Rate constant polymerization

When one compares the brutto polymerization rate constants, a measure of the reactivity of monomers during cationic homopolymerizations is obtained. It was found for p-substituted styrenes that lg kBr increased parallel to the reactivity, which the monomers show versus a constant acceptor 93). The reactivity graduation of the cationic chain ends is apparently overcomed by the structural influence on the monomers during the entire process of the cationic polymerization. The quantitative treatment of the substituent influences with the assistance of the LFE principle leads to the following Hammett-type equations for the brutto polymerization rate constants ... 

For all likely operating conditions, (ie., for t < X), the appropriate values of the concentration and the polymerization rate constant are the values calculated at t = t ( 2). To prove this, the exit age distribution function for a backmix reactor was used to weight the functions for Cg and kj and the product was integrated over all exit ages (6). It is enlightening at this point to compare equation 18 with one that describes the yield attainable in a typical laboratory semibatch reactor at comparable conditions. ... 

Both kjn and kd, which are the kinetic rate constants of this model, are functions of temperature and Arrhenius dependence is assumed for each (Equations 8 and 9.) In this model, kj is the net polymerization rate constant. 

Figure 2. Arrhenius plot for net polymerization rate constant.

Secondly, Fig. 5 shows that the polymeric rate constants parallel values of heterogeneous rate constants that have been observed for the electrochemical reactions of solutions of the corresponding dissolved porphyrin monomers. (The slope of the line is 0.5). This re-emphasizes what was said above, that measurements of electron hopping in polymers can give rate constants that are meaningful in the context of the metalloporphyrin s intrinsic electron transfer chemistry. 

In most cases, the metal-catalyzed ROP activity is best assessed by determining the polymerization rate constant (kp). A second order rate law is being followed by most of the catalytic lactide polymerizations ... 

Fig. 11 Dependence of apparent polymerization rate constant /ca on / Al/ Ndv D polymerization with the catalyst systems (1) NdV/DIBAH/EASC and (2) NdV/TIBA/ EASC [179], reproduced by permission of Taylor Francis Group, LLC., http //www. taylorandfrancis.com...

In the simplest case, with rapid initiation and participation of a single type of active centre, the rate of propagation is equal to the polymerization rate, and kp is the overall polymerization rate constant. Rapid initiation can be established in ionic processes the presence of several kinds of centres means unequal numbers of monomer molecule additions to different centres. Long macromolecules will be formed on "rapid centres, shorter ones on "slow centres. A practical example of this situation is anionic living polymerization with the participation of contact and solvent-separated ion pairs, and of free ions. 

The polymerization rate constants were measured by adjustment of the equations above to the experimental polymerization results. The activation energy of chain propagation and decay for active site 1 and 2 were the same because this catalyst system is single site. The results of the fitting of calculation and polymerization are shown in Figure 17.15. 

The second explanation of Cl was that the polymerization rate constants are dependent upon the radical DP for DP < 8, so that retardation occurs due to the higher value of kt for small radicals.44 As indicated above, the propagation rate constants actually increase at lower molecular weights. There are two additional reasons to believe that kt cannot be responsible for the Cl. 

In an emulsion polymerization of isoprene with 0.10 M potassium laurate at 50°C the estimated time required for 100% conversion at steady rate is 30 h. The final latex has 40 g of polymer per 100 mL with particles of 450 A diameter. During stage II, the growing swollen polymer particles contain 20 g of monomer per 100 mL of swollen polymer. Assuming that there is no change in total volume on polymerization, estimate the polymerization rate constant from these data. Assume that the polymer has a density of 0.90 g/cm . 

Using the above type of experimental setup for propylene polymerization with TiCls-AlEts in n-heptane, the rate of polymerization was measured [5] at different speeds of stirring and constant propylene pressure. The results obtained indicated that there were two different steady-state rate curves for the stirring speeds of 400 and 600 rpm. In each case, a steady bulk monomer concentration was reached in about 3-4 hours. Show how the overall process at steady state can be modelled to show dependence of the polymerization rate on stirring speed and to enable determination of both the mass transfer rate constant and polymerization rate constant from rate measurements at different stirring speeds. 

Hint Defining [M]o = monomer concentration at the gas-liquid interface, [M] = average concentration of monomer in solution, [cat] = concentration of catalyst, = mass transfer constant (dependent on stirring speed), and = polymerization rate constant, the mass balance for the... 

Fig. 4. Approximate character of the dependence of the polymerization rate constant k, for s-cis-and s-frans-conformation of quasisymmetric dienes on the polarity of the carbon-metal bond in the active center...

Fig. 2. Arrhenius plot of literature values of solution styrene polymerization rate constants (solid line is a least squares fit)...

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