction, making cross-linking reactions more likely to occur. Therefore, the two-time feeding method is superior to the one-time feeding method. 2.4 Influence of raw material ratio on the degree of amination: For the Mannich reaction, the ratio of amine to FD amount is particularly important. With the reaction temperature and reaction time held constant, the relationship between the molar ratios of PAM, FD, and amine and the degree of amination of the resulting product is shown in Table 4. As shown in Table 4, when the ratio of FD to PAM is 1:1 or 0.8:1, it has little effect on the degree of amination; choosing the latter can reduce the final residual amount, which is beneficial for the smooth progress of the reaction and the storage of the product. The molar ratio of DMA, DEA, or MEA to FD must be greater than 1.2:1 for the product not to cross-link, whereas the ratio of DMADA to FD needs to be between 1.2:1 and 3:1 to prevent cross-linking. The excessive cross-linking in FD occurs due to a dehydration reaction between the aldehyde and the methylolamine formed from the PAM chains; the reaction equation is shown in (1). By using a slight excess of amine and reducing the contact time and space between the alcohol amines, this cross-linking can be suppressed. The excessive cross-linking caused by DMADA is due to the fact that DMADA has two reactive amine groups; the reaction mechanism is shown in equation (2), and a high degree of cationicity tends to lead to such cross-linking. While ensuring no cross-linking, the higher the amount of amine used, the higher the degree of amination. Under the same conditions, MEA and DMADA exhibit a higher degree of amination of the products compared to DMA. Considering that excessive amine not only increases production costs but also contaminates water quality and the quality of flocculants, PAM/FD/amine (molar ratio) = 1:0 was selected. 8:1.6. 2. Influence of S reaction temperature and reaction time on the degree of amination: With the molar ratio of PAM/FD/amine fixed at 1:0.8:1.6, Figure 1 shows the relationship between the degree of amination of the various products and the reaction temperature after 2 hours of reaction. The relationship between the degree of amination of the product and reaction time at a reaction temperature of 50°C is shown in Figure 2. As can be seen from Figure 1, as the temperature increases, the reaction rate accelerates and the degree of amination increases. DMA and DMADA exhibit low conversion rates at low temperatures, whereas DEA and MEA achieve high degrees of amination at lower temperatures; the degree of amination of MEA reaches 54 at 50°C, indicating that DEA and MEA are more reactive than DMA and DMADA. As can also be seen from Figure 2, the degree of amination increases over time as the reaction proceeds, and this increase occurs within a short period; after a certain point, no significant changes are observed ； The time required for an increase in product viscosity varies among different amines; MEA shows the fastest response, while DMA takes longer. This further indicates that DEA and MEA not only have low reaction initiation temperatures but also fast reaction rates. 2.6 Effect of Mw of PAM on degree of amination Under the same reaction conditions, the degree of amination varies for different MPAMs, as shown in Table 5. The bite of PAM: the larger it is, the lower the degree of amination obtained through modification. This is because the amide groups on the same molecular chain exert a steric hindrance effect during the reaction, and the highly polar PAM molecular chains lack flexibility, resulting in low reaction efficiency. As can be seen from Tables 7 to 9, surfactants exhibit the best effect; at a mass concentration of 0.5 g/L, they are able to reduce the viscosity of the solution from 6.0 Pa·s to 4.6 Pa·s. This is because they not only mask the effective charges within the polymers but also reduce the surface hydrophilicity of these polymers to some extent, thereby causing the polymer chains to curl effectively and reducing the viscosity of the solution. Further increasing the amount of surfactant has little effect on viscosity, and beyond a certain amount, the presence of the surfactant affects its reverse demulsification efficiency during use. Therefore, a dosage of 0.5 g/L is advisable. 3 Conclusions a. PAM with an average molecular weight of approximately 1.0×10^7 can be modified via the Mannich reaction to yield cationic polyacrylamide with an amine content of over 50% and excellent flocculation properties. b. Binary amines and some low-alkyl amines such as DMA, DEA, MEA, EDA, and DMADA can all undergo Mannich reactions. DEA and MEA exhibit higher reactivity; when MEA is reacted at 50°C for 2 hours, products with a high degree of amination are obtained, and these products have good flocculation properties. c. Adjust the pH of the system using an organic base to 11.5–12; at a molar ratio of PAM/FD/amine of 1:0.8:1.6, a two-step addition method can facilitate a smoother reaction. d. The average molecular weight of PAM affects the degree of amination; the higher the average molecular weight, the lower the degree of amination. e. Adding 0.5 g/L of non-ionic surfactant can reduce the viscosity of the solution.