Continuous precipitation polymerization

Perhaps the most challenging reactor design problem is the design of the continuous precipitation polymerization reactor. Although several patents (45,46,47) are concerned with this problem, the topic has been generally neglected in the reactor-... 

However, since virtually no published data are available on the mechanism of continuous particle formation and growth, particlarly under the influence of mechanical agitation, continuous precipitation polymerization remains a vast engineering wilderness waiting for experimental and theoretical explorations. 

On the other hand, very little is known about the mechanism of continuous precipitation polymerization. In particular, the mechanism of continuous particle formation and growth and the effects of starvation feeding on reaction rate and copolymer composition are areas of particular interest. 

Recently, Charpentier et al. [36] demonstrated the synthesis of PVDF by a continuous precipitation polymerization in SCCO2, using diethyl per-oxydicarbonate (DEPDC) as an initiator. Low molecular weight polymers (Mjj<20,000 g/mol) were reported in this first work. However, subsequent research has yielded PVDF with number-average molecular weights upwards of 79,000 g/mol [51,52]. PVDF made in the continuous CO2-based system had molecular weights comparable to commercial polymers, but also exhibited unique properties not observed in PVDF made by conventional processes. 

Liu, T. Desimone, J.M. Roberts, G.W. Continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide The polymerization rate and the polymer molecular weight. J. Polym. Sci. A 2005, 43 (12), 2546-2555. 

A major issue associated with the use of SCCO2 as a solvent for polymerization is the reaction pressure many of the processes published so far operate at pressures in the range 20.0-40.0 MPa [1, 15], which has significant implications for capital equipment and running costs. This problem has been approached in a number of ways. For example, DeSimone and coworkers have developed methods for the continuous precipitation polymerization of fiuoropolymers [16]. In general, continuous SCF processes are likely to be more readily implemented than batch processes, and a continuous approach has also been applied to the processing of porous PVDF foams [17]. 

In dispersion polymerization, the monomer and initiator are dissolved in the continuous phase, which acts as a nonsolvent for the developing polymer. The continuous phase can be organic, aqueous, or a mixture of miscible phases. Two methods of initiation have been employed, including gamma radiation [75] and chemical initiation by potassium perox-odisulphate [76]. As the polymer is formed, it precipitates as nanoparticles. These particles are not polymeric precipitates as in precipitation polymerization. Rather, they are swollen by a mixture of the monomer and the continuous phase [39],... 

When a monomer such as acrylonitrile is polymerized in a poor solvent, macroradicals precipitate as they are formed. Since these are living polymers, polymerization continues as more acrylonitrile diffuses into the precipitated particles. This heterogeneous solution polymerization has been called precipitation polymerization. 

Copolymers Prepared with Benzene. Copolymers prepared with benzene (0.25 part) or small quantities of dichloroethane (<0.25 part) show continuous precipitation above n = 10. For polymerization with benzene, vinyl chloride content of the fraction is always about 51-53.5% compared with a mean value of 52.4 for the sample. How can we explain this ... 

Charpentier, P. A Kennedy, K. A. DeSimone, J. M. Roberts, G. W. Continuous Polymerizations in Supercritical Carbon Dioxide Chain-Growth Precipitation Polymerizations. Macromolecules 1999, 32, 5973-5975. 

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. 

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