Free radical polymerization propagation phase

As mentioned in Section 9.3, Jackson (141) has obtained estimates of the chain-transfer coefficient of the growing radical with polymer in the free-radical polymerization of ethylene, C,p, by choosing the value so as to fit the MWD. As the polymerization conditions for the polymers mentioned in Table 10.1 are not disclosed, it is necessary to choose typical conditions 220° C and 2000 atm will be selected. Under these conditions Ctp, the ratio of the rate constant for attack on polymer (per monomer unit) to that for propagation, in a homogeneous phase, was found to be about 4.0 x 10 3. This is in good agreement with the known transfer coefficients for the lower alkanes (160), when allowance is made for the differences in pressure and temperature (100). The relation between Ctp and k is ... 

Keywords aqueous-phase polymerization free-radical polymerization methacrylic acid PLP-SEC propagation rate coefficients pulsed-laser initiation water-soluble monomers... 

Projea No. 2004-034-1-400 Critically evaluated propagation rate coefficients for free-radical polymerization of water-soluble monomers polymerized in the aqueous phase Projea No. 2009-050-1-400 Critically evaluated rate coefficients associated with initiation of radical polymerization... 

The free-radical polymerization of vinylpyridine in emulsion has also been described [567-571]. In contrast to classical emulsion polymerizations in which the micelles are the sole propagating sites, for monomers with high hydrophilicity such as vinylpyridines, the aqueous phase is apparently important as the locus of polymerization. 

Free radical polymerization kinetics has received much attention and many aspects of the process are well understood (see Chapter 4). Most academic investigations have been carried out in idealized conditions where the extent of monomer conversion is low. The classical expression for the rate of polymerization (Rp), in a single-phase reaction, is Eq. (13), where kp is the propagation rate coefficient, Cm is monomer concentration, J i is the initiation rate and kt is the termination rate coefficient [63]. 

Most of the MIPs are fashioned through the free-radical polymerization (FRP) procedures that are initiated upon the decomposition of a radical producing compound, referred to as the initiator, by means of thermal or photochemical stimuli. Such reactions are commonly conducted imder mild temperature and pressure conditions. The FRP is appropriate for a variety of functional monomers and templates [28]. According to the general pattern of free-radical reactions, after the initiation phase, the number of the free radicals increases, leading to the propagation stage where the main portion of... 

Strictly speaking, any model based on the time-independent thermodynamics cannot be used to adequately predict the concentration of monomer in latex particles during Smith-Ewart Interval II. This is because the free radical polymerization of monomer in the discrete latex particles is governed by the simultaneous kinetic events such as the generation of free radicals in the continuous aqueous phase, the absorption of free radicals by the particles, the propagation of free radicals with monomer molecules in the particles, the bimolecular termination of free radicals in the particles, and the desorption of free radicals out of the particles. The equilibrium (or saturation) concentration of monomer in the growing latex particles may not be achieved if the rate of consumption of monomer in the major reaction loci is much faster than that of diffusion of monomer molecules from the monomer droplets to the reaction loci. Therefore, the equilibrium concentration of monomer in the latex particles represents an upper limit that is ultimately attainable in the course of polymerization. Nevertheless, the general... 

Monomers may be polymerized using a water-soluble initiator while dispersed, by agitation, in a concentrated soap solution. In this emulsion system initiation occurs in the aqueous phase and propagation occurs in the soap micelles. Since the growing macroradicals are not terminated until a new free radical enters the micelle, high molecular weight products are rapidly obtained. The rate of polymerization and DP is proportional to the number of activated micelles. 

It is believed that polymerization of hydrophobic monomers is initiated by free radicals in the aqueous phase and that the surface-active oligomers produced migrate to the interior of the emulsifier micelles where propagation continues. Monomer molecules dispersed in the water phase also solubilize by diffusing —to the expanding lamellar micelles. These micelles disappear as the polymerization continues and the rate may be measured by noting the increase in surface tension of llie system. 

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