Homogeneous and Heterogeneous Polymerizations

Tortosa K, Hamaide T, Boisson C, Spitz R (2001) Homogeneous and heterogeneous polymerization of e-caprolactone by neodymium alkoxydes prepared in situ. Macromol Chem Phys 202 1156-1160... 

The various homogeneous and heterogeneous polymerization processes used, generally yield mixtures of polymers having different stereoregularity, which can be fractionated by solvent extraction. 

The difference in formaldehyde equilibrium concentration between homogeneous and heterogeneous polymerization is large enough to indicate a difference in the physical state of cationic chain ends in the dissolved and in the crystalline polymer. Thus, Model B is ruled out. In the homopolymerization of trioxane and in the heterogeneous copolymerization with small amounts of dioxolane the active centers of chains which have precipitated from the solution predominantly are directly on the crystal surface (Model A). According to Wunderlich (20, 21), this is the first case in addition polymerization where Model A—simultaneous polymerization and crystallization—has been proved experimentally. 

Figure 24.11 Schematic model for homogeneous and heterogeneous polymerization mechanism.

J. B. McClain, T. J. Romack, and C. D. Mistele (1994). Homogeneous and Heterogeneous Polymerizations in Environmentally Responsible Carbon Dioxide. Preprints of Papers Presented at the 208th ACS National Meeting, August 21-25, 1994, Washington, DC, 212-214. Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee, WI Division of Environmental Chemistry, American Chemiccd Society. 

In summary, the results presented here demonstrate that the fiber optic ATR and TR FTIR methods developed in our laboratory can conveniently be used to monitor both homogeneous and heterogeneous polymerizations, and various ancillary reactions, yielding very useful information about these processes. Our research group has extensively been using the fiber optic mid-IR ATR-FTIR and TR-FTIR techniques for macromolecular engineering. ... 

Investigation of the Chain Length Dependence of kp. New Results Obtained with Homogeneous and Heterogeneous Polymerization... 

In general, we can distinguish homogeneous and heterogeneous polymerization processes. Homogeneous processes take place within the substance in question (with the monomer or the formed polymer acting as reaction medium) or in a solvent. Heterogeneous processes include precipitation, slurry phase, suspension, emulsion, or gas-phase polymerizations. 

With respect to the possibilities of carbon dioxide as a reaction medium for polymerization reactions, extensive reviews have been published by Scholsky [55], Shaffer et al. [56], Kendall et al. [57], and Cooper [58]. Typically, a division is made between homogeneous and heterogeneous polymerization in SCCO2. 

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