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Superporous Hydrogel Composites: A New Generation of Hydrogels with Fast Swelling Kinetics, High Swelling Ratio and High Mechanical Strength
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Kinam Park, Jun Chen, Haesun Park
In solution polymerization, monomers are usually mixed in a diluent that is good for both monomers and polymers. If, however, the diluent is a nonsolvent for the polymer formed (e.g., PHEMA in water), the solubility of the polymers dramatically decreases as the polymerization proceeds. This results in phase separation of the polymer-rich monomer phase into droplets, which then join together to form a network filled with large spaces (i.e., heterogeneous, porous hydrogels) by the end of the polymerization process. This process is called heterogeneous solution polymerization [14,17,24]. The pore sizes of macroporous hydrogels prepared by phase separation are typically only a few micrometers. In addition, the overall porosity is very low, and this implies that the pores are not well interconnected. The major limitation of the phase separation method is that only very limited types of porous hydrogels can be prepared. In addition, there is not much control over the porosity of the gels when prepared by phase separation.
Monomers, Polymers, and Plastics
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
In solution polymerization, an organic solvent dissolves the monomer. Solvents should have low-chain transfer activity to minimize chain transfer reactions that produce low molecular weight polymers. The presence of a solvent makes heat and viscosity control easier than in bulk polymerization. Removal of the solvent may not be necessary in certain applications such as coatings and adhesives.
Characteristics of Polymers and Polymerization Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
Solution polymerization is frequently employed in copolymerization, where the copolymer formed is soluble in the solvent, and the polymer solution is used directly in surface coating or as adhesive.
Development and Performance Study of a New Physicochemical Composite Inhibitor for Coal Spontaneous Combustion Control
Published in Combustion Science and Technology, 2021
Zhian Huang, Jinyang Li, Xiaohan Liu, Yukun Gao, Yinghua Zhang, Shihao Wang, Ziyou Li, Likai Yan
The formation mechanism of the composite hydrogel is shown in Figure 1. Tea polyphenol is a polyhydroxy compound. Under the action of potassium persulfate initiator, the hydrogen bonds are broken in the hydroxyl group, and a radical reaction occurs to produce the active center of Ar–O- on the tea polyphenol monomer. In Figure 1, the product of the radical reaction of tea polyphenols is represented by the molecular expression Ar–O-. In solution polymerization, the acrylic monomer has high molecular activity in an acidic solution. If the acidity is too high, the monomer will break and the solution will rush out of the reactor; however, if the acidity is too low, the monomer will have little activity and the polymerization reaction will be slow or unable to occur. Therefore, the NaOH solution should partially neutralize the acrylic acid to form sodium acrylate, adjust the pH of the solution, and control the degree of polymerization. The resulting tea polyphenol active center Ar–O- chemically reacts with methyl and methylene in the acrylic acid/sodium acrylate aliphatic group to form ether group C–O–C, and the tea polyphenol is grafted onto the acrylic acid/sodium acrylate molecule. Under the initiator and high-temperature conditions, the monomers polymerize to form longer carbon chains, that is, larger molecules. The crosslinking agent crosslinks macromolecular carbon chains together to form a three-dimensional network structure with a main chain, side chain, and crosslinking degree, which takes tea polyphenols as the skeleton and forms a polymer gel.
On the possibility of using combined polymerization and drying in synthesis of polyacrylamide
Published in Chemical Engineering Communications, 2019
A. A. Lipin, A. G. Lipin, R. Wójtowicz
As is shown below (Figure 6), solution polymerization at optimum temperature (TI = 30 °C) yields only 80% monomer conversion. Therefore, in a second step, a prepolymer prepared at 30°C (having a gelatinous state) was applied to metal plates with a uniform layer of 10 mm in thickness. Further polymerization was combined with solvent elimination from the prepolymer in a drying chamber with infrared heat supply and natural convection (Figure 1). Process temperature was varied in the following range: TII = 90–105 °C. The polymer temperature was measured continuously with a thermocouple placed in one of the samples. For measurement of moisture content and monomer conversion degree the samples were taken out from the thermostat alternately, at specified times. Polymer moisture content was measured by the weight method. A sample of polymer obtained by combined polymerization and drying is shown in Figure 3.
A Physical-chemical Synergetic Inhibitor for Coal Spontaneous Combustion and Its Fire Prevention Performance
Published in Combustion Science and Technology, 2022
Jiawen Cai, Shengqiang Yang, Yan Zhong, Wanxin Song, Wancheng Zheng
The main methods of SAP polymerization include bulk polymerization, solution polymerization and inverse suspension polymerization, etc. (Ma et al. 2011). The solution polymerization method, which is achieved by the free addition reaction of monomer olefin double bond, was adopted for SAP preparation. The experimental reagents included acrylic acid, cross-linking agent (methylene-bis-acrylamide), acrylamide (Analytical reagent (AR), Guangdong Wengjiang Chemical Reagent Co., Ltd), initiator ((NH4)2S2O8, AR, Shandong Jiaying Chemical Technology Co., Ltd) and NaOH (AR, Jinan Xiaoshi Chemical Co., Ltd). The SAP preparation process consists of five main steps (Figure 2). First of all, distilled water was added into 1 mol acrylic acid until the latter was fully dissolved. After that, the solution with 1 mol of NaOH was slowly added to the acrylic acid solution with constant stirring. Then, 0.5 mol of acrylamide and a cross-linking agent in a certain concentration were added to the sodium acrylate with constant stirring until they were fully dissolved. Next, nitrogen was charged to the four-neck flask for 5 min, in order to discharge oxygen from it. After a certain concentration of initiator was added, polymerization took place at the constant temperature of 70°C for 4 h. At the end of the reaction, the colorless transparent gel was obtained. After washing, the gel was dried in an oven at 100°C for 2 h, and then was cut into pieces and dried repeatedly to a constant weight. Finally, the obtained SAP was ground, sifted and sealed in tube for the performance test.