Preparation processes involving polymer precipitation

Processes Involving Precipitation of Polymer. Composite particles or micro-encapsulated particles may also be prepared by precipitating a (second) polymer onto the surface of pre-formed particles. For... 

Precipitation polymerization, also known as slurry polymerization, involves solution systems in which the monomer is soluble but the polymer is not. It is probably the most important process for the coordination polymerization of olefins. The process involves, essentially, a catalyst preparation step and polymerization at pressures usually less than 50 atm and low temperatures (less than 100°C). The resultant polymer, which is precipitated as fine floes, forms a slurry consisting of about 20% polymer strspended in the liquid hydrocarbon employed as solvent. The polymer is recovered by stripping off the solvent, washing off the catalyst, and if necessary, extracting any undesirable polymer components. Finally, the polymer is compounded with additives and stabilizers and then granulated. 

Synthesis of hydrophilic magnetic particles with an average size of 2.6p.m and PDI 1.02, and a 24.3% iron oxide content was carried out by Ma et al. [101], She used coprecipitafion of iron oxide inside an amino functional polymer matrix. The total process involves three steps (a) preparation of poly(glycidyl methacrylate) (PGMA) seed particles by a dispersion polymerization, (b) functionalization of the seed PGMA particles with ethylene diamine (EDA), and (c) impregnation of iron salts and precipitation with ammonium hydroxide solution inside the functional polymers matrix. 

Paraformaldehyde Manufacture. In general, commercial paraformalde-hj de is prepared from aqueous formaldehyde solutions by processes involving distillation and concentration to a point at which solidification or precipitation of polymer takes place. The process is so controlled that a product contaimng 95 per cent or more of formaldehyde is obtained. 

Chemical Phase Inversion Symmetrical phase-inversion membranes (Fig. 20-67) remain the most important commercial MF membranes produced. The process produces tortuous-flow membranes. It involves preparing a concentrated solution of a polymer in a solvent. The solution is spread into a thin film, then precipitated through the slow addition of a nonsolvent, usually water, sometimes from the vapor phase. The technique is impressively versatile, capable of producing fairly uniform membranes whose pore size may be varied within broad limits. 

Sun and Ruckenstein (44) prepared a composite of polypyrrole and a host polymer by an emulsion pathway that dispersed a host polymer and surfactant in an aqueous ferric chloride solution, followed by dropwise addition of pyrrole until the final product could be precipitated with methanol. The product was washed several times with methanol and the materials were then hot-pressed to form films. This process produced composites with conductivities as high as 1.3 S/cm, but the processing time was very high because of the multiple steps involved. Also, the process uses several toxic organic solvents. 

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