Dispersion polymerization process

Fig. 3. An aqueous dispersion polymerization process used in the manufacture of acrylic and modacrylic fibers.

Figure 9 The schematical representation of dispersion polymerization process, (a) initially homogeneous dispersion medium (b) particle formation and stabilizer adsorption onto the nucleated macroradicals (c) capturing of radicals generated in the continuous medium by the forming particles and monomer diffusion to the forming particles (d) polymerization within the monomer swollen latex particles, (e) latex particle stabilized by steric stabilizer and graft copolymer molecules (f) list of symbols.

Dispersion polymerization is a technique that permits the preparation of polymer particles typically in the range of 1-15 pm in a rapid process with high conversion. In a dispersion polymerization process, the continuous phase is chosen to be a solvent for monomer to be polymerized, a nonsolvent for the resultant polymer. A steric stabilizer is used to produce a colloidally stabilized dispersion. In the absence of stabilizer, the polymerization produces macroscopic particles of polymer of an uncontrolled size, and is called precipitation polymerization. 

The notion of levitation by density matching offers the possibility for a psuedo-dispersion polymerization process that is free of added stabilizers (such as surfactants) used in conventional dispersion polymerizations. 

Homopolymerizations via FRRPP process normally starts from solution, i.e., the monomer is in a soluble environment. When free radicals are formed from initiator compounds at a high enough temperature, propagation reactions occur and polymer chains are formed. As the polymer radicals attain a high enough chain length, it enters the LCST-based phase envelope and phase separates to form a polymer-rich material. This is where the reaction mechanism of the FREtPP process deviates from conventional solution or dispersion polymerization processes. 

Suspension and dispersion polymerization processes for production of high MW PTFE have been widely used since the 1940s but process modification for direct polymerization of low MW PTFE has been more recent. Dispersion polymerization of low MW PTFE is currently most commonly employed. The major difference in polymerization between high and low MW PTFE is the addition of a... 

Subsequently, there have been many improvements to the dispersion polymerization process that have allowed for AM/ AETAC and AM/DADMAC cationic, AM/sodium aaylate anionic, acrylamide nonionic, and AM//V7V-dimethyl-/V-acryloyloxyethyl-/V-(3-sulfopropyl) ammonium betaine polymeric dispersions [16, 38-41]. These improvements, such as the development and utilization of new dispersants, the use of polymeric seeds to fecilitate precipitation, optimization of... 

In the polyacrylamide dispersion polymerization process, multivalent salts are used for the purpose of insolubilizing and depositing the polymer and are formulated to produce a poor solvent for the particular polyacrylamide being synthesized. At the onset of polymerization reaction, the formed polymer is soluble in the polymerization medium. As the reaction progresses, the polymer phase separates forming particles (0.1-10 pm) that are kept from agglomeration by the use of polymeric stabilizers. A mechanistic hypothesis of the formation of polyacrylamide dispersions was reported by Selvarajan [43]. 

Ramesh M, Howland CP, Cramm JR. Dispersion polymerization process. European patent 630909. 1993. 

The second process developed by ICI, named Aquersymer [69], is actually a dispersion polymerization process, using as a continuous medium a mixture of alcohol (methanol, ethanol) and water the medium is a solvent of the monomer, but the polymer is not soluble. The stabilization is provided by the macromonomer of polyoxyethylene it may be used as a preformed copolymer or, preferably, produced in situ. Particle size in the range 10(f-450 nm can be produced at solid contents up to 40-50%. 

Dispenza et al. [118] synthesized PANI-ES nanoparticles through a chemical oxidative dispersion polymerization process in the vicinity of either poly(N-vinyl pyrrolidone) (PVP) or poly(vinyl alcohol) (PVA) as steric stabilizers. This was the first of two active steps, the second being gamma irradiation of the stabilized PANI... 

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